What is Corynebacterium Pseudotuberculosis Infection?
The Corynebacterium pseudotuberculosis bacteria can cause infections year round, but seems to be more common during the drier months of summer and fall. This may be due to a peak of insect activity this time of year, which provides a mode of transmission. The most common symptoms of visible swelling and abscesses can progress to more serious conditions of lameness, septic joints, and even bone infection. Treatment for many cases can be successful, although some severe cases can become fatal. The prevention of transmission to healthy horses is very important, as this infectious bacteria can survive outside its host for up to eight months.
Corynebacterium pseudotuberculosis is a bacteria that affects many different species. In horses, it causes abscesses in the lower limbs, along the pectoral and abdominal regions, and inside the body. This infection is also referred to as pigeon fever due to the associated swelling in the chest from the inflammation and abscesses that cause an appearance akin to the protruding breast of a pigeon.
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Symptoms of Corynebacterium Pseudotuberculosis Infection in Horses
Common symptoms of this infection in horses include:
- External abscesses, often on limbs, chest, or abdomen
- Small ulcerative nodules
- Localized swelling, often in the legs
- Decreased appetite
- Weight loss
- Respiratory disease
- Abdominal pain
- Splinted abdomen
- Swelling in limbs
- Swelling in pectoral muscles, giving a pigeon breast appearance
- Painful inflammation of soft tissues
- Bacterial skin infections
- Increased white blood cell counts in blood
- Septic joints
- Osteomyelitis, or bone infection
Internal abscesses can lead to more serious symptoms, such as:
- Ventral edema, or swelling of the lowest part of the belly
- Ventral midline dermatitis
- Loss of body movement control
- Hematuria, or blood in the urine
Three forms of this infection have been seen to affect horses.
This is the least common form of the infection, and starts as inflammation of the limbs, with painful oozing ulcers or nodules. Fluid is thick, odorless, tan in color, and can be tinged with blood. Horses can exhibit fever, lethargy, and severe lameness. Without aggressive treatment, the condition can become chronic.
This is the most common type of infection, with abscesses developing mainly on the pectoral region and along the abdomen. Abscesses can also develop on the limbs, head, triceps, mammary glands, and prepuce. Horses can exhibit single or multiple abscesses on different parts of the body, containing an odorless, tan fluid. Signs of systemic illness are generally not seen in this type of infection, although 25% of horses develop fever. The external abscesses can grow large, to about 20 cm in diameter, and generally resolve on their own.
These abscesses are inside the body, most commonly affecting organs such as the liver, spleen, kidney, and lungs. Diagnosis is challenging, and the fatality rate of this type of infection is much higher. Weight loss, colic, abortion, fetal infections, and lethargy are prominent signs.
Causes of Corynebacterium Pseudotuberculosis Infection in Horses
his bacteria infects the horse through wounds or abrasions in the skin, or through mucous membranes. The organism can survive up to two months in shavings and hay, and longer than eight months hidden in the soil. Modes of transmission include:
- Horse to horse contact
- Bites from infected insects, such as horn flies, stable flies, or horse flies
- Contact with contaminated soil, hay or shavings
- Contact with contaminated objects
Diagnosis of Corynebacterium Pseudotuberculosis Infection in Horses
In all types of Corynebacterium pseudotuberculosis infection, a diagnosis begins with symptoms and is confirmed through testing, specifically with the isolation of the bacteria. This can be done through examination of cultures taken from abscesses, swabs of serum, and a synergistic hemolysis inhibition (SHI) test to detect the IgG antibody to this particular bacteria. While the SHI is very useful for internal abscess diagnosis, it may test negative for external abscesses when the infection is actually present. Blood samples are also taken.
Ultrasounds are used to identify internal abscesses, and to see the extent of the infection. They are also helpful when collecting internal tissue samples for testing, such as for a kidney or liver biopsies. They can also be used to monitor treatment and the drainage of abscesses causing lameness. Other tests involved with internal abscesses can include a rectal exam, a tracheal wash analysis, and exploratory abdominal surgery, as well as additional cultures and fluid samples.
Ulcerative lymphangitis may also require punch biopsies for a definitive diagnosis. External abscesses may need further testing to rule out any internal abscess formations. Once the type and severity of infection have been correctly diagnosed, a treatment plan can be created.
Treatment of Corynebacterium Pseudotuberculosis Infection in Horses
The treatment of external abscesses can be catered to your horse’s particular condition, but generally follows similar procedures. Sometimes, the abscesses are encouraged to mature or rupture by way of hot packs, poultices or hydrotherapy. Aspiration and draining of the abscess to remove infected materials leads to a faster healing time. The abscesses are then flushed with an antiseptic solution. Antimicrobials are rarely used in external abscesses conditions as they can prohibit maturation. Pain relievers may be prescribed. Surgical resection of deep abscesses is performed when needed.
For internal abscesses and ulcerative lymphangitis, the treatment is more aggressive and should be early in the life of the infection to prevent residual lameness. Single or combinations of antimicrobials are used, both intravenously and orally until symptoms improve. After that, they are given orally to prevent a relapse. Internal abscesses are lanced if possible, and can be guided by ultrasound. Leg wraps, hydrotherapy, physical therapy, and pain relievers are given as needed, as is any supportive care.
Recovery of Corynebacterium Pseudotuberculosis Infection in Horses
Treatments to help your horse recover may include medications from your veterinarian, daily cleaning and drying of affected limbs, light exercise, and physiotherapy. Successful treatment will result in a gradual reduction of swelling over days to weeks, and recovery is usually good. Internal abscesses have a higher rate of mortality, 30% to 40% with treatment, and 100% without treatment.
Prevent the spread of this bacteria by using good biosecurity practices. Since Corynebacterium pseudotuberculosis can live 2 months in hay, and 8 months in soil, it can easily transfer to other horses in the population. Ways to stop this from happening include isolating infected horses, using disposable gloves for each horse, practicing hand washing, using insect repellents near or on horses, and preventing infection with good wound care.