By Patty Wilber

Well, I waited until it was a bit late to start the blog because I was 100% sure I had written about pigeon fever before…like back in 2012 or something, and I was going to modify that post.  But dang. I could not find it. So, starting from scratch…

Pigeon fever is caused by an infection with the bacterium Corynebacterium pseudotuberculosis. The bacteria can be transmitted by fly bites, and the disease has a long incubation period (1-4 weeks). Thus, the disease outbreaks are often in the fall, following peak fly season. (UC Davis) Large abscesses can form in the muscles of the chest or the belly, and they can drain super gross and disgusting pus. In quantity.

The disease is called pigeon fever because the abscesses in the chest muscle make the horse chest look like a bird breast. It is also called dryland distemper and false strangles.

In 2012 or so, Risa, one of my horses, got pigeon fever.  She had to go to the vet several times to have her chest and abdominal abscesses lanced.  She was a very tempermental sort of horse, and the vet missed the vein when trying to administer a sedative on our first visit.  Due to this “terrible error” (according to Risa), the vet was persona non grata, and on the next visit, Risa tried to kick the vet.  Sigh. Risa was not put on antibiotics, as the vet felt that would just slow the formation of the abscesses and slow the healing.

It took a long time for Risa’s wounds to heal, but on the bright side, after infection 90% horses develop long-term immunity.

In a case where a horse comes down with this disease, isolation is not necessary because, basically, it is too late to contain the pathogen–it is already in the soil.  But luckily, in large herds, only about 5% of the horses will get sick. (Dr. Novick) In my previous case, Risa was the only horse to become infected.

Interestingly (I thought), for a short while, there was a vaccine for this, but it was withdrawn from the market.  It sounded like the side effects of the vaccine were fairly severe.

Today I was out at the barn looking at Trigger, thinking maybe I needed to get him on a diet.  He is a mustang, and he not only likes to eat, but he is efficient at turning hay into fat. Then I noticed a swelling on his belly. Uh oh. Pigeon Fever? My Risa had the classic pectoral muscle abscesses, but five or six years ago, my friend MaryAnn’s horse Rosebud showed this belly swelling symptom. She got on antibiotics, and never had the nasty pus-fest.

I got a hold of Dr. Dixon.  Yes, he thought pigeon fever. He put Trigger on 20cc of enrofloxocin + two grams of bute for five days. The antibiotic inhibits DNA synthesis in the bacteria.  The bute reduces inflammation and helps limit the growth of the abscess. I am hopeful this will go like Rosebud’s case and resolve without a big mess!

Fingers crossed!

Special for Bio nerds: C. pseudotuberculosis has mycolic acid but stains G+ and not acid fast because the mycolic acids are shorter and less abundant than in the true acid fast genera like Nocardia and Mycobacterium. The cell wall is not very G+ like, though, as you can see in the image.

Cell wall of Cornybacterium sp.