Zoonotic Onchocercosis in a Resident of Illinois and Observations on the Identification of Onchocerca Species *

Abstract
A female Onchocerca was found in a nodular swelling removed from the wrist of a 48-year-old woman who had not been outside the area of Illinois, Wisconsin, and Missouri. Detailed examination of Onchocerca from man, horse, and cow demonstrated that on the basis of cuticle morphology the worm from the patient was distinguishable from O. volvulus obtained from subcutaneous nodules from man, O. lienalis from the gastrosplenic ligament of cattle, O. reticulata from the ligaments and flexor tendons of the legs of horses, and an Onchocerca species from the stifle joint of cattle. It closely resembled O. gutturosa and O. cervicalis from the ligamentum nuchae of the cow and horse, respectively. Its location in dense connective tissues possibly favors the likelihood of its being eventually identified as O. cervicalis. Neither O. gutturosa or O. cervicalis has been reported from the immediate locality of the patient's residence but both species probably occur there as do also their respective vectors, Culicoides and Simulium species. Three authentic cases of zoonotic onchocerciasis have been reported previously, one each from Switzerland, Crimea (USSR), and Canada.

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