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| {{SI}} | | __NOTOC__ |
| {{CMG}}
| | {{Infectious disease}} |
| | '''For patient information, click [[Infectious disease (patient information)|here]]''' |
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| '''Associate Editor-In-Chief:''' {{CZ}} | | {{CMG}}; '''Associate Editor-In-Chief:''' {{CZ}} |
| | ==[[Infectious disease overview|Overview]]== |
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| {{EH}}
| | ==[[Infectious disease historical perspective|Historical Perspective]]== |
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| ==Overview== | | ==[[Infectious disease classification|Classification]]== |
| [[Image:Malaria.jpg|200px|thumb|left|This false-colored [[electron micrograph]] shows a [[malaria]] [[sporozoite]] migrating through the midgut [[epithelia]]]] | |
| An '''infectious disease''' is a clinically evident [[disease]] resulting from the presence of pathogenic [[microbial]] agents, including [[virus]]es, [[bacteria]], [[fungi]], [[protozoa]], multicellular [[parasite]]s, and aberrant proteins known as [[prion]]s. These [[pathogen]]s are able to cause disease in animals and/or plants.
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| Infectious pathologies are usually qualified as '''contagious diseases''' (also called communicable diseases) due to their potentiality of transmission from one person or species to another. <ref>[http://www.mercksource.com/pp/us/cns/cns_hl_dorlands.jspzQzpgzEzzSzppdocszSzuszSzcommonzSzdorlandszSzdorlandzSzdmd_c_49zPzhtm Dorland's Illustrated Medical Dictionary] 2004 WB Saunders.</ref> Transmission of an infectious disease may occur through one or more of diverse pathways including physical contact with infected individuals. These infecting agents may also be transmitted through liquids, food, body fluids, contaminated objects, airborne inhalation, or through [[Vector (biology)|vector]]-borne spread.<ref name= McGraw/> | | ==[[Infectious disease pathophysiology|Pathophysiology]]== |
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| The term ''[[infectivity]]'' describes the ability of an organism to enter, survive and multiply in the host, while the ''infectiousness'' of a disease indicates the comparative ease with which the disease is transmitted to other hosts.<ref>[http://www.doh.wa.gov/notify/other/glossary.htm Glossary of Notifiable Conditions] Washington State Department of Health</ref> An [[infection]] however, is not synonymous with an infectious disease, as an infection may not cause important clinical symptoms or impair host function.<ref name= McGraw>"Infectious disease." McGraw-Hill Encyclopedia of Science and Technology. The McGraw-Hill Companies, Inc., 2005.</ref>
| | ==[[Infectious disease causes|Causes]]== |
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| ==Classification== | | ==[[Infectious disease differential diagnosis|Differentiating Infectious Disease from other Diseases]]== |
| Among the almost infinite varieties of microorganisms, relatively few cause disease in otherwise healthy individuals.<ref name= Baron> This section incorporates [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed public domain] materials included in the text: [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowTOC&rid=mmed.TOC&depth=10 Medical Microbiology] Fourth Edition: [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.chapter.594 Chapter 8] (1996) . Baron, Samuel MD. The University of Texas Medical Branch at Galveston.</ref> Infectious disease results from the interplay between those few pathogens and the defenses of the hosts they infect. The appearance and severity of disease resulting from any pathogen depends upon the ability of that pathogen to damage the host as well as the ability of the host to resist the pathogen. Infectious microorganisms, or microbes, are therefore classified as either ''primary pathogens'' or as ''opportunistic pathogens'' according to the status of host defenses.
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| Primary pathogens cause disease as a result of their presence or activity within the normal, healthy host, and their intrinsic [[virulence]] (the severity of the disease they cause) is, in part, a necessary consequence of their need to reproduce and spread. Many of the most common primary pathogens of humans only infect humans, however many serious diseases are caused by organisms acquired from the environment or which infect non-human hosts.
| | ==[[Infectious disease epidemiology and demographics|Epidemiology and Demographics]]== |
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| Organisms which cause an infectious disease in a host with depressed resistance are classified as ''opportunistic pathogens''. Opportunistic disease may be caused by microbes that are ordinarily in contact with the host, such as bacteria or fungi in the [[gastrointestinal]] or the [[upper respiratory tract]], and they may also result from (otherwise innocuous) microbes acquired from other hosts (as in [[Clostridium difficile]] [[enterocolitis]]) or from the environment as a result of [[Physical trauma|traumatic]] introduction (as in [[surgical]] wound infections or compound fractures). An opportunistic disease requires impairment of host defenses, which may occur as a result of [[genetic defect]]s (such as [[Chronic granulomatous disease]]), exposure to [[antimicrobial]] drugs or [[immunosuppressive]] chemicals (as might occur following [[poison]]ing or [[cancer]] [[chemotherapy]]), exposure to [[ionizing radiation]], or as a result of an infectious disease with immunosuppressive activity (such as with [[measles]], [[malaria]] or [[HIV|HIV disease]]). Primary pathogens may also cause more severe disease in a host with depressed resistance than would normally occur in an immunosufficient host.
| | ==[[Infectious disease risk factors|Risk Factors]]== |
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| One way of proving that a given disease is "infectious", is to satisfy [[Koch's postulates]] (first proposed by [[Robert Koch]]), which demands that the [[infectious agent]] be identified only in patients and not in healthy controls, and that patients who contract the agent also develop the disease. These postulates were first used in the discovery that [[Mycobacteria]] species cause [[tuberculosis]]. Koch's postulates cannot be met ethically for many human diseases because they require experimental infection of a healthy individual with a pathogen produced as a pure culture. Often, even diseases that are quite clearly infectious do not meet the infectious criteria. For example, ''[[Treponema pallidum]]'', the causative [[spirochete]] of [[syphilis]], cannot be [[microbiological culture|cultured]] ''in vitro'' - however the organism can be cultured in rabbit [[testes]]. It is less clear that a pure culture comes from an animal source serving as host than it is when derived from microbes derived from plate culture.
| | ==[[Infectious disease natural history, complications and prognosis|Natural History, Complications and Prognosis]]== |
| [[Epidemiology]] is another important tool used to study disease in a population. For infectious diseases it helps to determine if a disease [[outbreak]] is sporadic (occasional occurrence), [[endemic (epidemiology)|endemic]] (regular cases often occurring in a region), [[epidemic]] (an unusually high number of cases in a region), or [[pandemic]] (a global epidemic).
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| ==Transmission== | | ==[[Infectious disease transmission|Transmission]]== |
| An infectious disease is transmitted from some source. Defining the means of transmission plays an important part in understanding the biology of an infectious agent, and in addressing the disease it causes. Transmission may occur through several different mechanisms. [[Respiration (physiology)|Respiratory]] diseases and [[meningitis]] are commonly acquired by contact with aerosolized droplets, spread by sneezing, coughing, talking or even singing. [[Gastrointestinal]] diseases are often acquired by ingesting contaminated food and water. [[Sexually transmitted disease]]s are acquired through contact with bodily fluids, generally as a result of sexual activity. Some infectious agents may be spread as a result of contact with a contaminated, inanimate object (known as a [[fomite]]), such as a coin passed from one person to another, while other diseases penetrate the [[skin]] directly.<ref name= Sherris>Kenneth J. Ryan and C. George Ray, Sherris Medical Microbiology Fourth Edition McGraw Hill 2004. </ref>
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| Transmission of infectious diseases may also involve a "[[Vector (biology)|vector]]". Vectors may be mechanical or biological. A mechanical vector picks up an infectious agent on the outside of its body and transmits it in a passive manner. An example of a mechanical vector is a housefly, which lands on cow dung, contaminating its appendages with bacteria from the feces, and then lands on food prior to consumption. The pathogen never enters the body of the fly. [[Image:CulexNil.jpg|thumb|220px|left|Culex mosquitos (''Culex quinquefasciatus'' shown) are biological vectors that transmit [[West Nile Virus]].]]In contrast, biological vectors harbor pathogens within their bodies and deliver pathogens to new hosts in an active manner, usually a bite. Biological vectors are often responsible for serious [[blood-borne disease]]s, such as [[malaria]], [[encephalitis|viral encephalitis]], [[Chagas disease]] and African sleeping sickness. Biological vectors are usually, though not exclusively, arthropods, such as mosquitoes, ticks, fleas and lice. Vectors are often required in the life cycle of a pathogen. A common strategy, used to control vector borne infectious diseases, is to interrupt the life cycle of a pathogen, by killing the vector.
| | ==Diagnosis== |
| | [[Infectious disease indication of tests|Indication of Tests]] | [[Infectious disease history and symptoms|History and Symptoms]] | [[Infectious disease physical examination|Physical Examination]]| [[Infectious disease laboratory findings|Laboratory Findings]] | [[Infectious disease electrocardiogram|Electrocardiogram]] | [[Infectious disease x ray|X Ray]] | [[Infectious disease CT|CT]] | [[Infectious disease MRI|MRI]] | [[Infectious disease echocardiography or ultrasound|Echocardiography or Ultrasound]] | [[Infectious disease other imaging findings|Other Imaging Findings]] | [[Infectious disease other diagnostic studies|Other Diagnostic Studies]] |
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| The relationship between virulence and transmission is complex, and has important consequences for the long term evolution of a pathogen. Since it takes time for a microbe and a new host species to co-evolve, an emerging pathogen may hit its earliest victims especially hard. It is usually in the first wave of a new disease that death rates are highest. If a disease is rapidly fatal, the host may die before the microbe can get passed along to another host. However, this cost may be overwhelmed by the short term benefit of higher infectiousness if transmission is linked to virulence, as it is for instance in the case of cholera (the explosive diarrhea aids the bacterium in finding new hosts) or many respiratory infections (sneezing and coughing create infectious [[aerosol]]s).
| | ==Treatment== |
| | | [[Infectious disease medical therapy|Medical Therapy]] | [[Infectious disease surgery|Surgery]] | [[Infectious disease primary prevention|Primary Prevention]] | [[Infectious disease secondary prevention|Secondary Prevention]] | [[Infectious disease cost-effectiveness of therapy|Cost-Effectiveness of Therapy]] | [[Infectious disease future or investigational therapies|Future or Investigational Therapies]] |
| ==Diagnosis and therapy== | |
| Diagnosis of infectious disease sometimes involves identifying an infectious agent either directly or indirectly. In practice most minor infectious diseases such as [[warts]], [[cutaneous]] [[abscesses]], [[respiratory system]] infections and diarrheal diseases are diagnosed by their clinical presentation. Conclusions about the cause of the disease are based upon the likelihood that a patient came in contact with a particular agent, the presence of a microbe in a community, and other epidemiological considerations. Given sufficient effort, all known infectious agents can be specifically identified.
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| The benefits of identification, however, are often greatly outweighed by the cost, as often there is no specific treatment, the cause is obvious, or the outcome of an infection is [[benign]].
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| Specific identification of an infectious agent is usually only determined when such identification can aid in the treatment or prevention of the disease, or to advance knowledge of the course of an illness prior to the development of effective therapeutic or preventative measures. For example, in the early 1980s, prior to the appearance [[AZT]] for the treatment of [[AIDS]], the course of the disease was closely followed by monitoring the composition of patient blood samples, even though the outcome would not offer the patient any further treatment options. In part, these studies on the appearance of [[HIV]] in specific communities permitted the advancement of hypotheses as to the route of transmission of the virus. By understanding how the disease was transmitted, resources could be targeted to the communities at greatest risk in campaigns aimed at reducing the number of new infections. The specific [[serological]] diagnostic identification, and later genotypic or molecular identification, of HIV also enabled the development of hypotheses as to the temporal and geographical origins of the virus, as well as a myriad of other hypothesis. The development of molecular diagnostic tools have enabled physicians and researchers to monitor the efficacy of treatment with anti-retroviral drugs. Molecular diagnostics are now commonly used to identify HIV in healthy people long before the onset of illness and have been used to demonstrate the existence of people who are genetically resistant to HIV infection. Thus, while there still is no cure for AIDS, there is great therapeutic and predictive benefit to identifying the virus and monitoring the virus levels within the blood of infected indiviuals, both for the patient and for the community at large.
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| ===Methods of Diagnosis===
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| Diagnosis of infectious disease is nearly always initiated by medical history and physical examination. More detailed identification techniques involve the culture of infectious agents isolated from a patient. Culture allows identification of infectious organisms by examining their microscopic features, by detecting the presence of substances produced by pathogens, and by directly identifying an organism by its genotype. Other techniques (such as [[X-ray]]s, [[CT scans]], [[PET scan]]s or [[NMR]]) are used to produce images of internal abnormalities resulting from the growth of an infectious agent. The images are useful in detection of, for example, a bone [[abscess]] or a [[spongiform encephalopathy]] produced by a [[prion]].
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| ====Microbial culture====
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| [[Image:K pneumoniae M morganii providencia styphimuriuma.JPG|thumb|200px|Four nutrient agar plates growing colonies of common Gram negative bacteria.]]
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| [[Microbiological culture]] is a principal tool used to diagnose infectious disease. In a microbial culture, a [[growth medium]] is provided for a specific agent. A sample taken from potentially diseased tissue or fluid is then tested for the presence of an infectious agent able to grow within that medium. Most pathogenic bacteria are easily grown on nutrient [[agar]], a form of solid medium that supplies carbohydrates and proteins necessary for growth of a bacterium, along with copious amounts of water. A single bacterium will grow into a visible mound on the surface of the plate called a [[Colony (biology)|colony]], which may be separated from other colonies or melded together into a "lawn". The size, color, shape and form of a colony is characteristic of the bacterial species, its specific genetic makeup (its strain), and the environment which supports its growth. Other ingredients are often added to the plate to aid in identification. Plates may contain substances that permit the growth of some bacteria and not others, or that change color in response to certain bacteria and not others. Bacteriological plates such as these are commonly used in the clinical identification of infectious [[bacterium|bacteria]]. Microbial culture may also be used in the identification of [[virus]]es: the medium in this case being cells grown in culture that the virus can infect, and then alter or kill. In the case of viral identification, a region of dead cells results from viral growth, and is called a "plaque". [[Eukaryotic]] [[parasites]] may also be grown in culture as a means of identifying a particular agent.
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| In the absence of suitable plate culture techniques, some microbes require culture within live animals. Bacteria such as ''Mycobacterium leprae'' and ''T. pallidum'' can be grown in animals, although serological and microscopic techniques make the use of live animals unnecessary. Viruses are also usually identified using alternatives to growth in culture or animals. Some viruses may be grown in [[embryo]]nated eggs. Another useful identification method is Xenodiagnosis, or the use of a vector to support the growth of an infectious agent. [[Chagas disease]] is the most significant example, because it is difficult to directly demonstrate the presence of the causative agent, ''[[Trypanosoma cruzi]]'' in a patient, which therefore makes it difficult to definitively make a diagnosis. In this case, xenodiagnosis involves the use of the [[Vector (biology)|vector]] of the Chaga's agent ''T. cruzi'', an uninfected triatomine bug (subfamily [[Triatominae]]), which takes a blood meal from a person suspected of having been infected. The bug is later inspected for growth of ''T. cruzi'' within its gut.
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| ====Microscopy====
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| Another principle tool in the diagnosis of infectious disease is [[microscopy]]. Virtually all of the culture techniques discussed above rely, at some point, on microscopic examination for definitive identification of the infectious agent. [[Microscopy]] may be carried out with simple instruments, such as the compound [[light microscope]], or with instruments as complex as an [[electron microscope]]. Samples obtained from patients may be viewed directly under the light microscope, and can often rapidly lead to identification. Microscopy is often also used in conjunction with [[biochemical]] [[staining]] techniques, and can be made exquisitely specific when used in combination with [[antibody]] based techniques. For example, the use of [[antibodies]] made artificially [[fluorescent]] (fluorescently labeled antibodies) can be directed to bind to and identify a specific [[antigens]] present on a pathogen. A [[fluorescence microscope]] is then used to detect fluorescently labeled antibodies bound to internalized antigens within clinical samples or cultured cells. This technique is especially useful in the diagnosis of viral diseases, where the light microscope is incapable of identifying a virus directly.
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| Other microscopic procedures may also aid in identifying infectious agents. Almost all cells readily stain with a number of basic [[dye]]s due to the electrostatic attraction between negatively charged cellular molecules and the positive charge on the dye. A cell is normally transparent under a microscope, and using a stain increases the contrast of a cell with its background. Staining a cell with a dye such as [[Giemsa]] stain or [[crystal violet]] allows a microscopist to describe its size, shape, internal and external components and its associations with other cells. The response of bacteria to different staining procedures is used in the taxonomic classification of microbes as well. Two methods, the [[Gram stain]] and the [[acid-fast]] stain, are the standard approaches used to classify bacteria and to diagnosis of disease. The Gram stain identifies the bacterial groups [[Firmicutes]] and [[Actinobacteria]], both of which contain many significant human pathogens. The acid-fast staining procedure identifies the Actinobacterial genera ''[[Mycobacterium]]'' and ''[[Nocardia]]''.
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| ====Biochemical tests====
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| Biochemical tests used in the identification of infectious agents include the detection of [[metabolic]] or enzymatic products characteristic of a particular infectious agent. Since bacteria ferment [[carbohydrate]]s in patterns characteristic of their [[genus]] and [[species]], the detection of [[Fermentation (biochemistry)|fermentation]] products is commonly used in bacterial identification. Acids, [[alcohols]] and [[gases]] are usually detected in these tests when bacteria are grown in [[Growth medium#Selective media|selective]] liquid or solid media.
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| The isolation of [[enzymes]] from infected tissue can also provide the basis of a biochemical diagnosis of an infectious disease. For example, humans can make neither [[RNA replicase]]s nor [[reverse transcriptase]], and the presence of these enzymes are characteristic of specific types of viral infections. The ability of the viral protein [[hemagglutinin]] to bind [[red blood cells]] together into a detectable matrix may also be characterized as a biochemical test for viral infection, although strictly speaking hemagglutinin is not an ''enzyme'' and has no metabolic function.
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| [[Serological]] methods are highly sensitive, specific and often extremely rapid tests used to identify microorganisms. These tests are based upon the ability of an antibody to bind specifically to an antigen. The antigen, usually a protein or carbohydrate made by an infectious agent, is bound by the antibody. This binding then sets off a chain of events that can be visibly obvious in various ways, dependent upon the test. For example, "[[Strep throat]]" is often diagnosed within minutes, and is based on the appearance of antigens made by the causative agent, ''[[Streptococcus pyogenes]]'', that is retrieved from a patients throat with a cotton swab. Serological tests, if available, are usually the preferred route of identification, however the tests are costly to develop and the reagents used in the test often require refrigeration. Some serological methods are extremely costly, although when commonly used, such as with the "strep test", they can be inexpensive.
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| ====Molecular diagnostics====
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| Technologies based upon the [[polymerase chain reaction]] (PCR) will become nearly ubiquitous gold standards of diagnostics of the near future, for several reasons. First, the catalog of infectious agents has grown to the point that virtually all of the significant infectious agents of the human population have been identified. Second, an infectious agent must grow within the human body to cause disease; essentially it must amplify its own nucleic acids in order to cause a disease. This amplification nucleic acid in infected tissue offers an opportunity to detect the infectious agent by using [[PCR]]. Third, the essential tools for generating PCR (primers) are defined by the genomes of the infectious agents, and with time those genomes will be known, if they are not already.
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| Thus, the technological ability to detect any infectious agent rapidly and specifically are currently available. The only remaining blockades to the use of PCR as a standard tool of diagnosis are in its cost and application, neither of which is insurmountable. The diagnosis of a few diseases will not benefit from the development of PCR methods, such as some of the [[clostridia]]l diseases ([[tetanus]] and [[botulism]]). These diseases are fundamentally biological poisonings by relatively small numbers of infectious bacteria that produce extremely potent [[neurotoxin]]s. A significant proliferation of the infectious agent does not occur, this limits the ability of PCR to detect the presence of any bacteria.
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| ==Clearance and immunity==
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| [[Image:Mallon-Mary 01.jpg|thumb|150px|Mary Mallon (a.k.a Typhoid Mary) was an asymptomatic carrier of [[typhoid fever]]. Over the course of her career as a cook, she infected 53 people, three of whom died.]]
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| Infection with most pathogens does not result in death of the host and the offending organism is ultimately cleared after the symptoms of the disease have waned.<ref name= Baron/> This process requires [[immune system|immune mechanisms]] to kill or inactivate the inoculum of the pathogen. Specific acquired [[immunity (medical)|immunity]] against infectious diseases may be mediated by [[antibodies]] and/or [[T lymphocyte]]s. Immunity mediated by these two factors may be manifested by:
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| * a direct effect upon a pathogen, such as antibody-initiated [[complement system|complement]]-dependent bacteriolysis, [[Opsonin|opsonoization]], [[phagocytosis]] and killing, as occurs for some bacteria,
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| * neutralization of viruses so that these organisms cannot enter cells,
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| * or by T lymphocytes which will kill a cell parasitized by a microorganism.
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| The immune response to a microorganism often causes symptoms such as a high [[fever]] and [[inflammation]], and has the potential to be more devastating than direct damage caused by a microbe.
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| Resistance to infection ([[immunity (medical)|immunity]]) may be acquired following a disease, by [[asymptomatic carrier|asymptomatic carriage]] of the pathogen, by harboring an organism with a similar structure (crossreacting), or by [[vaccination]]. Knowledge of the protective antigens and specific acquired host immune factors is more complete for primary pathogens than for opportunistic pathogens.
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| Immune resistance to an infectious disease requires a critical level of either antigen-specific antibodies and/or T cells when the host encounters the pathogen. Some individuals develop natural [[serum]] antibodies to the surface [[polysaccharide]]s of some agents although they have had little or no contact with the agent, these natural antibodies confer specific protection to adults and are [[passive immunization|passively transmitted]] to newborns.
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| ==Mortality from infectious diseases==
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| The [[World Health Organization]] collects information on global deaths by [[ICD|International Classification of Disease (ICD) code categories]]. The following table lists the top infectious disease killers which caused more than 100,000 deaths in 2002 (estimated). 1993 data is included for comparison.
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| {| class="wikitable" style="margin: 1em auto 1em auto"
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| |+ '''Worldwide mortality due to infectious diseases'''<ref>[http://www.who.int/whr/en/ The World Health Report] - [http://www.who.int/whr/2004/annex/topic/en/annex_2_en.pdf 2004 Annex Table 2 '''(pdf)'''] and [http://www.who.int/whr/1995/en/whr95_ch1_en.pdf 1995 Table 5 '''(pdf-large!)''']</ref>
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| ! Rank|| Cause of death || Deaths 2002 || Percentage of<br /> all deaths || Deaths 1993|| 1993 Rank
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| |colspan="1" style="background:#ffdead;"|N/A||colspan="1" style="background:#ffdead;" | All infectious diseases ||colspan="1" style="background:#ffdead;" |14.7 million ||colspan="1" style="background:#ffdead;" align="center"|25.9% ||colspan="1" style="background:#ffdead;"| 16.4 million || colspan="1" style="background:#ffdead;" align="center" |32.2%
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| | 1 ||[[Lower respiratory tract infection|Lower respiratory infection]]s<ref>Lower respiratory infections include various [[pneumonia]]s, [[influenza]]s and [[bronchitis]].</ref>
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| ||3.9 million ||align="center"|6.9%||4.1 million||1
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| | 2 |||[[HIV]]/[[AIDS]] ||2.8 million || align="center" |4.9% || 0.7 million||7
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| | 3 ||[[Gastroenteritis|Diarrheal disease]]s<ref>Diarrheal diseases are caused by many different organisms, including [[cholera]], [[botulism]], and [[E. coli]] to name a few. See also: [[ICD-10 Chapter I: Certain infectious and parasitic diseases#A00-A79 - Bacterial infections, and other intestinal infectious diseases, and STDs|Intestinal infectious diseases]]</ref>||1.8 million ||align="center" |3.2% ||3.0 million||2
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| | 4 ||[[Tuberculosis]] (TB)|| 1.6 million || align="center" |2.7% ||2.7 million ||3
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| | 5 ||[[Malaria]] ||1.3 million ||align="center" |2.2% ||2.0 million ||4
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| | 6 || [[Measles]] ||0.6 million ||align="center" |1.1% ||1.1 million ||5
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| | 7 ||[[Pertussis]] ||0.29 million||align="center" |0.5% ||0.36 million ||7
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| | 8 ||[[Tetanus]] ||0.21 million ||align="center" |0.4% ||0.15 million ||12
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| | 9 ||[[Meningitis]]||0.17 million ||align="center" |0.3% ||0.25 million ||8
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| | 10 ||[[Syphilis]]||0.16 million ||align="center" |0.3% ||0.19 million || 11
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| | 11 ||[[Hepatitis B]] ||0.10 million ||align="center" |0.2% ||0.93 million || 6
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| | 12-17 ||[[Tropical disease]]s (6)<ref>Tropical diseases include [[Chagas disease]], [[dengue fever]], [[filariasis|lymphatic filariasis]], [[leishmaniasis]], [[onchocerciasis]], [[schistosomiasis]] and [[trypanosomiasis]].</ref> ||0.13 million ||align="center" |0.2% ||0.53 million ||9, 10, 16-18
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| |align="left" colspan="6"| <small>''Note: Other causes of death include maternal and perinatal conditions (5.2%), nutritional deficiencies (0.9%),<br /> noncommunicable conditions (58.8%), and injuries (9.1%).''</small>
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| |}
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| The top three single agent/disease killers are [[HIV]]/[[AIDS]], [[tuberculosis|TB]] and [[malaria]]. While the number of deaths due to nearly every disease have decreased, deaths due to HIV/AIDS have increased fourfold. Childhood diseases include [[pertussis]], [[poliomyelitis]], [[diphtheria]], [[measles]] and [[tetanus]]. Children also make up a large percentage of lower respiratory and diarrheal deaths.
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| ===Historic pandemics===
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| [[Image:Smallpox PHIL 3265 lores.jpg|thumb|A young [[Bangladeshi]] girl infected with smallpox (1973). Thanks to the development of the smallpox [[vaccine]], the disease was officially [[eradicate]]d in 1979.]]
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| A [[pandemic]] (or global [[epidemic]]) is a disease that affects people over an extensive geographical area.
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| * [[Plague of Justinian]], from 541 to 750, killed between 50 and 60 percent of Europe's population.<ref>[http://eee.uci.edu/clients/bjbecker/PlaguesandPeople/lecture3.html Infectious and Epidemic Disease in History]</ref>
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| * The [[Black Death]] of 1347 to 1352 killed 25 million in Europe over 5 years (estimated to be between 25 and 50% of the populations of Europe, Asia, and Africa - the world population at the time was 500 million).
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| * The introduction of [[smallpox]], measles and [[typhus]] to the areas of Central and South America by European explorers during the 15th and 16th centuries caused pandemics among the native inhabitants. Between 1518 and 1568 disease pandemics are said to have caused the population of Mexico to fall from 20 million to 3 million.<ref name= Dobson>Dobson, Andrew P. and E. Robin Carter (1996) [http://www.erin.utoronto.ca/~w3gwynne/BIO418/Dobson1996.pdf Infectious Diseases and Human Population History '''(full-text pdf)'''] Bioscience;46 2.</ref>
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| * The first European [[influenza]] epidemic occurred between 1556 and 1560, with an estimated mortality rate of 20%.<ref name= Dobson/>
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| * [[Smallpox]] killed an estimated 60 million Europeans in the 18th century alone. Up to 30% percent of those infected, including 80% of the children under 5 years of age, died from the disease, and one third of the survivors went blind. <ref>[http://www.annals.org/cgi/content/full/127/8_Part_1/635 Smallpox: The Triumph over the Most Terrible of the Ministers of Death]</ref>
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| * The Influenza Pandemic of 1918 (or the [[Spanish Flu]]) killed 25-50 million people (about 2% of world population of 1.7 billion).<ref>[http://www.history.navy.mil/library/online/influenza_main.htm Influenza of 1918 (Spanish Flu) and the US Navy]</ref> Today [[Influenza]] kills about 250,000 to 500,000 worldwide each year.
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| ===Emerging diseases and pandemics===
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| In most cases, microorganisms live in harmony with their hosts. Such is the case for many tropical viruses and the insects, monkeys, or other animals in which they have lived and reproduced. Because the microbes and their hosts have co-evolved, the hosts gradually become resistant to the microorganisms. When a microbe jumps from a long-time animal host to a human being, it may cease to be a harmless parasite and become pathogenic.<ref name= Krauss>H. Krauss, A. Weber, M. Appel, B. Enders, A. v. Graevenitz, H. D. Isenberg, H. G. Schiefer, W. Slenczka, H. Zahner: Zoonoses. Infectious Diseases Transmissible from Animals to Humans. 3rd Edition, 456 pages. ASM Press. American Society for Microbiology, Washington DC., USA. 2003. ISBN 1-55581-236-8</ref>
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| With most new infectious diseases, some human action is involved, changing the environment so that an existing [[microbe]] can take up residence in a new niche. When that happens, a [[pathogen]] that had been confined to a remote habitat appears in a new or wider region, or a microbe that had infected only animals suddenly begins to cause human disease.
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| Several human activities have led to the emergence and spread of new diseases,<ref name= Krauss/> see also [[Globalization and Disease]]:
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| * Encroachment on wildlife [[habitat]]s. The construction of new villages and housing developments in rural areas brings people into contact with animals--and the microbes they harbor.
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| * Changes in agriculture. The introduction of new crops attracts new crop pests and the microbes they carry to farming communities, exposing people to unfamiliar diseases.
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| * The destruction of rain forests. As countries make use of their rain forests, by building roads through forests and clearing areas for settlement or commercial ventures, people encounter insects and other animals harboring previously unknown microorganisms.
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| * Uncontrolled urbanization. The rapid growth of cities in many developing countries tends to concentrate large numbers of people into crowded areas with poor sanitation. These conditions foster transmission of contagious diseases.
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| * Modern transport. Ships and other cargo carriers often harbor unintended "passengers", that can spread diseases to faraway destinations. While with international jet-airplane travel, people infected with a disease can carry it to distant lands, or home to their families, before their first symptoms appear.
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| ==The study of infectious disease==
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| ===History===
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| [[Image:4microssopes4.jpg|thumb|German postage stamps depicting four antique [[microscope]]s. Advancements in microscopy were essential to the early study of infectious diseases.]]
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| [[Abū Alī ibn Sīnā]] (Avicenna) discovered the contagious nature of infectious [[disease]]s in the early 11th century, for which he is considered the father of modern medicine. He introduced [[quarantine]] as a means of limiting the spread of contagious and infectious diseases in ''[[The Canon of Medicine]]'', ''circa'' 1020.<ref>David W. Tschanz, MSPH, PhD (August 2003). "Arab Roots of European Medicine", ''Heart Views'' '''4''' (2).</ref> He also stated that bodily [[secretion]] is contaminated by foul foreign earthly bodies before being infected, but he did not view them as primary causes of [[disease]].<ref name=Syed>Ibrahim B. Syed, Ph.D. (2002). "Islamic Medicine: 1000 years ahead of its times", ''Journal of the Islamic Medical Association'' '''2''', p. 2-9.</ref>
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| When the [[Black Death]] [[bubonic plague]] reached al-Andalus in the 14th century, Ibn Khatima and Ibn al-Khatib hypothesized that infectious diseases are caused by microorganisms which enter the human body.<ref name=Syed/> Such ideas became more popular in Europe during the renaissance, particularly through the writing of the Italian monk [[Girolamo Fracastoro]].<ref>{{cite journal |author=Beretta M |title=The revival of Lucretian atomism and contagious diseases during the renaissance |journal=Medicina nei secoli |volume=15 |issue=2 |pages=129-54 |year=2003 |pmid=15309812}}</ref>
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| [[Anton van Leeuwenhoek]] (1632-1723) advanced the science of [[microscopy]], allowing for easy visualization of bacteria.
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| [[Louis Pasteur]] proved beyond doubt that certain diseases are caused by infectious agents, and developed a vaccine for [[rabies]].
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| [[Robert Koch]], provided the study of infectious diseases with a scientific basis known as [[Koch's postulates]].
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| [[Edward Jenner]], [[Jonas Salk]] and [[Albert Sabin]] developed effective vaccines for [[smallpox]] and [[polio]], which would later result in the eradication and near-eradication of these diseases, respectively.
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| [[Alexander Fleming]] discovered the world's first [[antibiotic]] [[Penicillin]].
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| Gerhard Domagk develops [[Sulphonamide]]s, the first broad spectrum synthetic antibacterial drugs.
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| ===Medical specialists===
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| The [[medicine|medical treatment]] of infectious diseases falls into the medical field of '''Infectiology''' and in some cases the study of propagation pertains to the field of [[Epidemiology]]. Generally, [[infection]]s are initially diagnosed by [[primary care]] physicians or [[internal medicine]] specialists. For example, an "uncomplicated" [[pneumonia]] will generally be treated by the [[internist]] or the pulmonologist (lung physician).The work of the infectiologist therefore entails working with both patients and general practitioners, as well as [[Research|laboratory scientists]], [[immunology|immunologists]], [[bacteriology|bacteriologists]] and other specialists..
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| An infectious disease team may be alerted when:
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| * The disease has not been definitively diagnosed after an initial workup
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| * The patient is [[immunocompromised]] (for example, in [[AIDS]] or after [[chemotherapy]]);
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| * The [[infectious agent]] is of an uncommon nature (e.g. [[tropical disease]]s);
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| * The disease has not responded to first line [[antibiotic]]s;
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| * The disease might be dangerous to other patients, and the patient might have to be isolated.
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| ==Prevention and Therapy==
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| [[Immunization Principles]]
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| [[Prophylaxis of Bacterial Infections]]
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| [http://en.wikidoc.org/index.php/Category:Infectious_Disease_Drugs Infectious Disease Pharmacotherapy]
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| ==Specific Syndromes==
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| [[Acute Diarrhea]]
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| [[Animal Bites and Scratches]]
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| [[Hospital Acquired Infections]]
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| [[Infective Endocarditis]]
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| [[Joint Infections]]
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| [[Osteomyelitis]]
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| [[Pelvic Inflammatory Disease]]
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| [[Septic Shock]]
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| [[Sexually Transmitted Diseases]]
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| [[Urinary Tract Infections]]
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| [[Pyelonephritis]]
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| ==Gram-Positive Organism Diseases==
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| [[Anthrax]]
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| [[Botulism]]
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| [[Diptheria]]
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| [[Gas Gangrene and other Clostridial Infections]]
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| [[Listeria monocytogenes and Eryspelothrix Rhusiopathiae]]
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| [[Mixed Anaerobic Infections]]
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| [[Pneumococcal Infections]]
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| [[Staphylococcal Infections]]
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| [[Streptococcal Infections]]
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| [[Tetanus]]
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| ==Gram-Negative Organism Diseases==
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| [[Bartonellosis]]
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| [[Brucellosis]]
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| [[Chancroid]]
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| [[Cholera]]
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| [[Donovanosis (Granuloma Inguinale)]]
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| [[Enteric Bacilli]]
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| [[Gonococcal Infections]]
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| [[Haemophilus Infections]]
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| [[Legionella Infections]]
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| [[Melioidosis and Glanders]]
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| [[Meningococcal Infections]]
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| [[Salmonellosis]]
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| [[Shigellosis]]
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| [[Tularemia]]
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| [[Yersinia enterocolitica Infection (Yersiniosis)]]
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| [[Yersinia Pestis Infection]]
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| [[Whooping Cough]]
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| ==Mycobacterial Diseases==
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| * [[Tuberculosis]]
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| * [[Leprosy]] ([[Hansen's disease]])
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| * Other Mycobacterial Infections
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| ==Spirochetal Diseases==
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| * [[Syphilis]]
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| * Non-venereal Treponematosis: [[Yaws]], [[Pinta]], and Endemic Syphilis
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| * [[Leptospirosis]]
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| * [[Relapsing Fever]]
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| * [[Lyme disease]] ([[Borreliosis]])
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| ==Viral Diseases==
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| [[Arbovirus |Arbovirus Infections]]
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| [[Arenavirus|Arenavirus Infections]]
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| [[Viruses|The Biology of Viruses]]
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| [[Cytomegalovirus|Cytomegalovirus Infection]]
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| [[Enteroviruses]] and [[Reoviruses]]
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| [[Epstein-Barr Virus|Epstein-Barr Virus Infections]], Including [[Infectious Mononucleosis]]
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| [[Herpes Simplex Viruses]]
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| [[Human Papillomavirus|Human Papillomavirus Infections]]
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| [[Influenza]]
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| [[Measles]] ([[Rubeola]])
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| [[Mumps]]
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| [[Rabies]], [[Rhabdovirus]], and [[Marburg virus|Marburg-like Agents]]
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| Common Viral Respiratory Infections
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| [[Retroviruses|The Human Retroviruses]]
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| [[Rubella]] ("[[German Measles]]") and Other Viral Exanthems
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| [[Smallpox]], [[Vaccinia]] and [[Poxvirus|Other Poxviruses]]
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| [[Varicella Zoster|Varicella-Zoster Virus Infections]]
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| [[Viral Gastroenteritis]]
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| [[West Nile Virus]]
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| [[Yellow Fever|Yellow Fever Virus]]
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| ==Infection Caused by Fungi and Higher Bacteria==
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| * [[Actinomycosis]] and [[Nocardiosis]]
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| * [[Fungal infection]]s
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| ==Rickettsia, Mycoplasma and Chlamydia==
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| [[Rickettsia|Rickettsial diseases]]
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| [[Mycoplasma Infections]]
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| [[Chlamydial Infections]]
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| ==Protozoal and Helminthic Infections==
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| [[Amebiasis]]
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| [[Babesiosis]]
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| [[Cryptosporidiosis]]
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| Diagnosis of Parasitic Infections
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| [[Filariasis]]
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| [[Giardiasis]]
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| The Immunology of Parasites
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| [[Leishmaniasis]]
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| [[Malaria]]
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| [[Nematodes]], [[Cestodes]], and Hermaphroditic Trematodes
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| [[Pneumocystis Carinii pneumonia]]
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| [[Scabies]], [[Chigger]]s, and other ectoparasites
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| [[Schistosomiasis]]
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| [[Toxoplasmosis]]
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| [[Trichinosis]]
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| [[Trypanosomiasis]]
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| ==See also==
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|
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|
| | == Case Studies == |
| | [[Infectious disease case study one|Case #1]] |
| | ==Related Chapters== |
| * [[Infection]] | | * [[Infection]] |
| * [[Microbiology]] | | * [[Microbiology]] |
| Line 368: |
Line 46: |
| * Vectorborne disease | | * Vectorborne disease |
| * [[Blood-borne disease]] | | * [[Blood-borne disease]] |
|
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| ==References==
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| {{Reflist|2}}
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|
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| ==External links== | | ==External links== |
| * [http://www.idsociety.org The Infectious Disease Society of America]
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| * [http://www.idri.org Infectious Disease Research Institute]
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| * http://www.medical-microbiology.de/Dateien/zoo_eng.html | | * http://www.medical-microbiology.de/Dateien/zoo_eng.html |
|
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| {{Medicine}} | | {{Medicine}} |
| {{SIB}}
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| [[ar:إسهال سكري]]
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| [[zh-min-nan:Thoân-jiám-pīⁿ]]
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| [[eu:Gaixotasun infekzioso]]
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| [[fr:Maladie infectieuse]]
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| [[hi:औपसर्गिक रोग]]
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| [[nl:Infectieziekte]]
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| [[ru:Инфекционные заболевания]]
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| [[simple:Infectious disease]]
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| [[sk:Infekčná choroba]]
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| [[sv:Infektionssjukdom]]
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| [[uk:Інфекційні захворювання]]
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| [[zh:傳染病]]
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| {{WH}} | | {{WH}} |
| {{WS}} | | {{WS}} |
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| [[Category:Infectious disease|*]] | | [[Category:Infectious disease|*]] |
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