The aging population increase in the US and throughout the developed world appears to correlate with a switch from acute infectious diseases to chronic diseases as the major cause of morbidity and mortality.
Some diseases like ulcers and certain types of cancer, once thought to be primarily related to lifestyle factors, are now known to be caused by microorganisms, and many more syndromes, including some psychiatric conditions, may have a connection to infection, according to a report released today by the American Academy of Microbiology.
"A number of chronic human illnesses are triggered, either directly or indirectly, by microorganisms," says Ronald Luftig of the Louisiana State University Medical Center, one of the authors of the report, Microbial Triggers of Chronic Human Illness. "Other diseases, including some extremely common and devastating conditions, exhibit characteristics that indicate they may have an infectious etiology as well. Over 90 million Americans live with chronic illnesses, conditions that account for 70 percent of all deaths in the United States. Researching the causes of these chronic illnesses, infectious or otherwise, will lead to the development of therapies, cures and strategies for prevention that will affect the lives of millions of individuals."
Up until the late 20th century, health professionals believed that chronic diseases such as peptic ulcers and cervical cancer were caused in part by lifestyle factors such as diet, stress and exposure to environmental toxins. In the last several decades, researchers have compiled strong evidence that most peptic ulcers are caused by an infection with the bacterium Helicobacter pylori and can be treated with antibiotics. An infection with human papillomavirus (HPV), the cause of genital warts, appears to be the cause of cervical and other cancers.
In addition to H. pylori and HPV, the report lists 30 other microorganisms for which there exists strong evidence of an associated chronic disease. The report also lists over 40 other chronic diseases, including heart disease, Alzheimer's and schizophrenia, which are suspected of having an infectious cause.
Proving causation is difficult. Scientists have traditionally applied a series of tests, known as Koch's postulates, to establish that a specific microorganism does indeed cause the associated disease. Because of the complex nature of chronic illnesses, oftentimes it is not practical or even possible to use Koch's postulates to prove the infectious nature of chronic illness. The report recommends that new criteria for evaluating the strength of association between microbes and chronic illnesses be developed.
"Atherosclerosis, diabetes and Alzheimer's disease are all devastating chronic illnesses that cost millions of dollars in healthcare every year and exact incalculable tolls of pain and suffering. Each of these diseases was once thought to be caused exclusively by environmental exposures or genetic predisposition. Now they are all suspected of being in infectious diseases," says Luftig.
The report is the outcome of a colloquium convened by the Academy in June 2004 to discuss the microbial causes of chronic diseases. Research professionals from the fields of microbiology, medicine, oncology, vaccine development, immunology and other related fields participated in discussing topics related to pathogens and chronic illnesses.