Is Blastomycosis the Same as Valley Fever?

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Is Blastomycosis the Same as Valley Fever?

Recently, we posted an article about Valley Fever, which triggered the question, “Is Valley Fever the same disease as Blastomycosis?” We can see how the confusion arose, so we decided to explore the similarities and differences.

Blastomycosis and Valley Fever are both fungal infections.

However, they are different because the fungus causing each disease is different. The fungus causing Blastomycosis is Blastomyces dermatitidisThe fungi causing Valley Fever are fungi Coccidioides immitis and C. posadasii.


Each disease is known at this time to be endemic in different parts of North America. The Valley Fever fungi are predominantly found in the Southwestern United States and in South Central Washington state.

The Blastomycosis fungus mainly lives around Canada and the area of the United States surrounding the Great Lakes, and the Ohio and Mississippi River Valleys. Thus, the ambient environment most likely
affects where these fungi thrive.

When soil is disturbed, both fungi become airborne so that inhalation is the primary route of infection. Rarely, infection can occur from direct fungal contact.

Symptoms in Dogs

Valley FeverBlastomycosis
CoughingDifficulty breathing (coughing, wheezing and other unusual breathing sounds)
Weight lossWeight loss
Lack of appetiteLack of appetite
Reduced energyEye discharge
Rashes on skin and extremitiesSkin lesions that are frequently filled with pus
Can develop into pneumoniaEye inflammation – specifically of the iris
Disseminated Valley Fever: lameness or swelling of limbs, back or neck pain (with or without weakness/paralysis), seizures and other manifestations of brain swelling, soft abscess-like swelling under the skin, swollen lymph nodes, non-healing skin wounds that ooze fluid, eye inflammation with pain or cloudiness, unexpected heart failure in a young dog, and swollen testicles.


Both diseases are often misdiagnosed. Valley Fever is usually diagnosed through a blood test (Coccidioides IgG and IgM antibody screen and titer) and sometimes with chest, bone or joint x-rays. Confirmation can be obtained, if needed, by Real-Time PCR testing for the organism.

On the other hand, Blastomycosis is best diagnosed by an examination of lymph nodes’ cells, fluid analysis from skin lesions, a tracheal wash that collects windpipe fluids or an examination of lung tissues. Other tests for Blastomycosis include tissue samples that detect the presence of fungal organisms, urine analysis, and lung x-rays. Confirmation can be obtained, if needed, by Real-Time PCR testing for the organism.


Valley Fever and Blastomycosis are both treated with oral antifungal medications. However, the length of time is different. Valley Fever treatment lasts 6-12 months. Dogs with disseminated Valley Fever usually require longer courses of medication. If the central nervous system is affected, lifetime treatment with medication is typically needed to stop symptomatic recurrence. For Blastomycosis, the treatment time is a minimum of 60 days, or 30 days after symptoms have disappeared.

W. Jean Dodds, DVM
Hemopet / NutriScan
11561 Salinaz Avenue
Garden Grove, CA 92843

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