A number of chronic human illnesses are triggered, either directly or indirectly, by microorganisms. Among these are diseases that many scientists never suspected of having an infectious etiology, including peptic ulcer disease, brought on by the bacterium Helicobacter pylori, and cervical cancer, a condition caused by a human papilloma virus (HPV). Scientists have had to apply multiple and different lines of evidence to convincingly link a given chronic disease to a causative agent, employing cultivation, molecular methods of detection, epidemiological studies, preventive intervention studies, transmission studies, animal models and other methods to compile sufficient evidence. Numerous host factors and microbial factors have been found to come into play in determining the outcome of infections with the pathogens that trigger these diseases.
Other diseases, including some extremely common and devastating conditions, exhibit characteristics that indicate they may be infectious as well. Characteristics that can tip off investigators to a possible microbial cause range from pathogen presence in diseased tissues, to an increased risk of disease in the immune suppressed,to the response of the condition to antimicrobial therapy. A number of complicating factors can make it more difficult for researchers to investigate these putative microbial links. If an infection is ubiquitous in a population, for example, it can be challenging to draw a one-to-one relationship between infection and illness.
Because of the difficulty of applying Koch’s postulates to identifying the microbial triggers of chronic diseases, new criteria are needed for establishing proof of associations of this kind.
In releasing the results of research that associates devastating illnesses with infectious causes, some thought should be given to the possible social consequences and impacts on risk-associated behaviors.
In investigating possible microbial links to chronic illnesses, it is extremely important to be able to detect the presence of any pathogens in affected tissues. Currently available technologies for pathogen detection have their strengths, but there is room for improvement. Other technological needs include better markers of early disease states and better information on disease occurrence to help to identify new syndromes and recognize patterns in old syndromes.
Research on chronic infectious diseases can incorporate many different elements, including medical, microbiological, epidemiological, and genetic components. Accordingly, the best research will be multidisciplinary, involving experts from multiple areas of experience to derive the most complete picture of the issues at hand.
Kathryn M. Carbone, Ronald B. Luftig, Merry Buckley. 2005. Microbial triggers of chronic human illness.
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