Part III: Helminthological Observations and Their Bearing on Certain Aspects of the Biology of Onchocerca

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In Part II of the Report on Onchocerciasis in Guatemala published by this Department in 1934, the writer presented a critical taxonomic review of the genus Onchocerca. In this review there was included a study in relation to the specific distinction that had been drawn between O. volvulus (Leuckart, 1893) and O. caecutiens Brumpt, 1919, the parasites which affect man in Equatorial Africa and Central America. Soon after the inquiry had been initiated it became apparent that the morphological problem involved could not be decided without giving consideration to certain related, though presumably distinct, species of Onchocerca which are found particularly in cattle in various parts of the world.

Based on an extensive series of specimens that we had secured for purposes of comparison, our enquiry revealed a paucity of structural differences accompanied by an extraordinarily wide range of variability in the commensural relationships of the twelve species that comprized the genus.

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