Outbreak of equid herpesvirus 1 abortions

Here is a informative study of a EHV-1 outbreak with several important lessons for those who run breeding facilities. The first is that EHV-1 is never really gone from a horse. The virus remains quiescent until some event allows for recrudesce. Two, it seems that regular vaccination for EHV-1/4 was keeping the EHV-1 repressed and the herd free of abortions.
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Outbreak of equid herpesvirus 1 abortions at the Arabian stud in Poland
BMC Vet Res. 2020 Oct 6;16(1):374. doi: 10.1186/s12917-020-02586-y.
Authors
Karol Stasiak 1 , Magdalena Dunowska 2 , Jerzy Rola 3
Affiliations

1 Department of Virology, National Veterinary Research Institute, Al. Partyzantow 57, 24-100, Pulawy, Poland.
2 Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston, North, New Zealand.
3 Department of Virology, National Veterinary Research Institute, Al. Partyzantow 57, 24-100, Pulawy, Poland.

Abstract

Background: Equid herpesvirus 1 (EHV-1) infections are endemic worldwide, including Poland. Many are subclinical, but some are associated with respiratory disease, abortion, neonatal foal death, or neurological disease. We describe an outbreak of abortions in Arabian mares at a well-managed State stud farm in Poland.

Case presentation: Eight of 30 pregnant mares aborted and one gave birth to a weak foal that died within 72 h after birth. EHV-1 was isolated from all fetuses as well as from the diseased foal. All viruses belonged to the N752 variant based on the predicted open reading frame (ORF) 30 amino acid sequence. All were identical to each other and to previous EHV-1 viruses from the same stud based on the ORF68 sequence analysis. The outbreak coincided with the lapse in the routine yearly EHV-1/4 vaccinations of the mares.

Conclusions: Multiple abortion due to EHV-1 infection can occur in well-managed groups of horses. Reactivation of latent EHV-1 in one of the resident mares followed by a horizontal spread was considered the most likely explanation for the outbreak. Routine vaccination is an important part of a herd-heath program.