Heart Attack (cont.)
In the laboratory, for example, chickens infected with a strain of herpes virus were discovered to have aggressive atherosclerosis in their coronary arteries. Prior vaccination against the virus protected against much of the coronary atherosclerosis.
From epidemiology, it is known that there is a higher incidence of heart attacks in the winter and spring than in the summer and autumn, possibly related to the seasonal increase of the common cold and influenza infections.
On a clinical level, in some cases, common cold or flu-like symptoms are known to have preceded the heart attack. However, common colds are by definition common and flu-like symptoms are quite common, too. Such circumstantial evidence hardly constitutes concrete proof that infections cause coronary atherosclerosis and heart attacks.
One of the more provocative clues pointing to infection as a factor in the development of coronary atherosclerosis and heart disease involves a small bacteria, Chlamydia pneumoniae (C. pneumoniae). As its name suggests, C. pneumoniae causes respiratory tract infections and, in fact, it does so very commonly. About half of middle-aged adults have had C. pneumoniae. Most initial infections with C. pneumoniae cause no symptoms or just mild flu-like symptoms. Many people with C. pneumoniae are unaware they have it.
The projected role of C. pneumoniae infection in atherosclerosis and coronary heart disease rests upon the remarkable capacity of this bacteria to cause chronic occult infection, long-lasting hidden infection that smolders below the surface. Antibodies are proteins produced by the body's immune system to fight infection. In most types of infections, the appearance of antibodies in the blood signals the eventual eradication of the infection and the development of immunity against the infectious agent However, with C. pneumoniae infection, the antibodies produced by the body against C. pneumoniae may be ineffective in
eradicating the bacteria. Therefore. finding C. pneumoniae antibodies in the blood can signify prior exposure or (more importantly) ongoing infection with C. pneumoniae.
Scientists in Europe and the U.S. have independently observed an association between elevated blood antibodies against C. pneumoniae and coronary atherosclerosis and heart attacks. Finnish researchers showed that patients with recent heart attacks had significantly elevated blood levels of antibodies against C. pneumoniae compared with healthy subjects. In Seattle, doctors measured antibodies against C. pneumoniae in patients undergoing coronary angiography, an X-ray dye study to detect narrowing of the coronary arteries due to atherosclerosis. They found a two-fold increase in coronary artery disease in patients with elevated blood antibodies against C. pneumoniae.