25 April 2005
Microorganisms Behind Schizophrenia And Alzheimer's?
by Kate Melville

Conditions like heart disease, Alzheimer's and schizophrenia could be caused by microorganisms, according to a report from 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. 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. "Other diseases, including some extremely common and devastating conditions, exhibit characteristics that indicate they may have an infectious etiology as well," said Luftig.

Until recently, doctors 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. Now, 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 cancer. 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. "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.

But proving causation is difficult. In the past, scientists have applied a series of tests to establish that a specific microorganism does indeed cause the associated disease. Because of the complex nature of chronic illnesses, it is often not practical or even possible to use these tests 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.