Molecular epidemiology of Nigerian and Ghanaian measles virus isolates reveals a genotype circulating widely in western and central Africa

Sub-Saharan Africa is one of the regions of the globe with the highest meas les-related morbidity and mortality. Yet only seven virus isolates from thi s vast region have been phylogenetically characterized on the basis of thei r nucleoprotein, the last one in 1991. To characterize the prevalent wild-t ype viruses and to understand their circulation pattern, a large panel (n = 45) of isolates was collected in Ghana and Nigeria in 1997 and 1998. On th e basis of their nucleoprotein sequence, the viruses clearly belong to clad e B but a reshuffling of the structure of this clade was proposed, tentativ ely extending the number of genotypes from two to three on the basis of qua ntitative criteria. The sequences revealed the co-circulation of at least t wo distinct viruses in the cities of Lagos and Ibadan, suggesting that the number of susceptible individuals seems to be high enough to support endemi c circulation of at least two distinct viruses. The endemic co-circulation of several viruses may well be a characteristic of communities with low vac cination rates. One of these viruses was also found in Accra in 1998 as wel l as in a 1994 case linked to distant Kenya, suggesting that clade B viruse s are prevalent in sub-Saharan Africa while non-B viruses seem to dominate the south of Africa.