VIABILITY OF ONCHOCERCA-VOLVULUS IN-VITRO

The use of a selective schedule of tests to identify a viable populati on of isolated adult Onchocerca volvulus (Nematoda: Filarioidea) has b een investigated in a large worm population. The study was initiated t o develop methodology appropriate to test new candidate macrofilaricid es for their in vitro activity against O. volvulus. After removal from the host the viability of isolated intact parasites was estimated by assessing the motility indices of male worms, and the colorimetric qua ntification of the reduction of the bioreducible tetrazolium reagent X TT and lactate output by female worms. Additionally the motility of wh ole females and the movement of inner organs of female worms were scor ed quantitatively. These response parameters were used to sort the adu lt worms into viability groups at the start of the in vitro culture. T he adult worms were then observed for 6 days and viability was assesse d regularly during the culture period. At the end of the culture perio d, the reduction of the water-insoluble tetrazolium reagent MTT was us ed to determine the formazan formed by the entire male and female worm s. The response parameters used at the start of the culture proved to be highly predictive for detecting viable and non-viable adult worms. In the group of worms selected as 'viable' around 70% kept their motil ity and metabolic activity at a high level until the end of the cultur e compared to the initial level. In contrast, none of the female worms and only 13% of the male worms categorized as 'poorly viable' demonst rated a motility index or metabolic level at the end of the culture pe riod that was comparable to that of the worms in the 'viable' groups. For female worms the lactate output correlated significantly with weig ht whereas no correlation was seen between MTT reduction and weight.