Q: One of our cats had...

Q: One of our cats had a blood test for feline infectious peritonitis (FIP) and the antibody titer was 1:100. A month later it was 1:400, and she is to be tested again in another month. She is not ill, and our veterinarian is not sure of her prognosis. Does the cat have FIP, and is there a danger to our other cats?

--J.F.

A: FIP is one of the most frequently misdiagnosed diseases of cats because of the prevailing over-reliance on nothing but the results of serologic blood tests. FIP is caused by a coronavirus, but there are other coronaviruses that affect cats, and one of these causes only a mild diarrheal disease. A cat that has had this diarrhea can give a false positive reading on the FIP blood antibody test. For that reason, a diagnosis of FIP based on that test alone is not guaranteed to be accurate.

I do not think your cat has FIP, because the titer is very low, and unless it keeps rising and she develops signs of illness, I would not worry about her. Nor would I worry about your other two cats; they already have been exposed to whatever is ailing the first cat.

The signs of FIP develop over a period of one to six weeks and include loss of appetite and weight, weakness and fever, as well as abdominal swelling and difficult breathing caused by fluid accumulation. That is the “wet” form of the disease. In the “dry” form, the last two signs mentioned do not occur. Treatment can prolong life, but once a diagnosis is confirmed, it is probably kinder to ask a veterinarian to end the cat’s life.

FIP is transmitted directly from cat to cat. Most cats that become infected recover completely and develop immunity to FIP. Those that do not die in a few months. Dr. Clarke welcomes pet-care questions for use in this column, but regrets she cannot answer mail personally. Send your questions to Pet Doctor, Home magazine, Los Angeles Times, Times Mirror Square, Los Angeles 90053.