Daytime variation in the density of Onchocerca volvulus microfilariae in human skin

One aim of this study was to determine whether a corneal-scleral punch biopsy instrument provides skin specimens of sufficiently uniform size so as to eliminate the need to weigh or measure the specimens in order to provide a reproducible index of the density of Onchocerca volvulus microfilariae in the skin. A second aim was to determine whether the density of microfilariae in the skin varies with the time of day. The reports of others on the latter are contradictory. Duplicate skin specimens were taken from 10 people four times during one day with a corneal-scleral punch biopsy instrument. Each specimen was weighed and measured, and the number of microfilariae were counted. Although the specimens were not of uniform weight or surface area, the number of microfilariae per specimen was as good an index of the density of larvae in the skin as the number of microfilariae per mg, or per mm(2) of skin. This may not be true when other methods of procuring skin specimens are utilized. A universally acceptable standard method is advocated. The density of microfilariae in the skin approximately doubled from morning to midday, and began to decline by early evening.