Two outbreaks of neuropathogenic equine herpesvirus type 1 with breed-dependent clinical signs.

This research looks at two outbreaks of a horse ailment known as equine herpesvirus type 1 (EHV-1) in Eastern Croatia in 2009. The study found that despite different clinical signs, the same virus caused both outbreaks, and the difference in these signs might be explained by different breed-related risk factors.

Overview of the Research

• The research is based on two outbreaks of equine herpesvirus type 1 (EHV-1), a virus commonly found in horses across the globe, which occurred during 2009 in two stud farms located in Eastern Croatia.
• The EHV-1 virus is particularly damaging as it can lead to abortion, respiratory issues, and neurological diseases in horses – subsequently leading to significant economic losses within equine industries due to horse mortality and morbidity.

First Outbreak

• The first outbreak took place in February after the introduction of 12 American horses, all of which were proven to be EHV-1 negative through a serological test before transport.
• The result of the outbreak included: four mares aborting late in their pregnancies, one perinatal death, and six mares displaying clinical signs of myeloencephalopathy, a neurological disorder, leading to the death of four of these.

Second Outbreak & Epidemiological Findings

• A month later, a second outbreak occurred in another stud farm situated roughly 100km away from the initial outbreak site. This resulted in 17 abortions, three more perinatal deaths, and one mild case of neurological impairment.
• Epidemiological data suggests that the disease might have been introduced to the initial farm via international transport. The second outbreak is believed to have started from the introduction of a clinically healthy stallion from the first affected stud farm.
• The investigators managed to validate these hypotheses using molecular characterization and phylogenetic analysis, which ascertained that, despite differing clinical symptoms between the two outbreaks, the same virus was responsible for both.

Interactions with Breeds and the Absence of Prior Infection

• The equine populations involved in both outbreaks were uninfected by EHV-1 prior to the events and had not received vaccinations against the virus.
• The researchers theorize that the significant discrepancies observed in the clinical signs between the horse populations during both outbreaks could be attributed to various breed-related risk factors.