Distribution of Onchocerca spp. microfilariae in the dermis of cattle.

A grid was drawn on a lateral half of 10 hides, from cattle infected with both Onchocerca gutturosa and Onchocerca lienalis, which were obtained from an abattoir in central Florida. Paired 7-mm diameter skin cores were taken from 24 grid sites on each hide and microfilariae (mff) extracted to determine their distribution. The only consistent pattern distribution was that mff were recovered from all 10 hides at four sample sites along the ventral midline near the umbilicus. Microfilariae were also frequently found in large numbers along the dorsal cervical midline and in the region of the tarsal and carpal-metacarpal joints.

Onchocerca gutturosa and Onchocerca lienalis in cattle: variation in length of microfilariae by site of recovery.

Dermal microfilariae recovered from specimens obtained from umbilical and cervical sites of cattle infected with adult Onchocerca gutturosa alone or with adults of O gutturosa and O lienalis were measured and compared with uterine microfilariae obtained directly from gravid female worms of each species. Uterine microfilariae of O gutturosa were longer than dermal microfilariae obtained from cattle harboring only adults of O gutturosa. Dermal microfilariae were recovered from umbilical and cervical sites in these cattle. Those found at the cervical site had lengths equal to or greater than lengths of microfilariae recovered from the umbilical site. There was a significant (P less than 0.0001) shift in length across populations of microfilariae of O gutturosa from various sites in its bovine host, with a progressive decrease in length between microfilariae recovered from the worm's uterus, microfilariae from the cervical dermis, and microfilariae from the umbilical dermis, respectively. A similar direct comparison was not possible for microfilariae of O lienalis, because none of the cattle was infected with only adult worms of this species. In an indirect comparison, microfilariae of O lienalis were identified at the umbilicus, but their presence in the cervical region could not be determined unequivocally because of confounding of microfilariae length by concurrent infection with O gutturosa. Uterine microfilariae from O lienalis were longer than uterine microfilariae of O gutturosa, although a degree of overlap in the range of measurements existed between species.