Outbreaks Cause Uneasiness

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Strangles Outbreaks
When the state of Georgia quarantined a 115-horse public barn in Georgia for strangles this past April, a number of horse owners took note. However, this move was taken because this large a number of horses potentially exposed or incubating the disease could translate into exposure of a large number of horses if they were moved off the premises, not because strangles is reaching epidemic proportions.

Panic hit the West Coast, too, when a March quarantine imposed on a Los Angeles County barn caught the attention of the media because some caretakers were reporting “flu-like” symptoms. However, S. equi and S. zooepidemicus (the Strep strains that cause symptoms of Strangles) rarely cause infections in people, and primarily in the immunocompromised. The human cold symptoms haven’t been confirmed as being related.

Strangles also hit national news item in connection with the Kentucky Derby when 49 horses were quarantined at a Churchill Downs-operated training facility, Trackside, on March 11. Later in the month, a few cases appeared in Florida racing barns.

Florida is considering making strangles a reportable disease, as it already is in Georgia, Maine and the state of Washington. Other tracks are requiring all incoming horses have health certificates, although this measure doesn’t prevent horses that are incubating or shedding the organisms from entering the track.

Because of the high profile of these stories, headlines such as “epidemic” or “closed tracks” have started to appear, but there’s no epidemic in the sense that strangles has always been around and is is no stranger to young horses.

Neurological Herpes
In December, a case of neurological herpes (rhinopneumonitis virus) at a Michigan Standardbred track led to some rather sensationalized depictions of the virus both in the media and even a press release by the Michigan Racing Commission, calling it “highly contagious and potentially deadly.”

What they failed to mention is that a large percentage of adult horses have herpes/rhinopneumonitis viruses colonizing their respiratory tract and causing them no problems whatsoever. Exactly why this virus sometimes triggers neurological disease is unknown, although mutations are suspected. The neurological form occurs sporadically, typically in crowded, high-traffic facilities.

The news led to many tracks in Canada and across the United States either refusing entry to horses from the involved track or requiring that all horses coming onto their track be vaccinated, despite that no vaccines protect against this strain. Many veterinarians strongly suspect that frequent vaccination may actually be a risk factor for the neurological form. All the horses in the large outbreak at the University of Findlay (Ohio) last year were on heavy vaccination schedules.

The Columbia Horse Center in Maryland has been under two consecutive 21-day quarantines for a few neurological Herpes cases there, although all the horses were vaccinated. There’s no known connection between the Maryland and Michigan horses.

The number of horses that develop neurological herpes infections compared to those exposed to herpes is small. Nothing suggests that these outbreaks are increasing.

Whisper Syndrome
A number of horse owners became distressed by a message sent to horse groups on the Internet about a supposed epidemic of a new, deadly disease dubbed Whisper Syndrome. It’s said to be caused by a mutated strain of Listeria bacteria (see page 2). However, state veterinarians, universities and private clinics have consistently reported they have seen no indication of an epidemic or new disease.

Listeria antibody titers were drawn on three of the horses that ate from the round bales, as well as a yearling on the same farm with no access to them, and a horse from another farm. The three round-bale-fed horses had higher titers and will be checked again to see if the titers drop after they were removed them from the round bales.

While this would seem strong evidence that the round bales were a source of the Listeria organism, it doesn’t mean Listeria caused the problems. A positive Listeria titer means exposure, not proof of the diease. Listeria is a well-documented contaminant on ground, in hay, in feces and in partially fermented silage. The interiors/bottoms of round bales are an ideal location for Listeria to multiply, as well as other pathogens, including both other bacteria and fungi.

These organisms aren’t new, and your horse has been bombarded by potentially harmful “bugs” from the minute he hit the ground. Take sensible precautions about taking your horse to areas that are actively experiencing problems, but don’t succumb to sensationalized reports of “outbreaks.”

While it’s important to stay informed about disease in your area, we suggest you consult your veterinarian or other source that you know is reliable.