Blastomycosis comes from the ground, not from other animals. Dogs and people breathe in spores that are released when damp soil, leaves or rotting wood are disturbed.
What releases the spores
- Digging and sniffing. Dogs are especially at risk because they put their noses in the dirt and dig.
- Construction and excavation. Outbreaks have been linked to building sites and other work that moves soil.
- Yard and trail work. Gardening, landscaping, clearing brush and moving leaf piles or wood.
- Outdoor recreation. Camping, hunting, fishing and hiking near water.
- Weather. The CDC says high winds can raise risk. Vets note that rain, dew or fog may help release the spores.
Less often, the fungus enters through a cut or puncture wound in the skin.
What about water, puddles and streams?
Drinking water: We found no health agency or veterinary source saying dogs or people catch blastomycosis by drinking water. Infection comes from breathing in spores. Still, don’t let your dog drink from puddles or stagnant ponds, because they can carry other infections.
Streams, ponds and shorelines: The risk is the wet ground around the water more than the water itself. The fungus favors moist, organically rich soil, silt and rotting leaves along riverbanks and shorelines. A Vermont veterinary team put it this way: swimming is considered safe, but “kicking up silt along shorelines and sniffing can stir up blastomycosis organisms.”
Mud and puddles: No study has looked at puddles specifically. But muddy ground in the woods or near water is the kind of moist, leafy soil the fungus prefers, so treat it with the same caution.
After floods: The same Vermont vets suspect floodwater may carry spores onto silty shores, and they recommend keeping dogs away from shorelines and sandy areas that have recently flooded. This is their suspicion, not a proven finding.
Contaminated areas: There’s no test to tell which spots carry the fungus, so you can’t know for sure where it is. A clue is a cluster of cases. In 2021–22, 5 people and 6 dogs in a Wisconsin neighborhood beside the Willow River got sick, and one person died. Homes were a median of 342 meters from the river. Investigators couldn’t pin down one source but pointed to the riverbank, riverside trails and yards, and dust from nearby construction. If a dog or person near you is diagnosed, be extra careful around the same riverbanks, trails and building sites.
Is it contagious?
No, in almost all cases. It does not spread from person to person or from dog to dog, and dogs don’t give it to people by coughing. The CDC notes very rare cases of spread through animal bites or needle-stick injuries.
If you’re caring for a dog with draining skin sores, wear gloves, wash your hands afterward and don’t let pets lick broken skin. Follow your vet’s advice on caring for the wounds.
Your dog can be an early warning
Your dog can’t infect you, but you may have walked the same ground. The New York State Department of Health says dogs “can act as an early warning sign.” If your dog is diagnosed, watch for symptoms in yourself and your family. If you develop a cough, fever or pneumonia that isn’t getting better, tell your doctor about your dog’s diagnosis.
How long until symptoms?
- People: 3 weeks to 3 months after breathing in spores.
- Dogs: from a few weeks to several months.
Think back over the past few months, not just the past few days, when you tell your vet or doctor where you’ve been.
Blasto Awareness shares public information for awareness only. It is not veterinary or medical advice. Sources: CDC; Merck Veterinary Manual; NYS Department of Health; Wisconsin Department of Health Services; Ontario Animal Health Network; Purina Pro Club. Full list on the Sources page.