Blastomycosis: A Fungus Among Us
November 2, 2004
By Kim Marie Labak

When your dog is coughing and has a fever, it could have pneumonia. Unbeknownst to many, pneumonia is not caused only by bacteria and viruses—it can also be caused by fungi from the environment. Blastomyces dermatitidis, or “Blasto,” is a disease-causing fungus that can cause skin and respiratory infections in dogs, humans, and occasionally cats. In some individuals it can spread to infect other organ systems.

Blasto is natural part of environment. According to Dr. Thomas Graves, veterinary internist at the University of Illinois Veterinary Teaching Hospital in Urbana, it is very common in acidic soils of the Midwest and central south. The fungus exists as a mold in the environment and becomes a yeast at body temperature.

According to Dr. Karen Campbell, a veterinary internist and veterinary dermatologist at the teaching hospital, animals can get infected only by direct contact with mold spores: spores can be inhaled or enter through broken skin when a person or animal rolls in contaminated soil. An infected animal cannot spread the disease, since the yeast form is not contagious.

Signs of blasto infection depend on the body system infected. The three forms of blastomycosis—cutaneous, respiratory, and disseminated—often occur at the same time.

Cutaneous infection appears as skin lesions, resulting from spores entering the skin directly through a sore or cut or as part of a disseminated infection that originated in the lungs. The lesions are very itchy and wet. Although these infections can stay contained, according to Dr. Campbell, they can seriously damage nearby muscle and bone tissue if untreated.

The most life-threatening (and most common) form of blasto is pneumonia, since respiratory infection, if left untreated, can lead to severe inflammation of the lungs and eventual death. As with other respiratory diseases, infected dogs often cough, lose their appetite, become lethargic, and have difficulty breathing.

In some individuals, especially those with weakened immunity, the respiratory infection can disseminate to the kidneys, eyes, or skin, and occasionally the spinal cord and brain.

Blastomycosis is very treatable with antifungal drugs, and improvement is usually seen within a few days, but the treatment can take a long time (up to six months) and gets expensive. Treatment is most effective when the disease is caught early, however, so proper treatment requires proper diagnosis.

Dr. Graves explains that when an animal is misdiagnosed with a bacterial infection and receives antibiotics, the fungal infection is allowed to progress, and by the time the animal is properly diagnosed with blasto, it may be too late, especially in pneumonia cases.

He explains that the best way to diagnose blasto is to look for blastomyces organisms in the body. Discharge from a skin wound can be swabbed, the trachea or lungs can be rinsed with saline, or fluid from organs such as lymph nodes can be extracted with needle; these fluids can be then examined under a microscope to identify blasto yeast cells.

Blasto is more common in larger dogs, males, young dogs, and sporting and hunting breeds. Dr. Campbell and Dr. Graves suspect that these correlations may be due to certain behaviors, since these dogs may spend more time outdoors, sniffing soil. Disease signs may not show until 5 to 12 weeks after exposure to blasto.

While blasto infection is virtually impossible to prevent since the fungus is a natural part of the environment—“You can’t ask people to keep their dogs indoors all the time,” says Dr. Graves—blastomycosis can be overcome if diagnosed and treated early.

For more information about blastomycosis, consult your veterinarian.

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