Effect of Cocaine and Tetracaine on Microfilariae of Onchocerca Volvulus in Vitro and in Conjunctival Biopsies

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Abstract
Summary Microfilariae of Onchocerca volvulus are rapidly immobilized when exposed in vitro to cocaine hydrochloride and tetracaine hydrochloride in concentrations normally used for conjunctival anesthesia. In conjunctival snips the microfilarial count usually rises following instillation of each anesthetic; the rise is marked following cocaine. This indicates that the local anesthetic is selectively absorbed by the tissue and only a small amount comes in contact with the microfilariae. Microfilariae show a positive chemotaxis to concentrations of cocaine that do not impair their motility. It is shown that local anesthesia with cocaine or tetracaine does not interfere with the diagnostic value of conjunctival biopsies in cases of suspected ocular onchocerciasis, and that instillation with cocaine would seem to offer a better chance of finding microfilariae when their number is small.

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