The ‘New’ Equine Liver Ailment That Isn’t

Beware Dr. Google. That’s the warning from Rood and Riddle internal medicine specialist Dr. Peter Morresey, who said he gets questions about “new” types of liver diseases being detected in horses.

“There’s good stuff on the internet and there’s bad, as you’ve heard before, but there’s actually some viruses that have turned up that people are actually starting to think are new,” Morresey told the audience at the Rood and Riddle annual client education seminar last month.

Morresey said liver disease in horses can manifest in relatively minor ways like diminished performance or major symptoms like serious weight loss, gastrointestinal issues, neurological problems and even death. Liver disease also has a number of potential causes — toxicity from a plant, metabolic causes from weight gain, or cancers that have spread to the liver from elsewhere. The equine liver can be impacted by bacterial infections, particularly if a horse has recently had a gastrointestinal issue that allowed bacteria to enter the organ. Morresey said the liver is “a nice place to be if you’re a bacteria — there’s a lot of nutrients there and it’s warm.”

Most of the recent focus Morresey has seen from clients is on Theiler’s disease, which some believe is a new illness.

“It was first described in 1918 so I just want to emphasize the point that it’s not actually new,” pointed out Morresey.

Theiler’s disease was discovered by Sir Arnold Theiler who subsequently had the dubious honor of the illness being named for him. Theiler was trying to combat African horse sickness (a different, insidious disease which remains a challenge today) by taking antiserum from horses recovering from the illness and putting it into horses in hopes it would provide immunity. Between four and 12 weeks after he put the antiserum in the healthy horses however, he began seeing signs that liver tissue was dying off in some of those patients.

Today, we know that Theiler’s disease has some association with a variety of biologic products, including tetanus or botulism toxins, plasma, or even stem cells — products that come from one horse’s body and are put into another horse’s body.

Theiler’s disease has also been found in horses that had not received a biologic product recently, but had been exposed to horses who had symptoms, suggesting that the illness is transmissible. These exposures seemed to be more common during the summer months.

Veterinarians believe Theiler’s disease is likely caused by a virus, but since Theiler’s disease describes a set of symptoms rather than a single cause, it can probably be blamed on more than one strain of virus. Research has identified some potential viral causes, including nonprimate hepacivirus (NPHV). Some of those viruses seem to have a high seroprevalence in horses, meaning lots of apparently healthy horses seem to have been exposed to the virus at some point and developed an immune response. Morresey said NPHV has been found in as many as 40 percent of horses who were showing no symptoms of illness.

In 2018, researchers did identify a new virus that seemed to be associated with Theiler’s disease. A study published in the journal Emerging Infectious Diseases found a new type of parvovirus both in a horse that died from Theiler’s disease and a tetanus antitoxin the horse had received about two months earlier.

Despite an association with biologic products, particularly antitoxins, Morresey said horse owners can sleep well at night — those products are now tested for viruses that may cause liver disease, and should be considered safe to use at the direction of your veterinarian.

The post The ‘New’ Equine Liver Ailment That Isn’t appeared first on Horse Racing News | Paulick Report.

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