Fungal Infection (Blastomycosis) in Dogs

Dogs with blastomycosis have a poor prognosis, with high mortality rates reported. Dogs with milder disease have a much better prognosis if aggressive and long term antifungal treatment is started at the onset of clinical signs. Dogs with severe lung and brain disease have the poorest prognosis. Relapse is also common anywhere between 3-6 months following treatment.

Blastomycosis is a potentially zoonotic disease, but it is only rarely spread from animals to humans through bite wounds. More commonly, humans are likewise exposed through inhalation, and thus an infected pet may indicate a concurrent owner exposure.

Blastomycosis is much more common in dogs than it is in cats and humans. The prevalence in dogs is approximately 1% in endemic areas. A higher number of cases are reported in dogs that reside close to water, following heavy rainfalls, and in the late summer to early fall. Certain dog breeds (such as hounds and pointers), male dogs, and hunting dogs tend to have a higher risk of infection (likely lifestyle-related).

As the fungal infection spreads throughout the body, other signs of illness might become apparent.

Blastomycosis is caused by the fungal organism, Blastomyces dermatitidis. Dogs become infected by the fungal organism by inhaling fungal spores, which are found in contaminated soil.

Initial symptoms appear weeks to months after infection.

Diagnosis of blastomycosis involves a thorough physical examination, bloodwork, diagnostic imaging (x-rays, ultrasound, CT, and/or MRI), urinalysis, and cytology or biopsy of the affected tissue/organ. Fungal culture may also be performed to identify the organism.

Dogs diagnosed with blastomycosis are treated with long term antifungal therapy, often lasting several months. Other treatments may include intravenous fluids, oxygen supplementation, pain medications, wound care and treatment, antibiotics for secondary infections, anti-inflammatory medications, and topical steroid eye drops for ocular infections. Surgery may be required for more serious infections, such as those affecting the eyes (i.e., enucleation, or surgical removal of the affected eye).

Although dogs that respond well to treatment and have milder symptoms have a good chance of recovery with long term antifungal treatment, recurrence of disease is common after treatment is stopped. Severely affected dogs have a much poorer prognosis, even with treatment, and those with central nervous system signs often die.

Avoiding high risk behaviors such as scent tracking (i.e., sniffing potentially contaminated soil) in endemic areas may help prevent infection with Blastomyces.

Blastomycosis is a potentially zoonotic disease, but it is only rarely spread from animals to humans through bite wounds. The presence of blastomycosis in dogs may indicate a concurrent owner exposure. Immunocompromised humans are more susceptible to infection. Extra preventative measures in humans, such as wearing gloves and other protective clothing, and practicing proper hand hygiene after contact with dogs affected by blastomycosis is key in human prevention.

Blastomycosis is uncommon in dogs, but it is more common than in cats and humans.

Medical treatments:

• Antifungals
• Antibiotics (for secondary infections) Supportive therapies:
• Oxygen supplementation
• IV fluids
• Pain medications
• Wound care
• Anti-inflammatories
• Topical steroid eye drops Potential surgical treatments:
• Enucleation