Equine Rotavirus A Outbreaks in Ireland (2023-2024): An Epidemiological Investigation and Virus Genotyping

Abstract

Equine rotavirus A (RVA) is a major cause of debilitating diarrhoea in neonatal foals globally. The aim of this study was to characterise RVA viruses currently circulating in Ireland and to identify risk factors associated with disease outbreaks. Of the 377 samples submitted during 2023 and 2024, 48 foals from 36 outbreaks were confirmed to be RVA-positive by real-time PCR. The viruses detected were genotyped by VP7 and VP4 gene sequencing. In 2024, the attending veterinary surgeon was contacted, and epidemiological data were collected. These included the vaccination status of the foal's dam and the clinician's opinion of the hygiene standard and stocking density on the farm. During the study period, 37 G3 RVAs were detected on 26 premises and 7 G14 RVAs were detected on 6 premises. Phylogenetic analysis indicated that all the viruses characterised were of the G3A subtype and the P[12]genotype and were closely related to viruses previously identified in Europe and Japan. Farm hygiene standards and stocking rates, with some exceptions, were considered satisfactory by the clinicians. However, vaccination coverage needs to be improved as the dams of the affected foals were unvaccinated on 68% of farms.

Keywords: Ireland; VP4; VP7; epidemiology; equine; genotype; rotavirus A; vaccination.

Figure 1

Phylogenetic analysis of 90 nucleotide sequences (763 bp) of the VP7 gene of group A rotaviruses (RVAs). Irish equine G3P[12] and G14P[12] RVAs examined in this study are indicated by dark and light green circles, respectively. The H-2 strain is indicated by a red diamond. The percentage of bootstrap support is indicated by the value at each node. Scale bars indicate nucleotide substitutions per site. *G13P[18] viruses are rarely detected in horses.

Figure 2

Phylogenetic analysis of 90 nucleotide sequences (730 bp) of the VP4 gene of group A rotaviruses (RVAs). Irish equine G3P[12] and G14P[12] RVAs examined in this study are indicated by dark and light green circles, respectively. The unknown G3 genotype is denoted by an open circle. The H-2 strain is indicated by a red diamond. The percentage of bootstrap support is indicated by the value at each node. Scale bars indicate nucleotide substitutions per site.