Loa loa: output of microfilariae in single pair infections

The intent of the present study was to assess the production and release of microfilariae by a single female filaria, in an in vivo system. Experimental infections of Loa loa were established in baboons by implantation of juvenile worms, typically, one female and two or three males. Infected animals were bled weekly and the number of microfilariae counted. Microfilarial counts were converted to number of microfilariae per milliliter and then the total number of microfilariae present calculated for the total volume of blood. Weekly increases in microfilarial counts were calculated for each animal. During the primary wave of microfilariae, the average weekly increase ranged from 16,000 to 194,000 (ave. 74,000). This figure gave an average daily output of 10,000 microfilariae per female. During the secondary wave of microfilariae following splenectomy, the average weekly increase ranged from 83,000 to 270,000 (ave. 157,000), giving an average daily output of 22,000 microfilariae per female. It is postulated that this level of production occurs only during the early phase of infection and is markedly reduced after the microfilaremia plateaus. The results indicate that the shedding of microfilariae by the female worm does not occur necessarily on a daily or weekly basis, and that female worms do not shed uniform numbers of microfilariae over a given period of time.