Pigeon Fever. Dryland Strangles, Bastard Strangles, Dryland Distemper.
Condensed article from The Stud Farm Diaries by Cindy Reich
It had been an unusually long, dry, hot autumn and flies were still hanging around the barns long past their usual demise.
Both horses had identical swellings all along their midline, from sheath to just between their front legs. The swelling was hard and painful. The stallion appeared depressed, the gelding bright, alert and responsive.
Upon taking each horses temperature, the stallion’s temp was 104 and the geldings 102. Normal temp for them would have been 99 to 100. The horses were isolated from the rest of the population and the Veterinarian was called.
When the Vet examined the horses, he found a spot on one of the midline swellings. While he was fairly sure of what it was, a culture of the abscess was in order for proper diagnosis. The area was opened with a scalpel blade and out ran a stream of yellow-brown pus. A sterile swab was taken of the pus and in a few days we knew what the Vet had suspected. “Corynebacterium pseudotuberculosis”, otherwise know as Dryland Distemper, Dryland Strangles, Bastard Strangles or most commonly, Pigeon Fever.
What is Pigeon Fever?
The classic “Pigeon fever” is so-called because the abscesses usually form in the chest or pectoral region, causing exaggerated swelling of the chest—ergo, a pigeon chest. The bacterium lives in the soil and is carried by flies. Cases of pigeon fever are usually seen in the late fall to early winter, especially if the weather has been hot and dry and the flies are more numerous later into the year.
In order for the organism to cause the disease in horses it must enter through a break in the skin. Flies transmit the disease and they land on a horse with a break in the skin, they will congregate on that wound and the disease enters the horse’s body.
When flies are bothersome, it is not unusual for horses to kick at their bellies, often creating small tears in the skin that become the entry point for the infection. When the organism enters the horse it can cause several different types of symptoms.
Among these are: The classic pigeon chest, in which abscesses form deep in the muscle tissue in the pectoral muscles; Ventral midline infections (all along the belly); or an infection of the legs known as ulcerative lymphangitis.
Swellings that are visible and open to the outside are known as external abscesses. A further complication involves internal abscesses, which we will discuss later in this article. The infection follows the lymph system once it enters the horse and can go forward toward the armpits and chest, or back along the midline to the groin. The form known as “ulcerative lymphangitis” impairs lymph drainage and the legs become grossly swollen, requiring intensive nursing care. This form of the disease can require months of treatment.
What can you do?
The first thing you can do is to separate a horse suspected of having pigeon fever from the rest of the horses on the farm and then contact your veterinarian for a proper course of treatment. The use of antibiotics for external abscesses is controversial. There are some indications that the use of antibiotics where there are external abscesses, especially early in the formation of the abscess, may cause the organism to go internally. If you have a horse with the external abscess form of the disease, it would be wise to consult with your vet before beginning treatment. Antibiotic treatment for internal abscesses, however, is vital.
Hot packing external abscesses and causing them to “draw” to a point so that they can be drained is a good management practice. Flushing the abscesses once they have been drained will help them heal faster. Monitor the temp of the horse and its attitude. If a mare has midline abscesses, it is also possible for her udder to become infected (as can the sheath of male horses). Any pus or drainage from these abscesses is apt to be picked up by flies and transported to other horses, so disposal of this material is necessary. Disinfect all surfaces with a phenolic compound to lessen the chance of re-infection.
Internal VS external abscesses
The most common type of pigeon fever is manifested by either the abscess in the chest or along the midline. However, any horse that has this type of infection is also at risk for forming internal abscesses. While very few horses develop the internal abscesses, if they do, it can be fatal. Often the horse will present itself with depression, fever, lameness (it is painful to walk), loss of appetite, etc. If internal abscesses are suspected, a rectal ultrasound may be necessary to try to identify them. Antibiotic treatment is absolutely necessary in the case of internal abscesses and your vet can best advise in the treatment protocol. Fortunately, this organism is sensitive to many antibiotics.
Once pigeon fever has made an appearance on your farm, you can assume it will be there forever. Therefore, programs to reduce fly populations are the best defense to avoid further infection. Keeping paddocks and stalls as clean as possible, removing all manure from the farm as opposed to manure mountains, composting manure to reduce flies, use of fly-eating wasps and prudent use of pesticides are all ways to decrease the fly population on your farm. Instruct your personnel to be alert, especially in the late fall and winter to any unusual swellings on horses, or any signs of illness or lameness.
The prognosis for recovery is excellent with the external abscess form of pigeon fever, but more guarded for the internal form. Be advises that it is also possible for an abscess to re-form, weeks or even months after all other signs have ceased.