My cat recently died because it had FIV, which I was told was like AIDS in people. Can cats spread viruses to humans?
Cats are very susceptible to viral infections, but with the exception of rabies, cat viruses generally don’t infect humans. However, the emergence of covid-19 and new types of influenza has raised concern about cats spreading viruses to humans — and even sparking another pandemic. Here’s what you need to know.
The main viruses that lead to illness in cats
Rabies and panleukopenia viruses rarely cause disease because of vaccination. But there are other viruses of concern. None of these infect humans, but some — like feline herpesvirus and FIV — cause diseases that resemble those seen in humans. Others rapidly develop mutations, generating new strains that can either cause more severe disease or potentially jump from one host species to another (such as from cats to dogs, or cats to humans).
Respiratory viruses
Anyone who has visited an animal shelter has probably seen cats that have watery or thick discharge coming from their eyes and nose. These signs usually indicate herpesvirus or calicivirus infections. Calicivirus can also cause chronic gingivitis and mouth ulcers, which are painful and stop cats from eating.
Most cats are vaccinated for both diseases, but as with many human respiratory diseases, vaccines don’t completely prevent disease — they just reduce severity of illness.
Virtually all cats get infected with herpesvirus as kittens. Like cold sores and shingles in humans, stress — such as overcrowding in a shelter, a visit to the vet, a new house or adoption of a new pet can make herpesvirus reactivate, with recurrent bouts of illness. Herpesviruses are host-specific, so it’s unlikely they would mutate and infect humans.
In contrast, calicivirus is shed continuously in the saliva of as many as 1 in 5 apparently healthy cats. In these cats, the virus mutates continuously, generating new strains. Occasionally a “hot” strain emerges that can replicate throughout a cat’s body, leading to disease outbreaks with more than 50 percent mortality. Although there’s recent evidence that some feline calicivirus strains can mutate and infect dogs, so far there’s nothing to suggest they would ever infect humans.
Retroviruses
Retroviruses are so named because they possess an enzyme, reverse transcriptase, that allows them to incorporate a copy of their genetic material into the DNA of their host. The two most important retroviruses that infect cats are feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV). Both destroy the immune system and predispose cats to other infectious diseases and cancer. FIV is transmitted mostly by biting, so male cats that fight are most at risk. It can be at least a decade before FIV damages the immune system enough to cause death, so cats often die earlier from other diseases. FeLV, shed in saliva, is mostly spread from cat to cat through close contact. Cats that fail to eliminate the virus typically die of cancer and bone marrow problems months to a few years after diagnosis. No effective antiviral drugs exist for these diseases, but there are good vaccines for FeLV.
Although FIV is similar to human immunodeficiency virus (which causes AIDS), and some early studies raised concern about possible human infections with FeLV, there’s no solid evidence that either of these viruses infect humans.
Feline infectious peritonitis
Imagine adopting a perfectly healthy 6-month-old cat from a shelter. Your vet vaccinates it for all the major cat viral infections — rabies, panleukopenia, feline leukemia, herpes and calicivirus. Six months later, your cat is lethargic, not eating well; its muscles are twitching, and it’s walking in circles. Your vet finds it has a fever and makes a diagnosis of feline infectious peritonitis, or FIP.
This common and lethal viral disease most often affects young cats in multiple cat households, shelters and breeding catteries. It’s caused by feline coronavirus, which is related to SARS-CoV-2 (the cause of covid). Because it can take time for illness to develop, cats can appear healthy when adopted, only to die weeks to months later.
Feline coronavirus has an impressive ability to mutate. There are two forms of the virus: The “mild” form persists in the intestinal tract for long periods, often in the absence of signs of illness. The “severe” form damages the kidneys, liver, lungs, brain and other tissues, leading to signs of organ dysfunction and death.
Virtually all kittens in multiple cat households get infected with mild strains of feline coronavirus when they are exposed to virus in fecal material. These cats then act as “factories” for production of more virus, which occurs in their intestinal tract. In some unlucky cats, a flip of a switch can later cause the intestinal form to transform into the severe form, leading to FIP.
Only the mild form spreads from one cat to another, so cats that have FIP are not a danger to other cats. Furthermore, most cats with the mild form ultimately eliminate the virus, especially if they’re moved out of a multiple-cat household. But in 2023, a new “hot” feline coronavirus strain appeared in Cyprus, which caused many cats to die. This strain acquired genetic material from a canine coronavirus, raising concern about the possibility of the creation of new strains that could lead to human infections. Researchers are actively working to understand this outbreak and its implications for cats and other animals.
Cats with FIP used to have death sentences. There was zero chance that such cats would live longer than a few months. Vets used steroids to dampen the inflammatory reaction to the virus, but weeks to months later the cats would die.
Things have changed since the covid pandemic, but even before that, Niels Pedersen, a professor emeritus at the University of California at Davis, had shown that drugs like those used to treat covid could cure FIP. Initially, desperate cat owners were getting these drugs on the black market, but now they can obtain them legally. Anti-covid drugs have saved the lives of thousands of cats. However, researchers have raised concern that overuse of such drugs will lead to resistant viral strains — putting us back where we started.
Covid and influenza
Cats can be infected with the virus that causes covid, but it typically causes no signs or just mild respiratory disease. Cat-to-human transmission is considered rare; most of the time, it’s the cats that get infected from their owners.
In 2016, an influenza outbreak affected more than 500 cats in a shelter in New York City. Affected cats showed mild to severe respiratory disease, and shelter workers and people who adopted cats from the shelter became infected, sometimes with mild respiratory illness. The virus strain subsequently disappeared, with no further transmission in the wider community.
Of greater concern, since 2022 the H5N1 avian influenza virus (“bird flu”) that has wreaked havoc on poultry and dairy cattle production facilities has caused the deaths of hundreds of cats worldwide. Some of these were outdoor cats that were probably infected when they ate wild birds or rodents; others were from affected dairy or poultry farms. However, many have died after being fed raw poultry diets, including those available at boutique pet stores or farmers markets. Once illness appears, infected cats typically die within two to three days, often with neurological signs that resemble rabies. Although the antiviral drug oseltamivir (Tamiflu) has been used to treat some cats, a safe dose for cats is unknown, and because cats die so quickly usually there’s no time for treatment. Last month came the first report of likely transmission of this virus from a cat to a human (a veterinarian) in Los Angeles. Because cats can act as “mixing vessels” where new strains generate, researchers have expressed concern that cats could be a ticking time bomb for the generation of a new pandemic virus.
How to protect your cat
The best way to keep your cat safe is to:
- Keep it indoors (or build a “cat patio”).
- Limit the number of cats in your house. (FIP often becomes a problem in households with 10 or more cats, especially if it’s mostly juvenile cats.)
- Ensure there are plenty of clean litter boxes (one for each cat, plus one extra; scoop the litter daily, and clean and disinfect the entire litter box every 2-3 weeks, or more often if needed, such as when cats have diarrhea).
- Follow your veterinarian’s vaccination recommendations.
- Feed commercial, heat-processed diets (no raw milk, or raw or freeze-dried foods, even if they’ve been frozen).
- Make sure newly adopted cats test negative for retrovirus before introducing them to existing cats and, ideally, keep them separated until a second test is negative six to eight weeks later. Although this can be challenging, it can help you avoid heartbreak in the long term.
The post Ask a Vet: Can I catch a virus from my cat? appeared first on Washington Post.
