Horses as Sentinels for the Circulation of Flaviviruses in Eastern-Central Germany

Viruses. 2023 Apr 30;15(5):1108. doi: 10.3390/v15051108.

Abstract

Since 2018, autochthonous West Nile virus (WNV) infections have been regularly reported in eastern-central Germany. While clinically apparent infections in humans and horses are not frequent, seroprevalence studies in horses may allow the tracing of WNV and related flaviviruses transmission, such as tick-borne encephalitis virus (TBEV) and Usutu virus (USUV), and consequently help to estimate the risk of human infections. Hence, the aim of our study was to follow the seropositive ratio against these three viruses in horses in Saxony, Saxony Anhalt, and Brandenburg and to describe their geographic distribution for the year 2021. In early 2022, i.e., before the virus transmission season, sera from 1232 unvaccinated horses were tested using a competitive pan-flavivirus ELISA (cELISA). In order to estimate the true seropositive ratio of infection with WNV, TBEV, and USUV for 2021, positive and equivocal results were confirmed by a virus neutralization test (VNT). In addition, possible risk factors for seropositivity using questionnaires were analyzed using logistic regression based on questionnaires similar to our previous study from 2020. In total, 125 horse sera reacted positive in the cELISA. Based on the VNT, 40 sera showed neutralizing antibodies against WNV, 69 against TBEV, and 5 against USUV. Three sera showed antibodies against more than one virus, and eight were negative based on the VNT. The overall seropositive ratio was 3.3% (95% CI: 2.38-4.40) for WNV, 5.6% (95% CI: 4.44-7.04) for TBEV, and 0.4% (95% CI: 0.14-0.98) for USUV infections. While age and number of horses on the holding were factors predicting TBEV seropositivity, no risk factors were discovered for WNV seropositivity. We conclude that horses are useful sentinels to determine the flavivirus circulation in eastern-central Germany, as long as they are not vaccinated against WNV.

Keywords: Germany; Usutu virus; West Nile virus; flaviviruses; horses; risk factors; seroprevalence; tick-borne encephalitis virus; vector-borne zoonoses; virus neutralization test.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Viral
  • Encephalitis Viruses, Tick-Borne*
  • Flavivirus Infections* / epidemiology
  • Flavivirus Infections* / veterinary
  • Flavivirus*
  • Horse Diseases* / epidemiology
  • Horses
  • Humans
  • Seroepidemiologic Studies
  • West Nile Fever* / epidemiology
  • West Nile Fever* / veterinary
  • West Nile virus*

Substances

  • Antibodies, Viral

Supplementary concepts

  • Usutu virus

Grants and funding

This project was funded as part of the collaborative project “WISSDIP” (Prevalence of WNV infections in mosquitoes and mammals in endemically affected rural and urban areas in Germany—possible immunoprophylaxis in horses) by the Federal Ministry of Education and Research (01KI2026B), Boehringer Ingelheim Vetmedica GmbH, Germany (funding number: 493469), and the Albrecht Daniel Thaer-Institute of Agricultural and Horticultural Sciences. The funding bodies had no role in the design of the study; in the implementation of the experiment; in the collection, analysis, or interpretation of the data; in the writing of the manuscript; or in the decision to publish the results.