List of Human Diseases Associated with Infectious Pathogens from Wikipedia, the Free Encyclopedia

Lista de doenças provocadas por bactérias - Wikipédia List of human diseases associated with infectious pathogens From Wikipedia, the free encyclopedia Jump to: navigation, search This article is about diseases with possible (but as yet unconfirmed) infectious microbial causes. For a list of diseases with proven infectious causes, see List of infectious diseases. This article provides a list of diseases with possible (but unconfirmed) infectious etiologies. Many chronic diseases are linked or associated with infectious pathogens.[1][2] A disease is said to be linked or associated with an infectious pathogen when that pathogen is found more frequently in patients with the disease than in healthy controls. Often, infectious pathogens associated with a disease may be suspected of playing a causal role in that disease — and some scientists believe a substantial portion of chronic diseases may in part be caused by infectious agents[3] — though association alone does not automatically prove causality (because correlation does not imply causation). Indeed, the terms linked and associated are used here in a strict technical sense: they mean there is a frequent co-occurrence of certain pathogens in certain diseases; but it should not be read that linked and associated imply there is a proven causal relationship between pathogen and disease. An observed association only flags up the possibility that there might be a causal relation. For an infectious pathogenic microbe that has been noted to frequently accompany a disease, there are several logical possibilities that can explain this observed association: An epithelial cell infected with Chlamydophila pneumoniae bacteria. The pathogen is an "innocent bystander" that plays no causal role in the etiology of the disease, but for some reason is more prevalent in patients with the disease (perhaps because the disease compromises the immune response, for example). The pathogen predisposes to disease development (increases the risk of getting the disease), but the pathogen does not cause the disease (for example, genital herpes increases the risk of acquiring HIV).[4] The pathogen is a necessary, but not sufficient, cause of the disease: in other words, the pathogen can cause the disease, but does so only in combination with one or more other causal factors (such as host genetic factors, or toxin exposure). The pathogen is a direct and singular cause of the disease, but this causality has yet to be proven. Determining whether a pathogen plays a causal role in a chronic disease is often difficult[5] for the following reasons: The time between contracting an infectious pathogen and the appearance of the first disease symptoms can be lengthy, sometimes decades. An infectious pathogen may not cause disease in every person. An infection may be asymptomatic in its acute phase (when first contracted), and so go unnoticed; symptoms may only appear much later — in the form of a chronic disease. Sometimes, only specific strains of a pathogen are linked to a disease; other strains of the same microbe may be harmless. A pathogen may precipitate the disease only in combination with one or more other causal factors. There may be more than one pathogen that can precipitate a given disease. A given pathogen may not always cause the same disease — infection with it may lead to one of several different diseases. There may be pathogens that are not readily detectable that play a causal role in a disease. For obvious ethical reasons, you cannot inoculate infectious pathogens into humans to see if these do cause the disease or not. A pathogenic microbe may cause disease by relatively easy to track direct means, such as by infecting and destroying cells; or may cause disease via more complex and convoluted indirect means, such as through the damage created by inflammatory cytokines or autoimmune processes that are induced by the microbial infection (for example, tuberculosis infection induces an inflammatory cytokine that then itself causes severe tissue damage).[6][7] A pathogenic microbe may not necessarily be present in the diseased tissues or organs (bacterial toxins for example can travel and damage tissues at sites distant from the infection site; and inflammatory or autoimmune processes precipitated by infectious pathogens can also act at tissue sites far removed from the infection). In spite of the difficulties in obtaining proof of causality, evolutionary biologist Paul W. Ewald and physicist Gregory M. Cochran are noted for their assertion that many common chronic diseases of currently unknown etiology are likely caused by chronic low-level microbial infection,[8][9] countering the prevailing view that genes are predominantly responsible for the development of chronic disease. Ewald and Cochran support their thesis with the logic of evolutionary biology, with Ewald explaining that: "chronic diseases, if they are common and damaging, must be powerful eliminators of any genetic instruction that may cause them."[10] In other words, any disease-causing gene that reduces survival and reproduction will eliminate itself over a number of generations, just by evolutionary pressures; therefore such genetic diseases are self-extinguishing. Ewald says the only genetic diseases that will persist are those that provide a compensating benefit. For example, genes that encode for sickle cell anemia disease are maintained and persist down generations, as these genes also protect against malaria, which kills millions worldwide each year.[10] Infectious pathogens are one of several potential causes of disease; other causal factors include: environmental toxins, certain types of radiation exposure, diet and lifestyle factors, stress, genetics, and epigenetics. All these factors are generally explored as potential causes of a disease. Diseases may also be multifactorial,[11] such that the disease only manifests when multiple causal factors occur in combination. For example: in a murine model, Crohn's disease can be precipitated by a norovirus, but only when both a specific gene variant is present and a certain toxin has damaged the gut.[12] Thus a pathogen's causal role in a disease may well be contingent upon several other causal factors. Infectious pathogen-associated diseases include many of the most common and costly[13] chronic illnesses. About 70% of all deaths in the United States result from chronic diseases,[5] with the treatment of chronic diseases accounting for 75% of all US healthcare costs (amounting to $1.7 trillion in 2009).[14] List of diseases associated with infectious pathogens[edit] In the list of diseases associated with infectious pathogens given below, bear in mind that there is no definitive proof that the associated pathogens do play a causal role in the disease, just a possibility that they might. Further research is required to determine whether or not these pathogens participate causally in their associated diseases. Note that this list covers some of the most common human diseases associated with infectious pathogens, but it is not intended to be a comprehensive list. Alzheimer's disease Alzheimer's disease is associated with the bacteria Chlamydia pneumoniae[15] and Helicobacter pylori,[16] and with the protozoan parasite Toxoplasma gondii.[17] Herpes simplex virus 1 is associated with Alzheimer's disease in individuals who possess the APOE-4 form of the APOE gene (APOE-4 enables the herpes virus to enter the brain).[18] Amyotrophic lateral sclerosis Amyotrophic lateral sclerosis, the most common of five forms of motor neuron disease, is associated with echovirus (an enterovirus) infection of the central nervous system,[19] and with retrovirus[20] activity (it is not known whether this retrovirus activity arises from a human endogenous retrovirus, or from an exogenous retrovirus). [21] Anorexia nervosa Infection with Borrelia species bacteria is associated with anorexia nervosa. In rare cases, anorexia nervosa may arise after infection with Streptococcus[22] species bacteria. Anorexia (which is distinct from anorexia nervosa) is associated with the protozoan parasite Dientamoeba fragilis.[23] Anxiety disorder Anxiety is associated with cytomegalovirus,[24] and the bacterium Helicobacter pylori.[25] Asthma Asthma is associated with rhinovirus, human respiratory syncytial virus,[26] and the bacterium Chlamydia pneumoniae.[27] Chlamydia pneumoniae is particularly associated with adult-onset asthma.[28] Atherosclerosis Atherosclerosis is associated with the bacterium Chlamydia pneumoniae.[29][30] Attention deficit hyperactivity disorder Attention deficit hyperactivity disorder (ADHD) and learning disorders are associated with the bacteria Borrelia burgdorferi and Streptococcus, and with HIV and enterovirus 71. Febrile seizures due to human herpesvirus 6 or influenza A are a risk factor for ADHD. Viral infections during pregnancy, at birth, and in early childhood are risk factors for ADHD.[31] Autism Autism is associated with prenatal maternal infection with rubeolla virus or cytomegalovirus.[32][33] Clostridia bacteria species are associated with autism (these bacteria are present in greater numbers in the guts of autistic children).[34] Autoimmune diseases Autoimmune diseases are strongly associated with enteroviruses such as Coxsackie B virus.[35] Autoimmune diseases are also associated with Epstein- Barr virus,[36] cytomegalovirus,[37] parvovirus B19,[38] and HIV,[39] and the bacterium Mycobacterium tuberculosis.[40] Autoimmune thyroid disease is associated with Epstein-Barr

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