Equine Herpesvirus Myeloencephalopathy (EHM) in Sonoma County, California.

A recent report from The Horse highlights a concerning case of equine herpesvirus myeloencephalopathy (EHM) in Sonoma County, California. A 23-year-old pony mare tested positive for EHM, a neurological disease secondary to equine herpesvirus-1 (EHV-1), and was subsequently euthanized. Following this incident, 36 horses on the same premises have been quarantined to prevent further spread of the virus.

Understanding EHV-1 and EHM

Equine herpesvirus-1 (EHV-1) is a highly contagious virus among horses, capable of causing respiratory disease, abortion in pregnant mares, and the neurological condition known as EHM. While some infected horses may only exhibit a fever, others can develop severe neurological symptoms, including ataxia (loss of coordination), weakness, and even paralysis. The virus spreads through direct horse-to-horse contact, contaminated equipment, and human handlers who have interacted with infected animals.

Preventative Measures

Currently, vaccines for EHV-1 may reduce viral shedding but do not offer protection against the neurological form, EHM. Therefore, implementing strict biosecurity measures is crucial. These include:thehorse.com

• Isolating new or returning horses for a minimum of 21 days.
• Regularly disinfecting equipment and facilities.
• Monitoring horses for signs of illness, such as fever or nasal discharge.
• Limiting horse-to-horse contact, especially during outbreaks.

Staying informed about local and regional outbreaks can also aid in early detection and prevention. Resources like the Equine Disease Communication Center (EDCC) provide timely updates on equine disease incidents.

For more detailed information on this case and EHV-1, please refer to the original article on The Horse: thehorse.com.

It’s always heartbreaking to hear of a pony lost — especially to something as sneaky and serious as EHM. If you’re a horse owner, barn manager, or just someone who loves giving pony noses a kiss, this is your nudge to double down on biosecurity and barn hygiene. Keep thermometers handy. Don’t skip those daily checks. If a horse is acting a little off — maybe they’re dragging their toes, or just not their usual curious self — trust your gut. Early action is everything. And let’s all remember: keeping our barns safe doesn’t mean living in fear. It means living informed, proactive, and pony-positive.

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