By Dr Duncan Houston
A cat with breathing changes, weight loss and unusual skin or eye problems may need investigation for a disease affecting more than one organ. Blastomycosis is one possibility, especially after living in a region where the fungus occurs.
It is less common in cats than dogs. That makes the history and appropriate diagnostic testing especially important.
Quick Answer
Blastomycosis is an infection caused by Blastomyces fungi, usually acquired by inhaling environmental spores. It can begin in the lungs and spread to the eyes, skin, nervous system or other tissues. Breathing difficulty, neurological signs or sudden vision loss needs urgent care; confirmed infection generally requires prolonged antifungal treatment and monitoring.
Where does exposure occur?
The fungus is associated with soil and decaying organic material. Important endemic regions are in North America, including areas around major river valleys and the Great Lakes. Tell the vet where your cat has lived and travelled, even if you have since moved elsewhere.
Cornell's feline blastomycosis guidance explains the environmental route and geographical context. A cat does not need to have recently fought with another animal to acquire infection, and indoor status does not completely rule it out.
Which signs should prompt assessment?
Possible signs include poor appetite, fever, weight loss, rapid breathing, cough, skin nodules or draining lesions, lameness and eye inflammation. Some cats develop neurological abnormalities. Not every cat has all of these signs.
| Signs | Action |
|---|---|
| Persistent weight loss, poor appetite or unexplained skin lesions | Arrange prompt veterinary assessment and provide travel history. |
| Eye redness, squinting or a new limp with systemic illness | Seek same-day advice. |
| Laboured breathing, seizures, collapse or sudden blindness | Go to an emergency clinic immediately. |
What else could it be?
Bacterial infection, asthma, cancer and other fungal infections can produce overlapping findings. Histoplasmosis is particularly relevant when interpreting some fungal antigen tests because cross-reactions occur. A positive screening result needs to fit the full picture.
How is the diagnosis confirmed?
Chest imaging assesses lung involvement, while examination checks eyes, skin, lymph nodes and other affected areas. Identifying fungal organisms in cell or tissue samples can establish the diagnosis. Antigen testing and molecular tests may help, with their limitations explained by the vet.
The ABCD blastomycosis guideline describes current feline testing and treatment evidence. Fungal culture requires appropriate laboratory precautions and is not a home or routine in-clinic experiment.
What does treatment involve?
Systemic antifungal medication is usually needed for months, with the choice influenced by the sites affected and the cat's response. Itraconazole is commonly used; severe disease or involvement of the eyes or nervous system may require a different or combined approach. Hospital support may be necessary for oxygen, nutrition or other complications.
The outlook depends on organ involvement and severity. Feline studies are limited, so a dog's treatment result should not be treated as a prediction for your cat.
What should you do at home?
- Give the prescribed formulation exactly as directed; do not substitute products without checking.
- Monitor appetite, breathing at rest, activity and any skin or eye changes.
- Attend blood-test and imaging reviews to assess response and medication tolerance.
- Report deterioration promptly rather than waiting for the next appointment.
- Continue until the vet confirms the treatment endpoint, even if outward signs improve.
Common mistakes and prevention
Avoid assuming a draining lesion is always a bite abscess, relying on one screening test without confirmation, or stopping antifungals early. Restricting access to contaminated outdoor environments may reduce exposure in endemic areas, but there is no guaranteed preventive routine. Use normal hygiene and avoid direct contact with draining lesions.
Frequently Asked Questions
Can I catch it by living with my cat?
Ordinary contact is not the usual route; people and cats mainly acquire it from the environment. Use sensible hygiene and follow veterinary advice for lesions.
Can it affect the eyes?
Yes. Eye involvement may threaten vision and requires prompt assessment.
Is a positive antigen test enough?
Not always. Cross-reaction with other fungi and the clinical findings must be considered.
Can treatment stop when my cat looks better?
No. The infection may persist after visible improvement, so follow the planned reviews and endpoint.
A complete exposure history and a confirmed diagnosis make treatment more targeted. Consistent follow-up is a major part of recovery.
For more practical animal health information, explore ASK A VET™. Your own veterinary team can help tailor the next steps to your cat or dog.
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- Blastomycosis
- Cats
- Fungal Disease
- Respiratory Health
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