Basic studies on the laboratory assessment of macrofilaricides using Brugia malayi in the jird, Meriones unguiculatus. 1. Longevity and periodicity of microfilaremia.

The longevity and periodicity of microfilaremia were examined in the jird infected with Brugia malayi to be used for assessing the filaricides. Jirds 4 to 6 weeks old were inoculated subcutaneously with 100 to 200 infective larvae of B. malayi. Microfilariae were present in 75 out of 94 jirds observed over 3 years and high microfilaremia, with 10 mf/microliters or higher, developed in 43 out of 75 jirds. Such a high level of microfilaremia was necessary for narrowing the variation of microfilaria counts among the blood samples. The microfilaria negative jirds, 4 months after inoculation, were abandoned, because in those cases where they became patent later the microfilaria density did not reach an appropriate level. The selected jirds were used for experiment from 6 to 15 months after inoculation when most of them revealed the maximal count of microfilariae. The jirds that failed to develop microfilaremia to the level of 10 mf/microliters by 9 months after inoculation were also abandoned because they did not continue the appropriate level of microfilaremia even when they reached this level later. Although a significant periodicity was observed only in of 10 jirds examined by the Aikat and Das method, the peak hour of microfilaria density was observed in most animals in the afternoon and the time was nearly the same in each animal. Therefore, the blood sampling would be performed preferably in the afternoon.