# Infections associated with diseases

Infections associated with diseases are those infections that are associated with possible infectious etiologies that meet the requirements of Koch's postulates. Other methods of causation are described by the Bradford Hill criteria and evidence-based medicine.
Koch's postulates have been modified by some epidemiologists, based on the sequence-based detection of distinctive pathogenic nucleic acid sequences in tissue samples. When using this method, absolute statements regarding causation are not always possible. Higher amounts of distinctive pathogenic nucleic acid sequences should be in those exhibiting disease, compared to controls. In addition, the DNA load should become lower with the resolution of the disease. The distinctive pathogenic nucleic acid sequences load should also increase upon recurrence.
Other conditions are met to establish cause or association including studies in disease transmission. This means that there should be a high disease occurrence in those carrying a pathogen, evidence of a serological response to the pathogen, and the success of vaccination prevention. Direct visualization of the pathogen, the identification of different strains, immunological responses in the host, how the infection is spread and, the combination of these should all be taken into account to determine the probability that an infectious agent is the cause of the disease. A conclusive determination of a causal role of an infectious agent for in a particular disease using Koch's postulates is desired yet this might not be possible.
The leading cause of death worldwide is cardiovascular disease, but infectious diseases are the second leading cause of death worldwide and the leading cause of death in infants and children.

## Other causes

Other causes or associations of disease are: a compromised immune system, environmental toxins, radiation exposure, diet and other lifestyle choices, stress, and genetics. Diseases may also be multifactorial, requiring multiple factors to induce disease. 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.

## List of diseases associated with infectious bacteria and viruses

A list of the more common and well-known diseases associated with infectious pathogens is provided and is not intended to be a complete listing.
| Asthma | Mycoplasma pneumoniae and Chlamydia pneumoniae infections are associated with the onset and symptoms of asthma. |
| Autoimmune diseases | Autoimmune diseases are associated with Neoehrlichia mikurensis infection, and Borrelia miyamotoi infection, and HIV, and the bacterium Mycobacterium tuberculosis. Autoimmune thyroid disease is associated with Epstein-Barr virus. |
| Cancer | Anal cancer is associated with human papillomaviruses. Bladder cancer Schistosoma helminths can cause cancer. Brain tumor. Glioblastoma multiforme is associated with cytomegalovirus, BK virus, JC virus, and simian virus 40. Breast cancer is associated with mouse mammary tumor virus, Epstein-Barr virus, and human papillomaviruses. Carcinoid tumors are associated with enterovirus infections. Cervical cancer can be caused by human papillomaviruses. Colorectal cancer is associated with the bacteria Helicobacter pylori, Streptococcus bovis and Fusobacterium nucleatum, with human papillomaviruses, and with the helminth Schistosoma japonicum. JC virus may be a risk factor for colorectal cancer. Gallbladder cancer is associated with the bacterium Salmonella Typhi. Hodgkin's lymphoma is associated with Epstein-Barr virus, hepatitis C virus, and HIV. Kaposi's Sarcoma can be caused by Kaposi's sarcoma herpesvirus and HIV. Liver cancer. Hepatocellular carcinoma can be caused by hepatitis B virus, hepatitis C virus, and by the helminth Schistosoma japonicum. Lung cancer is associated with the bacterium Chlamydia pneumoniae, with human papillomaviruses, and with Merkel cell polyomavirus. Leukemia. Adult T-cell leukemia can be caused by human T-cell leukemia virus-1. Mesothelioma is associated with simian virus 40, especially in conjunction with asbestos exposure. Nasopharyngeal carcinoma can be caused by Epstein-Barr virus. Non-Hodgkin lymphoma is associated with HIV and simian virus 40. Oropharyngeal cancer can be caused by human papillomaviruses. Ovarian cancer is associated with mumps virus. Pancreatic cancer is associated with hepatitis B virus and the bacterium Helicobacter pylori. Prostate cancer is associated with xenotropic murine leukemia virus-related virus and BK virus. Skin neoplasm is associated with human papillomaviruses. Squamous cell carcinoma is associated with human papillomaviruses. Stomach cancer is associated with the bacterium Helicobacter pylori. Thyroid cancer is associated with simian virus 40. |
| Chronic fatigue syndrome | Chronic fatigue syndrome (also known as myalgic encephalomyelitis) is associated with enteroviruses (such as Coxsackie B virus), human herpesvirus 6 variant A, human herpesvirus 7, and parvovirus B19. The bacteria Coxiella burnetii and Chlamydia pneumoniae are known causes of chronic fatigue syndrome (antibiotics can cure these bacterial forms of chronic fatigue syndrome). |
| Common cold | The common cold is also known as Acute rhinosinusitis (ARS) and is caused by a viral infection. Efforts to develop vaccines are ongoing. |
| Crohn's disease | One study found ileocecal Crohn's disease is associated with viral species from the enterovirus genus (but note that all the study cohort with ileocecal Crohn's disease had disease-associated mutations in either their NOD2 or ATG16L1 genes). Crohn's disease is associated with Mycobacterium avium subspecies paratuberculosis. In a murine model, Crohn's disease is precipitated by the norovirus CR6 strain, but only in combination with a variant of the Crohn's susceptibility gene ATG16L1, and chemical toxic damage to the gut. In other words, in this mouse model, Crohn's is precipitated only when these three causal factors (virus, gene, and toxin) act in combination. |
| Coronary heart disease | Coronary heart disease is associated with herpes simplex virus 1 and the bacterium Chlamydia pneumoniae. |
| Dementia | Dementia is associated with herpes simplex virus type 1, herpes simplex virus type 2, cytomegalovirus, West Nile virus, bornavirus, and HIV. Dementia is also associated with the helminth Taenia solium (pork tapeworm), and with Borrelia species bacteria. |
| Depression | Depression is associated with cytomegalovirus and West Nile virus, and the protozoan parasite Toxoplasma gondii. It is thought that depression may be precipitated by the effect of immune signals (such as pro-inflammatory cytokines) reaching the brain from infections located in the peripheries of the body. Major depressive disorder is associated with bornavirus, as well as Bartonella and Borrelia species bacteria. Seasonal affective disorder is associated with Epstein-Barr virus. |
| Diabetes mellitus type 1 | Diabetes mellitus type 1 is associated with viral species from the enterovirus genus, specifically echovirus 4 and Coxsackie B virus (the latter it is thought may infect and destroy the insulin producing beta-cells in the pancreas and also damage these cells via indirect autoimmune mechanisms). One study found Coxsackie B1 virus associated with a higher risk of the beta cell autoimmunity that portends type 1 diabetes; though Coxsackie B3 and B6 viruses were found to be associated with a reduced risk of such autoimmunity (possibly due to immune cross-protection against Coxsackie B1 virus). In boys, human parechovirus infection has been linked to a subsequent appearance of diabetes-associated autoantibodies. |
| Diabetes mellitus type 2 | Diabetes mellitus type 2 is associated with cytomegalovirus, hepatitis C virus, enteroviruses, Ljungan virus |
| Dilated cardiomyopathy | Dilated cardiomyopathy is associated with enteroviruses such as Coxsackie B virus. |
| Epilepsy | Epilepsy is associated with human herpesvirus 6. |
| Gonorrhea | Men who have had a gonorrhea infection have a risk of having prostate cancer. |
| Guillain–Barré syndrome | Guillain–Barré syndrome is associated with the bacterium Campylobacter jejuni, and with the viruses cytomegalovirus and enterovirus. |
| Irritable bowel syndrome | Irritable bowel syndrome (IBS) is associated with the bacteria enteroaggregative Escherichia coli and Mycobacterium avium subspecies paratuberculosis, the protozoan parasite Giardia lamblia, and pathogenic strains of the protozoan parasite Blastocystis hominis. Irritable bowel syndrome in those with HIV is associated with the protozoan Dientamoeba fragilis. |
| Low back pain | Lower back pain is associated with a spinal disc infection with anaerobic bacteria, especially the bacterium Cutibacterium acnes. |
| Lupus | Lupus is associated with the viruses parvovirus B19, Epstein-Barr virus, and cytomegalovirus. |
| Lyme disease | Lyme disease is associated with infection by Borrelia miyamotoi, and Rickettsia species. |
| Metabolic syndrome | Metabolic syndrome is associated with the bacteria Chlamydia pneumoniae and Helicobacter pylori, as well as the viruses cytomegalovirus and herpes simplex virus 1. |
| Multiple sclerosis | Multiple sclerosis, a demyelinating disease, is associated with Epstein-Barr virus (and strongly associated with certain genetic variants of this virus), human herpesvirus 6, varicella zoster virus, and the bacterium Chlamydia pneumoniae. |
| Myocardial infarction | Myocardial infarction (heart attack) is associated with Chlamydia pneumoniae, cytomegalovirus and Coxsackie B virus (an enterovirus). (Coxsackie B virus is also associated with sudden unexpected death due to myocarditis). |
| Obesity | Obesity is associated with adenovirus 36, which is found in 30% of obese people, but only in 11% of non-obese people. It has further been demonstrated that animals experimentally infected with adenovirus 36 (or adenovirus 5, or adenovirus 37) will develop increased obesity. Adenovirus 36 induces obesity by infecting fat cells (adipocytes), wherein the expression of the adenovirus E4orf1 gene turns on both the cell's fat producing enzymes and also instigates the generation of new fat cells. Evidence suggests that obesity can be a viral disease, and that the worldwide obesity epidemic that began in the 1980s may be in part due to viral infection. Obesity is also associated with higher gut levels of certain Bacillota bacteria in relation to Bacteroidota bacteria. Overweight individuals tend have more Bacillota bacteria (such as Clostridium, Staphylococcus, Streptococcus, and Helicobacter pylori) in their gut, whereas normal weight individuals tend have more Bacteroidota bacteria. |
| Obsessive–compulsive disorder | Obsessive–compulsive disorder is associated with Streptococcus and Borrelia species bacteria. |
| Panic disorder | Panic disorder is associated with Borrelia and Bartonella species bacteria. |
| Parkinson's disease | Parkinson's disease is associated with influenza A virus, as well as the protozoan parasite Toxoplasma gondii. |
| Psoriasis | Psoriasis is associated with a Helicobacter pylori trigger. |
| Rheumatoid arthritis | Rheumatoid arthritis is associated with parvovirus B19. |
| Sarcoidosis | Sarcoidosis is associated with Mycobacteria species and the bacterium Helicobacter pylori |
| Schizophrenia | Schizophrenia is associated with bornavirus, the bacterium Chlamydia trachomatis, as well as Borrelia species bacteria. Schizophrenia is also linked to neonatal infection with Coxsackie B virus (an enterovirus), which one study found carries an increased risk of adult onset schizophrenia. Prenatal exposure to influenza virus in the first trimester of pregnancy increases the risk of schizophrenia by 7-fold. |
| Severe acute respiratory syndrome | Severe acute respiratory syndrome is a viral disease. Efforts to develop a vaccine are ongoing. |
| Stroke | Stroke is associated with the bacteria Chlamydia pneumoniae, Helicobacter pylori, Mycobacterium tuberculosis, and Mycoplasma pneumoniae, as well as the virus varicella zoster virus and Histoplasma species fungi. |
| Thromboangiitis obliterans | Thromboangiitis obliterans is associated with Rickettsia species bacteria. |
| Tourette syndrome | Tourette syndrome is associated with Streptococcus species bacteria. Aggravating or contributory microbes in Tourette's may include the bacteria Mycoplasma pneumoniae, Chlamydia pneumoniae, Chlamydia trachomatis, and the protozoan parasite Toxoplasma gondii. |
| Vasculitis | Vasculitis is associated with HIV, parvovirus B19, and hepatitis B virus. The hepatitis C virus is an established cause of vasculitis. |

## Epidemiology

Infectious pathogen-associated diseases include many of the most common and costly chronic illnesses. The treatment of chronic diseases accounts for 75% of all US healthcare costs (amounting to $1.7 trillion in 2009).

## History

One of first examples of systematic study of disease causation was Avicenna, in the tenth century. The history of infection and disease were observed in the 1800s and related to the one of the tick-borne diseases, Rocky Mountain spotted fever. The cause of viral encephalitis was discovered in Russia based upon epidemiological clustering of cases. The virus causing this illness was isolated in 1937. The rash typical of Lyme borreliosis was identified the early 1900s. Historically, some chronic diseases were linked or associated with infectious pathogens.