Description

What was once considered a disease of California horses, pigeon fever is now a growing problem throughout the United States, with outbreaks in Oregon, Arizona, Wyoming, Idaho and several Midwestern and Eastern states.

Known by a number of names, including pigeon breast, dryland distemper, dryland strangles and false distemper, prognosis for a complete recovery is good, although some horses experience multiple episodes.

The disease occurs in three forms: external abscesses, internal abscesses and limb infection, also known as ulcerative lymphangitis.

The most common form of the disease in the United States involves external abscesses that form deep in the muscles and can be very large, giving the horse the appearance of having a pigeon breast.

Horses may become infected and yet not develop abscesses for quite some time. The disease usually occurs in younger horses, but can occur at any age and in any sex and breed.

Abscesses usually appear in the pectoral region, the ventral abdomen and the groin area, but can also occur along the back. They often rupture spontaneously and the wound exudes an ill-smelling, yellow and light tan-colored pus.

Functional problems can develop when abscesses are large and create pressure within the horse's muscles.

Ulcerative lymphangitis is the most common form worldwide and often involves one leg. Usually, multiple, small, draining sores develop above the fetlock.

When the disease is in the form of internal abscesses it is very difficult to diagnose and treat.

The disease is seasonal, with most cases occurring in the dry, hot months of early fall, though a number of cases have occurred during the winter and at other times of the year.

The incidence is low in foals, but the disease also affects cattle, and a similar disease affects sheep and goats.

Symptoms

• Fever
• Lethargy
• Lameness
• Weight loss
• Depression
• Appearance of swellings and abscesses

Causes

The disease is caused by the bacteria Corynebacterium pseudotuberculosis which is found worldwide. The bacteria lives in soil and usually enters the horse's body through wounds, broken skin or through mucous membranes. It is possibly transmitted by flies and other insects. Common houseflies have been shown to carry the bacteria.

The disease is highly contagious and can easily infect multiple horses on the premises. Hot, dry weather facilitates bacterial growth in soil and manure. The bacteria can be spread by the boots, hands and tools of a person working around an infected horse or churning up soil where the bacteria is found.

The bacterium in pus draining from abscesses in an infected horse can survive for up to 55 days in the environment. It can also survive for up to eight days on surface contaminants and from seven to 55 days within feces, hay, straw or wood shavings.

Prevention

Consistent and careful cleanliness wherever horses are kept, along with strong pest control measures for insects are very important. When an infected horse is on the premises, proper disinfection protocols should be utilized to limit the spread of the disease.

Gloves should be worn when handling infected horses. Any topsoil, bedding, mats, hay, straw or other material around an infected horse should be removed and replaced with clean soil or bedding.

Buckets or other containers used to collect pus from draining abscesses and any infectious material should be disposed of properly. All stalls, paddocks, utensils and tack should be thoroughly cleaned and disinfected.

Good sanitation practices should be followed, with thorough washing of hands and removal of clothing worn around infected horses, and any tools or implements used in the area, such as pitchforks or shovels, should be cleaned and disinfected.

Insect control measures should be carefully followed to limit flies and other pests.

Horses should be examined daily for wounds or abrasions that could become portals of entry for bacteria. Elective surgical procedures that require opening the skin should be scheduled for times when the disease is least likely to be active and when insect activity is at its lowest point.

Treatment

Hot packs or poultices should be applied to abscesses to encourage opening. Open abscesses should be drained and flushed with saline solution. Depending on the depth of the abscess, surgical or deep lancing may be required and should be done by a veterinarian.

Ultrasound is often used to assess the depth and size of abscesses so proper drainage can be achieved.

External abscesses can be cleaned with a 0.1 percent povidone-iodine solution and antiseptic-soaked gauze may be packed into open wounds.

Some veterinarians recommend nonsteroidal anti-inflammatory drugs, such as phenylbutazone (Bute), to control pain and swelling and keep the horse more comfortable.

The use of antibiotics is controversial. Studies have shown that improper use may contribute to abscesses and may encourage chronic problems with abscesses if insufficient quantities are administered.

In the case of internal abscesses, prolonged penicillin therapy is often necessary.

Recovery time can vary from two to ten weeks.