Theres EHV-1 virus in every little droplet coming out of an infected horses nose. | Adobe stockThe outbreak of equine herpesvirus-1 (EHV-1) in late 2025, with cases traced back to a show in Waco, Texas, brought with it a host of confusion and misinformation.In this excerpt from The Horses Equine Innovators podcast episode EHV-1 Explained: What the Science Tells Us, Lutz Goehring, DVM, MS, PhD, Dipl. ACVIM, professor of equine infectious diseases at the University of Kentuckys Gluck Equine Research Center, in Lexington, describes the basics of EHV-1 and how it progresses to the neurologic form, equine herpesvirus myeloencephalopathy (EHM). You can listen to the full conversation on TheHorse.com/equine-innovators-ehv1 or wherever you get your podcasts.How Does EHV-1 Spread in a Horse Population?EHV-1 is a virus that uses the cells in the respiratory tract to replicate. Theres virus in every little droplet that comes out of the horses nose. Once a horse becomes infected, he becomes a multiplier. So, imagine that in every sneeze, in every snort, there is virus in those little droplets. This is how virus spreads from one host to the other, most efficiently through direct contact, such as two horses rubbing noses.Short-distance travel is also a potent option for this virus to cross from one host into the other. What we call fomites (objects, hands, body parts, etc.) can transfer virus after contact from one horse to the other, and you initiate a cascade when this is not halted. Several horses start replicating, and this is how an outbreak gets rolling.Why Do Outbreaks Occur?A lot of horses are carriers of EHV-1; we call them latent carriers. These horses, when transported, when going to shows, when seeing the vet, they have the capacity to reactivate that dormant virus in their tissues, and it returns to the respiratory tract. They might shed the virus in small amounts (without showing clinical signs), and we need to make sure these horses or new arrivals on a farm are not in immediate contact with others.We see these outbreaks regularly. Over the years for Canada and the United States, we have somewhere between 40 to 80 outbreaks that are reported on the Equine Disease Communication Center (EDCC) webpage every year. Theres also probably a set of unreported outbreaks that add up to that. We see these home barn outbreaks regularly. Outbreaks at shows or events are rare.Special Feature: Everything You Need to Know About EHV-1How Does EHV-1 Become EHM?Equine herpes myeloencephalopathy is a multifactorial disease with a strict requirement that you have infection of the respiratory tract, and you have migration of virus to the local lymph nodes, where it replicates. From that point on, the virus can spread throughout the bloodstream and goes into the viremic phase. This is the transportation phase of the virus in the bloodstream, which is how this virus reaches the small vessels in the spinal cord and central nervous system. It causes multiple mini-strokes up and down the spinal cord. The more there are, the more the clinical picture changes from mild to moderate ataxia (incoordination) to complete paralysis (inability to get up).A factor needed for infection is this viremic phase. There are viral strains among the family of EHV-1 that go into a higher proportion of viremia for longer days. So, there is more going into the spinal cord to cause disease. But there are also host factors that favor the development of this neurologic component. And we have a strong connection with breed, age, and female sex. Only viremic horses are at risk to develop EHM. While viremia development is controlled by the immune system, EHM is a condition that involves host risk factors and, potentially, an immune system caught by surprise, as we see EHM developing more frequently and more severely during the first half of an outbreak. Taller horses like Thoroughbreds, Standardbreds, and Warmbloods are most frequently affected, while Arabians and pony breeds are spared.TakeHome Message Equine herpesvirus1 is a common respiratory virus that spreads through nasal droplets and contact between horses. While many infections remain mild, a slim proportion can progress to the serious neurologic form, EHM. The EHM outbreaks are infrequent and most commonly occur at home barns/training barns during winter and spring months. The shift to EHM depends on both viral behavior and immune status. Individual risk factors (age, breed, sex, immune status) are important in EHM development. Understanding how the virus spreads and which horses are most vulnerable is key to reducing transmission and improving outcomes.This article is from the Spring 2026 issue ofThe Horse: Your Guide to Equine Health Care. We at The Horse work to provide you with the latest and most reliable news and information on equine health, care, management, and welfare through our magazine and TheHorse.com. Your subscription helps The Horse continue to offer this vital resource to horse owners of all breeds, disciplines, and experience levels. To access current issues included in your subscription, please sign in to theAppleorGoogleapps ORclick herefor the desktop version.