Equid alphaherpesvirus 1 (EHV-1), formerly known as equine herpesvirus 1, is an important viral infection in horses with global prevalence. EHV-1 causes considerable economic losses for the equine industry while also resulting in a significant emotional hardship to horse owners when their horses become infected.
Noses of two horses in close contact with each other.
Transmission of EHV-1 from horse to horse occurs through direct contact, particularly via nose-to-nose contact, and indirectly through airspace or contaminated objects such as gear and buckets,
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The virus primarily spreads through the respiratory route, initially replicating in the upper respiratory tract. In some horses, it spreads further into the bloodstream, causing viremia, which can lead to complications such as abortions, neonatal death and Equine Herpesvirus associated Myeloencephalopathy (EHM). While all of these outcomes are significant, EHM typically garners the most attention when it causes sudden (mild, moderate or severe) spinal cord disease.
Transmission of EHV-1 from horse to horse occurs through direct contact, particularly via nose-to-nose contact, and indirectly through airspace or contaminated objects, such as gear and buckets, in addition to the sometimes- forgotten hands that go from horse to horse.
Like most, if not all, herpesviruses, EHV-1 can enter a latent or dormant state after an acute infection. EHV- latency can persist for years, and, potentially, for life in the trigeminal ganglion and the lymphatic system.
Upon reactivation, this virus returns to the respiratory tract where it may result in new rounds of infection transmission. Understanding EHV-1 latent infection and what circumstances trigger reactivation from latency is one important area of study in the laboratory at the University of Kentucky Department of Veterinary Science’s Gluck Equine Research Center. Leading the work in this area is Edward Olajide, DVM from Nigeria and PhD student in the lab of Lutz
Goehring, DVM, PhD.
Early results from Olajide’s research show that, as predicted, EHV-1 DNA most commonly found in the trigeminal ganglion of horses. Interestingly, EHV-1 DNA is also found in the mesenteric lymph node (lymph nodes in the abdomen), which was not anticipated.
Further, there was not consistency with regards to the detection of EHV-1 in the lymph nodes of the upper respiratory tract for the youngest horse with tissue samples positive for EHV-1 DNA at 14 months old.
It was also found that there was no linear increase of viral DNA presence with aging despite the fact that it is always assumed there is continuous EHV-1 exposure. These findings add to the complexity of ‘going dormant’ and ‘reawakening’ of herpesviruses and need further attention.
In collaboration with other laboratories, the lab also focuses on evaluating both current and newly developed vaccines and therapeutics, conducting immunogenicity studies and performing clinical trials to ensure the efficacy and safety of these vaccines. With collaborators at Kansas State University and Michigan State University, the lab is evaluating novel RNA vaccines similar to the potent Covid-19 vaccines introduced during the pandemic. These studies were made possible through a grant by the Grayson Jockey Club Research Foundation and are ongoing.
Vaccination should play an important role in EHV-1 infection control. However, limiting the exposure to EHV-1 is equally important as a regular vaccination schedule. Therefore, the lab is working to advance and standardize techniques and tools to better and more quickly detect EHV-1 in the environment, with the hope to do more studies about dynamics of virus transmission in the future.
While the lab focuses on three major areas, latency and reactivation; transmission and surveillance; and vaccine efficacy studies, with the latency research the lab hopes to get a better understanding through transcriptome studies the “listen” in on virus and host interactions in the near future.
Press release by Equine Quarterly - Gluck Equine Research Center