Feline Heartworm Statistics by State

Heartworm disease is usually discussed as a dog health issue, but cats can be infected too — and because cats are a biologically atypical host for the parasite, feline heartworm behaves differently enough that it deserves its own look at the state-by-state numbers.

The figures below come from the Companion Animal Parasite Council's (CAPC) live Parasite Prevalence Maps: real feline heartworm antigen test results from veterinary clinics and labs nationwide, year-to-date 2026.

Feline Heartworm Antigen Positivity Rate by State

Cats are far less commonly tested for heartworm than dogs — CAPC's dataset includes just 840,407 feline antigen tests nationwide year-to-date 2026, compared to 12.5 million canine tests over the same period, reflecting less routine screening in cats. Still, the results reveal a real, measurable geographic pattern.

A note on small samples: states marked "Low sample" had fewer than 2,000 cats tested, so a single positive or negative result swings the percentage sharply. Alaska, North Dakota, and South Dakota show 0.00% but each had under 2,000 tests — that likely reflects limited testing volume more than true zero risk.

Same Region as Canine Heartworm, Much Lower Rate

The geographic pattern mirrors canine heartworm closely: Mississippi (0.82%), Louisiana (0.79%), Alabama (0.58%), Arkansas (0.54%), and Texas (0.52%) lead the list, the same Deep South cluster that tops our canine heartworm statistics by state page. But the actual rates are roughly four to seven times lower than the equivalent state's canine rate. This is consistent with what veterinary parasitology has long established: cats are an atypical host for heartworm. They naturally carry far fewer adult worms than dogs, which makes infections both less common and harder to detect with standard antigen testing — but it does not mean cats are immune, and heartworm disease can still be serious or fatal in cats that do get infected.

What This Data Does and Doesn't Show

These figures reflect antigen-test positivity among tested cats, not the infection rate across each state's full cat population, and feline heartworm antigen tests are known to under-detect true infections because of cats' typically low worm burden (some infected cats never test positive on antigen tests). CAPC also tracks a separate antibody test, which detects past exposure rather than confirmed active infection and generally shows higher positivity rates than the antigen test used here.

For general national cat statistics, see our cat ownership statistics page, and for the equivalent canine data, see our heartworm statistics by state page.

The Big Picture

Feline heartworm follows the same Southeastern geographic pattern as canine heartworm — both are spread by the same mosquito vector — but at a fraction of the positivity rate, reflecting how much harder heartworm is to both acquire and detect in cats compared to dogs. That's a real biological difference, not just a testing artifact, though the much smaller number of cats tested nationwide (840K vs. 12.5M for dogs) means state-level feline figures, especially in lower-population states, come with wider uncertainty than the canine data.