West Nile Virus Infection in Horses in Jordan: Clinical Cases, Seroprevalence and Risk Factors

The objectives of this study are to report clinical WNV infection in horses and to determine the seroprevalence of and risk factors for WNV infection in horses in Jordan. In late summer and early fall of 2012, two mares were presented for evaluation of neurological signs. The first mare had hind-limb ataxia. The second mare was slightly depressed and lethargic. She had ataxia in her four limbs and cranial nerves deficits. Both horses were found positive for WNV IgM antibodies using commercial IgM-capture ELISA test. Both horses were treated symptomatically and recovered uneventfully. The occurrence of clinical cases initiated the need for a seroprevalence and risk factors study. Two hundred and fifty-three normal horses were randomly enrolled in the study. Enrolled horses were grouped into five major regions according to the geographical proximity and climatic similarities. From each region, around 50 horses were sampled. The serum collected from each horse was screened by a competitive ELISA, and those that reacted positive using the previous ELISA test were further tested using commercial IgM-capture ELISA test. Sixty-three horses (24.9%) of the 253 surveyed were seropositive to WNV. Of the 63 horses, none had IgM antibodies for WNV. The region with the highest prevalence was Jordan Valley and Balqa. Horses used for polo (OR = 9.77; 95% CI = 1.32-25.44) and horses located in Jordan Valley and Balqa region (OR = 13.31; 95% CI = 2.33-32.54) were identified as risk factors for seropositivity to WNV in Jordan. These risk factors were attributed to the hot and humid weather, which enhance vector availability. West Nile virus appears to be endemic in Jordan. Future studies are warranted to evaluate the virus situation in the country during the next few years in an attempt to control it.