by Barry B. Burtis D.V.M.
Feline Infectious Peritonitis - Part II
Feline infectious peritonitis (FIP) has been recognized as a disease since the 1960's. It has been causing the kind of problem I wrote about in my last column, for many decades. Despite some advances in that time, treatment, prevention and control of the disease remains a great problem.
It affects cats - both domestic and exotic ones. Lions, mountain lions, jaguars and leopards and small wild felines like the lynx may be affected. Among exotic cats the cheetah is particularly susceptible to FIP. With our pets, although any breed may be affected, some families or lines of domestic cats seem to have a higher risk of becoming infected.
The highest incidence of FIP occurs in kittens 3 months to 3 years of age. The likelihood of developing the disease decreases sharply after cats reach 3 years of age.
FIP is caused by a virus called the feline coronavirus. There are many coronaviruses that cause mild gastro-intestinal infections in cats. Diarrhea and/or vomiting are the most common signs shown by cats with such mild infections. These viruses are very common and many if not most indoor house cats have been exposed to these viruses at some time in their life. The FIP virus, currently, is thought to be a common gastro-intestinal corona virus that, for unknown reasons, has mutated (changed) within the body of the infected cat. Even though the common gastro-intestinal coronavirus can spread from one cat to another, the mutated virus ( FIP virus) cannot be spread to another cat and therefore cause FIP. The disease triggered by the FIP virus begins insidiously. The patient has a decreased appetite and gradually loses weight. Kittens are stunted in their growth. The abdomen gradually increases in size as fluid builds up internally. Affected cats usually have a persistent fever. They become depressed and less active. Occasionally eye changes develop and sometimes neurological signs occur. It is almost always, eventually fatal.
The tests that are presently available are only able to detect exposure to a coronavirus. These tests cannot differentiate between exposure to a common gastro-intestinal coronavirus or the mutated FIP virus. A positive test means that the cat has come in contact with a coronavirus and does not even necessarily mean it is still infected with the virus. Therefore these blood tests should not be used as the sole criterion for making a diagnosis of FIP.
Despite these limitations, these tests still can be helpful when investigating a cat that may have FIP. In a sick cat, if these tests are negative, then FIP is quite unlikely to be the cause of the illness. At the present time, a diagnosis of FIP can only be confirmed by microscopic evaluation of numerous body tissues infected by the virus. Unfortunately this is only possible in a cat that is no longer alive.
FIP is mainly a disease of catteries and multiple cat households. In homes with only 1 or 2 cats, the incidence of FIP is estimated to be 1 in 5,000. In environments with many cats and hence greater exposure to coronaviruses, FIP mortality rates of 5 in 100 cats can be expected.
It appears that the main method of transmission of coronaviruses is from a mother cat that has no symptoms of the infection to her kittens at 5-7 weeks of age. At this age any immunity or protection the kittens received initially from their mother is waning. In catteries it might be helpful to attempt to break the cycle of transmission by weaning the kittens at 4-5 weeks of age and isolating the litter from direct contact with other cats, including their mother. Routine disinfection of cat premises - including cages and food/water dishes - will inactivate the virus and reduce transmission.
There is an intranasal FIP vaccine but its efficacy appears to be low. It may be used in cattery situations but cannot be relied on as the only means of control. Veterinarians and cat owners look forward to the day when better treatment and prevention measures are available for this disease.