As of May 1, the Nevada Department of Agriculture (NDA) has lifted all equine herpesvirus-1 (EHV-1) quarantines in the state.
One additional case of EHV-1 abortion was confirmed in Humboldt County in April—the Nevada state veterinarian received confirmation April 30 that a 9-year-old Quarter Horse mare aborted April 11 due to non-neuropathogenic EHV-1. The mare was undervaccinated and was exposed at her home facility to horses that traveled to a high school rodeo March 8-10 in Nevada. The owner had self-imposed a travel ban on the premise after a positive case was reported April 1 in Humboldt County associated with the same rodeo in early March; no quarantine has been issued for this case because the incubation period has passed and no horses have been moved to or from the property.
“This case shows how the disease is spread among the equine population,” said JJ Goicoechea, NDA state veterinarian. “The mare that aborted was never moved. The virus was brought home from a rodeo on another horse that was exposed but never showed signs of disease.”
In Nevada EHV-1 is a reportable disease, meaning when veterinarians diagnose it, they are required to notify the NDA, per NRS 571.160. Find a list of reportable diseases at agri.nv.gov.
Herpesvirus is highly contagious among horses and can cause a variety of ailments in equids, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and equine herpes myeloencephalopathy (the neurologic form).
In many horses, the first or only sign of EHV-1 infection is fever, which can go undetected. In addition to fever, other common signs of EHV-1 infection in young horses include cough, decreased appetite, depression, and a nasal discharge. Pregnant mares typically show no signs of infection before they abort, and abortions usually occur late in gestation (around eight months), but can be earlier. Abortions can occur anywhere from two weeks to several months following infection with EHV-1.
Horses with the neurologic form usually have a fever at the onset of the disease and might show signs of a respiratory infection. A few days later, neurologic signs such as ataxia (incoordination), weakness or paralysis of the fore- and hind limbs, urine retention and dribbling, loss of tail tone, and recumbency (inability to rise) develop.
Herpesvirus is easily spread by nose-to-nose or close contact with an infectious horse; sharing contaminated equipment including bits, buckets, and towels; or clothing, hands, or equipment of people who have recently had contact with an infectious horse. Routine biosecurity measures, including hygiene and basic cleaning and disinfection practices, should be in place at all times to help present disease spread.
Goicoechea continues to recommend best biosecurity practices as event season is underway, and always monitoring horses for signs of disease, like fever or runny nose. Other basic practices include:
- Never share equipment between horses;
- Always wear clean clothes when going from ill horses to others;
- Always start chores at healthy horses and end with sick or recovering ones; and
- Avoid common areas such as hitching rails, wash racks, etc., during a disease outbreak.
Current EHV-1 vaccines might reduce viral shedding but are not protective against the neurologic form of the disease. Implementing routine biosecurity practices is the best way to minimize viral spread, and the best method of disease control is disease prevention.