538 Host-Parasite Relationships 



six species of flagellates — Trichomonas tenax (buccalis) of the mouth; 

 Giardia lamblia of the small intestine; and Chilomastix mesnili, Re- 

 tortomonas {Embadomonas) intestinalis, Tricercomonas intestinalis, and 

 Pentatrichomonas hominis of the colon — and six species of amoebae — 

 Entamoeba giyigivoUs of the mouth; Entamoeba coli, E. histolytica (which 

 sometimes invades other organs), Dientainoeba fragilis, Ejidolimax nana, 

 and lodamoeba butschlii of the colon. One ciliate, Balantidium coli, 

 sometimes invades the colon, while a coccidian, Isospora hominis, ap- 

 parently is a parasite of the small intestine. The urogenital tract may 

 harbor Trichomonas vaginalis, which is often found in the vagina and 

 urethra in the female, and in the urethra and prostate in the male. 

 Parasites of the blood and other tissues include species of Leishmania 

 (L. brasiliensis, L. donovani, L. tropica), Trypanosoma (T. cruzi, 

 T. gambiense, T. rhodesiense), and Plasmodium (P. falciparum., P. ma- 

 lariae, P. ovale, P. vivax). The status of Toxoplasma as a natural parasite 

 of man is somewhat uncertain, in view of the apparent rarity of human 

 infections and the low degree of host-specificity exhibited by these 

 organisms. 



The intestinal Protozoa of man are probably worldwide in distribution 

 and are fairly common parasites. The malarial parasites, although most 

 abundant in tropical areas, extend into the temperate zones. The trypano- 

 somes of sleeping sickness, on the other hand, seem to be limited to 

 central Africa by the geographical distribution of their vectors. Species 

 of Leishmania are much more widely distributed, and Trypanosoma 

 cruzi has an extensive range in the western hemisphere. 



The Americas 



In North America the usual intestinal Protozoa are to be expected. 

 The incidence of E. histolytica, for example, ranges from about 0.2 to 

 50 per cent of the population in different parts of the United States, 

 with an average possibly approaching 20 per cent (26a). Malaria remains 

 an important problem only in the southeastern United States (3). 

 Trypanosoma cruzi occurs at least as far north as central California, al- 

 though Chagas' disease has not been foimd in man. 



In Mexico and other Central American countries intestinal Protozoa 

 are probably no less common than they are in North America. Malaria is 

 important in lowland areas, both coastal and interior, and Costa Rica and 

 Panama in particular have suffered considerably. Sporadic cases of Chagas' 

 disease have appeared within this area, and both cutaneous and visceral 

 leishmaniasis are known from scattered localities. 



In the Caribbean area, malaria remains a public health problem in 

 Jamaica, Haiti, the Dominican Republic, Puerto Rico, and Trinidad. 

 Most of Cuba is free from endemic malaria although there are some 

 areas in which the disease is still important. Among the smaller islands, 



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