Litomosoides carinii: effect of diethylcarbamazine on microfilaremias of Mastomys natalensis harboring old infections, new infections, and transfused microfilariae.

Mastomys natalensis, matched according to age and microfilaremia, were divided into Experimental and Control groups. The former were given diethylcarbamazine (Caricide, 500 mg/kg) per os. Microfilariae counts were made at 15, 30, 60, and 120 min and at 1, 5, and 12 days. This protocol was performed on rats with: old infections (patent for 7 mo), new infections (patent for 10 days), and no infection but made microfilaremic by injection of blood or culture-derived microfilariae. In all treated groups, the microfilaremia dropped precipitously within the first 15 min. Microfilaremias of animals with old infections remained low until day 12 after treatment when they began to rise, whereas those of animals with new infections began to rise immediately, i.e., within minutes after the initial decline. Microfilaremias of animals with no adult worms present remained depressed for the duration of the experiment. Thus, the resurgence of microfilariae after treatment with diethylcarbamazine is the result of release of new microfilariae by the female worms rather than release of trapped microfilariae by the host. This investigation also demonstrates that elimination of microfilariae by a nonsensitized host is possible upon treatment with diethylcarbamazine.