Key Points:
- There have been 35 cases of histoplasmosis reported in 26 cats and 9 dogs in LA County between 2009 and December 2025. The cases all appear to be locally-acquired.
- In 20 cases (57%), the pet either died or was euthanized due to severe illness.
- Veterinarians should consider histoplasmosis in their differential diagnoses for pets that have compatible clinical signs, including indoor-only cats.
- Veterinarians in LA County are legally required to report cases of histoplasmosis to Veterinary Public Health.
- For more information, see the full Animal Health Advisory (05-29-2024) for veterinarians.
About Histoplasmosis in LA County
Histoplasmosis is an illness that can affect both people and animals. It is caused by a microscopic fungus called Histoplasma capsulatum. People can get this infection by breathing in tiny fungal spores in soil, dried bird droppings, bat droppings, or old wood. You cannot catch it directly from a sick animal or person.
This fungus can be found all over the world, but in the United States, most cases happen in the eastern half of the country. The risk of getting sick is higher in places where there are bat or bird droppings, or where the soil contains these droppings. Inhaling dust created when cutting decayed wood might also lead to infection. Cats are more likely to get this illness than dogs.
Symptoms in Dogs and Cats
It can be difficult to diagnose histoplasmosis because the symptoms are similar to those seen in many other diseases. Symptoms in dogs and cats vary, and may include:
- Loss of appetite
- Difficulty breathing
- Fever
- Weight loss
- Limping and bone pain (caused by fungus being in bones)
- Vision or eye problems (caused by the fungus being in or around the eye)
- Diarrhea (more common in dogs than cats)
- Bloody or black, tarry stool (poop)
- Skin swelling or sores
The severity of symptoms can vary. Animals may be infected and show no symptoms. In that case, the animal’s immune system might be able to fight off the fungus and keep them healthy. Animals may have severe symptoms if they inhale large amounts of the fungus, if their immune system is not strong because they already have other illnesses, or because of use of drug treatments that suppress the immune system.
Infected dogs and cats with histoplasmosis usually start to show symptoms 2-3 weeks after inhaling the fungus. This is called the incubation period. In some cases, the animal’s immune system may keep the fungus under control for a long time but not get rid of it completely – leaving the animal with what is called a “latent infection”. Animals with a latent histoplasmosis infection can start to become sick months later.
Local Histoplasmosis Cases in Pets (2009-2024)
Below is a high-level overview of reported cases of histoplasmosis in Los Angeles County since 2009. Also see the May 2024 Animal Health Advisory
Total Cases: 35 (26 cats, 9 dogs)
Outcome: 20 affected pets (57%) died or were euthanized.
Recent Cases: 4 reported in 2025.
Clinical Signs:
- Cats: Predominantly weight loss, respiratory issues, and lung lesions. Less common signs included ocular, bone, and skin lesions.
- Dogs: Common signs were chronic gastrointestinal disease with weight loss, followed by respiratory disease. Less common signs were skin and bone lesions.
Exposures:
- No pets had traveled to the eastern USA; most had no travel history outside of the area.
- Some had potential exposure to wild bird feces or recent tree trimming.
- The majority of cat cases involved indoor-only cats.
Geographic Range: Cases spread across San Fernando Valley, Crescenta Valley, San Gabriel Valley, Southeast LA County, and South Bay.
Household Clusters:
- South Bay (2009, 2013): Multiple indoor cats infected, with two deaths.
- Crescenta Valley (2009): Two outdoor cats from the same household infected and euthanized.
- San Gabriel Valley (2014): Feral and indoor cats died following tree trimming.
Reporting Histoplasmosis
Veterinarians practicing in Los Angeles County are required to report cases of Histoplasmosis.
Report cases to VPH (how to report) and include the medical records and laboratory results.
Diagnosis, Treatment & Prevention
Diagnosis
Histoplasmosis is diagnosed by a veterinarian via a combination of reviewing the clinical signs (symptoms) and response to any treatments already attempted. The most commonly used tests are:
- Antigen testing of urine and serum. Detects part of the fungus and is one of the more sensitive and least invasive tests.
- Antibody testing of serum. Less useful for diagnosis as it only indicates previous exposure to the fungus.
- Cytology or biopsy of affected tissues. The organism can often, but not always, be seen in affected tissues. Special staining techniques may be needed.
- Culture of affected tissues is possible but presents risk to laboratory workers and results make take several weeks. Warn your veterinary laboratory if histoplasmosis is suspected in a sample sent for culture.
Treatment
Histoplasmosis is treated through:
- Supportive care. Severely ill animals often need extensive supportive care. For example, animals with severe lung lesions typically require oxygen supplementation.
- Antifungal medication. Amphotericin B treatment may be needed for initial treatment of severe cases. Itraconazole is considered the first choice for treatment in most patients. Other azole drugs may be used although occasional resistance to fluconazole has been noted.
- Treatment is often prolonged. Monitoring for response to treatment, tolerance of the antifungal drug used, and Histoplasma urine antigen is helpful. Relapse is possible.
Prevention
There is currently no reliable way of preventing histoplasmosis, and there is no way to completely eliminate Histoplasma from the environment.
Since the fungal spores may be present in higher amounts in bat and bird feces, it is strongly recommended to take precautions when cleaning up bat or bird feces, especially if they are in a closed in, poorly ventilated area.
- Prevent aerosolization of the feces - do not sweep, vacuum, or kick dust into the air.
- Wear a high level of respiratory protection, like a well-fitting N95 respirator.
- Use wet cleaning methods, such as spraying disinfectant on the area before cleaning.
- Take precaution when trimming trees. Although risk of exposure has not yet been definitively linked to tree trimming, it is recommended to never inhale aerosolized wood and bark fragments, especially wood that is decayed or potentially contaminated with bird or bat feces.
Frequently Asked Questions
Yes. Histoplasmosis is caused by a fungus that grows in soil enriched with bat or bird droppings. People can become infected by inhaling fungal spores, especially when soil or droppings are disturbed.
Infection is more likely to cause symptoms in people who are immunocompromised, but healthy individuals can also get sick.
Yes. Dogs and cats can inhale fungal spores from contaminated environments and develop disease, especially in areas where histoplasmosis is endemic (like parts of the Midwest and South).
Common symptoms in pets include weight loss, coughing, fever, and poor appetite. It can affect the lungs, lymph nodes, or other organs.
No. Histoplasmosis does not spread directly from pets to people. Both humans and animals become infected from inhaling spores in the environment, not from one another.
However, pets with histoplasmosis may be a signal that the environment (such as soil or animal housing) may contain fungal spores and pose a risk to others.
Avoid allowing pets to dig in areas with bird or bat droppings, such as under trees where birds roost or in areas near old barns, caves, or chicken coops.
Keep pet enclosures clean and well-ventilated. If you must disturb soil or clean up droppings, wear a well-fitted mask and take precautions to avoid inhaling dust.