Niels C. Pedersen, DVM PhD
University of California, Davis


Mutian, the first Chinese company to sell GS-441524 on an unapproved market, recently advertised that using its oral formulation for one (or more?) Days would stop the fecal excretion of FeCV in healthy cats. Some veterinary researchers also take this approach. The reason is to prevent the formation of a mutant virus causing FIP (FIPV), and thus to prevent FIP. Although this approach is at first sight attractive, it is a very incorrect introduction of GS441524 in cats. Until now, GS441524 has only been recommended for the treatment of cats suffering from FIP. There are many problems associated with this approach.

In his advertisements, Mutian suggests that FeCV can be easily eliminated by a simple administration of oral GS441524. However, it does not talk about possible research that led to this approach. There is currently no published field research to demonstrate whether chronic FeCV excretion can be permanently cured by healthy cats. 40% or more individuals in any population of multiple cats may be positive for this virus. Naturally occurring FeCV infection appears at an early age and is not associated with any significant symptoms of the disease. Virus shedding takes weeks, months, and in some cases indefinitely, but in most cats it eventually stops building immunity. However, once immunity is stopped, antibody levels fall and cats become susceptible to infection again. This cycle of primary and secondary infections occurs in many cats throughout their lives. GS441524 treatment is very unlikely to result in more permanent immunity than is seen in nature. It would not be important if FeCV was short-lived in the environment and would not be easy to transfer to clothing, rubbish, hair and other items. FeCV survives in the environment for up to 2 weeks and transmission by contaminated objects is well documented. Therefore, although it is possible to treat FeCV in a particular cat, the virus easily returns to the population. This has also been documented in the experience of isolating mothers and prematurely weaning their kittens, which is a slightly similar strategy to preventing FeCV infection.

Although our current knowledge of FeCV infection calls this approach into question, there may be more compelling reasons not to treat healthy cats with GS441525 or any other safe and effective antiviral drugs in the future. It is unlikely that the excretion of FeCV can be stopped for a significant period by a single or short-term treatment, as stated, and this will undoubtedly require a longer period. This approach will be extremely expensive if applied to a large number of cats in a kennel, shelter or rescue station.

The most important reason to avoid this FIP prevention approach is the problem of drug resistance. We already know that some cats with naturally occurring FIP are infected with one or more GS441524-resistant FIPV strains. Our field experiment with 31 cats found that one was infected with a virus that was highly resistant. There is laboratory research confirming that resistance can develop very easily in cell cultures. Drug resistance is also well known in viral diseases such as HIV / AIDS and in people infected with the hepatitis C virus. The fastest way to achieve resistance to any microbes, including viruses, is to overuse drugs where they are not needed. The problem of antimicrobial drug resistance is sufficiently confirmed by our experience with bacteria in animals and viruses in humans. There is no doubt that overuse of drugs such as GS441524 in large groups of healthy cats will lead to a positive selection of FeCV strains that are partially or completely drug resistant. This resistance is also manifested in the mutant FIP-causing FeCV virus (FIPV), which precludes the use of GS441524 in a larger number of cats with FIP. Unfortunately, veterinary medicine does not have the resources of human medicine or financial incentives to discover, test and obtain multiple drug licenses in order to circumvent the acquired drug resistance.

I urge cat owners and scientists to refuse to use safe and effective antivirals in this way. I have nothing to do with voracious drug manufacturers who prefer profit to serious science, common sense and the fears of cat owners suffering from FIP now or in the future. There is a saying, "Just because we can do something doesn't mean we should." NC Pedersen