01/13/2017 5:27PM

Milder type of equine herpesvirus spreading rapidly at Fair Grounds

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A strain of the equine herpesvirus continues to spread rampantly among the horse population at Fair Grounds, but the virus has so far proven very mild and is not related to a more serious herpesvirus infection that killed one horse in late December at Fair Grounds and infected a second horse in the same barn.

Those two more serious cases of the virus, though, triggered widespread testing that already has produced 38 more positive EHV-1 tests and threatens to return scores more.

Six barns are quarantined and not permitted to race, with possible cases in two more barns as of Friday. If the quarantine goes much wider, Fair Grounds might lack sufficient horses to card races.

The track, in conjunction with authorities from the Louisiana Department of Agriculture and Forestry, also faces the daunting task of figuring out how to isolate horses who test positive for EHV-1, as is required by the current response protocol.

In the first Fair Grounds EHV-1 case, in barn 14, a horse got very sick and lost the ability to stand, a telltale sign of the neuropathogenic strain of EHV-1. The horse was euthanized and returned a positive test Dec. 26. A second horse in that barn tested positive for the neuropathogenic strain Dec. 31. That horse has since recovered.

So far, that is the extent of the neuropathogenic side of the EHV-1 event at Fair Grounds. Everything that has happened since involves the “wild” strain of EHV-1.

The two strains of the virus are closely related, but their slight chemical difference creates what essentially are different diseases. A horse can’t catch the wild-type virus from a horse with the neuropathogenic type.

EHV-1 is endemic in North American horse populations: Most, if not all, Thoroughbreds are exposed to it, and many harbor it latently. Wild-type EHV-1 crops up at racetracks regularly but goes undiagnosed because no testing is done. It’s just another bug going around a barn. And that is what almost certainly would be happening right now at Fair Grounds had the first two neuropathogenic-type cases not subjected so many more horses to EHV-1 testing.

“In a normal, everyday situation, those horses never would have been tested,” said Dr. Nathan Slovis, who is the director of the McGee Center at the Hagyard Equine Medical Institute in Kentucky. Slovis came to Fair Grounds this week as a consultant for track owner Churchill Downs Inc. and has been working with state and federal regulators.

General random testing for EHV-1 actually can be counterproductive. The well-respected veterinary school at the University of California-Davis in a published resource regarding EHV-1 diagnosis says interpreting sophisticated modern tests for the virus “should be done only in the context of the presenting clinical signs for disease in the horse being tested.”

But once the neuropathogenic cases were diagnosed at Fair Grounds, authorities were required to establish the strict protocols now governing the situation, Slovis said. Some wild-type outbreaks can be severe and damaging; regulators can take no chances.

“Herpes is herpes when it comes to regulatory agencies,” Slovis said.

Slovis said he thought the virus could run its course within 45 days. Some horsemen believe it might take considerably longer. Barns are quarantined 14 days after a positive test and come out of quarantine after every horse in the barn twice tests negative for EHV-1.

Horses in barns with EHV-1 positives at first were tested only if they ran a fever, but on Tuesday state officials decided to test every horse in affected barns. Twenty-one horses in barn 14 were found Thursday night to have tested positive for EHV-1. Positive tests from nine horses in barn 36 were returned Friday morning.

None of those 30 horses was sick, but all horses who test positive must be isolated. As of early Friday afternoon, nine horses were in temporary isolation stalls under tents on the backstretch, but even beyond the 30 new positives, test results from the other quarantined barns weren’t yet known early Friday afternoon, and similar findings would necessitate creating a way to isolate dozens – perhaps, eventually, hundreds – of horses. Fair Grounds officials were said to be visiting a farm in nearby Chalmette to determine its suitability as an isolation site.

The Department of Agriculture and Forestry on Thursday instituted a state-directed quarantine of the entire Fair Grounds backstretch, but Fair Grounds already had imposed a no-shipping restriction Jan. 2, and the state quarantine is only a change in an administrative sense.

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