Corynebacterium Pseudotuberculosis

This paper will address the common livestock disease known as pigeon fever, its history, transmission, common locations, ideal environment, types of infection and treatment, as well as personal experiences and relevance to this area of the country.

Pigeon fever, also called dryland, dryland strangles, dryland distemper, or Colorado strangles, is a bacterial disease caused by the gram positive bacteria Corynebacterium pseudotuberculosis. This disease is most commonly seen in horses, but has also been recorded in other mammalian livestock and very rarely humans. This bacteria typically causes large, pus filled abscesses down the animal's ventral midline; however they can appear anywhere in or on the body.

Contrary to what the name "pigeon fever" might have you believe, this disease is not actually spread by pigeons or any other kind of birds. Instead the bacteria is acquired through mucous membranes, wounds, and abrasions by contact with contaminated soil or surfaces such as bedding and feed or even pitchforks and the handler's boots, however it most commonly enters the horse's body through bites from flies that have been on other infected horses or contaminated soil. With abcesses commonly occuring down the ventral midline, especially the chest, infected animals look as though they have a puffed up breast much like a strutting male pigeon, hence the name pigeon fever.

There have been cases of pigeon fever recorded worldwide, but it is most common in the southern United States as well as specific regions of Texas, Nevada, and California, with the central coast unfortunately being one of those regions. Cases of Corynebacterium pseudotuberculosis have also recently been confirmed in the states of Utah, Colorado, Wyoming, Kentucky, Oregon, Idaho, Florida and even in Alberta, Canada. Corynebacterium pseudotuberculosis can survive up to eight months in the environment. This disease tends to be more prevalent in areas with sandy, rocky soil and when the fly populations are at their peak and conditions are dusty and dry, such as during late summer until the fall.

Once in the body, Corynebacterium pseudotuberculosis takes around three to four weeks for signs of disease to appear and causes three types of infection. The first consists of the external abscesses on the chest and abdomen that the disease is most known for. These types of abscesses commonly form in the muscle and can be quite large and painful. The abscesses can be reabsorbed but they usually burst of their own accord. They can also be lanced and drained when matured if necessary. Whichever way they end up bursting, the abscess should be thoroughly drained and cleaned to promote healing. The external abscess forming version of this disease is very rarely fatal.

Pigeon fever can also present as internal abscesses. This type of infection is more rare affecting only around 8% of horses afflicted with Corynebacterium pseudotuberculosis. However, these internal abscesses can be exceedingly difficult to diagnose and treat and typically have a 30-40% fatality rate due to late diagnosis and the involvement of such important organs as the lungs, kidneys, liver, and spleen.

The third type of infection is ulcerative lymphangitis where many small abscesses from along the lymph tracts of the animal's limbs. This type of infection is characterized by severe swelling and cellulitis, most commonly in one or both of the rear limbs, leading to lameness. Signs and symptoms of all forms of the disease may include: fever, lethargy, edema, going off feed, weight loss, and possibly death.

Treatment of Corynebacterium pseudotuberculosis depends on which type of infection the has animal contracted. External abscesses are very rarely treated with antimicrobial drugs unless they are exceptionally deep in the body or a recurring problem. More often pain relief such as hot packs and the drug phenylbutazone will be prescribed just to make the animal comfortable while the infection runs its course which usually takes about three weeks from first presentation. Internal abscesses and ulcerative lymphangitis however are always recommended to be treated with antimicrobial medications. Internal abscesses may take months to fully clear and even with aggressive medications prognosis may still be grim. The same goes for ulcerative lymphangitis, even with treatment many horses will have recurring swelling that can lead to chronic lameness issues such as laminitis which may be grounds for humane euthanasia depending on severity and lameness management.

In our area of California it is very common for horses to contract Corynebacterium pseudotuberculosis any time from the mid summer to the end of fall. In my personal experience I have seen at least a dozen cases, most of them cleared up and the horses were fine but two horses stand out. Mister and Little Miss Muffet both had fairly severe external abscesses, at one point Mister almost was part of the 0.8% fatality rate for the external infection, and both had lasting effects that are being attributed to the pigeon fever. Muffy now has issues with swelling in her hind legs when she is in a stall for too long but it easily goes away with exercise. Mister ended up with lameness issues and what was assumed to be some sort of mental trauma which unfortunately got worse over the next few years making him unsafe to handle and in chronic pain so he was humanely euthanized in 2018. This year alone, even with rigorous prevention, three horses in the barn that I ride at contracted pigeon fever. Luckily they all had uncomplicated external abscesses and are clearing up just fine. However this is a very contagious bacteria and living in an area where agriculture is very important this is cause for concern. Not only are people's beloved horses at risk but also to the other livestock raised as a food source, specifically cattle in this area, and with fly prevention and avoidance as the only semi reliable sources of control at this time some unlucky or uneducated animal owners could cause an epidemic.

Corynebacterium pseudotuberculosis is a highly contagious bacteria. It is relatively hardy and widely spread, thriving in the California climate. It can affect a variety of livestock animals and even rarely humans but mainly horses. This bacteria also causes subtypes of its disease, pigeon fever, in varying levels of severity. While the most prevalent type of infection is not frequently fatal there are only a few low tech ways of preventing the spread of Corynebacterium pseudotuberculosis. Further research into a reliable vaccination or development of an easier cure for the more fatal types of disease would not only save owners of pet livestock money and heartache but also save ranchers money in veterinary bills therefore saving the consumer money and bringing around a healthier world for commercial animals that may also be affected by Corynebacterium pseudotuberculosis.

Classic "pigeon" chest

External abscess

Ulcerative lymphangitis

Abscess and swelling on Wilbur

Bibliography

1. Dawes, Maisie E. "ACVIM Fact Sheet: Pigeon Fever (C. Pseudotuberculosis)." American College of Internal Veterinary Medicine, 2015, www.acvim.org/Portals/0/PDF/Animal%20Owner%20Fact%20Sheets/LAIM/Pigeon%20Fever%20Formatted.pdf.
2. Grenager, Nora, and Tim Eastman. "Pigeon Fever." Steinbeck Equine, 2018, steinbeckequine.com/pdf/PigeonFever2018.pdf.
3. "Pigeon Fever (Corynebacterium Pseudotuberculosis Infection)." American Association of Equine Practitioners, 2013, Pigeon Fever (Corynebacterium pseudotuberculosis infection).
4. "Pigeon Fever | Equimed - Horse Health Matters." EquiMed, equimed.com/diseases-and-conditions/reference/pigeon-fever.

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