Determination of the seroprevalence and risk factors that are associated with West Nile virus (WNV)
in horses is essential for adoption of effective prevention strategies. Our objective in this study,
therefore, was to determine the seroprevalence and to identify the risk factors associated with WNV
infection in the most densely horse-populated governorates in Egypt. A cross-sectional study was
conducted in 2018 on 930 horses, which were distributed over five governorates in the Nile delta
of Egypt. The horses, which were randomly selected, were serologically tested through use of an
ID screen West Nile competition enzyme-linked immunosorbent assay (ELISA) to detect anti-WNV
immunoglobulin G (IgG) and plaque reduction neutralization tests (PRNT; gold standard) to confirm
the seropositive status of animals and to avoid cross reaction with other flavi-viruses. Four variables
(geographical location, breed, sex and age) were considered in the risk analysis. Univariable and
stepwise forward multivariable logistic regression methods were used for risk-factor analysis. The odds
ratio (OR) was used as an approximate measure of relative risk. A total of 156 (16.8%; 95% confidence
interval (CI) 14.4–19.2; P < 0.001) serum samples were found to be serologically positive for WNV.
The highest seroprevalence rate was detected in horses of age ≥ 15 years (68.1%; 95% CI 49.8–72.4),
stallions (26.4%; 95% CI 22.7–30.4), and those of mixed breed (21.5%; 95% CI 17.7–27.5). Horses
older than 15 years were found to be at increased risk of WNV infection with OR = 4.3 (95% CI 3.0–6.2,
P < 0.001) compared with horses aged under 2.5 years. Also, when all the risk factors were considered,
stallions were more likely than mares to be WNV seropositive (OR = 2.4, 95% CI 1.6–3.7, P < 0.001),
and of the breeds, mixed-breed (OR = 1.9, 95% CI 1.2–2.8, P = 0.005) and Arabian horses (OR = 1.9,
95% CI 1.2–2.8, P = 0.005) were more likely to be seropositive. Geographical location seemed to have
no impact on the seroprevalence of exposure to WNV among these horses. Due to these findings, we
strongly recommend intensive surveillance and implementation of effective control and prevention
strategies against WNV, especially in stallion, mixed-breed horses with ages ≥ 15 years. |
