Fate of microfilariae of Dirofilaria immitis following use of levamisole as a microfilaricide.

A pretreatment liver biopsy was secured from each of three dogs with Dirofilaria immitis microfilariae counts of 29,500, 24,700, and 76,700/ml blood, respectively. Post-treatment biopsies were obtained 30 h later following treatment with a single dose of levamisole and a reduction in microfilariae counts of up to 80%. Both pre- and posttreatment biopsies were examined by light and electron microscopy. Microfilariae in dilated sinusoids of pretreatment liver biopsies were not degenerated and were unattended by an inflammatory reaction when examined by either method. However, degenerated microfilariae were present within granulomas in post-treatment liver biopsies examined by light and electron microscopy. Several stages of degeneration of microfilariae, including phagocytosis, were identified by the latter method.