Blastomycosis and dog bites
I just received this comment from a reader of an earlier post about blastomycosis:
What should be done if a person was bit by a dog with blasto? I was trying to pill a dog who has blasto and the dog just out of reflex shut her mouth on my finger. What are the chances of the blasto being transmitted to me?
It's a reasonable question and one that I get periodically. If the bite didn't break the skin, the risk is essential nil. If the bite broke the skin, the risk is still fairly low, but certainly not zero.
Simple contact with an infected dog cannot result in transmission of blastomycosis because Blastomyces is a dimorphic fungus, meaning it can take the form of either a mold or a yeast. The highly infectious mold form is found in soil at ambient temperatures, while the minimally transmissible yeast form is present in the body of an infected animal or person. However, bites can be a different story. A bite from a dog with advanced pulmonary blastomycosis (e.g. fungal pneumonia due to Blastomyces) can result in localized blastomycosis at the site of the bite (e.g. only the person's finger might get infected).
Considering the dog in this case was already being treated for the infection (and therefore hopefully was not shedding much of the fungus), and that there are very few reports of bite-associated blastomycosis, the risk is probably quite low. However, any bite that breaks the skin can result in infection from the multitude of bacteria in an animal's mouth. Any bite on the hand should be taken seriously because it's easy for sensitive structures like joints and tendon sheaths to become infected. Consulting your physician or getting medical attention is recommended.
More details about general issues regarding animal bites are available in our bites archives. Relevant information is also available in the Cat Bites information sheet on the Worms & Germs Resources page.
Photo: Light micrograph of the budding yeast form of a fungus.
Don't forget fungi: Blastomycosis in dogs
Most of the infectious disease topics that we've covered on Worms & Germs involve bacteria or viruses. Fungal diseases (other than ringworm) are often overlooked because they are less common, and because they tend to be more of a concern in certain areas only. However, when fungal infections occur they can cause serious problems.
Blastomyces dermatitidis is a dimorphic fungus (meaning it can exist in the form of a mold or a yeast) that lives in the soil in some areas. It is more common in wet, sandy, acid soils that have a high organic content. Animals (and people) can become infected by exposure to the mold form of the fungus in the soil. If the fungal spores are inhaled, it can result in severe pneumonia. Blastomycosis (infection with Blastomyces) can be difficult to diagnose and very difficult (and expensive) to treat. So while blastomycosis is rare in general, it is still an important disease, especially in areas where it is more common.
Recently, a study was published in the journal Medical Mycology (Chen et al, 2008, 46: 843-852), regarding blastomycosis in dogs in Tennessee. This was a case-control study that compared dogs with blastomycosis to dogs that did not have the disease. Here are some of the results:
- Male dogs were 2.7 times as likely to be affected as females.
- Working and sporting dogs were at higher risk (4.6 and 6.2 times as likely, respectively).
- Dogs 2-4 years of age were at highest risk.
- Close proximity to water was also a significant risk factor for infection.
In Ontario, blastomycosis seems to be most common around Georgian Bay. In the US, it is more common in central and northern states, with most cases reported in Wisconsin, Tennessee, Mississippi, Kentucky and Arkansas.
Blastomycosis can also occur in people, but blastomycosis cannot be transmitted from dogs to humans (or between any animal species). Only the mold form of the fungus that lives in the soil is infectious.
