Update on Maryland Equine Neurologic Herpesvirus

More horses tested positive for equine herpesvirus in Maryland and a different approach has been taken to only test symptomatic horses.

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The Maryland State Veterinarian in conjunction with the Equine Disease Communication Center released the following information the evening of March 30.

On March 22, 2021, three horses in a large barn at Laurel Park racetrack developed fevers and were tested. Also, a horse at Pimlico racetrack developed a fever and was tested. 

One of the horses in the large barn at Laurel Park tested positive for EHV-1 while the rest were negative. The positive horse was sent to the Bowie racetrack, which is now the quarantine facility. 

The positive test result triggered a reset of the quarantine timeline for Laurel Park. 

On March 24, 2021, the testing of the entire large barn was commenced. Approximately 120 asymptomatic horses were tested. In addition, the second round of testing on the index barn at Laurel was also conducted involving 14 asymptomatic horses. 

The first round of testing for the index barn consisting of 20 asymptomatic horses resulted in six positive horses for EHV-1. These horses were removed and sent to Bowie. 

The results for the index barn retest was one horse was positive. The positive horse was moved to Bowie. 

The result from testing of the large barn was 26 positive horses. These horses were moved to Bowie. 

A horse with fever at Pimlico was tested and found negative. The retest result of the horse from Pimlico was positive for EHV-1. This horse was also moved to Bowie.

Two more horses developed fevers from a different barn at Laurel Park and these horses were tested. One tested positive and was sent to Bowie. 

As of Sunday March 28, 2021, there were 36 positive horses at Bowie. 

After analyzing the results from the multi-barn and multi-horse testing, the decision was made to have separate quarantines for the three properties. It was necessary to have the separation so that events at one property would not affect the others. 

The decision was also made to stop further testing asymptomatic horses because the testing was not resolving the problem. Only symptomatic horses will be tested as defined by equine herpesvirus myeloencephalopathy (EHM) recommendations for State Animal Health Officials. 

All three properties are placed on a 21-day quarantine. The properties will be out of quarantine as follows: Pimlico will be release April 12, 2021, Bowie April 17, 2021, and Laurel April 18, 2021. 

This schedule is contingent on the fact that no horse with clinical signs tests positive on the initial testing during the 21-day period. 

The Maryland Department of Agriculture is working closely with racetrack officials to monitor the situation and adjust plans accordingly. 

For more information on equine herpesvirus read this AAEP Fact Sheet

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