Seroepidemiological Survey of West Nile Virus Infections in Horses from Berlin/Brandenburg and North Rhine-Westphalia, Germany

Abstract

Following the introduction of the West Nile virus (WNV) into eastern Germany in 2018, increasing infections have been diagnosed in birds, equines, and humans over time, while the spread of WNV into western Germany remained unclear. We screened 437 equine sera from 2018 to 2020, excluding vaccinated horses, collected from convenience sampled patients in the eastern and western parts of Germany, for WNV-specific antibodies (ELISAs followed by virus/specific neutralization tests) and genomes (RT-qPCRs). Clinical presentations, final diagnoses, and demographic data were also recorded. In the eastern part, a total of eight horses were found WNV seropositive in 2019 (seroprevalence of 8.16%) and 27 in 2020 (13.77%). There were also two clinically unsuspected horses with WNV-specific antibodies in the western part from 2020 (2.63%), albeit travel history-related infections could not be excluded. None of the horse sera contained WNV-specific genomes. Eight horses in eastern Germany carried WNV-IgM antibodies, but only four of these showed typical clinical signs. These results underline the difficulty of detecting a WNV infection in a horse solely based on clinical signs. Thus, WNV circulation is established in the horse population in eastern Germany, but not yet in the western part.

Keywords: Germany; West Nile virus; horses; seroepidemiological; seroprevalence.

Figure 1

Box plots (median and range) showing the age distribution in the sampled horses from the regions Berlin/Brandenburg (BE/BB) and North Rhine–Westphalia (NRW) (n total = 434, n in NRW 2018 = 66, n in NRW 2020 = 75, n in BE/BB in 2019 = 97, n in BE/BB in 2020 = 196, for 3 horses the age had not been reported). ***, p ≤ 0.0001; Berlin/Brandenburg (BE/BB) and North Rhine–Westphalia (NRW), mt, months, y, years.

Figure 2

Geographical distribution of the investigated horse sera from each panel (panel A sampled in Berlin/Brandeburg, panel B in North Rhine–Westphalia) and their serological results. Green dots = WNV antibody-negative horses (comp. ELISA negative); orange dots = WNV antibody-positive horses (comp. ELISA and VNT positive); red dots = WNV antibody-positive horses (additionally IgM-positive); blue dots = TBEV antibody-positive horses and yellow dots = USUV antibody-positive horses. In the magnified area from panel A (BE/BB), the endemic WNV areas are highlighted in different shades of orange, which represent the district levels where WNV positive birds and horses were detected in Germany from 2018 to 2020.

Figure 3

Box plots (median and range) showing the distribution of age in horses that were positive for both IgM and WNV antibodies (Ab (comp. ELISA and VNT positive) n = 8, positive for WNV Ab only (comp. ELISA and VNT positive) n = 30 and negative for WNV Ab (comp. ELISA negative) n = 396 in all horses sampled., for 3 horses the age had not been reported. * p < 0.05, mt, months, y, years.