Cornell Study: High-Risk Feline Coronavirus in US Cats Since 2013
A March 2026 Cornell study found FCoV-2 with spike deletions like Cyprus's deadly FCoV-23 in US cats from 2013 and 2016. What it means, plus FIP warning signs.
A Cornell study published on March 6, 2026, in the Journal of Feline Medicine and Surgery found a high-risk type of feline coronavirus, FCoV-2, in archived samples from three US cats from 2013 and 2016 (Olarte-Castillo et al., JFMS). Cornell announced the results on April 27, 2026, describing a lethal variant once thought to be confined to a 2023 outbreak in Cyprus (Cornell College of Veterinary Medicine). This is a look back at old samples, and it does not report an active US outbreak. For your cat, the practical question is FIP: know the signs, and see a vet quickly if they appear, because FIP is now treatable (Cornell Feline Health Center).
Status as of October 14, 2026: the latest verified update is Cornell’s April 27, 2026 news release. No later Cornell announcement or report of a US outbreak of this virus could be found. Cornell researcher Gary Whittaker holds a Morris Animal Foundation grant running from April 2026 to March 2028 to study a related FCoV-2 spike mutation (Cornell).
What the study found
Most feline coronavirus belongs to type 1. Type 2 (FCoV-2), thought to be a hybrid of feline and canine coronaviruses, causes about 5% of FIP cases worldwide, and the virus behind the Cyprus outbreak, called FCoV-23, is a type 2 virus (Cornell). FCoV-23 carries a deletion in the front end of its spike protein, a region called domain 0 (JFMS abstract).
The Cornell team sequenced 20 tissue, fluid and fecal samples from three US cats with FCoV-2 (JFMS abstract):
| Cat | Year | Illness | Spike gene |
|---|---|---|---|
| Cat 344 | 2013 | Signs for at least 2 months | Deletion in domain 0 |
| Cat 346 (daughter of cat 344) | 2013 | Euthanized shortly after showing signs | Intact (long) spike |
| Cat 597 | 2016 | Signs for at least 2 months | A different deletion in domain 0 |
The authors suggest that FCoV-2 with the long spike passes from cat to cat, while the shortened version arises inside each cat after a long infection and then spreads through the body (JFMS abstract). The abstract describes the US viruses as FCoV-2 and refers to FCoV-23 as the Cyprus variant. Cornell presents the role of domain 0 in transmission as a working model.
Why the US hasn’t seen a Cyprus-sized outbreak
The Cyprus outbreak in 2023 killed thousands of cats (Cornell). The US cases Cornell studied came mostly from single-cat households, which the researchers think may explain the difference, and they warn that growing shelter and free-roaming cat populations could change it (Cornell). They also say that telling type 1 from type 2 in a clinic is hard today, and that the team is working on rapid tests.
FIP: which cats are at risk
Feline coronavirus is everywhere, and most infected cats never develop FIP. Between 5% and 10% of cats exposed to the common enteric form go on to develop FIP, sometimes weeks and sometimes years later (Cornell Feline Health Center). Young cats carry most of the risk: about 70% of cases occur in cats under 18 months, and half in kittens under 7 months. Cats from shelters, catteries and other crowded homes also appear more susceptible (same source).
When to see a vet
FIP starts with signs that look like many other illnesses: poor appetite, weight loss, depression and fever. It then takes one of two forms (Cornell Feline Health Center):
- Wet (effusive) FIP: fluid builds up in the belly or chest, giving a pot-bellied look and sometimes making breathing hard. It tends to progress quickly.
- Dry (noneffusive) FIP: it can affect the nervous system, causing seizures and wobbly, uncoordinated walking. It tends to progress more slowly.
Go to a vet or emergency clinic now for labored or open-mouth breathing (see our guide to panting in cats), a seizure, or a sudden loss of coordination.
Book a visit within a day or two for a swollen belly, a fever, weight loss, or a young cat that has gone off its food (why a cat stops eating). Mention it if your cat came from a shelter or lives with other cats.
Speed matters more than it used to. GS-441524, the most studied FIP drug, appears safe and effective and is now available in the US as an oral compounded medication with a veterinary prescription (Cornell Feline Health Center). Unregulated online versions vary in strength and purity (same source). Cornell’s researchers add that treatment should start right away when a high-risk infection is suspected, and that a vet who finds type 2 should also act to keep it from spreading to other cats (Cornell).
For other cat health and safety alerts, see our coverage of H5N1 bird flu in raw cat food and the full list of recalls and safety alerts.
Sources
- Olarte-Castillo XA et al. Identification of within-host deletions in domain 0 of the spike gene of pathogenic feline coronavirus type 2 from the USA. Journal of Feline Medicine and Surgery, 2026;28(4)
- Cornell College of Veterinary Medicine: Deadly feline coronavirus variant has been present in the U.S. for over a decade (April 27, 2026)
- Cornell Feline Health Center: Feline Infectious Peritonitis
- Cornell College of Veterinary Medicine: A Novel FIP-Linked Internal Mutation Associated with FCoV-2 (research award)
