Blastomycosis is an infection caused by a fungus called Blastomyces. The fungus lives in damp, sandy, acidic soil, and rotting plants and animal waste help it grow [1].
If your dog has draining lumps or sores on the skin, see your vet. If your dog has trouble breathing, see your vet now.
Where it occurs
Most cases come from North America [1]. In the United States and Canada it is tied to the river valleys of the Ohio, Missouri, Mississippi and St. Lawrence, the middle Atlantic states, and the provinces of Quebec, Manitoba and Ontario [1]. Living close to water raises the risk, and so does digging or building work that stirs up soil [1][2].
How dogs get it
Dogs usually catch it by breathing in the fungus from soil [1]. From the lungs it can travel through the blood and lymph to other parts of the body, including the skin [1]. Infection straight through the skin, for example through a wound, can happen but is rare [1].
Dogs seem to be more at risk than people, probably because they keep their nose close to the ground [1]. Young male dogs of large and sporting breeds are affected most often [1]. Even indoor pets can be exposed, for example by playing in potting soil [1].
Skin signs
About half of dogs with the disease have skin problems [1]. These can be lumps (nodules) or raised flat patches (plaques) that may break open into sores [1]. Some sores have small tracts that leak fluid, which can look like a deep skin infection, and pockets of pus can form under the skin [1]. The fluid can be thin and blood-tinged [1].
Where the skin signs appear
Skin changes can show up anywhere on the body, but the hairless tip of the nose, the face and the skin around the nails are common places [1]. When the fungus enters through the skin itself, the legs and paws are usually affected [1].
Signs beyond the skin
The signs are not specific to this disease [1]. They often include coughing or hard breathing, fever, poor appetite and, over time, weight loss [1]. Swollen lymph nodes are common [1]. Eye problems develop in a large share of dogs, and bone infection can cause lameness [1].
Can people catch it from a dog?
People and dogs usually pick up the fungus the same way, by breathing it in from the environment [1][2]. When people and dogs in one neighbourhood fall ill, health officials look for a shared outdoor source, such as riverbanks, trails or dust from building work [2]. In rare cases the fungus has entered a person’s skin through a wound such as a bite [1]. If you have questions about your own health, talk to your doctor.
How vets diagnose it
Your vet looks at your dog’s history and signs and may take chest X-rays [1]. To confirm it, the vet usually takes a needle sample or a small biopsy from a lump, a sore or a lymph node and looks for the fungus under a microscope [1]. A urine or blood test for the fungus can help when it cannot be found in a sample [1].
Treatment
Your vet will advise on treatment for your dog.
At home, as directed by a vet:
- do not open, squeeze or drain a lump or sore yourself;
- do not give your dog human or leftover medicines unless your vet says so;
- do not stop or change any medicine without talking to your vet;
- give any treatment exactly as your vet prescribes, for as long as your vet says;
- go back for any recheck your vet books.
Outlook
The outlook is generally good for dogs that get through the first week of treatment [1]. It is poorer when lung disease is severe or when the brain or heart is involved [1]. Some dogs relapse after treatment ends, and eye involvement makes this more likely, which is why rechecks matter [1].
These are statements about groups of dogs. They cannot predict how one dog will do. Your vet can explain what this means for your dog.
When to see your vet
See your vet if your dog has:
- draining lumps on the skin [1];
- sores on the nose, face or around the nails [1];
- coughing, fever, poor appetite or weight loss [1];
- swollen lymph nodes [1];
- eye changes [1];
- pain or lameness [1];
- any lump or sore you are unsure about.
See your vet now if your dog has difficulty breathing [1].
The bottom line
Blastomycosis is a fungal infection that can start in the lungs and can also cause small draining lumps and sores in the skin, for example on the nose, face or nail beds. Only a vet can find the cause with lab tests.
This article is for general information only and does not replace advice from your veterinarian. If your dog has draining lumps on the skin or a cough, see your vet.
Sources
- Torres SMF. 4.4 Systemic Mycosis: Blastomycosis, Small Animals. In: Small and Large Animal Dermatology Handbook, Vol. 1. University of Minnesota Libraries Publishing, 2025. CC BY 4.0. https://open.lib.umn.edu/animaldermatology/chapter/systemic-mycosis-blastomycosis-small-and-large-animals/
- Segaloff HE, Wu K, Williams SL, et al. Human and Canine Blastomycosis Cases Associated with Riverside Neighborhood, Wisconsin, USA, December 2021 to March 2022. Emerging Infectious Diseases (CDC). 2024;30(12):2633-2638. https://doi.org/10.3201/eid3012.240390