Page 69 - March 2016

There are several types of viruses in the EHV family, including EHV-1, which can cause respiratory disease, abortion, neonatal death, or neurological disease.
So diagnosis is a matter of watching both the symptoms and the test results?
Dr. Traub-Dargatz: Yes. I think the key in the USAHA guidelines is the recommendation to focus testing on horses who have signs of
the disease. We know that a small percentage
of horses that are clinically normal can shed EHV-1 in their nasal secretions and look perfectly normal. Those horses may not pose much of a risk that we’re aware of. There was one study that sampled horses at shows and sales and around 3.8 percent had EHV-1 detected
in nasal swabs by PCR testing when there was no outbreak going on. Thus testing on clinical horses is the recommendation versus testing the general population.
Is that three percent of the population the reason for an outbreak?
Dr. Traub-Dargatz: I think that is a possibility, but it’s impractical to test all horses every day to see if they’re shedding. The majority of horses have been exposed to EHV-1. Some of them will develop a latent infection, which means the virus lives in places in the body (mostly in lymph nodes and areas around the head) and the body doesn’t recognize it’s there. That horse could then shed the virus out their nose and look perfectly normal.
We know EHV-1 is very contagious, but just how contagious is it—could using the same track surface as an exposed horse pose a risk?
Dr. Traub-Dargatz: I think sharing the same track surface would be minimal risk but having nose contact with contaminated surfaces like starting gates would be more concerning. The virus has to get up the horse’s nose in
a great enough amount to cause infection.
How much virus it takes to cause an infection depends on the horse’s immune status, but
it’s really the droplets that come out of the
nose that are a risk. Contaminated hands, contaminated equipment including buckets and wipe rags are much more worrisome. In the open air it’s probably less of a concern than in
a confined airspace. We really don’t know how long the virus lives on a pitchfork or how far
it can spread in the air. Some of the literature says 30 feet away, but that really hasn’t been investigated. Horses with EHV don’t typically cough as much as those with flu to move those droplets a long way.
What do we know about incubation times?
Dr. Traub-Dargatz: It depends how much virus they’re exposed to. If we get a huge exposure and they have very little immunity it
could be as short as one or two days. Also, onset of clinical signs can be different. They may have a fever one to three days after they’re exposed to this virus, and then some horses’ temperatures return to normal, and then they get a second fever. The neurologic signs usually develop six to 10 days after exposure if they’re going to become neurologic.
There are vaccines for EHV, so why can’t they prevent an outbreak like this?
Dr. Traub-Dargatz: There are around
25 different brand names of vaccines that contain EHV. None of them carry a claim for prevention of the EHV-1 neurologic disease. However, some of the vaccines could reduce the amount of virus being shed within a population, as some of the vaccines carry a claim to reduce virus shedding. There’s still a lot we’re learning.
When a facility has an outbreak, who decides what the quarantine protocols are going to be?
Dr. White: In a state where EHV is a reportable disease (that means that if it occurs, the veterinarian would call the state vet),
the state vet would make the decision about
the quarantine. The practicing veterinarian
that recognizes it initially would probably recommend at least immediate quarantine. And the state vet would try to assess where that horse has been and what other contacts may have happened. If you cross state lines, it goes to the next state veterinarian.
We really would like all states to make it a reportable disease. If it’s not, it would be the treating veterinarian making a recommendation, but there’s no way to enforce it. Most people would want to do that, but if it’s not reportable there’s no regulation that there has to be a quarantine.
Does the U.S. Department of Agriculture (USDA) or the Animal and Plant Health Inspection Service (APHIS) get involved at a certain point?
Dr. White: They don’t do that normally because each state has its own regulations
and USDA is more involved with foreign disease and imports. Back in 2011 when the Ogden, Utah outbreak occurred, state vets involved called USDA and asked them to help coordinate recording of the outbreaks. We’ve asked them to do more with that to work with the epidemiology of any reportable disease. Sometimes, state vets aren’t required to notify each other when there’s an outbreak going on, even if it’s in an adjacent state (though many times they will do so anyway).
Is there a standard recommendation for how long a quarantine should last?
Dr. White: It’s 21 days from the last fever. That wouldn’t necessarily make it 21 days from the last neurologic symptoms, because some horses develop neurologic symptoms that last for years. It’s really the fever indicating an active infection. They should then be negative on testing by that point. If it’s 21 days and they’re still positive, you’d still want to keep them quarantined. There are times when others have recommended 14 days, but each state can set their own policy.
Any other tips for racetracks and competition venues for dealing with an outbreak like this?
Dr. Traub-Dargatz: It’s not easy. This is not a disease that’s simple. Consider having precautions in place to keep sick horses from coming in, and have a plan for what to do
if horses become sick while at an event like
a race meet to minimize the risk of further exposure. Owners need to take precautions themselves to reduce the potential for exposure—monitoring temperatures before, during, and after shipping in and out for
an event. Fever is an early sign of several different causes of infection. Getting a veterinarian to examine a horse with a fever promptly to determine the cause and getting recommendations on how to reduce risk of disease spread can be best for the sick horse and for other horses at the event.
To get updates on this and other communicable disease outbreaks, follow updates online from
Dr. White’s Equine Disease Communication Center[5].
Endnotes:
1. According to the American Association of Equine Practitioners: http://www.aaep.org/info/ horse-health?publication=753
2. was detected at Sunland Park Jan. 21: http:// www.paulickreport.com/horse-care-category/ suspected_ehv_death_at_sunland_park/
3. Turf Paradise Jan. 27: http://www. paulickreport.com/horse-care-category/three- horses-quarantined-at-turf-paradise-after-ehv-1- concerns/
4. The recommendation from the U.S. Animal Health Association (USAHA: http://www.usaha. org/Portals/6/Committees/horses/IDOHC%20 EHM%20Guidance%20Document%20 Sept%202015%20Edited%20FINAL.pdf
5. Equine Disease Communication Center: http://www.equinediseasecc.org/
Source URL: http://www.paulickreport.com/ horse-care-category/vet-topics/ehv-1-separating- fact-fiction-and-confusion/
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