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Name
Blastomycosis
Short Description
Blastomycosis, Blastomyces dermatidis infection
Affected Animals: Dogs, humans, cats, horses, and occasionally
other animals may be affected. Most dogs with the infection are
between one and five years of age. Males have a higher risk than
females, and may be less responsive to treatment. Immunosuppressed
animals are more at risk; animals that become infected may have an
underlying immune-system defect, or may be on immunosuppressive
medications.
Overview: Blastomycosis is an infection caused by the
fungal organism Blastomyces dermatidis. The disease usually results
in respiratory infection; however, the organism can cause disease in
many body tissues including the eyes, skin, reproductive tract, and
bones. Blastomycosis is a serious disease that can be
fatal.Blastomyces dermatidis is found in the environment
predominantly in the Missouri, Ohio, Tennessee, and Mississippi
river valleys. Although all animals in these regions are exposed to
the organism, only some animals will develop infections. A
compromised immune system is the primary risk factor.
Symptoms depend upon the tissues infected by the organism. Treatment
requires the use of antifungal medications, often for several weeks
to months. In some instances, a cure is not possible and death may
result. However, constant medication may keep the disease under
control.
Clinical Signs: Clinical signs of blastomycosis infection include
coughing; dyspnea, or difficulty breathing; fever; uveitis, or eye
inflammation; depression; weight loss; lymphadenopathy, or enlarged
lymph nodes; draining skin lesions; and lameness.
Symptoms:
See Clinical Signs.
Description: Blastomycosis is a severe systemic infection
caused by the fungal organism Blastomyces dermatidis. The organism
grows in the soil in specific regions of the country, including the
Missouri, Ohio, Tennessee, and Mississippi River valleys. Dogs and
humans are most at risk for infection; however, cats, horses, and
other animals are occasionally affected.
Because many tissues can be infected by the organism, the signs of
the disease will vary. Signs such as difficulty breathing, exercise
intolerance, weight loss, and coughing will be seen when pneumonia,
a common manifestation of respiratory infection, is present. With
bone infections, lameness may be the only sign. A third of the cases
involve the eyes, resulting in pain, redness, glaucoma, retinal
detachment, and blindness. In addition, about one-fourth of affected
animals will have skin disease that may manifest as nodular areas or
draining wounds. The prostate and testes can also be affected.
Prostatic involvement may result in abdominal pain, a stiff gait,
and difficulty urinating. Testicular infections may result in
swelling, pain, and sterility.
Systemic fungal infections are always serious, and can be difficult
to treat. Many times affected animals are immunocompromised, or have
weakened immune systems, making the disease harder to eradicate. If
untreated, most infections are eventually fatal.
Diagnosis: A presumptive diagnosis can be made based on the
animal's clinical signs, history, geographical region of the
country, and serologic tests. A CBC, or complete blood count, and
chemistry panel are usually performed. Many animals will have an
elevated white blood cell count, and elevated calcium levels are
sometimes seen. Because respiratory disease is the most common
manifestation of infection, chest x-rays are usually taken. X-rays
of the abdomen, limbs, or other parts of the body may be indicated
if the animal is showing signs in these areas.
A definitive diagnosis is made by identification of the Blastomyces
dermatidis organism through biopsy, fine-needle aspiration, or
culture. Occasionally, imaging tests, such as a CT scan or nuclear
scintigraphy, may be performed to better identify which tissues are
infected and to monitor treatment. This equipment is typically
available only at universities or large referral institutions.
Prognosis: The prognosis for treatment is
guarded. Animals with severe respiratory or central nervous system
signs have the poorest prognoses. With severe disease, animals often
succumb during the first week of treatment, due to the inflammatory
response that occurs as the organism is killed. If the animal does
respond to treatment, the prognosis is more favorable; however,
recurrence is seen in about 20 percent of cases, generally occurring
within the first six months. A full course of therapy must be
reinitiated in cases of relapse. Rarely, animals require lifelong
treatment to control the disease.
Transmission or Cause: The causative agent of the disease is Blastomyces
dermatidis, a fungus. Most cases of infection occur by inhalation of
the infective spores present in the environment. The organism can
then disseminate or spread to other tissues such as eyes, skin,
bone, lymph nodes and other tissues. At body temperature, the fungus
exists as a single-celled yeast, while at environmental temperature
it exists as the infectious mycelial form. Animals infected with the
disease can not pass it on to others, unless there is drainage from
skin lesions.
Treatment: Antifungal drugs including ketoconazole,
itraconazole, fluconazole, and amphotericin B are the mainstay of
treatment. Amphotericin B was one of the first drugs found to be
effective in the treatment of blastomycosis. It can cause kidney
damage, and requires intravenous administration. Ketoconazole,
itraconazole, and fluconazole belong to the same drug family. Each
has been used effectively in the treatment of Blastomycosis.
Ketoconazole and itraconazole can cause liver damage, and are
available as oral medications. Itraconazole is generally more
effective than ketoconazole, but it is also more expensive.
Fluconazole is often used for treating infections of the central
nervous system and eye because of its better penetration into these
tissues.
Prevention: Other than avoiding endemic regions, there are no
preventive measures.
