African horse sickness virus antibodies in northern Nigeria 1974–1975

Abstract

A survey for complement fixing (CF) and neutralising (VN) antibodies to African horse sickness (AHS) viruses was carried out on sera, collected in October 1974 and April 1975, from 40 horses in Benue Plateau State, Nigeria. Group-specific CF antibodies were found in 31 of these in October and in 33 of them in April. In three cases there was a significant rise in CF antibody between October and April and in one a fall. In the sera collected in October, VN antibodies to AHS virus types 1, 2, 3, 4, 5, 6, 8 and 9 were found in 72.5, 55, 67.5, 57.5, 77.5, 22.5, 82.5 and 95 per cent of cases respectively. In seven horses, antibodies to all eight serotypes were demonstrated. In one horse between October and April there was a rise in VN antibodies, especially to type 9 virus, despite the absence of clinical disease. The sensitivity of the CF test could be increased by using it quantitatively but it was unable to detect all cases of previous contact with virus antigen. The incidence and titre of CF antibody were not related consistently to either the incidence or titre of VN antibodies. The results show that most types of AHS virus have been active in Nigeria in the past, the predominant one at present being type 9. The implications of the results on tests for the importation of horses from endemic areas, where the disease is subclinical, are discussed.