I’ve held off writing about this unusual outbreak of cat deaths on the island of Cyprus for a few reasons, a big one being a lack of clear information, but the situation has drawn a lot of attention.

In general, when we have reports of strange disease events, there are a few scenarios to consider:

  1. It’s a completely new disease
  2. Something has change regarding an known disease
  3. It’s a known disease doing what it normally does, but circumstances have led to a unique local, short term situation
  4. It’s a known disease doing what it normally does, but with more attention being paid to it

All of these happen. I’d say that numbers 3 and 4 are most common, with number 4 being particularly common due to amplification of routine disease situations by social media.

What’s going on in Cyprus?

Clear details have been pretty sparse, so I think it could still be any of these scenarios.

How many cats have been affected?

The story started around January 2023, with subsequent reports of “thousands” of cats dying in Cyprus. There appears to be some debate about the scope of the problem. One claim is that 200,000-300,000 cats, or roughly 20-30% of the cat population on the island, have died.

However, that claim has not been substantiated, and it has been suggested that the actual number of deaths is less than 10,000. That’s still a lot of cats, so clearly significant, but some context is needed.

  • How many feral cats normally die every week in Cyprus?
  • Is this mortality rate higher than normal, or are people just paying more attention to it?
    • If the true number of cats that have died is around 10,000, that would be approximately 1% mortality, and a 1% mortality rate over a few months is actually on the low side for what would normally be expected in such a population.

Those are key initial questions that need to be answered to help us determine if we actually have something different happening on the island.

What’s the cause?

The outbreak was quickly attributed to feline infectious peritonitis (FIP). This didn’t make a lot of sense based on what we know about FIP, which is caused by feline coronavirus (FCoV). The disease develops in a small minority of infected cats, when the FCoV mutates to become more virulent. FCoV is very common, especially in large cat populations. If you have more than 10 or so cats in a group (e.g. shelter, colony, feral cats), it’s almost certain that one or more of them are infected. So, finding FCoV in dead cats is not surprising. We’d find lots of it in live cats, too.

FIP outbreaks are uncommon, though. When they occur, they are usually small outbreaks associated with some local factors in the cat population (e.g. age, genetics, health status) that make a small group of cats more likely to develop FIP. A country-wide outbreak, even in a small country, would be pretty surprising.

Diagnosis of FIP involves more than just finding the virus. We have to figure out if it’s actually causing disease. I haven’t seen details about how the diagnosis of FIP has been made in these cases. It could be that a large number of cats have been solidly diagnosed with FIP, a small number of cats amongst a large number of untested dead cats had FIP, or that there wasn’t actually any solid diagnosis of FIP (and someone was just guessing).

The question is whether FCoV is causing disease or it’s just there, and whether any cats with FIP were representative of the outbreak or there were just some cats with FIP alongside something else. That’s what’s unclear to me. I’ve heard that FCoV from some infected cats is being sequenced, which is a great start. This will help determine if there’s something unique about the virus in these cats and if it’s one strain that’s present in the majority of affected cats.

A good epidemiological investigation to define what’s happening is key to sorting out situations like this, but often, that gets neglected (or at least done superficially). With a better understanding of the situation and context regarding how it compares to normal, we’re better able to target the laboratory investigation and figure out what we need to do to contain the outbreak. Hopefully that’s underway.

There was also a recent report that extra COVID-19 drugs are being used in some cats on the island. Details are sparse and it’s hard to see how that will help much in the context of an outbreak. Some COVID-19 drugs (mainly remdesivir) have great promise for treatment of FIP, which is usually a fatal disease in cats. However, while it will help the small number of sick cats that get access to the drug, it won’t help stop the outbreak since it will have no impact on transmission within the population. It’s circulation of the wild-type FCoV that’s the problem, and treatment of a handful of cats with FIP won’t do anything for that. Presumably they’re not treating healthy cats preventatively, since that probably wouldn’t help anyway, would require a massive amount of drug, would be impractical for feral cats (that would be the main reservoir) and, depending on the drug, might just be setting the scene for harmful mutations (especially if molnupiravir is used).

If this is something new, what do we have to do?

The first step is make a diagnosis. We need to know whether this is a new version of FCoV, a new disease or whether it’s just normal viruses doing their normal things. Until we know that, it would make sense to ban importation of cats from Cyprus.