After an unprecedented outbreak of a deadly cat disease in Cyprus in 2023, it is finally clear what was behind it: Researchers have identified the cause of the so-called "feline Covid" - and surprisingly, a canine coronavirus plays a central role in this.

The outbreak, in which thousands of cats fell ill with an unusually aggressive form of feline infectious peritonitis (FIP), made international headlines. Normally, FIP is a rare, usually non-communicable disease in cats that develops from a mutation of the harmless feline coronaviruses. But in the summer of 2023, there was an exceptionally sharp increase in these cases in Cyprus - with dramatic consequences for the cat population. 

An international research team led by Dr. Charalampos Attipa from the University of Edinburgh has sequenced and analyzed the pathogen. The result: The deadly variant called FCoV-23 is a recombination virus – i.e. a genetic mixture of a feline coronavirus and a so-called pantropic canine coronavirus (pCCoV). This dog virus is known to infect many tissues of a host. By absorbing part of the RNA of the dog virus strain, 

the cat virus has changed in several ways:

confirming a finding that had previously only been speculated: this virus is not simply a common mutation, but a hybrid virus whose properties go beyond the known behavior of normal feline coronaviruses. 

Earlier media reports about allegedly "300,000 dead cats" were based on rough projections and were scientifically doubted. Official veterinary data shows that in the period from January to August 2023, about several thousand cats presented to clinics with FIP symptoms. This is exceptionally high for this disease in itself, but it casts doubt on the extreme figures in the press. 

In addition, many of the affected animals did not have access to veterinary care – large parts of the stray cat population in Cyprus were involved. This makes it difficult to reconstruct a reliable mortality figure. 

During the epidemic, veterinarians initially had no clear treatment options. FIP was long considered virtually incurable, and drugs were expensive and difficult to obtain. The government eventually resorted to antiviral drugs, including drugs that were also used in humans to treat Covid (e.g., molnupiravir or GS-441524).
 
Although

current FIP case numbers have fallen, they are still above pre-2023 levels – partly because cats have developed a certain immunity and treatments are now routinely used. 

The big question remains: How could the virus develop?
The research shows that the recombination probably took place in a previously unidentified intermediate host – i.e. in an animal that carries both feline and canine coronaviruses. One theory is that animals from the Middle East may have introduced the hybrid virus to Cyprus, where it encountered a very dense stray cat population. 

One thing is clear: such recombinant coronaviruses do not simply arise "out of nowhere". They are the result of natural evolutionary processes that often occur in RNA viruses – especially coronaviruses. 

So far, there is no evidence that this cat-dog hybrid is transmissible to humans. The coronaviruses that infect cats and dogs belong to the same extended family as SARS-CoV-2, but have a different species specificity. Nevertheless, studies show that these viruses can basically recombine, which makes them particularly dynamic in the animal world. 

The mystery of "cat Covid" has been solved:
 A novel recombination virus (FCoV-23) between a feline and a canine coronavirus has enabled the severe FIP outbreak in Cyprus.
What we learn from this:

More on the topic Animals in Cyprus
Protest against the eviction of 2,000 animals from the Paphos
animal shelterAnimal shelter in Paphos on the verge of closure – dispute over animals, licenses and responsibility