Managing pigeon fever in horses

Pigeon fever is an elevated body temperature of a pigeon, right? In the words of Lee Corso, “not so fast my friend”. In this post, I’m referring to a bacterial infection that occurs in horses. Pigeon fever, also called dryland distemper and dryland strangles, is a bacterial infection in horses caused by the bacterium Corynebacterium pseudotuberculosis. The disease usually is characterized by swelling of the ventral chest causing a “pigeon breast” appearance. The swelling is a result of abscesses that occur deep within the tissue.

Establishing an effective biosecurity program currently is the best, and only, method of preventing pigeon fever in horses.

A horse with pigeon fever most often has swelling of the ventral chest that may be accompanied by a mild fever. Although the chest is the most common site for an abscess to develop, other areas may be involved. The swelling is due to an abscess that results from C. pseudotuberculosis infection and is located fairly deep in the tissue of the ventral chest or other site.  In order to heal, the abscess must mature and be drained. Finding and draining the abscess may be assisted by ultrasound. Antibiotics are often withheld from the treatment as they may only slow the maturation process of the abscess. A horse may become more systemically ill (e.g., have fever, lethargy, decreased appetite, etc.) if multiple abscesses are present. More rarely, the infection may present as an ulcerative lymphangitis of the legs. In this case, the infectious organism makes its way into the tissue and lymphatic system of the leg. The most deadly form of infection occurs when the bacteria causes an abscess internally (e.g., lungs, abdomen). Abscesses inside the body are unable to drain and antibiotics are unable to clear the infection. 

Pigeon fever only had been found in areas where the environment is dry, with California being the most common place the disease is found. However, the disease has spread to several other states including Texas, Louisiana, Arkansas, Kentucky and Florida. C. pseudotuberculosis tends to thrive in soil and manure found in warm, dry environments. With this movement to the east, we could be seeing a change in the environment or in the bacteria itself that makes it more able to survive in wetter climates. Most cases of pigeon fever are seen in late summer or early fall. However, another question remains: Could we see an increase in the number of cases seen when specific areas of the country suffer from a drought?

As mentioned earlier, the bacteria are found in the horse’s environment. In order to cause infection, the bacteria must make its way into the horse, which it does by entering the body through wounds, mucous membranes, or potentially through fly bites.

Preventing the disease certainly is better than having to treat the disease. The old adage, “an ounce of prevention is worth a pound of cure,” applies here. Unfortunately, there is no vaccination for pigeon fever at this point. However, we can take other steps to minimize spread of the disease. To help prevent infection, facilities should practice good hygiene, perform good wound care, and implement pest control strategies. These are a few components of a good biosecurity program. Every operation, no matter how large or small, should develop a biosecurity plan that fits their specific operation. If a facility has a horse that has developed a case of pigeon fever, these strategies become even more critical. If a facility has an infected horse, the following steps should be taken:

  • Any affected horse should be isolated immediately.
  • Any manure or bedding from an affected horse should be disposed of properly as the drainage from the abscesses contains extremely large numbers of the bacteria which can serve as a source of infection for other horses on the premise.
  • People should wear gloves when handling the horse or anything that is associated with the horse. The gloves should be discarded and hands should be washed when leaving the area and before coming in contact with other horses.
  • Footbaths that disinfect your shoes/boots should be used on entrance and exit of the affected horses stall. Ideally, one should change clothes before leaving the area.
  • No equipment, tack, feed pans, water buckets, etc. should be shared with other horses, and these things should be disinfected properly before being put back into use.
  • The stall and any other area where the affected horse has been should be cleaned and disinfected properly. Cleaning is an essential step in the disinfection process as most disinfectants are ineffective in the presence of organic material such as manure, pus, dirt and others.

Unfortunately there is no effective way to disinfect the soil to rid the environment of these disease-causing organisms. Fly control also is a crucial control measure as well. These pests can transport the bacteria to another horse’s wound or mucous membranes or provide the bacteria with a port of entry through its own bite. All of these things mentioned, from people to tack, feed buckets, bedding, stalls, flies, can serve as a means to get the bacteria from one spot to another and potentially infect another horse.

Once a horse is exposed to the organism, the horse’s immune status will play a role in determining whether or not it develops an infection. With that said, keeping horses healthy and boosting their immune system may help keep the infection from becoming established.

Pigeon fever, equine herpes virus, “strangles”, influenza, ringworm, salmonellosis and other equine diseases all have at least one thing in common — they are caused by an infectious agent. Biosecurity is a term that gets thrown around a lot and can be a little intimidating. It doesn’t have to be. As the horse industry continues to be mobile, the exposure of our horses to various pathogens will increase. Good biosecurity strategies and the horse’s immune status are two points where we as veterinarians and horse owners can impact the spread of disease.

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