How to prevent FCoV transmission, and therefore FIP
See also What's new in FCoV/FIP research for the latest information on how long cats shed FCoV, and the use of the virus detecting tests called RT-PCR.
Watch a video of a cat catching FCoV:
FCoV is a very contagious virus, infecting nearly all cats who encounter it. The major source of infection is the faeces of infected cats, and uninfected cats become infected by sharing litter trays with infected cats. The second major route of infection is the unintentional exposure of uninfected cats to tiny particles of infected faeces on peopleís shoes or clothing, hands, poop scoops, etc. The infected cat likely swallows the virus when grooming, or when particles of faeces contaminate their food.
FCoV is occasionally shed in the saliva, early in infection, so sharing food bowls or inhaling sneezed droplets could possibly allow infection to occur. Close contact with infected cats, for example in mutual grooming, might, rarely, result in infection.
Feline coronavirus almost never crosses the placenta to the unborn kitten. Most kittens which become infected do so after protective antibody they receive in their motherís milk has waned, usually when they are 5-7 weeks old.
FCoV is mainly shed in the faeces, and is only shed in the saliva very rarely. At present, there is no evidence that FCoV is present in the tears or urine.
If your cat uses a litter tray, then make sure it is declumped as often as possible and use dedicated poop scoops for each cat pen or tray. Better still, if possible, let the cat out to go to the toilet naturally outside (I am aware that this is not always possible or desirable where there is a lot of traffic). If you have several cats, make sure that you have enough litter trays, preferably one for each cat, and get covered or even self-cleaning litter trays. Site the litter tray away from food areas so that microscopic faecal particles cannot be blown onto the cat's food. Use a Fuller's Earth based non-tracking cat litter, to minimise spread of microscopic particles around the house. Once or twice a week, clean your litter tray with domestic bleach (sodium hypochlorite). Do stick to bleach disinfectants, as pine based ones are toxic to cats. Vacuum as often as possible to reduce the number of contaminated cat litter particles.
The best solution for indoor cats is shown in this video below:
We have assessed the activity of various cat litters against feline coronavirus (FCoV) in the laboratory and in some households. Dr Elsey's Cat Attract cat litter was shown to reduce, but not completely eliminate, virus transmission to cats sharing litter trays (Addie et al, 2019). The next best litter was Ever Clean.
Please bear in mind that cat litter cannot wholly prevent virus spreading from one cat to another by microscopic particles on shoes, poop scoops, etc. The virus will, to some extent, be protected by faecal material. We have established that tracking is almost as important a feature as anti-coronaviral activity and recommend cat litters which clump.
In the laboratory, we tested 15 cat litters and found that the Fuller's Earth based litters were able to inhibit infection of cell culture, presumably by binding the virus.
Dr Elsey Cat Attract Cat Litter can be purchased from most outlets in the US and they have one distributor -R and L Pet Products - in the UK. If you are in the USA, you can download and print this voucher to obtain a discount: https://www.drelseys.com/wp-content/uploads/2019/05/DrAddieCatAttract200_Cpn-Frnt_Bck_20220.pdf.
In natural circumstances, cats go outside to defaecate and bury their faeces, in which case the virus lasts hours to days (it survives slightly longer in freezing conditions). However, in domesticating the cat we have introduced litter trays: FCoV may survive for several days and possibly up to 7 weeks in dried up faeces in cat litter.
If you have lost a cat to FIP, wait around a month before obtaining another cat. However, if you have other cats already, remember they may be shedding FCoV, so wait until their antibody titres have reduced to zero before obtaining a new cat. Of course, donít forget to test the new cat for FCoV antibodies too.
FCoV infection can be eliminated from a cattery, but it may be a long and sometimes expensive process. Households of less than 10 cats will often spontaneously and naturally become FCoV free, but in households of more than 10 cats, the virus can keep passing from one cat to another (see fig 1.) because immunity is short lived, thus the infection persists in this way.
GS-441524 pills stop FCoV shedding and break the cycle of infection and re-infection.
Cat breeder Sheryl Curran discovered that Mutian X pills could stop FCoV shedding at a dose of one Mutian 100 pill per kg for 5 to 7 days (Addie et al, 2020). Subsequently it was shown that Mutian X pills contain GS-441524 (Krentz et al, 2021) and that they contain more GS-441524 than the 5mg per 100 that their product sheet claims (Addie et al, 2023). Early treatment of FCoV infection was found to prevent FIP (Addie et al, 2023).
Dose of GS-441524 for clearing FCoV infection
In the UK, Australia and other countries, legal 50mg GS-441524 pills can be obtained by veterinary surgeons from the compounding pharmacists Bova Specials.
To eliminate FCoV infection, the dose of Bova GS-441524 is 10mg/kg per day in divided doses for 5 to 7 days.
I recommend that the first dose is given on an empty stomach in the morning (following an overnight fast), then breakfast given, and the second dose given in the evening with a full meal. Always follow pilling with food or a drink to prevent inflammation of the oesophagus. This protocol allows maximal GS-441524 to reach the colon, which is the site of major FCoV replication, in the morning, then the slower transit through the gut in the evening, with the food, allows more drug to be absorbed systemically.
Be sure to send faecal samples to a good laboratory that reports virus quantity, not just positive or negative, to ensure that FCoV shedding has been effectively stopped because if even one cat is still shedding virus, it is so contagious that all cats will soon be re-infected. People with a lot of cats should isolate them into small groups of two or three cats until all the cats are negative.
Our experience is that young kittens, under 4 months of age, are the most difficult to clear of coronavirus, perhaps because they have a higher virus load than adult cats. My recommendation for cat breeders is to give the first 4 days of doses to a FCoV-infected kitten in the 4 days leading up to the kitten going to his or her new home, then give 3 days of pills to the new cat guardian to administer in the kitten's new home. I have written an explanatory leaflet to print out and give to the kitten's new guardian which you can download here.
Will early treatment cause drug-resistant viruses to emerge?
People worry that early treatment of FCoV infection will allow drug-resistant escape mutant viruses to appear: such mutant viruses have been demonstrated in vitro with GC376 protease inhibitors (Jiao et al, 2022), but not in vivo in cats treated with GS-441524 orally. However, virus resistance to Remdesivir (which gets metabolised to GS-441524) has been shown in people with COVID-19 because it penetrates the lungs poorly (Choi et al., 2020).
Drug resistance occurs in situations where drugs are used at sub-sterlising doses and for longer durations in the presence of the pathogen, which is why the major source of antibiotic-resistant bacteria in human medicine was from using antibiotics in farms as growth promoters therefore that practice was banned by the European Union in 2006 (Barros et al, 2023). The main site of FCoV replication is the intestine (Herrewegh et al, 1997): therefore oral antivirals are more effective in eradicating the virus from the body than injectable drugs because oral antivirals go directly to the site of major virus replication.
In FCoV infection, drug-resistant viruses are more likely to develop in cats with FIP being treated with injectable antivirals which do not adequately penetrate the gut: one FIP cat successfully treated with GS-441524 injections still shed virus in his faeces at least two years post-treatment (Addie et al, 2022). Viral RNA did not decrease over 26 days in one of 26 FIP cats treated with GS-441524 injections (Pedersen et al, 2019). In a recent study of 26 cats which experienced FIP treatment relapses, 23 were treated using injectable rather than oral GS-441524 (Roy et al,2022) but, unfortunately, no control group of cats without relapses was presented to prove that the reason for the relapses was beginning treatment by injection. The other site of poor drug penetration is the blood brain barrier, which is why FIP relapses frequently present with neurological signs (Pedersen et al, 2018; Pedersen et al, 2019; Roy et al, 2022).
Can other drugs be used to stop FCoV shedding?
GS-441524 / Remdesivir injections do NOT reliably stop FCoV shedding: use only oral drugs.
Molnupiravir / EIDD: it is likely that molnupiravir stops FCoV shedding, but so far as I know, there are no data on that yet.
Interferon: feline interferon omega (Virbagen Omega, Virbac, France) given orally reduces but does not abrogate FCoV shedding (Gil et al, 2013).
Itraconazole: we do know that itraconazole reduces, but does not stop FCoV shedding (Addie et al, 2023) and that virus load bounces back as soon as the itraconazole is stopped.
Mefloquine: although mefloquine inhibits FCoV in the laboratory, there is no data on its effect on FCoV shedding in faeces as yet.
Ivermectin: ivermectin must be used with zinc picolinate (Solgar brand: one quarter of a 22mg pill daily) because it is the zinc that has antiviral effects, ivermectin acts as a zinc ionophore. The ivermectin dose is borderline on the toxic dose, so be very careful with it: 0.25mg per kg per day for 2 to 4 weeks. This reduces FCoV shedding but doesn't consistently eradicate the infection as clearly as GS-441524 does.
Probiotics: more work is required to establish whether probiotics can eliminate FCoV shedding either on their own or in combination with another treatment.
VetImmune (Sass & Sass): unfortunately polyprenyl immunostimulant does not stop FCoV shedding.
A household from which FCoV was eliminated prior to the discovery of GS-441524
Table 1 shows an example of a household of cats who lived with Carol, Ann and Simon Hicks, who successfully eliminated FCoV infection. Cats were tested for antibodies and their faeces were tested by RT-PCR regularly. Cats who had stopped shedding FCoV and whose antibody titres were declining to below 40 were separated from the other cats. Fortunately, Carol was leaving home and was able to take 4 negative cats with her to her new home, but other cat lovers have successfully managed to keep infected and uninfected cats apart within one house). By August 1997, 17 months after the FCoV infection had been detected, only Sooty was still infected. Ann moved Sooty to the bedroom in complete isolation from the other cats. By January 1998, it was becoming clear that Sooty was a FCoV carrier and since she was miserable isolated in her bedroom, it seemed likely she would have to be euthanased. Fortunately, the Hicks agreed to give her to me (my own two cats had died a few months previously and I had no cats). Sooty lived 8 years with me, and was a wonderful cat. She was a healthy FCoV carrier for many years.
Table 1. A household of cats from which FCoV was successfully eradicated by isolating cats which had eliminated FCoV infection from those who were still shedding virus. The shaded boxes indicate when a cat was moved to another household.
At present, identifying carrier cats is a lengthy process (see What's new in FCoV/FIP research). We still need to find some test which will identify lifelong carriers sooner so that we can keep them apart from other cats, or to find a way to stop them shedding FCoV..... but these are the subjects of my future research.
Once your cats are FCoV free, take care not to re-introduce the virus. Test all new cats or kittens for FCoV antibodies using a reliable antibody test, such as the immunofluorescent antibody test from the University of Glasgow (see link to Companion Animal Diagnostics). There appear to be many antibody tests available which have no correlation with the Glasgow University gold standard test and using them will not only give you worthless results, but may endanger your catsí lives. Only cats with an antibody titre of zero should be allowed to come into a FCoV-free cattery.
Make sure that you only take your queen to stud cats with antibody titre zero and that only antibody titre zero queens visit your stud cat (see the Coronavirus tested stud and queen register). When you go on holiday, for preference, get somebody to come to your home and feed your cats rather than putting them in a cattery.
Quarantining your cat after risky sex, a visit to the cattery or cat show, or stay at the vets. If you decide to mate your negative cat to a cat with FCoV antibodies, or your cat has been at a show, cattery or had to stay in your vetís kennels, then place your cat in quarantine at home for 2 weeks and test him or her for FCoV antibodies, making sure (s)he is negative again before re-introducing him or her to your other cats.
Can I visit my friend, whose
cats have FCoV?
Iíve heard about canine coronavirus
Ė can my dog infect my cats?
In the UK, 84% of cats at cat shows have antibodies to FCoV. Since, on average, one in three cats with antibodies to FCoV sheds virus, it would be likely that 28% of cats at shows is shedding FCoV at any one time. FCoV is mainly shed in the faeces, so cats at shows should not share a litter tray or poop scoop with cats from other households. Judges and veterinary surgeons should disinfect their hands and the table between handling of each cat: remember that some cats in early infection shed FCoV briefly in their saliva.
Obviously it is wisest to mate only cats with an antibody titre of zero to other FCoV free cats and cats with antibodies to other cats with antibodies, hence the FCoV tested stud register to help breeders to find each other. However, sometimes cat breeders have reasons for wanting to do a risky mating (of their cats!!!). In this circumstance, it is best to do a controlled mating, that is where the queen and tom do not get to live together for a day or two (so, importantly for FCoV transmission, do NOT share a litter tray) but are only put together for the duration of the actual mating. Clearly, the cat who was previously negative should be tested for antibodies 14 days after the mating to find out whether he or she became infected in spite of the precautions.
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last update: 7 April 2023
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