Detection of African horse sickness virus antibodies by ELISA in sera collected from unvaccinated horses in Kaduna Metropolis, Nigeria

African horse sickness (AHS) is endemic in sub-Saharan Africa and is still recognized as one of the major life-threatening diseases of equids in Africa, the Middle East, the Eastern Mediterranean and some parts of Europe (10) because of its high mortality rate (up to 90% in epidemics), particularly in naïve populations (13). AHS is an acute or subacute insect-borne infectious disease of Equidae (horses, mules, donkeys and zebras) caused by African horse sickness virus (AHSV), a double-stranded RNA virus in the genus orbivirus, belonging to the Reoviridae family (2, 4). AHSV is a viscerotropic virus found in the blood, tissue fluids, serous exudates and several internal organs of Equidae (11). It is a non-contagious disease known to be transmitted to horses by midges, in particular by Culicoides imicola, the main field vector found in abundance in Nigeria during the warm rainy seasons (1, 5). The incubation period ranges from 2 to 14 days and the clinical signs appear 5 to 7 days after infection, associated with respiratory and circulatory impairment (11, 13). AHSV exists as nine immunologically distinct serotypes, all of which have been identified and are considered to be enzootic in sub-Saharan Africa (7). Since the first documented outbreak and subsequent isolation of the virus from a dead horse in Nigeria in 1970 (9), sporadic outbreaks of AHS have occurred in different regions of the country (3, 8, 16). Furthermore, Lazarus et al. (12) reported in 2010 AHSV in a captive zebra that died in a game reserve in Bauchi, Nigeria. AHSV was detected from tissue samples collected from the dead zebra at postmortem by realtime reverse-transcription polymerase chain reaction (rRT-PCR). Recently (in 2014), outbreaks of AHS have been reported in South Africa and Mozambique resulting in the death of several horses (15, 19). Historically, only serotypes 4 and 9 AHS viruses have been found in West Africa. In recent past, other types of AHSV have been reported for the first time in sub-Saharan Africa. AHSV serotype 6 was identified in Ethiopia in 2003 and AHSV serotype 2 was also confirmed in Senegal and Nigeria in 2007 (17). So far, only AHSV serotypes 2 and 9 have been confirmed in Nigeria (3, 8, 9).