D407 - Blastomyces dermatitidis

Description:

Blastomycosis is a systemic mycotic infection caused by the dimorphic fungus Blastomyces dermatitidis. In nature, Blastomyces grows in moist soil as a saprophytic mycelial form that produces infective spores. Under the appropriate conditions this parasitic fungus can release its spores into the environment, which can be inhaled by animals or humans. Young dogs that have access to the outdoors are prime candidates for blastomycosis infection, however, infection has also been described in cats, horses, ferrets, and even sea lions. Once a dog has inhaled the infectious spores, they enter the terminal airway and establish a primary infection in the lungs, transforming into thick walled budding yeast that can multiply and disseminate to other areas of the body. Because of the rarity of focal skin disease, cutaneous blastomycosis in dogs should be considered a manifestation of disseminated disease. The preferred sites of dissemination in dogs are the skin, eye, bone, lymph nodes, subcutaneous tissues, external nares, brain, and testes. Infected dogs usually have clinical signs that include fever, anorexia, weight loss, cough, dyspnea, ocular disease (40%), lameness, and skin lesions (20% - 40%). A majority of dogs (85%) with blastomycosis have lung lesions with characteristic dry, harsh lung sounds. Dogs with mild lung disease show exercise intolerance, while severely affected dogs have dyspnea at rest. Unfortunately, all breeds are susceptible to blastomycosis infection and symptoms may progress rapidly, often leading to death if early diagnosis and treatment is not provided.

Diagnosis:

Fungi are traditionally identified by morphology and metabolic charactersistics, and may require days or weeks to isolate on culture. Conclusive diagnosis of blastomycosis usually requires cytological and histopathological examination. These methods often require a biopsy and can be time consuming, allowing for continued proliferation and spread of the infection. Therefore, it is desirable to have a rapid and accurate method of identification. A PCR-based assay for the detection of Blastomyces dermatitidis is now available. For this test, our laboratory strongly recommends that veterinarians send a least two samples per dog: lung aspirates (or swab from throat) in a sterile container and whole blood (EDTA tube). Our laboratory will report each sample result independently so that the veterinarian may determine the exact location of the pathogen in the dog’s system, as well as, the stage of infection. It is very important to understand that the pathogen is first established in the respiratory system and therefore a blood sample alone is not always sufficient in detecting this infection. For this reason, lung aspirates or a swab from the throat are more suitable samples for this test in the early stages of the infection. A positive result from a blood sample will confirm the late stages of the infection.

Sample:

1. Whole Blood (3 ml) in a lavender top (EDTA) tube.
2. Throat swab or lung aspirates in a sterile container.
3. Tissue samples.

Special Handling:

Store samples at 4°C until pick up or shipment.

Test Code:

D407