Scientists Study Elapid Snakebites in Horses
A bite from an elapid snake (a family of venomous snakes that includes the deadly cobra, tiger snake, and mamba) can be a scary reality for owners of horses living in areas these reptiles reside. However, researchers from the University of Melbourne, in Australia, have determined that, if a veterinarian makes the right diagnosis based on clinical signs and administers antivenom promptly, survival rates can be quite high for equine snakebite patients.

The research team’s recent study was the first in which scientists looked at the clinical signs of elapid snake envenomation in a large population of horses. The team also evaluated laboratory findings, treatments, and outcomes from 52 elapid snake envenomation cases from several universities and private veterinary practices from 2006 to 2016.

Snakebite wounds aren’t always apparent, but affected horses often exhibit signs of envenomation. The researchers found that 94% of cases developed signs of neurotoxicity, typically characterized by neuromuscular weakness. Other associated neurologic signs included unsteady movement, muscle tremors, the inability to stand, pupil dilation (mydriasis), eyelid drooping (ptosis), and partial tongue paralysis. In addition, 50% and 19% of horses developed rhabdomyolysis (muscle damage) and hemolysis (red blood cell damage), respectively.

These clinical signs are quite different from those reported for crotalid (pit vipers, including rattlesnakes) snakebites, the team noted. Those signs can include, but aren’t limited to, pain and swelling at the bite site, tissue sloughing near the bite, coagulopathy and hemorrhage, respiratory distress, shock, collapse, and death.

When it comes to diagnosing elapid snakebites, the researchers discovered that urinalysis wasn’t overly helpful: Out of the 18 urine samples they evaluated, only 17% were positive for snake venom. As such, they recommended that veterinarians consider elapid snake envenomation as a differential diagnosis for any horse exhibiting the aforementioned clinical signs, especially in areas where these snakes are most common (the tropics and subtropics in Asia, Australia, Africa, North America, and South America).

Regarding treatments, “a multivalent elapid antivenom is available that can treat bites from several of the most common elapid snake species,” said lead researcher Nick Bamford, BVSc(Hons), PhD, MANZCVS, of the University of Melbourne’s Faculty of Veterinary and Agricultural Sciences. “When elapid snake envenomation is suspected we would encourage veterinarians to administer multivalent antivenom as soon as possible and monitor the response to treatment. Hypersensitivity reactions to antivenom are relatively common in humans, although we did not observe these problems in the horses in this study.”

In the current study, 86% of 49 horses that received antivenom survived. However, the team cautioned, a second round of antivenom might be necessary; this was true for 18 of those 49 surviving cases.

“It is likely that survival rate would be lower for horses that experience a delay in veterinary attention,” added Bamford.

The team said a positive response to antivenom administration can confirm the snakebite diagnosis.

The study, “Elapid snake envenomation in horses: 52 cases (2006-2016),” was published in the Equine Veterinary Journal.