Survival and behavior of Onchocerca gutturosa microfilariae in vitro

Microfilariae of Onchocerca gutturosa were extracted from the skin of the bovine naval by teasing in saline and then suspending the skin in a gauze bag overnight in Tyrode's solution with 20% human serum. They survived for ten days in this medium, with antibiotics, in plastic microtitration plates at 11 C. After dispersal in flat containers, microfilariae slowly assumed clumped dispersion patterns. They also accumulated in glass wool, suggesting that aggregation was a tactile phenomenon. Analysis of videotapes of microfilarial movement indicated that activity, expressed as the number of undulations present on the body and the rate of knot formation (where the microfilaria held itself tightly coiled), increased up to 40 C and thereafter declined. The rate of headwave formation, however, appeared constant up to 40 C after which it declined. Where the greatest number of undulations were found on the body the wave amplitude was minimal. Because greater apparent activity was not correlated with increased forward progression, microfilariae at lower temperatures may travel farther than those at 40 C. This may relate to site preference in the host and to uptake by the vector Simulium ornatum.