California: Locally acquired histoplasmosis in 18 cats and 6 dogs in Los Angeles County from 2009-2024
Los Angeles County Veterinary Public Health reports that from 2009 to 2024, the county has reported 24 cases of histoplasmosis- in 18 cats and 6 dogs- in which 18 cases (75%), either died or was euthanized due to severe illness.
Five of these cases were reported since the beginning of 2024.
Officials say all cases appear to have had locally acquired infection within LA County.
The cases were reported from a wide geographic range, including in the San Fernando Valley, and the Crescenta Valley, the San Gabriel Valley, Southeast LA County, and the South Bay area.
Veterinary officials described the the clinical signs of the animals, which were variable:
18 cases in cats: the majority had weight loss followed by respiratory signs and/or visible lesions in lungs seen on thoracic radiographs, 5 had ocular signs, 3 had bone lesions and 1 had skin lesions. Only a few had a documented fever. Just under half were tested for feline leukemia (FeLV) and feline immunodeficiency (FIV) viruses and were mostly negative, although one cat had an equivocal result on an FIV test.
6 cases in dogs: 5 had a documented fever, 4 had gastrointestinal signs, 3 had respiratory signs, 2 had skin lesions, and 1 had bone lesions.
It is unclear how these animals were exposed to the fungus. None of the pets had any travel to the eastern half of the USA, and most pets had no reported travel at all. There were no reported bat roosts linked to the cases. In a few cases, pets did have direct or indirect access to wild bird feces. In several cases there was a tree-trim near the house in the month before illness occurred, and it is possible that fungal spores were aerosolized from bat or bird feces in the trimming process, but the significance of this exposure is not known. One of the more striking findings was that 13 of the 18 cat cases (72%) occurred in indoor-only cats.
LA County veterinarians may be unaware that cases can occur locally.
Histoplasmosis is an illness in humans and animals caused by an infection with the fungus Histoplasma capsulatum. Infection most typically occurs when fungal spores in aerosolized soil, dried bird feces, bat feces, or potentially decayed wood are inhaled into the lungs. It is not transmissible directly from an infected animal to another animal or to a person. Cats are considered to be more susceptible to infection than dogs.
This fungus is found in the environment worldwide. However, in the USA, infections and illness caused by Histoplasma are most commonly reported in states in the eastern half of the USA. Risk of infection is higher in environments contaminated with bat or dried bird feces, or where soil is enriched with such feces. There is evidence that exposure to aerosolized decayed wood might cause infection.