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21.3: Infectious Diseases - Biology

21.3: Infectious Diseases - Biology


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Typhoid Mary

Her real name was Mary Mallon (1869-1938), but she was nicknamed “Typhoid Mary.” She gained notoriety (as evidenced by this newspaper article in Figure (PageIndex{1})) by being the first person in the United States to be identified as an asymptomatic carrier of the pathogen that causes typhoid fever. Over the course of her career as a cook, Mary Mallon was thought to have infected 51 people, three of whom died. She was twice forcibly quarantined by public health authorities and died after a total of nearly 30 years in isolation. Typhoid fever is caused by bacteria that are spread by eating or drinking food or water contaminated with the feces of an infected person. Risk factors include poor sanitation and poor hygiene. Typhoid fever is one of many infectious diseases that can spread in human populations.

All infectious diseases are caused by infections with pathogens or disease-causing agents, but not all infections cause infectious diseases. Infection is the invasion of an organism’s body tissues by pathogens, which multiply and damage or poison the host tissues. The reaction of the host’s immune system to the pathogens may contribute to the tissue damage. Infectious disease is an illness resulting from an infection. It occurs when an infection causes noticeable symptoms.

Types of Pathogens

Infectious diseases kill more people in low-income countries than any other cause, and they are important causes of death elsewhere. Many different types of pathogens can cause infectious diseases. Besides bacteria and viruses, human pathogens include fungi, protists, helminths, and prions.

  • Bacteria: The vast majority of bacteria are at least harmless if not beneficial to human hosts. Relatively few bacteria cause human diseases, but of those that do, the disease burden they exert on human populations may be great. Disease burden is the impact of a disease on a population as measured by financial cost, mortality, morbidity, or other indicators. One of the bacterial diseases with the highest disease burden worldwide is tuberculosis. It is caused by the bacterium Mycobacterium tuberculosis, which kills about 2 million people a year, most of them in sub-Saharan Africa. Other bacterial diseases that burden human populations include strep throat, pneumonia, shigellosis, tetanus, typhoid fever, cholera, diphtheria, syphilis, and leprosy.

  • Viruses: Viruses are little more than DNA or RNA in a protein coat. Viruses are not usually classified as living things because they cannot survive or reproduce on their own. They require the cells of a host to provide the machinery for protein synthesis and reproduction. Many types of viruses are pathogenic to humans. Common human diseases caused by viruses include influenza, mumps, measles, chickenpox, hepatitis, AIDS, yellow fever, coronavirus disease, herpes, polio, and the common cold.

  • Fungi: Fungi (singular, fungus) are eukaryotic organisms in the Fungus Kingdom. Some fungi are unicellular organisms; others are multicellular. Many fungi consume dead organisms. Many others are parasites of plants or animals, including humans. Human diseases caused by fungi include candidiasis, histoplasmosis, ringworm, and athlete’s foot. People with a compromised immune system are particularly susceptible to certain fungal diseases, such as candidiasis, which is pictured below, and cryptococcosis, which is a defining opportunistic infection for AIDS patients.

  • Protists: Protists are an informal grouping of simple eukaryotic organisms that are not plants, animals, or fungi. Some protists — particularly those called protozoa — are significant parasites of human organisms. They include five species of the parasitic genus Plasmodium that cause malaria. Malaria places a tremendous disease burden on human populations. In 2015, there were 214 million cases of malaria worldwide resulting in an estimated 438,000 deaths, 90 percent of which occurred in Africa. Other human diseases caused by protists include giardiasis, toxoplasmosis, trichomoniasis, Chagas disease, leishmaniasis, trypanosomiasis (sleeping sickness), and amoebic dysentery.

  • Helminths: Helminths, also commonly known as parasitic worms, are multicellular organisms, which when mature can generally be seen with the naked eye. Helminths infect animals including humans. Most live in the host’s intestines, but some live in other organs, such as muscles or blood vessels. Helminths take nourishment and protection from the host and cause disease in return. Examples of helminthic infections in humans include infections by tapeworms, roundworms, pinworms, and hookworms (Figure (PageIndex{3})).

  • Prions: Prions are infectious agents composed entirely of proteins. Prions are misfolded proteins that replicate by converting their properly folded counterparts, in their host, to the same misfolded structure they possess. Prions are transmissible and a few of them are known to cause human diseases, including Creutzfeldt–Jakob disease (CJD), an incurable and universally fatal neurodegenerative disease. CJD is similar to the better-known prion disease in cows, called mad-cow disease. In both the human and bovine (cow) diseases, brain tissue degenerates rapidly, and the brain develops holes like a kitchen sponge.

Identifying Pathogens: Koch’s Postulates

The human body has more microorganisms than it does human cells. The majority of microorganisms that live in or on the human organism are actually beneficial or at least harmless to the human host (except in the case of immune-compromised individuals). Given a huge load of microorganisms in and on the human organism, how can scientists determine which species of microorganism causes a particular disease? The 19th-century physician and microbiologist Robert Koch (Figure (PageIndex{4})) is best known for developing four basic criteria, or postulates, for deciding whether a disease is caused by a particular microorganism. Koch’s postulates are tabulated below:

Koch’s postulates

  1. The microorganism must be found in abundance in all individuals suffering from the disease and should not be found in healthy individuals.
  2. The microorganism must be isolated from a diseased individual and grown in pure culture.
  3. The cultured microorganism should cause disease when introduced into a healthy individual.
  4. The microorganism must be re-isolated from the inoculated individual and then identified as being identical to the original microorganism.

In the first and third postulates, Koch originally used the word “must” instead of “should.” He changed the wording when he learned that some carriers of cholera and typhoid were asymptomatic and remained healthy.

Since Koch presented his postulates, scientists have come to realize that all four postulates may not apply to every pathogenic microorganism. For example, while bacteria can be grown and identified in pure culture (Figure (PageIndex{5})), this is not the case with all pathogens, including viruses and prions. Therefore, these pathogens fail to meet the second postulate. Taking these and other exceptions into account, Koch’s postulates can be viewed as sufficient but not necessary criteria for establishing a specific agent as the cause of a disease. The postulates still inform the basic approach scientists take to this research. Koch’s postulates are also important for their historical significance. They led to the scientific identification of many human pathogens, which allowed the development of ways to prevent and cure diseases.

How Pathogens Cause Disease

Pathogens usually gain entrance to a human host through the mucosa in orifices like the oral cavity, nose, eyes, genitalia, or anus. Some pathogens may be swallowed and gain access through the mucosa lining the digestive tract. Other pathogens may enter a human host through breaks in the skin. Once pathogens gain entrance to a host, they multiply inside the host, either at the site of entry or at other sites after migrating from the entry site. Some pathogens live and multiply inside host cells; others live and multiply in host body fluids.

Within the host’s tissues, pathogens may cause damage by releasing toxins. For example, Clostridium tetani releases a toxin that paralyzes muscles, causing the disease known as tetanus. Typically, the more pathogens that are present, the greater the severity of illness, but there is considerable variation in the virulence of pathogens. The poliovirus is not very virulent. Fewer than 5 percent of people infected with poliovirus actually develop any noticeable symptoms of the disease. On the other hand, CJD prions are so virulent that they cause severe disease and death in every infected individual.

How Pathogens Are Transmitted

For pathogens to survive and repeat the cycle of infection in other hosts, they or their progeny must have a means of leaving one host and entering another. Transmission of pathogens from infected to noninfected human hosts occurs through many different routes.

  • Airborne Transmission: One of the most common routes is airborne transmission. As illustrated in Figure (PageIndex{6}), this occurs when pathogens in droplets are expelled from an infected host’s respiratory system during coughing or sneezing. The pathogens are then inhaled by nearby people, who become new hosts for the pathogens. Flu and the common cold can spread this way.

  • Direct Contact: Many pathogens spread from person to person through direct contact between an infected person and a new host. This can happen when people have skin-to-skin contact or touch the same surfaces. Athlete’s foot and warts are transmitted this way. Another form of direct contact is the oral transmission. This occurs when pathogens spread through direct oral contact, for example, by kissing, or by sharing items that go in the mouth, such as drinking glasses or eating utensils. Mononucleosis and oral herpes spread through oral contact.

  • Fecal-Oral Transmission: Fecal-oral transmission is also very common. It occurs when pathogens in feces from an infected host enter the mouth of a new human host in fecally contaminated food or water or on contaminated fingers. Cholera and many types of gastroenteritis are transmitted this way. Helminth infections are also usually spread via a fecal-oral route. Adult worms may live and produce eggs in the human host for several years. Generally, thousands or even hundreds of thousands of eggs are released each day. The eggs are then shed from the human host in feces. The eggs that hatch develop into larvae that may be consumed by a new human host in contaminated food or water. After being ingested, the larvae develop into adult worms that parasitize the new human host.

  • Vector Transmission: Vector transmission occurs when pathogens are carried by a vector organism from infected hosts to new hosts, usually through biting them. Mosquitoes, fleas, and other insects are common vectors. Figure (PageIndex{7}) describes four diseases that are spread by mosquito vectors.

  • Vertical Transmission: Vertical transmission occurs when pathogens travel from an infected woman to her embryo or fetus during pregnancy or to her infant during or soon after birth. Examples of diseases that can be transmitted this way include HIV infection and rubella. You can learn more about this type of transmission in the concept Embryonic Stage.

  • Sexual Transmission: Sexual transmission occurs when pathogens spread through sexual activity between an infected host and a new host. Sexual transmission generally requires direct contact between mucous membranes or their secretions. This can occur during any type of sexual contact, including vaginal, anal, or oral contact. Sexually transmitted infections include chlamydia and gonorrhea. To learn more about sexual transmission, read the concept of Sexually Transmitted Infections.

  • Transmission of Prions: Prions have unusual means of transmission. Some people have become infected with prions by eating meat from cows infected with mad cow disease. Prions that cause the human disease called kuru have been transmitted through cannibalism. Kuru is a deadly disease that was once commonly found in women and children of the Fore tribe in Papua New Guinea. Women and children were most often infected because they were more likely than males to eat highly infective brain material from the cannibalized bodies. Solving the mystery of this disease and its mode of transmission resulted in two Nobel Prizes.

Managing Infectious Disease

Infectious diseases must be correctly diagnosed so the appropriate treatment can be prescribed. Most infectious diseases can be treated if not cured. Many infectious diseases can be prevented through commonsense behaviors or immunizations.

Diagnosing Infectious Disease

Most minor infectious diseases, such as upper respiratory infections and diarrheal diseases, are usually diagnosed on the basis of their signs and symptoms. However, determining the specific pathogen that is causing the disease may be necessary to choose the best treatment. Many pathogens can be identified by growing samples from a patient on a culture medium or by examining samples from the patient under a microscope. Most bacteria can be identified from a culture based on the size, color, and shape of the colony. Viruses can be identified by using cells grown in culture as the medium. If viruses are pathogenic, they infect and kill the cultured cells. Biochemical tests can also be used to identify specific pathogens in patient samples. Some pathogens can be detected by testing for the chemical products they produce, such as acids, alcohols, or gases. Another potential diagnostic tool is a serological test, which identifies pathogens by their antigens and whether they bind to specific antibodies.

Treating Infectious Disease

Not all infectious diseases require treatment. Many minor infectious diseases are usually self-limiting and people get better on their own. For more serious infectious diseases, pharmaceutical drugs may be needed. Drugs have been developed to treat most types of infectious diseases. Different types of drugs are generally required to treat different types of pathogens.

  • Bacteria can often be killed with antibiotic drugs. Antibiotics typically work by destroying the cell wall of bacterial cells, causing the DNA inside to spill out. This makes the bacterial cells incapable of producing proteins, so they die. This generally cures the disease. Several different classes of antibiotics have been developed. Different types of bacteria are susceptible only to certain classes of antibiotics. Some bacteria have evolved the ability to resist some or all classes of antibiotics (see Explore More below).
  • Unlike bacteria, viruses are not killed by antibiotic drugs. However, antiviral drugs have been developed to help the immune system fight off viral infections. Antiviral drugs are generally not as effective at curing viral infections as antibiotics are at curing bacterial infections.
  • Most fungal infections can be treated or cured with antifungal medications. These may be taken orally or applied topically, depending on the disease. Most antifungal drugs are available only with a doctor’s prescription, but a few can be purchased over the counter (OTC). An example of an OTC antifungal product is pictured in Figure (PageIndex{8}).
  • Infections by protozoa are treated with antiprotozoal drugs. Because protozoans may vary greatly in their biology, drugs effective against one pathogen may not be effective against another. Several anti-malarial drugs have been developed, but the Plasmodium pathogens are evolving resistance to most of them.
  • Several drugs are available to kill worms in human hosts. Different drugs must be used for different helminthic parasites. The drugs kill off the adult worms, which are then shed in the host’s feces.

Unfortunately, infectious diseases caused by prions are not treatable at present. They are considered incurable and inevitably fatal diseases. The good news is that scientists are actively working to find ways to treat or cure prion diseases.

Preventing Infectious Disease

You have probably heard the expression “an ounce of prevention is worth a pound of cure.” It certainly applies to infectious diseases. Some side effects of treating minor infectious diseases can be worse than the disease symptoms. For example, taking an antibiotic for a minor sinus infection might lead to diarrhea or a vaginal yeast infection as beneficial bacteria are killed off along with harmful bacteria and causing homeostatic imbalance. It’s almost always better to avoid getting sick in the first place than to treat a disease after it occurs. Hygienic habits and immunizations are the most effective ways to prevent the spread of infectious diseases.

Hand washing and Other Behaviors

Frequent hand washing is the single most important defense against the spread of many pathogens, especially those transmitted through direct skin contact or the fecal-oral route. Hand washing can also reduce the spread of respiratory illnesses such as flu, coronavirus disease, and the common cold because the viruses can be spread on people’s hands when they touch their nose, mouth, or eyes. For the most effective way to wash your hands in order to prevent infection, see the Feature: My Human Body below.

What else can you do to protect yourself? You can use condoms to avoid sexually transmitted infections where there is a risk of transmission, for example, with a new partner. Condoms are the only method of contraception that also helps prevent the spread of such infections. Preventing the spread of infectious diseases transmitted by vectors often involves controlling the vectors or at least exposure to the vectors. For example, the number of mosquitoes can be reduced by removing sources of standing water around homes. Insect repellents and mosquito nets (like the one in Figure (PageIndex{9})) can be used to reduce human contact with vectors.

Immunization

Diseases that can be prevented with vaccinations include many otherwise common and potentially serious early childhood infections such as measles, mumps, chickenpox, whooping cough (pertussis), and diphtheria. Vaccinations also are recommended for older children against the human papillomavirus (HPV) that causes genital warts and may lead to cervical cancer in females. Annual vaccines for influenza (Figure (PageIndex{10})) are highly recommended as well, especially for young children and older adults. Pneumonia vaccines are also advised in certain people, particularly the elderly. Coronavirus diseases can also be combated by vaccination.

Some people cannot safely receive vaccines. For example, children with a compromised immune system or cancer may not be able to safely receive routine childhood vaccinations. To help protect such vulnerable people from being exposed to infectious diseases, it is important for populations to maintain high levels of vaccination. When a critical portion of a population is immunized against an infectious disease, most members of the population are protected against that disease even if they have not been immunized. This is known as herd immunity. You can see how it works in Figure (PageIndex{11}). The principle of herd immunity applies to many infectious diseases, including influenza, measles, and mumps, to name just a few.

Emerging Infectious Diseases

New infectious diseases are showing up in human populations. Called emerging infectious diseases, they can come about in a number of ways, most of which are influenced by human actions. New infectious diseases can emerge when previously harmless microorganisms evolve to become pathogenic to humans or when microorganisms that infect nonhuman animals jump to human hosts. Infectious diseases can also spread to faraway populations where people have no prior exposure and natural immunity to them. Human actions that influence the emergence of new infectious diseases include:

  • human encroachment on wild habitats. This may happen with residential development, mining, farming, or logging activities. It may bring humans into contact with insects and other animals that harbor previously unknown microorganisms that are pathogenic to people.
  • changes in agriculture. The introduction of new crops attracts new crop pests and the microbes they carry to farming communities. This exposes people to new pathogens.
  • uncontrolled urbanization. The rapid growth of cities in many developing countries concentrates large numbers of people in crowded areas with poor sanitation. Such conditions foster the transmission of pathogens that may not have been able to spread in small, dispersed rural populations.
  • modern transportation. Ships and other cargo carriers often inadvertently carry microscopic pathogens or their infected vectors to distant places where they can infect people who have never been exposed to them before. International jet travel allows infected people to carry pathogens to distant populations, even before their first symptoms appear.

Feature: My Human Body

Proper hand washing is the single most important behavior you can adapt to avoid infection by pathogens. The most effective hand washing method is to use soap and warm running water and the following procedure:

  1. Wet hands with warm water, keeping hands below the forearms to prevent contaminated water from moving from the hands to the arms.
  2. Apply about 5 mL (1 teaspoon) of liquid soap and rub it all over the hands for at least 20 seconds. Be sure to wash the most commonly missed areas, which are the thumb, wrist, areas between the fingers, and skin under the fingernails. Ideally, you should use a nail brush to remove any debris or microorganisms under the fingernails.
  3. Rinse thoroughly. Make sure the water flows from the wrist to the fingertips to ensure that any microorganisms are washed off the skin rather than up onto the arms.
  4. Dry hands thoroughly with a clean towel or hot air blower. Properly dispose of any used towels. If possible, use towels to turn faucets on and off and to open the bathroom door.

Review

  1. What are infectious diseases?
  2. Name types of pathogens and give an example of a human disease caused by each type of pathogen.
  3. What are Koch’s postulates? What is their current significance?
  4. How do pathogens cause disease? Identify two factors that influence the severity of an infectious disease.
  5. List six common routes of transmission of pathogens.
  6. Why is the correct diagnosis of a pathogen important for selecting the appropriate treatment of an infectious disease?
  7. What are the most effective ways to prevent the spread of infectious diseases?
  8. How does herd immunity come about, and why is it important?
  9. Explain how and why emerging infectious diseases are appearing in human populations.
  10. Explain why Koch’s first postulate alone would not provide sufficient evidence to prove that a specific microorganism causes a disease. In particular, discuss why postulates three and four are required.
  11. What is a disease burden?

    A. How many infectious pathogens are in an infected person.

    B. How many people are killed by an infectious disease each year?

    C. How rapidly an infectious disease spreads.

    D. The impact of a disease on a population, including the number of deaths and the associated financial impact.

  12. Give an example of a human disease that is caused by a protist and transmitted by a vector.

  13. What kind of treatment do you think might be given for leprosy? Explain your reasoning.

  14. True or False. The direct contact route of pathogen transmission requires skin-to-skin contact.

  15. True or False. Some people who are infected with a pathogen never show symptoms.

Explore More

For a fascinating read about an equally fascinating human infectious disease, check out Kuru Sorcery: Disease and Danger in the New Guinea Highlands by anthropologist Shirley Lindenbaum (2nd edition 2013, Routledge).

Scientists at Harvard Medical School have developed an innovative and fascinating way to study the emergence of antibiotic resistance in bacterial pathogens. To learn more, watch this video:

Attributions

  1. Typhoid Mary, public domain via Wikimedia Commons
  2. Candidiasis by CDC/ Sol Silverman, Jr., DDS, public domain via Wikimedia Commons
  3. Hookworms by CDC, public domain via Wikimedia Commons
  4. Robert Herman Koch, CC BY 4.0 via Wellcome Library
  5. Nutrient Agar growing common Gram negative Bacteria by Eukaryotica, public domain via Wikimedia Commons
  6. Disease Transmission sneezing by Centers for Disease Control and Prevention, public domain via Wikimedia Commons
  7. Mosquito carried diseases by NIAID, CC BY 2.0 via Wikimedia Commons
  8. Canesten by Editor182, public domain via Wikimedia Commons
  9. Javan bed canopy by Azt3cs, public domain via Wikimedia Commons
  10. A nurse vaccinates Barack Obama against H1N1 by White House (Pete Souza) / Maison Blanche (Pete Souza), public domain via Wikimedia Commons
  11. Community Immunity by National Institutes of Health (NIH), public domain via Wikimedia Commons
  12. Text adapted from Human Biology by CK-12 licensed CC BY-NC 3.0

How to manage Pseudomonas aeruginosa infections

Infections with Pseudomonas aeruginosa have become a real concern in hospital-acquired infections, especially in critically ill and immunocompromised patients. The major problem leading to high mortality lies in the appearance of drug-resistant strains. Therefore, a vast number of approaches to develop novel anti-infectives is currently pursued. Diverse strategies range from killing (new antibiotics) to disarming (antivirulence) the pathogen. In this review, selected aspects of P. aeruginosa antimicrobial resistance and infection management will be addressed. Many studies have been performed to evaluate the risk factors for resistance and the potential consequences on mortality and attributable mortality. The review also looks at the mechanisms associated with resistance – P. aeruginosa is a pathogen presenting a large genome, and it can develop a large number of factors associated with antibiotic resistance involving almost all classes of antibiotics. Clinical approaches to patients with bacteremia, ventilator-associated pneumonia, urinary tract infections and skin soft tissue infections are discussed. Antibiotic combinations are reviewed as well as an analysis of pharmacokinetic and pharmacodynamic parameters to optimize P. aeruginosa treatment. Limitations of current therapies, the potential for alternative drugs and new therapeutic options are also discussed.


Infectious Diseases

Illness and death from infectious diseases are particularly tragic because they are preventable and treatable. Not surprisingly, the poorest and most vulnerable are the most severely affected by infectious disease. Infectious diseases are a major cause of death, disability and social and economic turmoil for millions around the world. Poverty stricken countries lack access to health care. Reports show that in nations with the lowest economic status the causes of death are primarily infectious and nutritional diseases. Respiratory infections like the flu, pneumonia, diphtheria, and tuberculosis and gastrointestinal illnesses like dysentery and viral diarrhea kill children and adults most commonly in these countries. Unlike the United States, many children in these poor countries do not survive childhood diseases like chicken pox and measles. Also different from the United States, over 50% of deaths were due to infectious and parasitic diseases. In these developing countries chronic diseases such as cancer are only responsible for one fourth of all deaths, whereas in the US chronic diseases are responsible for about three fourths of all deaths.

Very crowded and poor living conditions make the people living in poverty vulnerable to infectious diseases such as tuberculosis and cholera. Poor nutrition and poor immune systems are high risk factors for several major killers including lower respiratory infections, tuberculosis and measles. In these poor countries there is limited access to health care. For example according to table 21.3, in the United States there are approximately 406 people per every doctor. In a poor country such as Ethiopia there are as many as 36,660 people per doctor. This means that for each person in the country to get seen one time a year every doctor would have to see over 100 patients a day every day of the week. Limited access to drugs makes treatable conditions like malaria, HIV, and tuberculosis fatal for the poor.

The most prominent infectious diseases in developing countries are malaria, schistosomiasis and trypanosomiasis. Malaria is the leading cause of death in tropical countries. More than one million deaths occur each year. Malaria is a vector borne parasitic infection. It is caused by a parasite that is transmitted through the bite of the Anopheles mosquito. Plasmodium is the causative organism. People infected with the parasite that causes malaria could experience weeks or months of bad health. Children and pregnant women are less likely to recover than adults who have built up immunity to the disease. Malaria has increased


Seroprevalence of Hepatitis B, Hepatitis C among Dental Technicans Admitted to Occupational Diseases Hospital

Citation: Cayci YT, Nadir OT, Dilek E, et al. Seroprevalence of Hepatitis B, Hepatitis C among Dental Technicans Admitted to Occupational Diseases Hospital. J Infec Dis Treat. 2016, 2:1. doi: 10.21767/2472-1093.10008

Abstract

Background: Hepatitis B (HBV) and Hepatitis C (HCV) are blood borne pathogens which are the major cause of viral hepatitis. And they are important occupational hazards for health care workers. In this we investigated the seroprevalance of HBV and HCV among dental technicans.
Materials and method: Sera samples were analyzed for Hepatitis B surface antigen (HBsAg), hepatitis B antibody (Anti-HBs) and hepatitis C antibody (Anti-HCV) in dental technicans who work in Ankara.
Results: Total of serology results of 583 dental technicans were evaluated. HBsAg, Anti-HBs and Anti-HCV were detected in 3.08%, 45.9% and 0%, respectively.
Conclusion: Dental technicans are not at risks for HBV and HCV more than the normal population.

Keywords

Hepatitis B Hepatitis C Dental personel Blood-borne pathogens

Introduction

Hepatitis B (HBV) and Hepatitis C (HCV) are blood borne pathogens which are health problems globally [1]. HBV and HCV viruses are the major cause of viral hepatitis. The cause acutechronic hepatitis which can lead cirrhosis and hepatocellular carcinoma [2]. It is estimated that 240 million people are infected with HBV and 130-170 million with HCV. Chronic hepatitis B and C are the cause of 60-70% of hepatocellular carcinoma worldwide [3]. Prevalence of HCV infection varies 0.3% to 13% among geographic regions. It has the highest prevalence in Central Africa and South-Eastern Asia [2]. Prevalence of HBV infection is classiified by the World Health Organisation (WHO) as high endemicity (>8%), intermediate (2-7%) and low endemicity (<2%) [4]. Turkey is accepted as intermediate endemicity country [5].

Both HBV and HCV are important occupational hazards for healthcare workers. HBV and HCV carriers are at risks for healthcare workers to transmit those viruses by contact of their blood and body fluids [2]. The dental personel, both dentists and technicans are at risk of occupational acquisition at HBV. In addition HBV, HCV is an another cause of parenterally acquired hepatitis in dental personel. Contemporary serological surveys have indicated that 2-30% of dental personel have serological evidence of pas tor current HBV infection. HCV risk appears to be lower than that for HBV [6].

The aim of this study is to determine the seroprevalence of HBV and HCV among dental technicans who work in Ankara, capital city of Turkey.

Material and Methods

Five hundred eigthy-three dental technicans who admitted Ankara Occupational Diseases Hospital in 2011-2013 were included in this study. All the serum samples taken from dental technicans were tested for HBsAg and Anti-HCV antibody by using Cobas 6000 (Roche Diagnostics) in 2011 and Architect i2000SR (Abbott Diagnostics) in 2012-2013.

Results

The dental technicans were included in this study who have been working in Ankara. The mean age of them was 33 (age range 17 and 61 years old). Of 583 dental technicans 562 (96.4%) of them were male and 21 (3.6%) of them were female.

HBsAg seropositivity was detected in 3.08% (18/583) of dental technicans. Of 18 dental technicans which were positive for HBV 1 was female. Among 538 dental technicans none have serological evidence for HCV. The positive AntiHBs titers (>10 mIU/ml) was detected in 45.9% (268/583) of them.

Discussion

HBV infection is an important problem that threating public health and estimated about two billion people has been infected by HBV at one time of their lives. HBV is responsible of 49.6% of acute viral hepatitis cases in Turkey. Turkey is accepted as medium endemicity (2-7%) region for HBV infection [7]. In our study, HBsAg seropositivity was found as 3.08% as predicted for Turkey. Incidence of HBV infection depends on several variable such as profession, enviromental factors, socio-economic status, level of education. It was reported that HBV prevalance is higher in Southeast Anatolia compared to other regions of Turkey [7].

Healthcare workers including doctors, nurses, laboratory personel, dentists, dental asistants and dental technicans are at risk for viral pathogens like HBV and HCV which are bloodborne pathogens [8,9]. The studies indicated that non-immunised general dental practitioners have 3 times more risks of acquiring HBV infection when compared with general population [6]. Studies showed that dental personel are at higher risk than general population. The HBV seropositivity among dentists were reported as 10.8% in Brazil, 9% in USA and 7% in Germany [10]. The prevelance HBV were varied in studies that conducted in our country among dental staff. HBV prevelance was determined as 8.2% in dental personel by Dogan et al. [11]. Ucmak et al. [12] reported that HBV prevelance was 2% in dental personel and none of them positive for HCV. Guzelant et al. [13] reported HBV prevelance as 2.5% in their study. In Germany, Ammon et al. [14] reported that HBV seropositivity was 1% and HCV seropositivity was 0% in dental asistants. Nagao et al. [10] were investigated 141 dental care workers in Japan and they did not detect any seropositivity for HBsAg and Anti-HCV. In New York city Anti-HCV seropositivity was investiagted among oral surgeons and general dentists and reported that Anti-HCV seropositivity was higher in oral surgeons than general dentists (9.3% vs 0.14%) [15]. In a study conducted by Thomas et al. [16] Anti-HCV and HBsAg seropositivity were found 2% and 21.2% in oral surgeons and 0.7% and 7.8% in general dentists, respectively.

Our study had some limitations. One of them is we did not have appropriate demographic datas about study population. The other issue was vaccination status of dental technicans not known.

Conclusion

In conclusion, in our country dental care workers are not at risks for HBV and HCV more than the normal population. However, it is important that infection control measures should be taken for safety of both health care workers and patients.


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List of Changes

Many thanks to reviewers of this text for their comments, suggestions, and corrections, most of which were incorporated throughout this new edition of Human Biology.

A thorough copy edit has improved the overall quality of the entire text.

As in the previous edition, the contributions of each organ system to maintaining homeostasis are emphasized throughout. A new homeostasis icon (scale) is used to identify homeostatic functions in the systems chapters, chapter 4 through chapter 16.

All statistics have been updated for this edition.

New Bioethical Focus readings present pros and cons on particular bioethical issues. Students are challenged to develop and defend his or her own opinions on the issues.

Chapter 4 - New title: Organization and Regulation of Body Systems. This was chapter 3, Introduction to Homeostasis, in the previous edition. The title was changed to better reflect the content of the chapter. Homeostasis was expanded and rewritten to provide better coverage of this topic.

Chapter 13: Nervous System has been extensively reorganized and rewritten. The discussion of the central nervous system now precedes that of the peripheral nervous system.

Chapter 19: Chromosomal Inheritance (previously chapter 18). This chapter has been reorganized. The human life cycle, including mitosis and meiosis, now begins the chapter. The chapter ends with a discussion of chromosomal inheritance abnormalities.

Chapter 23: Human Evolution (previously chapter 22: Evolution) has been completely rewritten and expanded. More detailed information on the origin of life and human evolution is given. This chapter contains many new, interesting, and helpful illustrations and photographs.

Chapter 24: Ecosystems and Human Interferences (previously chapter 23: Ecosystems). This chapter was rewritten and reorganized, and combines the material previously found in chapters 23 and 24.

Chapter 25: Conservation of Biodiversity is a completely new chapter, which discusses the current biodiversity crises including why we should care, the root causes, and how to preserve species and prevent extinctions.

e-Learning Connection is new to this edition, and gives access information to new learning technologies.

Chapter 1: A Human Perspective

This was the Introduction chapter in the previous edition.

1.2 The Process of Science includes an expanded explanation and summary of the scientific method.

New Bioethical Focus: Animals in the Laboratory

1.5 Flow diagram for the scientific method

Chapter 2: Chemistry of Life

This was chapter 1 in the previous edition.

2.6 Lipids. The discussion of soap was replaced by a discussion of emulsifiers.

New Bioethical Focus: Organic Pollutants

2.12 The pH scale 2.18 Glycogen structure and function

Chapter 3: Cell Structure and Function

This was chapter 2 in the previous edition.

3.3 Cellular Metabolism. The discussion of cellular respiration has been simplified. The phrase aerobic cellular respiration has been changed to cellular respiration for clarity.

New Bioethical Focus: Stem Cells

3.3 Animal cell 3.5 Tonicity 3.7 The nucleus and the nuclear envelope 3.9 The Golgi apparatus 3.12 Sperm cells 3.14 Cellular respiration

Chapter 4: Organization and Regulation of Body Systems

This was chapter 3, Introduction to Homeostasis, in the previous edition. The title was changed to better reflect the content of the chapter. Homeostasis was expanded and rewritten to provide better coverage of this topic.

4.1 Types of Tissues. As in the previous edition, this section covers the tissues, cavities, membranes, and organ systems of the human body. The term fiber (with regard to nerves) is explained. The phrase neuroglial cell has been changed to neuroglia throughout.

4.3 Organ Systems. This section has been reorganized so that the discussions of the Integumentary System and Regions of the Skin are kept together. The Working Together box has been moved to section 4.4 Homeostasis.

4.4 Homeostasis. The entire section has been rewritten and reorganized to give more emphasis on this topic. Negative and positive feedback mechanisms are more clearly explained in this edition. Regulation of Body Temperature has been moved to this section and rewritten. Homeostasis and Body Systems is new to this section.

4.2 Epithelial tissue 4.4 Connective tissue examples 4.6 Muscular tissue 4.11 Homeostasis 4.12 Negative feedback 4.13 Homeostasis and body temperature regulation 4.14 Regulation of tissue fluid composition

Part 2: Maintenance of the Human Body

Chapter 5: Digestive System and Nutrition

This was chapter 4 in the previous edition.

5.5 Nutrition. In the discussion of calcium, the usefulness of vitamin D and other vitamins in preventing osteoporosis is presented. The Health Focus "Weight Loss the Healthy Way" has been revised to improve clarity.

5.3 Swallowing 5.7 Hormonal control of digestive gland secretions

Chapter 6: Composition and Function of Blood

This was chapter 5 in the previous edition.

6.2 The White Blood Cells. Colony-stimulating factors (CSFs) are introduced.

6.3 Blood Clotting has been reorganized and rewritten.

6.5 Action of erythropoietin 6.8 Capillary exchange

Chapter 7: Cardiovascular System

This was chapter 6 in the previous edition. Throughout the chapter and entire text, the terms "O2-rich" and "O2-poor" replace the phrases "high in oxygen" and oxygenated" and "low in oxygen" or "deoxygenated."

7.4 The Vascular Pathways. The path of blood to and from the lower legs has been corrected and now includes the femoral artery, lower leg capillaries, and femoral vein.

7.6 Homeostasis. The end of the chapter has been repaged so that The Working Together page does not interrupt the end matter.

7.5 Internal view of the heart 7.6 Stages in the cardiac cycle 7.7 Conduction system of the heart

Chapter 8: Lymphatic and Immune Systems

This was chapter 7, Lymphatic System and Immunity, in the previous edition. The introductory story was revised to better introduce the immune system and its functions.

8.4 Induced Immunity. The immunization schedule for infants and young children has been updated to contain the latest requirements. In Cytokines and Immunity, the explanation of the technique to activate cytotoxic T cells to destroy cancer cells has been clarified. The explanation of the delayed allergic response has been simplified.

8.6 Clonal selection theory as it applies to B cells 8.8 Clonal selection theory as it applies to T cells 8.10b (updated Immunization table)

8.1 immunization table in Figure 8.10

Chapter 9: Respiratory System

This was chapter 8 in the previous edition.

9.3 The introductory paragraph was rewritten to emphasize the contribution of gas exchange to homeostasis.

9.5 Homeostasis has been rewritten and clearly explains how the respiratory system regulates pH and immunity.

9.1 The path of air(caption) 9.2 The respiratory tract 9.6 Vital capacity 9.8 Inspiration and expiration

Chapter 10: Urinary System and Excretion

This was chapter 9 in the previous edition.

10.1 has been revised to introduce the urinary system and the path of urine right away, before discussing the urinary organs. Some reorganization of heads allows the discussion of the role of kidneys in maintaining homeostasis to logically lead to a discussion of salt-water balance and acid-base balance.

10.7 Problems with Kidney Function. Replacing a kidney is a new topic to this edition.

New Bioethical Focus: Organ Transplants

10.1 Taking a drink of water 10.5 Nephron anatomy 10.7 Steps in urine formation 10.11 An artificial kidney machine

Part 3: Movement and Support in Humans

Chapter 11: Skeletal System

This was chapter 10 in the previous edition.

11.1 Tissues of the Skeletal System. The opening paragraph now introduces bone, cartilage, and connective tissues before discussing each in depth.

11.3 Bones of the Skeleton. The discussions of the pectoral girdle and arm have been rewritten, and the rotator cuff is mentioned.

11.4 Articulations has been revised - the discussion of arthritis has been expanded and was moved to the end of the section. The text for Figure 11.12 Joint Movements now more closely follows the illustration. The Working Together illustration now follows 11.5 Homeostasis, so it does not break up the text.

11.7 The vertebral column 11.8 Thoracic vertebrae and the rib cage 11.9 Bones of the pectoral girdle and arm 11.12 Joint movements, 11.13 Hip prosthesis

Chapter 12: Muscular System

This was chapter 11 in the previous edition.

12.4 Energy for Muscle Contraction introductory paragraphs have been rewritten for clarity. The discussion entitled Muscular Disorders is completely new and discusses muscle spasms and cramps, tendonitis, tetanus, muscular dystrophy, and myasthenia gravis.

12.7 Neuromuscular junction 12.12 Myasthenia gravis.

Part 4: Integration and Coordination in Humans

Chapter 13: Nervous System

This was chapter 12 in the previous edition. This chapter has been extensively reorganized. Many sections and topics have been rewritten. The central nervous system, limbic system, memory, language, and speech are discussed before the peripheral nervous system. Homeostasis ends the chapter.

13.1 Nervous Tissue was previously entitled Neurons and How They Work. Neuron Structure and Myelin Sheath have been rewritten. Synaptic Integration now follows the discussion of transmission across a synapse.

13.2 The Central Nervous System is discussed next in the logical sequence of spinal cord and brain. Functions of the Spinal Cord has been rewritten and now discusses the role the spinal cord plays in regulating internal organs in addition to the skeletal muscles. Parts of the brain are discussed in more depth.

13.3 The Limbic System and Higher Mental Functions contains discussions of the limbic system, memory and learning, and language and speech. (The discussion of Alzheimer disease has been moved to the end of the chapter).

13.4 The Peripheral System. The organization and content of this section remains essentially the same as in the last edition.

13.6 Homeostasis has been expanded to include discussions of two degenerative nervous system diseases, Alzheimer disease and Parkinson disease. The Alzheimer disease discussion has been updated with the newest information, and the Parkinson disease discussion is new to this chapter.

13.1 Organization of the nervous system 13.3 Myelin sheath 13.4 Resting and action potential 13.5 Synapse structure and function 13.6 Integration 13.7 Organization of the nervous system 13.9 The human brain 13.10 The cerebral cortex 13.12 The limbic system 13.13 Long-term memory circuits 13.15 Cranial and spinal nerves 13.16 A reflex arc 13.18 Drug actions at a synapse 13.19 Drug use 13.20 Alzheimer disease.

This was chapter 13 in the previous edition.

14.1 Sensory Receptors. Table 14.1 Exteroceptors is new and replaces Table 13.1 Special Sense Organs. Discussions of sensory receptors have been revised. How Sensation Occurs has been revised to include the influence of the reticular activating system, and how sensory receptors contribute to homeostasis.

14.2 Proprioceptors and Cutaneous Receptors. New A head title identifies and focuses the discussion of these topics. The topics Cutaneous Receptors and Pain Receptors were revised.

14.6 Sense of Equilibrium. Terminology has been changed. The term dynamic equilibrium has been changed to rotational equilibrium, and the term static equilibrium has been changed to gravitational equilibrium. The Health Focus reading Protecting Vision and Hearing now follows the discussion of hearing and is found at end of the chapter.

14.2 Sensation 14.10 Structure and function of the retina 14.15 Mechanoreceptors for equilibrium

14.1 Exteroceptors is new and replaces Table 13.1 Special Sense Organs

Chapter 15: Endocrine System

This was chapter 14 in the previous edition. The chapter has been reorganized, and some heads have changed. The chapter now ends with Chemical Signals (previously called Environmental Signals), instead of beginning with it. The introductory story is new. Terminology change: contrary hormone has been changed to antagonistic hormone. As before, each gland is discussed in turn with an emphasis on medical disorders caused by too much or too little hormones.

15.1 Endocrine Glands introduces and defines endocrine glands and hormones in general, and discusses the contribution of hormones to homeostasis. Table 15.1 logically ends this section.

15.4 Adrenal Glands. Glucocorticoids has been revised it now precedes the discussion of mineralocorticoids.

15.7 Chemical Signals. The information in this section has been reorganized and rewritten, and includes the discussion of steroid and peptide hormones. Hormonal versus Neural Signals includes the material formerly discussed in Environmental Signals.

New Health Focus: melatonin

New Bioethical Focus: Fertility Drugs

15.1 Puberty 15.9 Adrenal glands 15.14 Glucose tolerance test 15A Melatonin production 15.16 Cellular activity of hormones 15.17 Chemical signals 15B Higher-order multiple births

Part 5: Reproduction in Humans

The AIDS supplement and chapter 17 regarding STDs have been rewritten to include the latest research, techniques, and information.

Chapter 16: Reproductive System

This was chapter 15 in the previous edition. Development of Male and Female Sex Organs has been moved to chapter 18 Development and Agin.

16.1 Male Reproduction System. The discussion of sperm production and movement has been rewritten.

16.2 Female Reproduction System. The discussions of external genitals and orgasm in females has been rewritten.

16.3 Female Hormone Levels. The discussion of follicle development has been rewritten.

16.4 Control of Reproduction. Information about the "male pill" has been updated. Infertility is redefined. New to this section are discussions of fertility drugs, higher-order births, and vasectomy reversals. The terminology Assisted Reproductive replaces the terminology Alternative Methods of Reproduction in the previous edition. A new procedure called Intracytoplasmic Sperm Injection (ICSI) is covered in this section.

New Bioethical Focus: Assisted Reproductive Technologies.

16.3 Testis and sperm 16.9 Female hormone levels 16.10 Implantation 16.12 In vitro fertilization 16B Couples and children

Chapter 17: Sexually Transmitted Diseases

This was chapter 16 in the previous edition. The chapter has been revised to include non-sexually transmitted infectious diseases caused by viruses, bacteria, fungi, and other animals. Statistics of new cases of AIDS and other STDs have been updated to reflect the most current information from the Centers of Disease Control.

17.1 Viral Infectious Diseases (previously Viral in Origin) has been rewritten and the discussion of the typical DNA animal virus life cycle has been simplified for better understanding Figure 17.3 illustrating this life cycle has also been simplified. The discussion of HIV infections summarized and identifies types and subtypes of HIV found in Africa and in the United States. HIV infections and AIDS are covered in detail in the AIDS supplement.

17.2 Bacterial Infectious Diseases (previously Bacterial in Origin). All statistics have been updated.

17.3 Other Infectious Diseases (previously Other Sexually Transmitted Diseases) has been rewritten and includes a more detailed introduction to kingdoms Protista, Fungi, and Animalia, and how these organisms transmit infectious diseases. Several diseases caused by protozoa are discussed. There is a new topic on infectious diseases caused by fungi. The topic on infectious diseases caused by animals discusses head lice and parasitic worms, as well as pubic lice.

New Bioethical Focus: HIV Vaccine Testing in Africa

17.3 Life cycle of an animal DNA virus 17.4 Genital warts 17.5 Genital herpes 17.8 Chlamydial infection 17.10 Gonorrhea 17.12 Syphilis 17A AIDS in Africa 17.13 Organisms that cause vaginitis 17.14 Sexually transmitted animal

17.1 Infectious Diseases Caused by Viruses (revised) 17.2 Infectious Diseases Caused by Bacteria (revised) 17.3 Infectious Diseases Caused by Protozoa, Fungi, and Animals (new).

All sections of The AIDS Supplement have been rewritten and updated with the latest research, information, and statistics. The new introduction identifies the types and subtypes of HIV. The prevalence of AIDS in Africa and other less-developed countries is presented in the introductory story and reinforced in Figure S.2 and in Section S.1, which has been extensively rewritten.

S.2 Phases of an HIV Infection identifies HIV-1B as the prevalent subtype in the U.S. The definitions of the three categories remain the same. The discussions of the HIV structure and life cycle have been simplified for better understanding Figure S.5 illustrating the reproduction of HIV has also been simplified. The discussion of drug therapy and vaccines have been revised, reflecting the latest information on therapies now in use, in trials, and undergoing research.

A new Health Focus reading, Preventing Transmission of HIV, gives more emphasis to this information, which was contained in section S.4 in the previous edition.

S.2 Global HIV prevalence rates in adults at the end of 1999 S.5 Reproduction of HIV.

Chapter 18: Development and Aging

This was chapter 17 in the previous edition.

18.1 Fertilization has been completely rewritten and clearly shows the steps of fertilization. Figure 18.2 has been corrected.

18.2 Development Before Birth. The topic Gastrulation has been reorganized, rewritten, and clarified. The difference between embryonic development and fetal development is made clear in the discussion of embryonic development. New to this section, the discussion of the first month of embryonic development introduces stem cells and the controversy over using embryonic stem cells to cure human conditions. Much of the information in the First Month has been rewritten. Includes 18.3 Development of Male and Female Sex Organs (previously in the reproduction chapter).

18.4 Birth has been rewritten and explains the positive feedback mechanism in relation to the onset and continuation of labor.

There is a new discussion of the benefits of breast feeding to the mother and child under female breast and lactation.

New Bioethical Focus: Maternal Health Habits

18.2 Fertilization 18.3 Human development before implantation 18.4 Early developmental stages in cross section 18.7 Fetal circulation and the placenta 18.9 Human embryo at five weeks 18.10 A three- to four-month-old fetus 18.11 A six- to seven-month-old fetus 18B Health habits

Part 6: Human Genetics

Chapter 19: Chromosomal Inheritance

This was chapter 18 in the previous edition. The chapter has been reorganized. The human life cycle, including mitosis and meiosis, now begins the chapter. The chapter ends with a discussion of chromosomal inheritance abnormalities.

19.2 Mitosis contains a new topic Cytokinesis, which discusses cytokinesis and formation of a cleavage furrow.

19.4 Chromosomal Inheritance. The discussion of nondisjunction now precedes an expanded explanation of nondisjunction, how it occurs, and its resulting chromosomal abnormalities. Down syndrome and other syndromes caused by abnormalities in chromosome makeup follow the discussion of nondisjunction. The term triplo-X syndrome has been changed to poly-X syndrome.

New Bioethical Focus: Cloning in Humans

19.1 Life cycle of humans 19.8 Spermatogenesis and oogenesis 19.9 Human karyotype preparation

19.1 Meiosis I Versus Mitosis 19.2 Meiosis II Versus Mitosis These new tables help summarize the information given in the chapter.

Chapter 20: Genes and Medical Genetics

This was chapter 19 in the previous edition. This chapter has been fewer A heads. The new section 20.3 Beyond Simple Inheritance Patterns includes polygenic inheritance, multiple allelic traits, and incompletely dominant traits. Four sets of Practice Problems have been added.

20.2 Dominant/Recessive Traits. Recessive Disorders are now discussed before dominant disorders. Pedigree Charts makes it clear that with recessive genetic disorders, when both parents are affected, all children are affected (and why) and with dominant genetic disorders, two affected parents can have an unaffected child (and why). This information will help the student be able to understand and successfully answer the related practice problems.

20.3 Beyond Simple Inheritance Patterns includes polygenic inheritance, multiple allelic traits, and incompletely dominant traits.

New Bioethical Focus: Genetic Profiling

20.2 Genetic inheritance 20.9 Autosomal recessive pedigree chart 20.10 Autosomal dominant pedigree chart 20.12 Inheritance of blood type 20.13 Incomplete dominance 20.14 Cross involving an X-linked allele 20.15 X-linked recessive pedigree chart 20A Genetic profiling

Chapter 21: DNA and Biotechnology

This was chapter 20 in the previous edition. Most main sections and topics were rewritten for clarity.

21.1 DNA and RNA Structure and Function. Most topics in this section were rewritten for clarity.

21.2 Gene Expression. The DNA Code and Transcription topics were rewritten for clarity.

21.3 Biotechnology. Polymerase Chain Reaction was rewritten for clarity. Cloning of Transgenic Animals was updated, and the diagram (Fig. 21.18) that illustrates this procedure has been simplified for better understanding. The Human Genome Project discussion was updated to include recent achievements in that area. Gene sequencing of diseases or afflictions found on chromosome 17 is illustrated in new Figure 21.19. The Gene Therapy discussion has been updated and greatly expanded. It gives new information on gene therapy treatments for cystic fibrosis and for children with SCID using bone marrow stem cells. It also discussed the possibilities for the use of gene therapy to treat other illnesses, such as hemophilia, AIDS, cancer, and heart disease.

New Health Focus: Organs for Transplant

New Bioethical Focus: Transgenic Plants

21.2 DNA location and structure 21.9 Function of introns 21.16 Polymerase chain reaction 21.18 Genetically engineered animals 21.19 Genetic map of chromosome 17 Colors have been made consistent in all DNA/RNA illustrations.

21.2 Some DNA Codes and RNA Codons has been expanded.

This was chapter 21 in the previous edition. Statistics have been updated.

22.2 Origin of Cancer. Regulation of the Cell Cycle has been reorganized and rewritten for better understanding of the stimulatory and inhibitory pathways involved in the action of proto-oncogenes and tumor-suppressor genes. Apoptosis has been rewritten and contains new information on caspases and how they work to bring about apoptosis.

22.4 Diagnosis and Treatment. Future Therapies, which ends the section and the chapter has been updated and includes new information and a new illustration regarding cancer vaccine therapy and inhibitory drug therapy (previously called chemoprevention).

The Health Focus and Bioethical Focus readings have been moved to the end of the chapter so text is not interrupted.

New Bioethical Focus: Tobacco and Alcohol Use

22.3 Origin of cancer 22.4 Function of p53 22.5 Industrial chemicals 22.7 Treatment of cancer 22.8 Cancer vaccine

Part 7: Human Evolution and Ecology

Part 7 contains a new part introduction. Chapter 25 Conservation of Biodiversity is a completely new chapter.

Chapter 23: Human Evolution

This was chapter 22, Evolution, in the previous edition. The entire chapter has been completely rewritten and expanded to include more detailed information on the origin of life and human evolutionary events. This chapter contains many new, interesting, and helpful illustrations and photographs. The chapter has a new introductory story.

23.1 Origin of Life (previously 22.3 Organic Evolution). This section has been rewritten in more detail and Miller's experiment is explained. Taxonomy has been moved to 23.3 Humans are Primates. Only the classification of humans is examined.

23.2 Biological Evolution includes evidences of evolution - common descent and natural selection. The entire section has been rewritten. Each topic goes into more detail than previously.

23.3 Humans are Primates. This section has been completely rewritten. Characteristics of primates and the primate evolutionary tree are examined.

23.4 Evolution of Australopithecines. This new section gives details about the discoveries of australopithecine fossils in Southern and Eastern Africa.

23.5 Evolution of Humans. This entire section has been rewritten and has much more information and detail than in the previous edition.

New Bioethical Focus: The Theory of Evolution.

23.1 Chemical evolution 23.2 Fossils 23.3 Mechanism of evolution 23.4 Primate evolutionary tree 23.5 Australopithecus africanus 23.6 Human evolution 23.7 Homo erectus 23.8 Origin of modern humans 23.9 Neanderthals 23.10 Cro-Magnons 23A Australopithecus africanus skull

23.1 Evolution and Classification of Humans

Chapter 24: Ecosystems and Human Interferences

This was chapter 23 Ecosystems in the previous edition. This chapter has been rewritten and reorganized, and combines the material previously found in chapters 23 and 24.

24.2 Energy Flow and Chemical Cycling is now a main head, which emphasizes its importance. The content is the same as in the previous edition.

24.3 Global Biogeochemical Cycles. The order of the cycles has been changed to this: water cycle, carbon cycle, nitrogen cycle, and phosphorus cycle.

The discussion of the carbon cycle has been reorganized and rewritten. The topic Carbon Dioxide and Global Warming is new and contains information and statistics on global warming.

The discussion of the nitrogen cycle has been reorganized and rewritten. The topic Nitrogen and Air Pollution is new and contains information about acid rain, smog, and thermal inversions.

In the discussion of the phosphorus cycle, the Phosphorus and Water Pollution is new and contains information on eutrophication, biological magnification, and pollution of coastal regions and the seas.

New Health Focus: Stratospheric Ozone Depletion Threatens the Biosphere.

New Bioethical Focus: Preserving Ecosystems Abroad

24.2 Example of primary succession 24.5 Nature of an ecosystem 24A Ozone shield depletion 24B preserving ecosystems

Chapter 25: Conservation of Biodiversity

Chapter 25 Conservation of Biodiversity is a completely new chapter, which discusses the current biodiversity crises including why we should care, the root causes, and how to preserve species and prevent extinctions.


Conclusions

This study has demonstrated that high rates of natural ventilation may be achieved in healthcare facilities through simple modifications to existing infrastructure, greatly reducing the risk of TB infection for little or no cost. Where climate permits, such architectural modifications have great potential for reducing TB transmission in healthcare facilities and other institutional settings, and are ideally suited to low resource settings. In the current era of dual HIV and TB epidemics, and emerging MDR and XDR-TB, these simple interventions may help to prevent healthcare settings from propagating the very diseases they are attempting to treat.


Treatment of relapses

The overall goal of MS management is to control disease activity, halt progression and, ideally, induce reversal of neurological deficits. This endeavour involves long-term administration of disease-modifying drugs.

Two-thirds of patients experience a relapsing–remitting form of the disease. New or reoccurring focal neurological deficits or signs in the context of MS are considered to be relapses 22 . These relapses are usually treated with pulsed high doses of glucocorticosteroids, and steroid-refractory relapses can be treated with plasmapheresis. The anti-inflammatory effects of these treatment options attenuate acute exacerbations and hasten recovery. In contrast to DMTs, which are aimed at reducing disease activity, as reflected by the annual relapse rate and disease progression, the treatment of relapses is an acute intervention.

Glucocorticosteroids

In general, most patients start with relapsing–remitting MS (RRMS) which, over time, evolves into secondary progressive MS (SPMS). A minority of patients never present with RRMS but experience primary progressive MS (PPMS) from the start. Glucocorticosteroids are mainly used in high doses for short periods of time (0.5–3.0 g daily for 3–5 days, for example) to treat acute exacerbations in MS 23,24,25,26 . Although convincing class I evidence is lacking, repeated pulse therapy (every 3 months, for example) is also used in occasional patients with SPMS or PPMS 23,24,27 . Mechanistically, glucocorticosteroids have pleiotropic effects: they curtail the production of numerous inflammatory mediators and attenuate the migration of immune cells across the blood–brain barrier.

Long-term continuous glucocorticosteroid administration, which is not typically used in the treatment of MS, is associated with bacterial, viral, fungal and parasitic infections 28 . Patients receiving this uninterrupted therapy, to treat rheumatoid arthritis for example, are susceptible to more-severe courses of infection, and the treatment might reactivate dormant conditions 29 . Moreover, clinical signs of infection can be diminished or masked by glucocorticoid treatment, making localization of the infection site more difficult.

The association between pulsed high-dose glucocorticosteroid treatment and serious infectious complications is less clear. In contrast to continuous treatment, repeated pulse therapy, even at very high doses, does not increase the propensity to develop bacterial or fungal infections, but severe viral infections, such as varicella zoster virus (VZV) or herpes simplex virus (HSV), can develop 30 (Table 2). Therefore, it is advisable to routinely test for some of these potentially masked infections during the treatment of MS with glucocorticosteroids 31,32 (Table 3).

Plasmapheresis

Plasmapheresis (also known as plasma exchange), which rapidly removes pathogenic substances such as autoantibodies, immune complexes and cytokines from the circulation, can be a therapeutic option in glucocorticosteroid-refractory MS relapses 33,34,35,36,37 . In general, five to eight courses of plasmapheresis are used as escalating treatment. Plasmapheresis is an invasive therapy that exposes the patient to the risk of infection, primarily through the central venous catheter but also via the elimination of immunoglobulins or complement components 38 .

Several small studies and case series that involved patients with MS and with other diseases reported different rates of infectious complications associated with plasmapheresis 34,39,40,41 . In larger studies, the reported incidence of catheter-associated complications ranges from 0.5% to 3.3% in patients with chronic hepatitis C, Guillain–Barré syndrome or other neurological diseases 42,43,44 . A series of 1,283 plasmapheresis treatments in 79 patients with neurological conditions did not reveal any severe adverse effects or infection with hepatitis B, hepatitis C or HIV 42 . Similarly, no plasmapheresis-associated infections were detected in 2,502 plasmapheresis sessions in a cohort of 335 patients (among which over 90% had neurological diseases) 45 or in a smaller study of 154 courses of plasmapheresis in 17 patients with neurological conditions 46 . Transmission of viral infections becomes more frequent if plasmapheresis requires the use of fresh frozen plasma rather than albumin 34,47,48 .


Infectious agents and inflammation in donated hearts and dilated cardiomyopathies related to cardiovascular diseases, Chagas' heart disease, primary and secondary dilated cardiomyopathies

Clinical and experimental conflicting data have questioned the relationship between infectious agents, inflammation and dilated cardiomyopathy (DCM).

Objectives

The aim of this study was to determine the frequency of infectious agents and inflammation in endomyocardial biopsy (EMB) specimens from patients with idiopathic DCM, explanted hearts from different etiologies, including Chagas' disease, compared to donated hearts.

Methods

From 2008 to 2011, myocardial samples from 29 heart donors and 55 patients with DCMs from different etiologies were studied (32 idiopathic, 9 chagasic, 6 ischemic and 8 other specific etiologies). Inflammation was investigated by immunohistochemistry and infectious agents by immunohistochemistry, molecular biology, in situ hybridization and electron microscopy.

Results

There were no differences regarding the presence of macrophages, expression of HLA class II and ICAM-I in donors and DCM. Inflammation in Chagas' disease was predominant. By immunohistochemistry, in donors, there was a higher expression of antigens of enterovirus and Borrelia, hepatitis B and C in DCMs. By molecular biology, in all groups, the positivity was elevated to microorganisms, including co-infections, with a higher positivity to adenovirus and HHV6 in donors towards DCMs. This study was the first to demonstrate the presence of virus in the heart tissue of chagasic DCM.

Conclusions

The presence of inflammation and infectious agents is frequent in donated hearts, in the myocardium of patients with idiopathic DCM, myocardial dysfunction related to cardiovascular diseases, and primary and secondary cardiomyopathies, including Chagas' disease. The role of co-infection in Chagas' heart disease physiopathology deserves to be investigated in future studies.


Watch the video: Eliminating Infectious Diseases 2030 Full version (June 2022).


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