8 Things to Know About Pigeon Fever

Pigeon fever can strike any horse, anytime, and anywhere.

Pigeon fever, also called dryland distemper, can be vexing for horse owners. Outbreaks can happen seemingly at random – anytime and anyplace. Only one horse in the barn may be infected or it could strike multiple horses. The symptoms are gross (if you’re squeamish about bodily fluids) and treatment is time-consuming. The good news is that most horses will recover from a pigeon fever infection and the mortality rate is very low.

The Nevada Department of Agriculture tracks outbreaks of certain animal diseases in the state. Pigeon fever only became a reportable disease last year so there is no statewide
data available on the number of cases before then. But, there were three confirmed cases
of pigeon fever in Nevada in 2017. So far there have been no cases reported this year.
Since every horse in Nevada is potentially susceptible, here are eight things you should
know about pigeon fever:

1It’s everywhere.

Pigeon fever was first reported in the Bay Area of California in 1915. For much of the twentieth century, pigeon fever cases were concentrated in the southwest U.S., but in recent years it has been seen in horses as far away as Hawaii and Florida, as well as Mexico and Canada. Certain parts of the country see large outbreaks at a time. Dr. JJ Goicoechea, state veterinarian for the Nevada Department of Agriculture, says, “Anecdotally, it seems to have increased over the last 25 years.” He also says they see pigeon fever in all parts of Nevada.

2It’s a bacterial infection.

Pigeon fever is caused by a bacteria called corynebacterium pseudotuberculosis, which is typically found in dry, dusty soils in hot places. Once infected, the bacteria causes a horse’s body to build thick abscesses around the pathogen. “It’s actually very easily treated with antibiotics, but the problem is the abscess it builds around it is not easily penetrated,” says Dr. Betsy Lau of Comstock Equine Hospital.

3Transmission is a bit of a mystery.

Researchers are still trying to determine exactly how the bacteria enters the horse’s body, but the most likely culprit is fly bites or breaks in the skin. Cases tend to spike in late summer and early fall when the fly season is at its peak. “Good vector control and isolation of an infected horse is key,” says Dr. Goicoechea. Pigeon fever can be contagious from horse to horse, and humans can also infect horses, carrying the bacteria on their hands or equipment, but it doesn’t spread as rapidly as diseases like strangles.

4Symptoms vary and can take weeks to manifest.

“If the horse is stoic they might not notice that the horse has a fever, but a lot of times initially they’ll notice that their horse is maybe a little bit lethargic,” says Dr. Lau. “Or they notice, with a gelding, some sheath swelling. Pigeon fever is always one of the things we want to rule out if we have a gelding with sheath swelling in the fall.” As the bacteria progresses it can lead to external and/or internal abscesses, including in the pectoral region which causes a swelling like a pigeon breast, hence the name.

5There’s a lot of pus.

When abscesses open up, they drain. The pus is contagious, which is why proper cleaning and isolation of infected horses is so important. Treating the abscesses requires regular lancing, draining, and flushing. Warm compresses, drawing salves, and manual palpation will help break up the pus-filled chambers. “They’re almost like a little cave system sometimes,” says Dr. Lau. “You get one pocket open and you think you’re
doing well and it’ll either close off or you have another cavern of pus that needs to come to the surface.”

6Fatality rates are very low.

“Most horses, once you get those abscesses lanced and drained and flushed, they’ll heal within 5 to 7 days. The temperature will usually come down within a couple of days,” says Dr. Lau. “It really can be variable depending on the size of the abscess and the location of the abscess.” Internal abscesses can be more difficult to treat, particularly in older horses or horses with a compromised immune system.

7Pigeon fever can come back.

“Once it becomes established in the soil and environment, it is difficult to eliminate,” says Dr. Goicoechea. The bacteria can survive in soils, hay, or bedding for months leading to unpredictable future outbreaks. There is some evidence that outbreaks are cyclical, with some years worse than others.

8There could be a vaccine coming.

A vaccine did appear on the market about three years ago but it was voluntarily recalled after some incidents of gastrointestinal upset and colic. The company has been working to revamp the vaccine. “There’s been rumblings that it is coming back but we have not gotten it,” says Dr. Lau. “At this point, it’s still being done in trial or it’s a limited release to certain testing farms. Right now there is no
definitive vaccine on the market.”

The bottom line is good fly control and manure management will help reduce the risk of
disease in your barn and keep your horses safe. As always, check your horses regularly for
any unusual injuries or symptoms and contact your veterinarian immediately if you notice
anything irregular. “Pigeon fever may continue to spread in Nevada,” says Dr. Goicoechea.
“But diligent biosecurity and a good relationship with your veterinarian are key
components to protecting our equines.”

Story by Samantha Szesciorka