Here’s a summary of the most recent and significant diseases affecting cats in the United States, including new outbreaks, emerging threats, and ongoing concerns vets are watching in 2026.
Avian Influenza (Bird Flu) – Highly Pathogenic H5N1
There have been confirmed H5N1 infections in domestic cats, including at least one reported death in Washington state in early 2026 from bird flu.
The case surfaced after a San Francisco pet became ill and was euthanized. Tests tied the virus in the cat to the same virus in bags of RAWR Raw Cat Food Chicken Eats. [Earth.com, Adrian Villellas – FDA issues health alert for raw pet food contaminated with avian influenza]
Feline Infectious Peritonitis (FIP) — Coronavirus-Related
Feline infectious peritonitis, caused by a mutation of feline coronavirus, remains a serious and often fatal disease in cats unless treated appropriately.
Researchers at the University of California, Davis, have uncovered new details about how a once-deadly coronavirus disease in cats spreads through the immune system. The findings may help scientists better understand long COVID and other long-lasting inflammatory illnesses in people. [UCDavis.edu, Amy Quinton, January 12, 2026 – Cat Disease Challenges What Scientists Thought About Coronaviruses – Study Finds Viruses May Hide and Persist in Immune Cells]
Parasitic and Vector-Borne Diseases
Heartworm disease: Cats can be infected by a single mosquito bite. While less common than in dogs, heartworm incidence in cats has been noted, especially in warmer states.
Certain US states saw elevated rates of parasite-borne illnesses in cats and dogs last year, according to 2024 data from the Companion Animal Parasite Council, a nonprofit organization focused on bringing awareness to the risks posed by parasites. Although parasite-related illness rates in dogs and cats varied by state, these organisms affect all states, including during the winter months. [DVM360.com, Abi Bautista-Alejandre, April 3, 2025 – States with the highest cases of parasite-borne diseases in cats and dogs]
Recommended Reading
Cat Owner’s Home Veterinary Handbook, Fully Revised and Updated
For years, many veterinary treatments for cats were based on research conducted with dogs because it was wrongly assumed that cats were very similar. Recently, there have been giant strides in feline veterinary research. This classic reference is fully updated and revised to reflect these advances and gives you the most up-to-date guidance on cat health and cat care. It includes:
- An index of signs and symptoms to help you find information fast
- Clearly written, step-by-step directions for handling common feline ailments and problems
- Hundreds of photos, drawings, and tables that illustrate what to look for and how to provide the best care for your cats
- All new anatomical drawings and diagrams
- New information on genetics, geriatrics, drug sensitivities, raw diets, arthritis medications, dental disease, and more
- Information on supplements, nutraceuticals, and holistic treatments that have proven beneficial
- Interesting findings on cat behavior
- Whether you have a kitten or a senior cat, this resource helps you quickly identify potential problems, take proper steps in emergency situations, better understand diagnoses and treatment options, and communicate more effectively with your veterinarian. This is the hands-on reference you’ll trust again and again.
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