Dr. Addie - What's New in FCoV/FIP Research

Many of you will be aware that it is now possible to detect Feline Coronavirus (FCoV) itself using a technique called RT-PCR (see What is RT-PCR?). In the UK, 155 cats, 7 dogs, 29 people and their veterinary surgeons all took part in a 5 year survey monitoring natural FCoV excretion using the RT-PCR developed at the University of Utrecht.

There are 4 possible outcomes of exposure to FCoV infection:

1. The kitten or cat develops FIP (around 10% of infections).

2. The vast majority of cats shed FCoV for a while, develop antibodies, stop shedding FCoV and their antibody titre returns to zero. 58% of FCoV shedding lasts up to one month and 95% of virus shedding lasts less than 9 months.

3. The cat becomes a lifelong FCoV carrier (13% of infected cats). These cats shed FCoV continually in their faeces and most remain perfectly healthy although some develop chronic diarrhoea.

4. Resistant cats – around 4% of cats appear to be completely resistant to FCoV infection, they don’t shed the virus and they mount an almost undetectable antibody response.

The results of the survey are as follows:

1. FCoV is very rarely shed in the saliva and it tends to be shed at the beginning of infection in those few cats who do excrete it in their saliva. Monitoring the saliva for virus shedding will therefore miss the majority of infected cats – so monitor the faeces.

2. A single faecal RT-PCR result on its own is meaningless: if the cat is intermittently shedding FCoV, by the day following sampling the cat may have changed from being a shedder to a non-shedder or vice versa. RT-PCR testing has to be part of a series of tests and is best accompanied by immunofluorescent antibody (IFA) testing because RT-PCR can be prone to both false positive results and false negative results.

3. To establish that a cat has eliminated FCoV infection, 5 consecutive negative monthly RT-PCR results on faeces are required. Alternatively, a reduction in FCoV antibody status to <10 indicates elimination of infection (IFA titre as measured by Glasgow University Veterinary School – see link to Companion Animal Diagnostics for downloading a submission form to submit a sample). One survey cat’s antibody titre only began to go down 25 months after she stopped shedding virus.

4. To establish that a cat is a lifelong FCoV carrier, he or she should have had continual positive RT-PCR results for a minimum of 8 months. A very few cats will cease shedding FCoV after 9 months, but 95% of shedding in our survey had stopped by then.

Acknowledgements
I am very grateful to the cats, dogs and humans who made this study possible. I thank the Winn Feline Foundation and the Feline Virus Unit for funding the study and Mr Wayne Carr for a very generous donation in memory of his cat, Angelica.

Reference:
Addie D.D., Jarrett O. 2001 The use of a reverse transcriptase-polymerase chain reaction for monitoring the shedding of feline coronavirus by healthy cats. Veterinary Record. Vol. 148