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Protozoan Diseases - AMERICAN TRYPANOSOMIASIS
(Chagas's Disease, Chagas-Mazza Disease, South American Trypanosomiasis)
RESERVOIR AND INCIDENCE
Dogs, cats, and guinea pigs are the main reservoirs for human infection. T. cruzi occurs only in the Americas; it is found from southern South America to northern Mexico, Texas, and the southwestern U.S. An estimated 12 million people are infected, mostly in rural areas, resulting in about 60,000 deaths yearly.
Humans are infected when the insect's feces become rubbed into the wound caused by the bite of an infected bloodsucking insect (triatomid) or when the conjunctiva, mucous membranes or abrasions become contaminated. After invading local reticuloendothelial cells, the trypanosome multiplies in the blood. Adaption of triatomid vector to the human domestic environment allows transfer of infection between animals, from animals to humans or from human to human. Transmission by blood transfusions from infected persons, congenital infection, breast milk and laboratory accidents are possible.
DISEASE IN ANIMALS:
Acute and inapparent infection occur in wild animals and chronic disease is seen in dogs. The acute form, which includes fever, enlarged liver and lymph nodes and heart irregularities, lasts 10-30 days before becoming chronic without further clinical signs, though sometimes myocarditis occurs. Lesions in dogs resemble those in humans.
DISEASE IN HUMANS:
Acute illness usually occurs in children with a furuncle at the site of infection. Signs include fever, malaise, enlarged lymph nodes, liver and spleen. If the primary site of infection is the eye there is unilateral edema of eyelids and conjunctivitis. Rarely myocarditis and meningoencephalitis occur. Chronic symptoms in adults result from arrhythmias and dilation of the heart, esophagus and colon. Furuncles (chagoma) appear at the point of entry of the infection. Enlarged liver and spleen, myocarditis, grossly dilated heart, intestines, esophagus, ureter and bladder and meningoencephalitis occur.
Several serologic tests are available and are of presumptive value; when possible, more than one test should be used. In the acute stage, trypanosomes should be looked for by examination of anticoagulated fresh blood for motile organisms. In the chronic stage, the parasite can only be detected by culture or xenodiagnosis.
Therapy is unsatisfactory; the drugs are toxic and often ineffective. In the acute phase, however, cure is usually possible. In the chronic phase, although parasitemia and xenodiagnosis become negative, treatment does not alter the serologic reaction, cardiac function, or progression of the disease. Nifurtimox or benznidazole is used. Ketoconazole shows promise also.
Destroy the vector by insecticides. Use insect nets to prevent bites. Screen blood donors.