Emergence of an influenza virus that is as deadly as the avian H5N1 virus and is spread between people as easily as the swine H1N1 virus would be a very serious threat to human health. These three viruses, which all cause severe respiratory illnesses and can be fatal, originated in bats and spilled over into the human population through close contact with an intermediate animal.
For SARS, an unprecedented global response halted the spread of the causative virus but not before people had been infected and died. MERS has been largely contained but not before spreading to 27 countries and causing 2, infections and close to deaths. Aided by delayed and uncoordinated global responses, insufficient containment measures, and the fact that infected people can transmit the virus even in the absence of symptoms, the virus raged beyond the ability to control its spread and resulted in a worldwide pandemic that has lasted over a year and caused around three million deaths globally.
An example of an emerging infectious disease that can be attributed to human practices is HIV. It is thought that humans were first infected with HIV through close contact with chimpanzees, perhaps through bushmeat hunting, in isolated regions of Africa.
It is likely that HIV then spread from rural regions into cities and then internationally through air travel. Further factors in human behavior, such as intravenous drug use, sexual transmission, and transfer of blood products before the disease was recognized, aided the rapid and extensive spread of HIV. One instance of a tropical disease that has spread recently into new areas that may be due, at least in part, to changing climate is chikungunya.
Chikungunya disease is caused by the chikungunya virus, a relative of the virus that causes Dengue fever. It is transmitted by the tiger mosquito, and in the past was confined to tropical regions around the Indian Ocean. In late summer of , more than residents of the town of Ravenna, Italy suffered from a mysterious disease that produced fever, exhaustion, and severe bone pain. The outbreak was eventually shown to be caused by chikungunya virus.
The virus arrived in the United States in the summer of , although thus far local transmission of chikungunya virus has been limited to Florida and Texas. Although chikungunya virus does not usually cause a fatal disease, it serves as a warning that other, more devastating tropical diseases could follow. In fact, a more serious threat is the recently emergent Zika virus in the Americas which is associated with a birth defect known as microcephaly.
Finally, the Ebola virus epidemic that emerged in in West Africa illustrates how a virus that previously affected only small groups of people, perhaps a few hundred, can sweep rapidly through an area to affect tens of thousands, and become extremely difficult to contain. A combination of factors including high population densities, increased travel, closer contact with wild animals, weak health care systems, and a slow response led to the worst outbreak of Ebola the world has ever seen.
The development of vaccines and antimicrobial drugs and the remarkable eradication of smallpox had created hope that infectious diseases could be controlled or even eliminated. However, the current realization that infectious diseases continue to emerge and re-emerge including the possibility of bioterrorism , underscores the challenges ahead in infectious disease research. Enzymes that use ATP will A: Enzymes are generally proteins and these are not used up in the reaction.
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These molecu Q: Which choice is true of both cardiac and skeletal muscle? A: The Muscle is a soft tissue that contains actin and myosin protein filament that are responsible for Q: What mechanisms link low systemic blood pressure in this patient to the low urine output? A: Filteration of blood for waste takes place in the kidney' functional unit called the nephron. Q: Explain haplosufficient and haploinsufficient and give an example. Factors in the emergence of infectious diseases.
Emerging Infectious Diseases [Serial online], 1 1. June ; Satcher, D. Emerging more A review of Figure 7 reveals that environmental changes are related to the emergence of many infectious diseases. For example, Lyme disease, hantavirus pulmonary syndrome HPS , and Lassa fever all emerged when humans began encountering the insect vector for Lyme disease or rodent host for HPS and Lassa fever of the causative agents in greater numbers than ever before.
Factors related to the emergence of infectious diseases such as Legionnaire disease and hemolytic uremic syndrome include changing technologies: air conditioning systems for the former disease and mass food production for the latter.
Re-emerging infectious diseases are diseases that once were major health problems globally or in a particular country, and then declined dramatically, but are again becoming health problems for a significant proportion of the population malaria and tuberculosis are examples. Many specialists in infectious diseases include re-emerging diseases as a subcategory of emerging diseases.
Figure 8 lists examples of re-emerging infectious diseases. The origin of plagues: Old and new. Science, : —; Measles—United States, April 17, Morbidity and Mortality Weekly Report, 47 14 : —; more A review of Figure 8 reveals some explanations for the re-emergence of infectious diseases.
Tuberculosis has re-emerged due to evolution of the causative bacteria. The pathogen has acquired resistance to the antibiotics used to treat tuberculosis either through mutation or genetic exchange and the long-term use of antibiotics both within one individual and across the population has selected for the pathogen's proliferation. Malaria has also become drug resistant, and the vector mosquito has acquired resistance to pesticides as well. The re-emergence of diseases such as diphtheria and whooping cough pertussis is related to inadequate vaccination of the population.
When the proportion of immune individuals in a population drops below a particular threshold, introduction of the pathogen into the population leads to an outbreak of the disease.
Despite the challenges of emerging and re-emerging infectious diseases, the results of basic research, such as that sponsored by NIH, show that there is reason for hope. AIDS was first described in , and it took two years to identify the retrovirus that causes AIDS, which was named the human immunodeficiency virus. In contrast, less than four months elapsed between the description of hantavirus pulmonary syndrome HPS in and the identification of the previously unknown viral agent, now called Sin Nombre virus.
One difference between these two cases is that the years that intervened between the advent of AIDS and the advent of HPS saw the development of polymerase chain reaction, a powerful new research technique that allows rapid identification of causative agents. Other examples of the benefits of basic research include the development of HIV protease inhibitors by researchers funded by NIH and others.
One active area of research at NIH is the development of new types of vaccines based on our new understanding of the immune system. In addition, basic research on the immune system and host pathogen interactions has revealed new points at which vaccines could work to prevent diseases.
Finally, basic research on the ecology of disease organisms—their reservoirs, modes of transmission, and vectors, if any—reveals points at which preventive measures can be used to interrupt this cycle and prevent the spread of disease. For example, research supported by NIAID delineated the mechanism of Lyme disease transmission and how disease results: The tick vector was identified and the life cycle of the causative bacterium was traced through deer and rodent hosts.
Understanding this ecology has led to predictions about the regions where and years when the threat of Lyme disease is greatest, as well as recommendations to the public for avoiding infection. These examples and others demonstrate that investment in basic research has great long-term payoffs in the battle against infectious diseases. What are the implications of using science to improve personal and public health in a pluralist society?
As noted earlier, one of the objectives of this module is to convey to students the relationship between basic biomedical research and the improvement of personal and public health. One way to address this question is by attending to the ethical and public policy issues raised by our understanding and treatment of infectious diseases. Ethics is the study of good and bad, right and wrong. It has to do with the actions and character of individuals, families, communities, institutions, and societies.
During the last two and one-half millennia, Western philosophy has developed a variety of powerful methods and a reliable set of concepts and technical terms for studying and talking about the ethical life. Generally speaking, we apply the terms "right" and "good" to those actions and qualities that foster the interests of individuals, families, communities, institutions, and society. Here, an "interest" refers to a participant's share or participation in a situation.
The terms "wrong" or "bad" apply to those actions and qualities that impair interests. Ethical considerations are complex, multifaceted, and raise many questions. Often, there are competing, well-reasoned answers to questions about what is right and wrong, and good and bad about an individual's or group's conduct or actions.
Thus, although science has developed vaccines against many diseases, and public health laws encourage their widespread use, individuals are permitted in most, but not all, states to choose not to be vaccinated.
Typically, answers to these questions all involve an appeal to values. A value is something that has significance or worth in a given situation. One of the exciting events to witness in any discussion in ethics in a pluralist society is the varying ways in which the individuals involved assign value to things, persons, and states of affairs. Examples of values that students may appeal to in discussions of ethical issues include autonomy, freedom, privacy, protecting another from harm, promoting another's good, justice, fairness, economic stability, relationships, scientific knowledge, and technological progress.
Acknowledging the complex, multifaceted nature of ethical discussions is not to suggest that "anything goes. First, ethics is a process of rational inquiry. It involves posing clearly formulated questions and seeking well-reasoned answers to those questions.
For example, developing countries suffer particularly severely from many infectious diseases because conditions of crowding and poor sanitation are ideal for the growth and spread of pathogens.
The same is true for many inner city environments. These places provide a constant reservoir of disease-causing agents. We can ask questions about what constitutes an appropriate ethical standard for allocating health care funds for curtailing the spread of infectious diseases. Should we expend public research dollars to develop drugs whose cost will be out of reach for developing countries or those in the inner cities?
Is there any legal and ethical way for the United States to prevent over-the-counter sales of antibiotics in other countries, a practice that may enhance the evolution of antibiotic resistant pathogens? Well-reasoned answers to ethical questions constitute arguments.
Ethical analysis and argument, then, result from successful ethical inquiry. Second, ethics requires a solid foundation of information and rigorous interpretation of that information. For example, one must have a solid understanding of infectious disease to discuss the ethics of requiring immunizations and reporting of infectious diseases. Ethics is not strictly a theoretical discipline but is concerned in vital ways with practical matters. This is especially true in a pluralist society.
Third, because tradeoffs among interests are complex, constantly changing, and sometimes uncertain, discussions of ethical questions often lead to very different answers to questions about what is right and wrong and good and bad.
For example, we acknowledge that individuals have a right to privacy regarding their infectious disease status. Yet, some argue that AIDS patients who knowingly infect others may have their right to privacy overridden so that partners may be notified of the risk of contracting AIDS.
It is our hope that completing the activities in this module will help students see how understanding science can help individuals and society make reasoned decisions about issues relating to infectious diseases and health. Science provides evidence that can be used to support ways of understanding and treating human disease, illness, deformity, and dysfunction.
But the relationships between scientific information and human choices, and between choices and behaviors, are not linear. Human choice allows individuals to choose against sound knowledge, and choice does not necessarily lead to particular actions.
Nevertheless, it is increasingly difficult for most of us to deny the claims of science. We are continually presented with great amounts of relevant scientific and medical knowledge that is publicly accessible. As a consequence, we can think about the relationships among knowledge, choice, behavior, and human welfare in the following ways:.
One of the goals of this module is to encourage students to think in terms of these relationships, now and as they grow older. Infectious disease syndrome that is caused by the human immunodeficiency virus HIV. Characterized by the loss of a normal immune response and increased susceptibility to opportunistic infections and some cancers. Specific immunity that develops after exposure to a particular antigen or after antibodies are transferred from one individual to another.
Synthetic drug with antiviral activity against herpes simplex virus. Often used to treat genital herpes. Transmission of an infectious organism in which the organism is truly suspended in the air and travels a meter or more from the source to the host. Chicken pox, flu, measles, and polio are examples of diseases that are caused by airborne agents.
Infection with amoebae. Usually refers to an infection by Entamoeba histolytica. Symptoms are highly variable, ranging from an asymptomatic infection to severe dysentery. Antibiotic used to treat systemic fungal infections and also used topically to treat candidiasis. Infectious disease of animals caused by ingesting the spores of Bacillus anthracis. Can occur in humans. Microbial product, or its derivative, that kills or inhibits the growth of susceptible microorganisms. Glycoprotein produced in response to an antigen.
Antibodies have the ability to combine with the antigen that stimulated their production. Chemical applied to tissue to prevent infection by killing or inhibiting the growth of pathogens.
Type of lymphocyte derived from bone marrow stem cells that matures into an immunologically competent cell under the influence of the bone marrow. Following interaction with an antigen, a B-cell becomes a plasma cell, which synthesizes antibodies. Disease transmission in which an infectious organism undergoes some morphologic or physiologic change during its passage through the vector. Form of food poisoning caused by a neurotoxin produced by Clostridium botulinum.
Sometimes found in improperly canned or preserved food. Compound used in the treatment of disease that kills or inhibits the growth of microorganisms and does so at concentrations low enough to avoid doing damage to the host. Highly contagious skin disease caused by the varicella-zoster virus. Acquired by droplet inhalation into the respiratory system. Host with lowered resistance to infection and disease for any reason for example, malnutrition, illness, trauma, or immunosuppression.
Plasmid that carries the genes for sex pili and can transfer copies of itself to other bacteria during conjugation. Transmission of an infectious agent by direct contact of the source or its reservoir with the host. Vaccine containing three antigens that is used to immunize people against diphtheria, whooping cough, and tetanus. Disease that is commonly or constantly present in a population, usually at a relatively constant low level.
Study of the factors determining and influencing the frequency and distribution of disease, injury, and disability in a population. Differential staining procedure that allows categorization of bacteria into two groups gram-positive and gram-negative based on their ability to retain crystal violet when decolorized with an organic solvent such as ethanol. Type of RNA virus. Hantavirus pulmonary syndrome and Korean hemorrhagic fever are caused by viruses in the genus Hantavirus.
Disease transmission in which an infectious agent does not undergo morphologic or physiologic change during its time inside the vector. Type of hepatitis that is transmitted by fecal-oral contamination.
It affects mostly children and young adults, especially under conditions of overcrowding and poor sanitation. Caused by the hepatitis A virus. Resistance of a population to spread of an infectious organism due to the immunity of a high proportion of the population. Body of an organism that harbors another organism. The host provides a microenvironment that supports the growth and reproduction of the parasitic organism.
Response of the body to contact with an antigen that leads to the formation of antibodies and sensitized lymphocytes.
Designed to render harmless the antigen and the pathogen producing it. Science concerned with understanding the immune system and the many factors that are involved with producing both acquired and innate immunity. Invasion of a host by an agent, with subsequent establishment and multiplication of the agent. An infection may or may not lead to disease. Living or quasi-living organism or particle that causes an infectious disease.
Bacteria, viruses, fungi, protozoa, helminths, and prions are infectious agents. Change from a state of health to a state in which part or all of a host's body cannot function normally because of the presence of an infectious agent or its products. Localized protective response to tissue injury or destruction. In an acute form, it is characterized by pain, heat, redness, and swelling in the injured area.
Acute viral infection of the respiratory tract caused by one of three strains of influenza virus A, B, and C. Host that serves as a temporary but essential environment for the completion of a parasite's life cycle. Type of white blood cell. Lymphocytes transmit chemical signals that help coordinate the immune system. Infectious disease caused by the protozoon Plasmodium. Characterized by fever and chills that occur at regular intervals.
Highly contagious skin disease caused by a virus in family Paramyxoviridae. The virus enters the body through the respiratory tract or the conjunctiva.
Measles is endemic throughout the world. Number of individuals who become ill with a particular disease within a susceptible population during a specified time period. Ratio of the number of deaths from a particular disease to the total number of cases of the disease. General defense mechanisms that provide animals with protection from infection and disease but are not targeted at a particular pathogen. Infection produced by a pathogenic agent that a patient acquires during hospitalization or treatment inside another health care facility.
Increase in the occurrence of a disease in a large and geographically widespread population. Sometimes called a worldwide epidemic.
Organism that lives on or within another organism the host. The relationship benefits the parasite and harms the host. Process of heating milk and other liquids to destroy microorganisms that can cause spoiling or disease. Circular, double-stranded DNA molecule that can exist and replicate independently of the host cell chromosome or be integrated with it. Although a plasmid is stably inherited, it is not required for bacterial cell growth and reproduction. Total number of people infected at one time in a population, regardless of when the disease began.
Infectious particle that is responsible for certain slow-acting diseases such as scrapie in sheep and goats, and Creutzfeldt-Jakob disease in humans.
Prions have a protein component, but scientists have not yet detected a nucleic acid component. Cell that lacks a membrane-delimited nucleus and other membrane-bound organelles. Bacteria are prokaryotic cells. Acute infectious disease of the central nervous system caused by an RNA virus of the rhabdovirus group. Site, alternate host, or carrier that harbors pathogenic organisms and serves as a source from which other individuals can be infected.
RNA virus that carries the enzyme reverse transcriptase and forms a DNA copy of its genome during its reproductive cycle. Highly contagious, often fatal disease caused by a poxvirus. Smallpox has been eradicated throughout the world. Collection of several immunological events in which lymphocytes recognize the presence of a particular antigen and act to eliminate it. Lymphocyte derived from bone marrow stem cells that matures into an immunologically competent cell under the influence of the thymus.
Involved in cell-mediated immune reactions. Tuberculin hypersensitivity test to detect a current or past infection with Mycobacterium tuberculosis. Often fatal disease caused by the anaerobic, spore-forming bacterium Clostridium tetani. Characterized by muscle spasms and convulsions. Mode of gene transfer in bacteria in which a piece of DNA in the environment is taken up by a bacterium and integrated into the bacterium's genome.
DNA segment that carries the genes required for transposition and can move from one place to another in the genome. Often carries genes unrelated to transposition as well. Infectious disease resulting from infection by a species of Mycobacterium.
Infection is usually by inhalation, and the disease usually affects the lungs, although it can occur elsewhere in the body. Preparation of killed microorganisms; living, weakened attenuated microorganisms; inactive or attenuated virus particles; inactivated bacterial toxins; or components protein, carbohydrate, or nucleic acid of the microorganism that is administered to stimulate an immune response. Vaccines protect an individual against the pathogenic agent or substance in the future.
Infectious agent composed of a protein coat and a single type of nucleic acid. Lacks an independent metabolism and reproduces only within a host cell. Turn recording back on. National Center for Biotechnology Information , U.
Search term. Understanding Emerging and Re-emerging Infectious Diseases. Nature of Infectious Diseases Microorganisms that are capable of causing disease are called pathogens. Figure 3 Emerging and re-emerging infectious diseases threaten all countries. Microbes That Cause Infectious Diseases There are five major types of infectious agents: bacteria, viruses, fungi, protozoa, and helminths.
Bacteria Bacteria are unicellular prokaryotic organisms; that is, they have no organized internal membranous structures such as nuclei, mitochondria, or lysosomes. Viruses Microbiologists have found viruses that infect all organisms, from plants and animals to fungi and bacteria. Fungi Fungi are eukaryotic, heterotrophic organisms that have rigid cellulose- or chitin-based cell walls and reproduce primarily by forming spores.
Protozoa Protozoa are unicellular, heterotrophic eukaryotes that include the familiar amoeba and paramecium. Helminths Helminths are simple, invertebrate animals, some of which are infectious parasites.
Prions During the past two decades, evidence has linked some degenerative disorders of the central nervous system to infectious particles that consist only of protein. Occurrence of Infectious Diseases Epidemiology is the study of the occurrence of disease in populations. Disease reservoirs The reservoir for a disease is the site where the infectious agent survives. Modes of transmission Infectious agents may be transmitted through either direct or indirect contact. Role of Research in Prevention Infectious diseases can be prevented at a variety of points, depending on the infectious cycle for the particular disease Figure 4.
Figure 4 The black arrows illustrate a generalized infectious cycle; the shaded arrows indicate points where infectious diseases can be prevented. Host Defenses Against Infectious Diseases The human body has several general mechanisms for preventing infectious diseases. Nonspecific mechanisms Nonspecific mechanisms are the body's primary defense against disease.
Specific mechanisms of host resistance When these nonspecific mechanisms fail, the body initiates a second, specific line of defense. Figure 5 This diagram provides an overview of specific immunity. Immunity When a host encounters an antigen that triggers a specific immune response for the second or later time, the memory lymphocytes recognize it and quickly begin growing and dividing, as well as producing high levels of lymphokines and antibodies.
Vaccination A vaccine is either a killed or weakened attenuated strain of a particular pathogen, or a solution containing critical antigens from the pathogen.
Public Health Measures to Prevent Infectious Diseases Developed countries have regulations that help protect the general public from infectious diseases.
Safe water Many pathogens that cause gastrointestinal diseases for example, those that cause cholera and typhoid fever are transmitted via water. Sewage treatment and disposal Sewage includes wash water, water from toilets, and storm run-off. Food safety programs The United States has many standards, inspection plans, and regulations about food preparation, handling, and distribution.
Animal control programs Animals are carriers of many diseases that also affect humans. Vaccination programs Most states now require that parents or guardians show proof of vaccination before their children can be enrolled in day-care facilities or public schools, although some states allow certain exemptions, including exemptions based on religious beliefs.
Public health organizations Cities and other local areas have public health agencies that enforce regulations, provide public health services such as vaccination programs, and monitor and report the incidence of particular diseases to state and federal agencies.
Figure 6 Vaccination programs are important components of public health systems. Treatment of Infectious Diseases While literally meaning "destroyer of life," the term "antibiotic" has become the most commonly used word to refer to a chemical substance used to treat bacterial infections. Treatment of bacterial diseases Because bacteria are prokaryotes, it has been relatively easy to find and develop antibacterial drugs that have minimal side effects.
Treatment of viral diseases In general, drugs that effectively inhibit viral infections are highly toxic to host cells because viruses use the host's metabolic enzymes in their reproduction.
Treatment of fungal and parasitic diseases The development of drugs to treat fungal, protozoan, and helminthic diseases is challenging because agents that kill or inhibit the growth of these eukaryotic organisms are also highly toxic to mammalian cells. Resistance to antimicrobial agents One of the ongoing problems scientists and medical workers face in the fight against infectious diseases is the development of resistance to the agents used to control them.
Mechanisms of antimicrobial resistance Antibiotic resistance appears as a result of changes in genes or the acquisition of genes that allow the pathogen to evade the action of antimicrobial drugs.
Transfer of antimicrobial-resistance genes Bacteria have many methods for developing resistance. Emerging and Re-emerging Infectious Diseases Fifty years ago many people believed the age-old battle of humans against infectious disease was virtually over, with humankind the winners.
Infectious Diseases and Society What are the implications of using science to improve personal and public health in a pluralist society?
Figure 9 Most states allow exemptions to immunization law. Infectious diseases of humans: Dynamics and control.
New York: Oxford University Press;
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