The flagellate leishmania is transmitted to humans by the bite of the female sandfly of the genus Phlebotomus. Three principal diseases result from infection with Leishmania spp. L. donovani causes visceral leishmania-sis (kala-azar); L. tropica and L. major produce cutaneous leishmaniasis, and L. braziliensis causes South American mucocutaneous leishmaniasis. In visceral leishmaniasis, the protozoan parasitizes the reticuloen-dothelial cells, and this results in an enlargement of the lymph nodes, liver, and spleen; the spleen can become massive. Cutaneous leishmaniasis remains localized to the site of inoculation, where it forms a raised disfiguring ulcerative lesion. South American leishmaniasis is variable in its presentation. It is characterized by ulceration of the mucous membranes of the nose, mouth, and pharynx; some disfiguring skin involvement also is possible.
African trypanosomiasis follows the bite of Glossina, a tsetse fly infected with the protozoan Trypano-soma brucei. The ensuing illness (sleeping sickness) is initially characterized by the hemolymphatic stage of fever, headache, and lymph node enlargement. These symptoms are followed by meningoencephalopathic involvement, with wasting, mental disturbances, and drowsiness as the disease progresses. This latter more serious stage requires different, more potentially toxic drugs than does the hemolymphatic stage. There are geographical variations of the disease. Rhodesian sleeping sickness, acquired in the savannah and woodlands of East Africa from Glossina morsitans, is a much more acute and rapidly progressive disease than Gambian sleeping sickness, acquired in riverine areas of West Africa from Glossina palpalis, in which the incubation period can be more prolonged and the disease more protracted.
Chagas' disease, the South American variety of trypanosomiasis, is caused by Trypanosoma cruzi. It is quite different from African trypanosomiasis in its clinical and pathological presentation and in its failure to respond to many agents effective in that disease. It has both an acute and chronic phase. The latter frequently results in gastrointestinal and myocardial disease that ends in death.
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