By Dr Duncan Houston
Weight loss, persistent fever and faster breathing can be signs of several illnesses. In a cat with relevant exposure, histoplasmosis belongs on the list.
This fungal infection can spread beyond the lungs, so skin, eyes, bone marrow or digestive signs may be part of the same disease.
Quick Answer
Histoplasmosis is usually acquired by inhaling fungal particles from the environment. Cats may develop lung disease or infection affecting multiple organs. Diagnosis combines tissue or cell samples with appropriate antigen testing; treatment usually takes many months and should not stop simply because the cat looks better.
Where does the infection come from?
Histoplasma is associated with soil and organic material, including areas contaminated by bird or bat droppings. It occurs worldwide, with particular endemic regions. Travel history and environmental exposure matter, but indoor living does not completely exclude infection.
The Merck review of animal histoplasmosis describes inhalation as the usual route. The disease is not normally transmitted directly from a sick cat to another pet or person. Shared environmental exposure is the more relevant concern.
How is it confirmed?
A vet may sample an enlarged lymph node, skin lesion or other affected tissue and look for the organism microscopically. Urine antigen testing can be useful, but a routine urine dipstick is not this test. Some fungal antigen tests cross-react with other fungi.
Blood tests, chest imaging and an eye examination help map the affected organs. A negative result does not settle every case; additional testing may be needed if the pattern remains suspicious. Tell the clinic about past residence and travel, even if the move was not recent.
What does treatment involve?
Prescription antifungal treatment, often itraconazole or another drug chosen for the sites involved, is usually prolonged. Severe illness may require hospital care and additional treatment. Appetite, weight and medicine tolerance need monitoring alongside laboratory results.
Stopping treatment is a clinical decision based on recovery and follow-up testing, not a fixed calendar date. Relapse is possible. Merck’s feline fungal infection guidance explains why widespread disease requires both antifungal and supportive care.
How worried should you be?
| What you notice | Why it matters | What to do |
|---|---|---|
| Persistent weight loss or fever, comfortable breathing | Chronic disease needs investigation | Arrange a veterinary appointment promptly. |
| Poor intake, eye changes or worsening weakness | More extensive organ involvement is possible | Contact your vet today. |
| Laboured or open-mouth breathing, collapse or seizures | Potential critical disease | Seek emergency care now. |
What else could explain these signs?
Cancer, other fungal infections, bacterial infection, FIP and several inflammatory disorders can resemble histoplasmosis. Respiratory signs also overlap with heart disease and asthma. Geographic history guides testing but cannot establish the diagnosis alone.
When is this an emergency?
Breathing effort, open-mouth breathing, blue-grey gums, collapse or seizures requires immediate care. Keep handling minimal and call ahead. A suddenly painful eye or loss of vision also needs urgent assessment because infection can damage sight.
What should you do next?
- Record weight, appetite, breathing changes and any eye or skin lesions.
- Provide complete travel, outdoor access and medication history.
- Give the exact prescribed antifungal formulation; do not substitute products without checking.
- Attend rechecks for treatment response and possible adverse effects.
- Contact your vet if eating deteriorates, vomiting develops or signs return after improvement.
Common mistakes to avoid
- Treating every positive fungal test as uniquely diagnostic.
- Stopping medication when appetite first returns.
- Trying household antifungals or essential oils.
- Disturbing bird or bat accumulations while trying to clean the environment.
Prevention and ongoing care
Limit access to contaminated soil, demolition dust and bird or bat roosts. Significant droppings accumulations need appropriate professional advice rather than casual dry sweeping.
There is no routine vaccine that prevents feline histoplasmosis. Reducing exposure is helpful but cannot guarantee prevention.
Frequently asked questions
Can I catch histoplasmosis from my cat?
Direct transmission from the cat is not the usual route. People and animals can be exposed to the same contaminated environment.
How long does treatment take?
Often many months. Your vet uses clinical progress and follow-up testing to decide when stopping is appropriate.
Can indoor cats get it?
Yes. Indoor status lowers some exposures but does not rule it out.
Does every cat recover?
No. Many respond, but severe disseminated disease and organ complications can make the outlook guarded.
Histoplasmosis is treatable, but it needs a confirmed diagnosis and patient follow-through. Persistent weight loss or respiratory changes deserve investigation, and difficult breathing should never wait.
For more practical animal health information, explore ASK A VET™. If your animal has emergency signs, contact a veterinary clinic immediately.
The ASK A VET™ Tracker logs live location and activity trends, so a change in routine never goes unnoticed.
- Cats
- Fungal Infections
- Histoplasmosis
- Pet Health
Every ASK A VET article is written and reviewed by qualified veterinarians.
