Fungus and our Pets: Blastomycosis
When I discuss infections with people and their pets, the majority of us think of bacteria. Although bacterial infections are common in dogs and cats, other bugs pose a major risk to our pet population including fungus. This update is to let you know that THE FUNGUS IS AMONG US!
What is a fungus?
Fungi are not plants nor are they animals. They are classified into their own group of infectious agents. For the most part these organisms can only be identified through the use of a microscope. Fungi are found in the environment and can cause life-threating illnesses in dogs, cats and people.
What is Blastomycosis?
Blastomycosis dermatidis is one of the more common fungal organisms that is a potential threat to your pet. Blastomycosis is mostly seen in dogs and is very rare in cats. This organism is endemic to Canada with increasingly reports along the Georgian Bay coastline (including Midland and Penetanguishene), Dryden, and in Southern Ontario.
Blastomycocsis is found in the environment in areas that generally have acidic, sandy soil, decaying wood, and animal feces. Humidity, fog, rain, and heavy dew are thought to increase the infectious nature of Blastomycosis. Living or exercising close to waterways has also been implicated as a risk factor for infection in dogs.
The organism is primarily transmitted by breathing in the fungal agent. The spores get into the lung, multiple and can distribute to the entire body. Skin or oral infection of the organism has also been reported leading to localized disease. The infection is not transmissible between humans, between animals and very unlikely from animals to humans and, therefore for the most part is not considered contagious to people if their pets become infected.
Clinical signs and Physical examination Findings
Dogs can develop an array of clinical signs. The most common is a young, male, large-breed dog that develops a cough, increased breathing rate and effort. Skin lesions that appear like little nodules some have a plaque-like appearance and commonly draining pus.
When your primary care veterinarian does a physical examination they may find enlarged lymph nodes (lymphadenopathy), inflammation in the eyes (uveitis), they may have an elevated temperature (pyrexia) and can develop lameness due to possible bone infection.
If your veterinarian has a suspicion that your pet may be infected with a fungal agent including Blastomycosis they will need to perform further diagnostic tests including blood work, radiographs (x-rays) and urine testing.
Dogs that are infected with Blastomycosis may have completely normal blood work. The main reason for performing this test is to ensure that there are no other abnormalities that need to be addressed prior to further test and treatments; kidney disease, liver disease etc. A relatively common finding on blood work is an elevated white blood cell count.
b. Radiography (x-rays)
Like blood work x-rays of the chest/lungs not definitive for a fungal infection, but certain patterns increase the level of suspicion for a fungal disease and prompt further testing. In a study of 125 dogs with Blastomycosis in their lungs, almost 60% had abnormalities noted, but it was not possible to determine if it was from bacteria or a fungus. This highlights the importance of using x-rays as a guide and to perform confirmatory tests for fungal infections like Blastomycosis.
Cytology is the study of cells. Finding and identifying the Blastomycosis organisms from a sample obtained from an infected dog: lymph node, lung, skin lesion is the gold standard and most common method of diagnosis.
d. Blastomycosis antigen
An antigen is a substance from the Blastomycosis organism that causes your dog’s or cat’s immune system to produce substances known as antibodies that fight off the infection. Up to 30% of dogs that are infected by Blastomycosis do not have detectable antibodies when they present to the primary care veterinarian. So a test was created that measures the antigen from the Blastomycosis in the urine of infected dogs. This test has a very high level of accuracy for the detection of Blastomycosis infections.
The treatment of bacterial infections with antibiotics is not a benign coarse of action, but in the majority of cases the drugs that are administered are not life threating. Anti-fungal agents on the other hand have serious side effects and the initiation of such drugs should only be performed once a diagnosis of a fungal infection has been confirmed.
Majority of the cases of Blastomycosis infections are treated with an anti-fungal agent Itraconazole (Spornax). Itraconazole works by “punching” holes in the fungus and causing it to swell and burst. In dogs, a decreased appetite is the most common adverse effect seen. Liver toxicity appears to be the most significant adverse effect and occurs in approximately 10% of dogs receiving Itraconazole, but it generally resolves following drug discontinuation. The other major issue surrounding Itraconazole is that it can be expensive depending on the weight of your dog and the duration of treatment, which in some cases can be months.
The overall treatment success has been report to be up to 80%. Unfortunately successful treatment doesn’t mean that your pet is safe from this fungus for life. A 25% recurrence rate has been documented in dogs with Blastomycosis infections, so routine follow ups examinations and blood and urine testing are pivotal in identifying recurrence before it becomes a problem.
If your pet develops any of clinical signs noted above and have traveled to areas where Blastomycosis is endemic please ask your veterinarian if further testing is warranted.
Posted by: Michael Goldstein, DVM, Diplomate ACVIM
Categorised as: Blog & Articles
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