Periodicity of microfilariae. XII. The effect of variations in host body temperature on the cycle of Loa loa, Monnigofilaria setariosa, Dirofilria immitis and other filariae.

Abstract

When the body temperature of men or drills infected with Loa loa is slightly raised (by night), the number of microfilariae in the blood increases after a short lag period; and conversely, if the body temperature of drills is slightly lowered (by day), the number of microfilariae is lowered. Similarly (but in the opposite direction) when the body temperature of mongooses infected with Monnigofilaria setariosa (which has a nocturnal periodicity) is raised by night, the number of microfilariae in the blood is diminished, and conversely. Apparently L. loa and M. setariosa (together with Edesonfilaria malayensis) form a group of filariae in which the 24-hour cycle of the microfilariae is controlled by the 24-hour cycle of the host. The microfilaria count of Dirofilaria immitis is not affected by lowering the body temperature of the host (dog), unless the lowering is extreme (below 30°), when the microfilaria count falls. This phenomenon probably has no significance for the 24-hour microfilaria cycle. The microfilaria count of Litomosoides carinii in the cotton rat is raised if the body temperature is slightly reduced, and conversely. The same is apparently the case for Dipetalonema witei of the jird. This phenomenon may facilitate the transmission of microfilariae to the respective vectors, Liponyssus bacoti and Ornithodorus tartakowskyi, which feed when the animals are in their “nest” or burrow. The microfilaria counts of Dipetalonema gracile and Acanthocheilonema perstans are apparently unaffected by slight changes of body temperature.