Antigenic relationships among Nigerian strains of West Nile virus by complement fixation and agar gel precipitation techniques.

Using two serological techniques, eight Nigerian West Nile virus isolates were investigated to determine antigenic relationships among them, and to find out if these virus isolates were related to West Nile virus strains from the different zoogeographic areas of the world. One virus differed significantly from the seven other strains and was later found to be a strain of Usutu virus. The remaining strains were differentiated into two serological intratypic groups depending on their cross reactions with two strains which served as prototypes for each group. Five virus isolates which constitute one of the antigenic groups were found to be related to the Egypt 101 strain of West Nile virus originating from general Palearctic zone (European and Middle East). The other two virus isolates did not show any relationship to the strains from any of the different zoogeographic zones.