Pet Talk: Danger lurking in the soil
By DANIELLE ENGEL
UI College of Veterinary Medicine
The unsuspecting victim inhales microscopic spores, which travel from the lungs throughout the body, causing disease. It may sound like something out of science fiction, but the fungus Blastomyces dermatitidis — the agent responsible for the systemic infection blastomycosis — is commonly found right here in the Midwest.
Fungus infects cats, dogs, horses, humans
Dr. Ian Sprandel is a veterinarian pursuing specialization in pathology at the UI Veterinary Diagnostic Laboratory in Urbana. He says this fungus lives in the soil and most frequently infects dogs, although cases have also been recorded in horses and cats, both domestic and feral.
People can also be infected; however, there is virtually no risk of transmission from infected dogs to humans. Humans have to contract the fungal disease the same way as dogs: from inhaling conidia (a form of the organism) from the environment. Immunosuppression in people increases risk of infection.
Infections arise most commonly in dogs between the ages of 1 and 5. Sporting dogs or hunting dogs are at greater risk because these breeds spend a lot of time with their noses close to the dirt, sniffing out a scent or a trail.
Indoor dogs also infected
"Exposure to the outdoors or soil is not required for infection, however. Many strictly indoor dogs have also been infected," Sprandel said. "Living near a waterway increases the risk of infection for dogs and people. However, our poor understanding of exactly where and how this organism grows and thrives in nature greatly limits our prediction of exposure risk and infection."
Nevertheless, blastomycosis is 10 times more prevalent in dogs than in humans, presumably because dogs spend more time with their noses in the dirt.
Clinical signs vary widely
Because the fungal spores are carried by the bloodstream and lymphatic vessels throughout the body, blastomycosis has a wide variety of clinical signs, including loss of appetite, weight loss, trouble breathing, cough, eye disease, lameness and sores on the skin. Frustratingly, clinical signs are often non-specific and vary based on organ system involvement.
"Don't be fooled if signs don't show up right away after exposure," Sprandel said. "In some patients, it takes weeks or months for signs to develop."
If you notice your dog displaying any of these problems, visit your veterinarian immediately. Very few dogs with blastomycosis can recover on their own; most require veterinary care and aggressive treatment with antifungal medications.
Start treatment early
A veterinarian can employ a urine test for blastomycosis, and chest X-rays can show fungal damage in the lungs. Needle sampling and microscopic examination of affected tissues may also provide a diagnosis, but sometimes histopathology (biopsy of the site) is required.
Since blastomyces cannot be seen and can rarely be detected in the soil, it is hard to prevent infection. Sprandel advises owners of high-risk hunting dogs to be especially vigilant regarding their pet's health, keep a watchful eye out for any early signs of infection and voice any concerns quickly to their veterinarian. The earlier the fungal infection is detected, the easier it is to treat.
To learn more about Blastomyces dermatitidis, talk to your local veterinarian.
An archive of pet columns from the UI College of Veterinary Medicine is available at vetmed.illinois.edu/petcolumns/. Requests for reprints of this article may be directed to Chris Beuoy at firstname.lastname@example.org.