By Christa Lesté-Lasserre, MA
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It happens every year. First, it’s a 2-year-old that’s feverish and coughing. Then, a pregnant mare loses her foal. A week later, a seasoned sport horse becomes incontinent, falls down, and never gets back on his feet. Suddenly, you have a barn full of horses with fevers—and it seems like as soon as one gets better, two others get worse. If you’re lucky, none of the animals have moved to other locations recently where they might infect other horses.
What’s going on? Quite simply, an infectious microbe has declared war. Equine herpesvirus type 1 (EHV-1), also known as equid alphaherpesvirus-1, has awakened from the depths of its hiding place in the immune or nervous tissues of one horse, replicated, and spread out of control among horses on your premises and beyond.
Fortunately, with advancing scientific knowledge, we’re learning how to curb EHV-1’s devastating—and sometimes deadly—path of destruction. In this article we’ll present you with the basics of this equine-specific virus and how we’re managing it in light of what researchers have learned through experience and laboratory studies.
In a small percentage of EHV-1 cases, horses develop neurologic signs referred to as equine herpesvirus myeloencephalopathy (EHM). All three of the known EHV-1 variants can provoke EHM, although it’s less common with N752, Pusterla says.
Scientists are still trying to understand why some horses develop EHM, says Goehring. Tall breeds—such as Thoroughbreds and Warmbloods—appear to be more susceptible, and older horses and mares seem to develop more severe signs. Researchers suspect this might have to do with a weakening immune system or medications used to manipulate estrus in sport horse mares, respectively.
Researchers have found EHM is more likely to occur when the virus gets transported away from the respiratory tract and lymph nodes, through the bloodstream, and into the spinal cord, says Goehring.
Perhaps that’s why EHM generally appears later after infection than respiratory disease does. Gisela Hussey, DVM, MS, PhD, associate professor of pathobiology and diagnostic investigation at the Michigan State University College of Veterinary Medicine, in East Lansing, has been studying the disease and discovered horses with EHM developed fever later than those with the respiratory form of EHV-1. Horses with EHM also started showing signs of disease about nine to 13 days after infection, whereas horses with respiratory disease became sick after only four days, she says.
Plus, the D752 variant is the one that usually causes more cases of EHM, says Goehring. Its presence in the bloodstream—known as viremia—lasts longer, compared to the other variants, he says.
Therefore, EHM might arise from a different or delayed immune response than the respiratory form. Why horses would have that different response remains to be determined.
Horses with EHM started showing signs of disease about
after infection, whereas horses with respiratory disease became sick after only
Unchecked, EHV-1 can swoop through equestrian communities, causing financial and emotional losses and compromising equine welfare. But by staying up to date on scientific knowledge about the virus and the diseases it causes, and following recommended biosecurity protocols for both preventing EHV-1 and stopping its spread, owners and veterinarians can collaborate to keep transmission—and its consequences—to a minimum.
An important part of an overall equine health care plan is a vaccination protocol. While a “standard” plan doesn’t exist for all horses, the American Association of Equine Practitioners (AAEP) recommends horses be vaccinated for the following diseases: Eastern and Western equine encephalomyelitis, rabies, tetanus, and West Nile virus.
Horses should also be evaluated to determine whether or not they should be vaccinated for other diseases, such as equine influenza, equine herpes, strangles, and Potomac horse fever, depending on their potential exposure to the disease, age, breed, use, geography, travel, and consequences of the disease, also known as a risk-based analysis.
The Boehringer Ingelheim line of Vetera© vaccines includes combinations to meet any horse’s specific needs and also includes VETERA GoldXP, the industry’s No. 1 vaccine.1 At the cutting edge of developments in the ever-changing equine infectious disease landscape, the VETERA line was the first in the U.S. updated to contain both Florida sublineage clade 1 and clade 2 equine influenza virus (EIV), as recommended by the Expert Surveillance Panel on Equine Influenza and the AAEP. All VETERA vaccines are backed by a yearlong assurance program.
Ask your veterinarian about a vaccination protocol that’s designed specifically for your horse’s needs.
Learn more about Boehringer Ingelheim vaccines at: https://bi-animalhealth.com/equine/vaccines.
Vetera© is a registered trademark of Boehringer Ingelheim Vetmedica GmbH, used under license. ©2023 Boehringer Ingelheim Animal Health USA Inc., Duluth, GA. All Rights Reserved. US-EQU-0082-2023
1 Data on file at Boehringer Ingelheim
Christa Lesté-Lasserre, MA
Passionate about horses and science from the time she was riding her first Shetland Pony in Texas, Christa Lesté-Lasserre writes about scientific research that contributes to a better understanding of all equids. After undergrad studies in science, journalism, and literature, she received a master’s degree in creative writing. Now based in France, she aims to present the most fascinating aspect of equine science: the story it creates. Follow Lesté-Lasserre on Twitter @christalestelas.
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