Effect of cat litters on feline coronavirus infection of cell culture and cats

Abstract

Objectives: Feline infectious peritonitis (FIP) is caused by infection with feline coronavirus (FCoV). FCoV is incredibly contagious and transmission is via the faecal-oral route. FCoV infection, and therefore FIP, is most common in breeder and rescue catteries, where many cats are kept indoors, using litter trays. Whether it is possible to break the cycle of FCoV infection and reinfection using cat litters has never been investigated. The aim of the study was to examine the effect of cat litters on FCoV infectivity and virus load in multi-cat households, and transmission frequency.

Methods: Fifteen cat litters were mixed and incubated with FCoV, centrifuged and the supernatants tested in vitro for the ability to prevent virus infection of cell culture. To test applicability of in vitro results to real life, virus load was measured in two households in a double crossover study of four Fuller's earth-based cat litters by testing rectal swabs using FCoV reverse transcriptase quantitative PCR.

Results: Four litters abrogated FCoV infection of cell culture, nine reduced it to a greater or lesser extent and two had no effect. One brand had different virus inhibitory properties depending on where it was manufactured. Fuller's earth-based litters performed best, presumably by adsorbing virus. In the field study, there appeared to be less virus shedding on one Fuller's earth-based cat litter.

Conclusions and relevance: The in vitro study successfully identified cat litters that inactivate FCoV; such litters exist so do not need to be developed. Fuller's earth-based litters best prevented infection of cell culture, but did not completely abrogate FCoV transmission in two multi-cat households. A dust-free clumping Fuller's earth litter appeared to fare best, but virus shedding also varied on the control litters, complicating interpretation. Sawdust-based cat litters are not useful in FCoV-endemic households because they track badly and have a poor effect on virus infection.

Keywords: Bentonite; Dr Elsey; FCoV infection; FIP; Feline coronavirus; Fuller’s earth; cat litter; feline infectious peritonitis; reducing virus load; virus inhibition.

Figure 1

(a) Percentage of cats shedding feline coronavirus (FCoV) on crossover trial of cat litters A, X and Y in household H. (b) Percentage of FCoV-positive samples on crossover trial of cat litters B, X and Y in household L. Cats in households H and L were sampled on various occasions while using control cat litters A and B (white bars) and test litters X and Y (black and grey bars, respectively). This figure shows that the percentage of cats shedding FCoV was lower on cat litter X when compared with litters A, B or Y in a crossover study involving two households, H and L. It can be seen that the percentage of cats shedding FCoV decreased in both households when cat litter X was introduced, increased when the cat litter was changed from X to Y, then decreased again on litter X in both households. The difference between cat litters X and A was statistically significant (P <0.05), but the difference between X and B was not (P >0.05). Cat litter Y was not significantly different from litters A or B (P >0.05). All of the cat litters were Fuller’s earth based, but cat litter X was formulated to be dust-free and so to track less. The possibility that the reduction in virus shedding was related to summertime, as opposed to the cat litter, could not be excluded