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. 2024 May 9;11(5):209.
doi: 10.3390/vetsci11050209.

Seroprevalence of West Nile Virus among Equids in Bulgaria in 2022 and Assessment of Some Risk Factors

Nikolina Rusenova  1 , Anton Rusenov  2 , Mihail Chervenkov  3   4 , Ivo Sirakov  5
Affiliations

Seroprevalence of West Nile Virus among Equids in Bulgaria in 2022 and Assessment of Some Risk Factors

Nikolina Rusenova et al. Vet Sci. .

Abstract

The aim of this study was to analyze the seroprevalence of West Nile virus (WNV) among equids in Bulgaria, confirm the results of a competitive ELISA versus the virus neutralization test (VNT) and investigate some predisposing factors for WNV seropositivity. A total of 378 serum samples from 15 provinces in northern and southern Bulgaria were tested. The samples originated from 314 horses and 64 donkeys, 135 males and 243 females, aged from 1 to 30 years. IgG and IgM antibodies against WNV protein E were detected by ELISA. ELISA-positive samples were additionally tested via VNT for WNV and Usutu virus. Thirty-five samples were WNV-positive by ELISA (9.26% [CI = 6.45-12.88]), of which 15 were confirmed by VNT; hence, the seroprevalence was 3.97% (CI = 2.22-6.55). No virus-neutralizing antibodies to Usutu virus were detected among the 35 WNV-ELISA-positive equids in Bulgaria. When compared with VNT, ELISA showed 100.0% sensitivity and 94.5% specificity. A statistical analysis showed that the risk factors associated with WNV seropositivity were the region (p < 0.0001), altitude of the locality (p < 0.0001), type of housing (p < 0.0001) and breed (p = 0.0365). The results of the study demonstrate, albeit indirectly, that WNV circulates among equids in northern and southern Bulgaria, indicating that they could be suitable sentinel animals for predicting human cases and determining the risk in these areas or regions of the country.

Keywords: ELISA; Usutu virus; VNT; WNV; donkeys; horses; seroprevalence.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
(a). Map of Bulgaria showing sampling provinces and ELISA- and VNT-positive samples within provinces. Note: NW—Northwestern; NC—North Central; NE—Northeastern; SW—Southwestern; SC—South Central, SE—Southeastern. Sampling provinces are shown in gray; the provinces from which samples were not collected are white. Black circles indicate the number of WNV-ELISA-seropositive samples and red circles indicate the number of WNV-VNT-seropositive samples in each province. (b). Elevation map of Bulgaria showing the distribution of WNV-VNT-seropositive samples.
Figure 2
Figure 2
ROC curve analysis for the diagnostic performance of c-ELISA.
Figure 3
Figure 3
Logistic regression plot of the relationship between the altitude of sampling sites as an independent variable (X-axis) and the probability of having a positive VN test (Y-axis).
See this image and copyright information in PMC

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