Myocarditis is an inflammation of the heart muscle that decreases the ability of the heart to pump blood normally. It can be caused by:
An infection —Many infections have been associated with myocarditis. Some of the more likely germs include:
Viral infections — A common cause of myocarditis. Many different viruses can cause myocarditis. Examples include adenovirus, coxsackievirus, Epstein-Barr virus, HIV, varicella (chickenpox) and human herpes virus 6. Often the person has no preceding symptoms of a cold, cough, nasal congestion or rash and only becomes aware of the infection when heart failure occurs.
Bacteria — Rarely, myocarditis is a complication of endocarditis, an infection of the heart valves and the lining inside the heart's chambers caused by bacteria. In some people with diphtheria, a toxin (poison) produced by C. diphtheriae bacteria causes a form of myocarditis that leads to a flabby, stretched-out heart muscle. Because the flabby, enlarged heart cannot pump blood efficiently, severe heart failure may develop within the first week of illness.
Chagas' disease — This infection, caused by the protozoan Trypanosoma cruzi, is transmitted by an insect bite. In the United States, myocarditis caused by Chagas' disease is most common among travelers to or immigrants from Central and South America. In up to one-third of people with Chagas' disease, a form of chronic (long-term) myocarditis develops many years after the first infection. This chronic myocarditis leads to significant destruction of heart muscle with progressive heart failure.
Lyme myocarditis — Lyme disease, an infection caused by the tick-borne bacterium Borrelia burgdorferi, can cause myocarditis or other heart problems.
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