RECENT EVOLUTIONARY HISTORY OF AMERICAN ONCHOCERCA-VOLVULUS, BASED ONANALYSIS OF A TANDEMLY REPEATED DNA-SEQUENCE FAMILY

Polymerase chain reaction (PCR) products were characterized for a repe ated sequence family (designated ''O-150'') of the human filarial para site Onchocerca volvulus. In phylogenetic inferences, the O-150 sequen ces clustered into closely related groups, suggesting that concerted e volution maintains sequence homology in this family. Using a novel mat hematical model based on a nested application of an analysis of varian ce, we demonstrated that African rainforest and savannah strain parasi te populations are significantly different. In contrast, parasites col lected in the New World are indistinguishable from African savannah st rains of O. volvulus. This finding supports the hypothesis that onchoc erciasis was recently introduced into the New World, possibly as a res ult of the slave trade.