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One of the most lethal of all human diseases, sleeping sickness, is carried by the Tsetse fly. In South America, another related organism infects several million people leaving many with severe heart and gastrointestinal lesions (Chagas’ disease). It is carried by the kissing bug, found in many homes of underprivileged people living in South America. Ten percent of the world’ s population, including 2-5% in the United States are infected with the intestinal protozoa (Entamoeba histolytica). Toxoplasmosis, giardiasis, and trichomoniasis are three cosmopolitan protozoan infections well known to American physicians. Some of the most common of these will be discussed briefly.
Entamoeba histolytica causes amebic dysentery Amebiasis is an infection of the large intestine, produced by Entamoeba histolytica. It produces a disease ranging from chronic mild diarrhea to life— threatening dysentery. Liver abscesses may result, at times rupturing into the abdominal or chest cavities. These diseases are diagnosed primarily by an examination of the stool. Careful microscopic investigation can disclose the presence of the cyst or adult form, a trophozoite. Treatment should be aimed at relief of symptoms, replacement of fluids, electrolytes, and blood loss, and eradication of the organism. The prevention of amebiasis is even more important. For example, the avoidance of contaminated food and water, scalding of vegetables and the use of iodine release tablets in drinking water are important measures. Improvement in the general sanitation, detection of “cyst passers”, and their removal from food-handling duties, are general measures in prevention. Malaria is a protozoal disease transmitted to humans by the bite of the Anopheles mosquito. It remains the major infectious disease problem in the world. Malaria is characterized by enlargement of the spleen, fever, anemia, and a chronic relapsing course. Today malaria survives best in areas of South and Central America, Africa, and Asia, where the mosquito and the infected human population co-exist. The incidence of the disease has decreased since 1945, due to an active international cooperative program aimed at its eradication.