The New Mexico Livestock Board (NMLB) reported Feb. 15 that 70 horses have now tested positive for equine herpesvirus-1 (EHV-1) in connection with an outbreak that began last month at Sunland Park Racetrack.

The NMLB reported that five horses were released from the isolation barn on Feb. 15, and 15 exposed barns have been returned to nonexposed status. Sunland Park and one local training center—Frontera Training Center—remain within the quarantine perimeter, while two other local training centers—Jovi and Lazy S—have been released from quarantine.

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 myeloencephalopathy (the neurologic form). In many horses, fever is the only sign of EHV-1 infection, which can go undetected.

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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, urin