Blister diseases causing trouble for horses and pigs this year

Farm Forum

“Doctor, there’s a veterinarian on the line who wants to talk to you about some blisters he’s seeing in a group of pigs.”

That doesn’t sound like a big deal, right? But if you are a regulatory veterinarian – tasked with protecting animal populations from incursions of serious diseases – this is the call you dread taking.

The reason for the anxiety has to do with the most feared of foreign animal diseases – Foot and Mouth Disease. The US has not seen FMD since 1929. It is among the most contagious diseases known to the animal world, affecting cloven-hoofed animal species. Were it to enter our livestock herds, it would devastate not just the livestock economy, but likely the entire US economy as well. When state and federal veterinarians have trouble sleeping at night, they’re probably having a nightmare about FMD in their backyard.

The main effect of FMD infection is to cause blisters, or vesicles, in the mouth, tongue, and on the coronary band (where the hoof meets the skin) of the animal. Affected animals can’t eat, drink, or walk without pain. Often, by the time the animal is examined, the blisters have broken, leaving raw sores in the mouth and on the tongue. Livestock veterinarians have these images burned into their brain from the day they hit vet school. Finding vesicles or sores in the mouth of a cow or pig sets off the alarm bells and results in a call to the state vet’s office to rule out FMD. Of course, there can be many causes of these lesions, including the harmless situation when animals eat something they shouldn’t have.

But this summer, we’ve seen the emergence of two infectious livestock diseases that create vesicles similar to FMD. They create problems for the affected animals, but they are not usually debilitating. The major issue with these diseases is that they can look just like FMD. When these diseases pop up, each one has to be treated like a foreign animal disease until FMD can be ruled out.

The first of these to show up in South Dakota this summer was Vesicular Stomatitis. This has mainly affected horses – which is helpful from a regulatory standpoint since horses don’t get FMD – but can also affect cattle. Vesicular stomatitis pops up every year, but it’s typically been a problem only in southwestern states. This year it crept up to western South Dakota. The disease is caused by a virus spread by biting flies and gnats, so it dies out after a good freeze. Affected farms are quarantined because animals can spread it directly between themselves, or via a person using contaminated tack or clothing.

Then there was the discovery of Seneca Valley Virus. First noticed in show pigs and finisher pigs, it’s now been observed in breeding stock as well – and we’ve had it here in South Dakota. Affected pigs develop blisters on their snouts and feet. Accordingly, lameness has been a clinical feature of Seneca Valley Virus infection.

Unlike Vesicular Stomatitis, no one had an inkling Seneca Valley Virus was a potential pathogen. It was an obscure virus found contaminating a lab culture back in 2002. Now it’s emerged as a pathogen. We know very little about how it’s transmitted between animals or farms, but we’re learning more every day.

Seneca Valley Virus is yet another example of how viruses once considered rare and harmless can emerge to create restless nights for those trusted to protect animal health. It’s why veterinary labs and universities need to stay up to date with the ability to detect and research these emerging pathogens.

Vesicular stomatitis and Seneca Valley Virus aren’t Foot and Mouth Disease, thank goodness. But danger still exists from their presence. The worry is that animal owners and veterinarians might become complacent and ascribe these events to something harmless, not bothering to rule out FMD. Foot and Mouth Disease remains a threat – it’s prevalent worldwide and could be just a plane ride away. If it ever gets here, time is of the essence if there’s any hope of containing it. Even though the chances are slim, it’s important enough that when animals show up with these signs, you should call your veterinarian right away.

Russ Daly, DVM, is the Extension Veterinarian at South Dakota State University. He can be reached via e-mail at or at 605-688-5171.