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"Pigeon Fever" is a disease about which horse
owners in Central California should be aware.Pigeons
have nothing to do with the disease other than that the
disease can cause a pronounced swelling on the horse's
chest that resembles a pigeon.Other names for the disease
include "Dryland Distemper", "Pigeon Breast
Fever", "Dryland Strangles", and Corynebacterium
Pseudotuberculosis.
This disease is caused by a bacteria that can survive
for long periods of time in the soil. It is thought
to be transmitted to horses by flies feeding on abrasions
or small wounds already present. The flies can plant
the bacteria which then penetrate and proliferate in
these warm, moist environments. Although also seen
throughout the southern United States, California is
particularly well known for having a high incidence of
this disease, especially during the late summer and early
fall. The more arid parts of our state are heavier hit
by Pigeon Fever. Like so many other diseases, there are
some years in which the prevalence seems to be much higher
than others.
 The typical signs include abscesses anywhere along the
ventral midline including the chest, sheath/mammary glands,
or in small chains along the lymphatic channel of a leg.
Large plaques of ventral edema are also frequently present
adjacent to the abscesses (ventral
edema causes sponge-like swelling on the underbelly
of horses). Rarely, it can cause an internal abscess
as well (less than 3% of all cases). Fever, weight
loss, depression and lameness are also frequently present
in some combination with internal and external abscesses.
Pigeon Fever abscesses usually take several weeks to
mature, but occasionally can cause long-lasting infections
over a year in duration.
Pigeon Fever should be considered at the top of the
list in any horse that has an abscess in a typical
location. The diagnosis can be confirmed by culturing
fluid taken from an abscess and identifying the bacteria,
but often the diagnosis is presumptive. If a positive
culture is not obtained or if your veterinarian suspects
an internal abscess, there is also a blood test that
can be performed to help diagnose the disease. This
blood test is performed at the University of California
at Davis and is very affordable.
Treatment of the disease may vary
depending on the severity of infection and on which body
systems are involved. Draining the abscess is the mainstay
of treatment but should not be performed until the abscess
is mature. If done prematurely, the abscess is more
likely to recur. Abscess maturity can be determined
by palpation (they generally get soft in the middle
when they are mature) and by ultrasound. Ultrasound
is also helpful to determine if there are multiple
pockets of fluid and to identify deep abscesses.
Once opened, the abscess cavity should be flushed
daily with an antiseptic solution such as betadyne
or nolvasan.
Most horses will be completely over the disease within
3 weeks of draining the abscess. Once the abscess matures
and the condition resolves, over 90% of horses will remain
immune to the disease in the future.In those rare instances
where the disease recurs, it is unknown whether recurrence
is due to re-infection or relapse of the original disease.
Horses that have difficulty clearing the infection should
be evaluated for possible causes of immune suppression
(such as Equine Cushings Disease). Horses affected with
external abscesses have an excellent prognosis, but internal
abscesses can be more devastating and are fatal in 40%
of cases.
Antibiotic usage is controversial.
Many veterinarians advise against administering antibiotics
for external abscesses because of the potential to
delay abscess maturation. However, in cases involving
internal abscesses or involving the lymph channels
of a leg ("Lymphangitis"),
long-term antibiotics are generally prescribed.
Prevention is centered on
good sanitation practices and fly control. Quarantine
of affected individuals is not generally necessary
because the insects carrying the bacteria can travel
long distances anyway. Practicing good fly control
can help reduce other diseases as well. At our hospital
we use a spray system and "fly
predators" as well as daily manure evacuation
to accomplish this. In a barn setting, daily feeding
of a small scoop of a new product called "Solitude
IGR" made by Pfizer is thought to dramatically
reduce fly populations. Research is currently focused
on creating a vaccine against this disease.
Tim G. Eastman DVM, DACVS, MPVM was raised in Monterey
County California where his family had deep roots
in the local horse industry. Like many veterinarians,
he decided to become an equine veterinarian at
a very young age. He obtained a degree in Animal Science
at Cal Poly San Luis Obispo and a business minor.
He also obtained a doctorate in Veterinary Medicine
from the University of California at Davis in
1996' as well as a Master's Degree in Preventative
Veterinary Medicine. He performed a one year internship
at Littleton Large Animal Clinic in Littleton Colorado
and then a 3 year surgical residency at Texas A&M
University in College Station Texas. He met his wife,
Alexandra (Alex) in veterinary school and got married
during his surgical residency. They now work together
as co-owners of Steinbeck Country Equine Clinic
in Salinas California.
Copyright © 2006 All rights
reserved. The above article is the property of the
Author and may not be duplicated or redistributed in
any way without permission.
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Your Horse's Health