Page 68 - March 2016

EQUINE
Copyright © 2016, PaulickReport.com • Reprinted with permission
VIRUS-1
by Natalie Voss
Separating Fact, Fiction, and Confusion
Paulick Report Reprint, February 2, 2016--As Sunland Park and Turf Paradise remain under quarantine due to an outbreak of EHV-1 (equine herpesvirus), we turned to the experts for answers on this serious and highly contagious illness. According to the American Association of Equine Practitioners[1], equine herpesvirus is found
in most horses, though many of them do not become ill as a result. There are several types of viruses in the EHV family, including EHV-1, which can cause respiratory disease, abortion, neonatal death, or neurological disease. Officials announced that a strain of EHV-1 associated with neurological disease was detected at Sunland Park Jan. 21[2] and at Turf Paradise Jan. 27[3]. Horses exposed to EHV-1 may or may not become feverish, and of the horses that develop a fever, not all develop neurological signs. However, there is no cure for the neurological symptoms associated with EHV-1 if they do occur.
We spoke with Dr. Nathaniel White, professor of large animal clinical sciences at the Virginia-Maryland Regional College of Veterinary Medicine at Virginia Tech and Dr. Josie Traub- Dargatz, professor of equine internal medicine at the James L. Voss Veterinary Teaching Hospital at Colorado State University, about the disease, its spread, and good biosecurity practices.
We’ve been hearing there are actually two kinds of EHV-1—a “wild” strain and a second strain. What’s the difference, and how do health officials handle these differently?
Dr. Traub-Dargatz: If we have a case that’s suspected or confirmed EHV-1, neurologic form, the actions that would be indicated to control the spread of disease would be the same whether it’s the “wild
type” or the neuropathogenic strain. Our initial actions aren’t going to vary based on which subtype of the virus it is.The wild and neuropathogenic strains are different only by one amino acid in their DNA. They do seem to vary in a couple of ways—in challenge studies, the amount of virus that’s in the blood of the horse seems to be higher with the neuropathogenic strain than the wild type. Also, some people believe the scope of disease and the severity among an exposed population would be greater for this neuropathogenic strain, but there have been a couple of outbreaks associated with the wild type and multiple horses were affected.
Some laboratories only report that a sample is EHV-1 and don’t do subtyping.
How reliable are nasal swabs or whole blood testing for this?
Dr. Traub-Dargatz: The recommendation from the U.S. Animal Health Association (USAHA[4]) is that
both types of samples be tested, not just one. Depending upon where the horse is in the course of the disease and how much virus it might be shedding in the nasal secretions, one [test] may be positive and the other not. When we collect whole blood for testing, we’re going to get a representative sample of the horse’s blood in a tube; with the nasal swab we’re sticking a swab up the horse’s nose and some horses are not very tractable for that procedure so we may not get an optimal sample of the nasal secretions on the swab. So it is important that we recognize it doesn’t just come down to the lab test methods, it’s how good a sample we get on the swab for the lab to then test.There have been one or two outbreaks where at the onset of fever, the horse might not be positive for EHV-1 on the swab and by the time they develop the neurologic disease, they are positive. If we have highly suspect horses, that might mean doing more than one test on that horse a few days later in order to make the diagnosis.
66 SPEEDHORSE, March 2016