MOLECULAR EPIDEMIOLOGY OF TYPE-1 POLIOVIRUSES FROM AFRICA

The genetic relationships between type 1 polioviruses circulating in s ub-Saharan Africa during the past decade have been investigated by par tial genomic sequencing across the VP1/2A region of the polioviral gen ome. Sequencing templates were generated by single-step reverse transc ription PCR amplification of the viral RNA using poliovirus-specific p rimers. Seven poliovirus genotypes, circulating in different geographi cal regions during different periods, were identified. Considerable ge netic variation was exhibited by strains within several of these genot ypes, indicative of sustained endemic transmission within individual c ountries. Two genotypes appear to be circulating in Africa at present; one major genotype, which has been in circulation since at least 1980 , covers a wide geographical region and includes countries in western, central and southern Africa. Within this genotype are several smaller clusters, possibly representing strains in the process of evolving in to new genotypes. The second genotype presently in circulation has bee n found only in Tanzania and Zambia to date, associated with a relativ ely small number of cases. Imported genotypes, introduced from the Mid dle East and the Indian subcontinent, have also recently been in circu lation in eastern and central Africa. In South Africa, three genotypes , one unique to the country and the others imported from west Africa a nd the Middle East, co-circulated endemically between 1980 and 1985. A fourth genotype, introduced from countries to the north, displaced th e endemic strains and continued to circulate until 1989. This study ha s generated a meaningful overview of the endemic circulation and regio nal transmission of type 1 polioviruses throughout sub-Saharan Africa.