Pythiosis: Is Your Horse at Risk?
Recognizing
the early signs of this destructive
disease can save your horse.
By Toots
A. Banner, DVM
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| Pythiosis,
also called “Florida horse leeches”, “swamp
cancer”, “kunkers”, or “bursatti”,
is caused by an aquatic oomycete called Pythium insidiosum.
It is more closely related to algae than to fungi and as the
names implies, can be a very serious disease of the skin and
subcutaneous tissue in horses. Pythiosis can also cause disease
in dogs, cats, calves and humans. There are no reports of animal
to animal, or animal to human transmission of this pathogen.
The disease was first reported in India in the mid 1800’s
and was isolated in the early 1900’s by Dutch investigators.
In the United States, most cases are found in the southeast
and Gulf Coast states. There have been reports of Pythiosis
as far west as Kansas and as far north as New Jersey.
Exposure
P. insidiosum normally lives in a warm aquatic environment
and adheres itself to wounds on the horse. Lesions can occur
on any part of the horse's body, but it is more common on
the lower limbs because they first come in contact with the
organism in infested wet environments.
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Typical
cutaneous pythiosis in an equine. Small white masses, known
as “kunkers”, are observed in the lesion.
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Symptoms
Lesions of pythiosis contain a characteristic yellow, coral-like
material within a granulating fleshy surface and sinus tract
openings. The sinus or draining tracts contain multiple, 1mm
to 7mm, branching masses that are commonly referred to as “kunkers”
or “leaches”. These kunkers are composed of necrotic
debris, hyphae, collagen, fibrin and inflammatory cells. These
ulcerating lesions usually drain a thick fluid and cause an
intense itch will cause many horses to chew and self-mutilate
in an attempt to get some relief. Lesions are characterized
by cutaneous ulcerative granulomas and horses with advanced
pythiosis may spread from distant lesions, through lymphatic
vessels to regional lymph nodes, lungs, tendon sheath, joints
or bones.
Diagnosis
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| Due
to the ability of a small lesion to worsen quickly, your veterinarian
should be called to help evaluate and diagnose the lesions.
Proper diagnosis and treatment are very important to prevent
P. insidiosum from causing excessive damage. There are several
other diseases that can appear like pythiosis including cutaneous
habronemiasis, excessive granulation tissue (proud flesh), squamous
cell carcinoma and zygomycosis. Diagnosis is often initially
made by clinical appearance as it can be tricky to isolate and
conclusively identify the pathogen through cytology |
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| of
the exudate from the draining tracts and/or a culture of the
infected tissue. However, many recent developments have greatly
assisted in the proper identification of pythiosis.
Serology
using ELISA and immunoblot have been used successfully to
recognize antigens but the only assay available to practicing
veterinarians has not been tested for specificity so the rate
of false-positives is unknown. Another recent development
has an assay for the DNA extract called a Molecular Assay,
the major advantage is a high degree of specificity. IHC or
immunohistochemical techiniques using polyclonal antibodies
has been used to confirm the diagnosis of pythiosis but at
least one of the antibodies has shown cross reactive staining.
A new polyclonal anti-P. insidiosum antibody raised in chickens
appears to be very specific but not yet commercially available.
Treatment
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Treatment
of pythiosis is often difficult and can be challenging to
say the least. Surgical resection or cutting away of as much
infected tissue as possible is the most important initial
step if possible. The surgical removal of the lesion should
be made with 2-cm margins in an attempt to remove all of the
infected tissue. Many times the infected tissue, “kunkers”
and draining tracts may invade deeper tissues where surgery
many not completely remove them. Debridement or scraping of
the tissue is performed to eliminate as much debris as possible.
Laser therapy called photoablation has been recommended to
aid in thermal or heat necrosis (death) of the pathogen |
While
pythiosis is most commonly seen in the legs of the horse in
can appear anywhere on the body, including the inside of the
mouth.
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Medical
therapy using antifungal drugs such as ketoconazole, amphotericin
B and iodides have been used but with limited and usually
poor success. Sodium Iodide which is a treatment for “lumpy
jaw” in cattle has been described as having some effectiveness
in the treatment of pythiosis. Dr. Murray Brown at the University
of Florida has developed a topical solution called “phycofixer”.
The solution does include some of these drugs and is applied
directly to the lesion has been used with some success over
the years.
Immunotherapy,
which is treatment by stimulation of the immune system, has
been used to treat pythiosis. A P. insidiosum vaccine was
first developed in the early 80’s and used as weekly
injections. Initial response to the treatment was usually
seen in the first 10 days and was effective in about half
the cases when used alone and higher rates when used with
surgical debridement. Adverse effects included severe, local
tissue reactions with pain and edema. A second type of vaccine
was developed by Mendoza which consisted of secreted antigens
from the Pythium insidiosum organism. The Mendoza vaccine
had less tissue reaction and had cure rates of 100% if the
infection was present for less than 15 days and a 0% cure
rate for infections going on more than 2 months. Another vaccine
is now available which has 2 types of antigens and was shown
to be effective in 13 of 18 horses when surgery and medical
therapy were ineffective. The protocol is 0.1 ml intradermally
followed by subcutaneous injection 15 days later. The local
reaction to the first injection is usually a strong indicator
into how effective the treatment will be.
Conclusion
In conclusion, Pythiosis is a very destructive disease that
can be fatal and correct diagnoses with appropriate therapy
are essential in having a positive outcome for your horse.
Closely monitor and treat even small lesions on the lower
legs to reduce the chance of exposure to P. insidiosum.
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Toots
A. Banner, DVM, from Micanopy, Florida owns Riverside
Equine Dental Services, a practive specializing in equine
dentistry serving the state of Florida. |
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