DNA PROBE-BASED CLASSIFICATION OF SIMULIUM-DAMNOSUM S L-BORNE AND HUMAN-DERIVED FILARIAL PARASITES IN THE ONCHOCERCIASIS CONTROL PROGRAM AREA

The development of polymerase chain reaction-based methods using strai n- and species-specific DNA probes for Onchocerca volvulus has permitt ed classification of individual parasites from every stage of the para site's life cycle. This technology has been applied on a large scale b asis by Onchocerciasis Control Program (OCP) in West Africa. The prima ry objective of the OCP in using the DNA probes was to obtain accurate estimates of the annual transmission potential of the blinding strain of O. volvulus. The DNA probe classification of larvae collected thro ughout the OCP area demonstrated that larvae of less pathogenic strain s of O. volvulus and other filarial parasites carried by Simulium damn osum s.l. have resulted in a significant overestimation of the annual transmission potential for blinding onchocerciasis. This effect is par ticularly pronounced along the southern border of the OCP, where the b linding and less pathogenic strains of O. volvulus coexist, and in the north of the control area, where animal parasites, particularly O. oc hengi, may even predominate. A second objective of the OCP in applying the DNA probe technology was to determine the distribution of blindin g and less pathogenic O. volvulus in infected individuals along the so uthern border of the control area. Results obtained from these studies have generally confirmed the distribution pattern established by prev ious epidemiologic studies. In addition, DNA probe classifications hav e demonstrated that in areas where the blinding and less pathogenic st rains of O. volvulus coexist, a single individual may simultaneously b e infected with both strains of the parasite.