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Protecting your cats from FIP by Frank Utchen, DVM

Dr. Utchen my cat just passed away from a disease called FIP. Can you explain what this is and how long should I wait before I can get another cat? 


I'm sorry about your cat. Feline infectious peritonitis is a devastating disease of cats for which there is no treatment. It can affect any cat at any age, although the typical disease occurs in young cats. 

This condition is caused when a common, essentially harmless virus called the feline enteric (intestinal) coronavirus — of which many cats are carriers — mutates inside the cat's body to turn into the lethal FIP virus. 

The harmless version of the virus is estimated to be harbored by 40 to 50 percent of cats — in one study 80 percent of cats were carriers of the harmless form of the virus — and virtually all cats harboring this virus live their entire life without the virus mutating.

That is to say, there are about even odds that any cat you might see is a carrier of the virus in its harmless form and very good odds that none of those cats will ever become sick from it. 

It is uncommon that this virus mutates to the fatal FIP form, and it is unpredictable in which cats this will happen. Fortunately, once the virus mutates to become the lethal FIP virus inside a cat, it is no longer contagious to other cats, although we do not know why this is. 

What this means is that the cat you just lost will not have left any of the fatal FIP virus in the environment, although it is likely the harmless form of the virus is present in the environment.

We know that the harmless version of the virus can persist in the environment for up to two months, so waiting longer than that before adopting another cat will reduce the chances of that cat coming in contact with the virus even in its premutated, harmless form. 

Bear in mind, however, that this virus is so common that a cat can pick it up almost anywhere (as is the case for 40 to 50 percent of cats), so waiting two to three months is no assurance that another cat won't encounter the virus at locations other than your house.

Some basics about this virus are: 

  • It is common wherever cats are housed in groups and it is readily transmitted between them. 
  • Transmission is typically by contact with infected feces. This means that the litter box is the usual place of infection. This infection is unusual in cats that free-roam outdoors (no litter box) or who live in homes where there is only one cat. The virus enters the new host's body via the nose and mouth. 
  • An active infection lasts several weeks to a few months. The harmless form of the virus is shed in the infected cat's stool during this period. If the cat is reinfected, the virus sheds again for weeks to months. During this time, the cat may not seem at all ill. Some infected cats do not shed virus.
  • Households with fewer than five cats eventually spontaneously become clear of the coronavirus. Households with more than five cats virtually never become clear of the coronavirus. 
  • Most household disinfectants readily kill the coronavirus immediately, and on flat inanimate surfaces at room temperature the coronavirus usually dies within 48 hours. Carpeting protects the virus and it can survive in carpeting for at least seven weeks. 
  • Once a cat has been infected with the virus and recovered, the cat can be easily re-infected by continued exposure to infected feces. In this way, many catteries where there are always cats sharing litter boxes never rid themselves of this infection.
  • The enteric coronavirus (the viral form that is essentially harmless) attacks intestinal cells and can cause diarrhea, which is usually mild. As long as the infection is confined to the intestinal system, there will be no FIP. If the virus mutates, however, it is able to gain access to the blood stream and cause FIP. 
  • The mutation to a form of virus that can cause FIP is more likely to occur in a cat with an immune deficiency. Most cats with FIP are under 1 year old, before their immune systems are mature. Overcrowding of cats is also an important contributing factor to a reduction in a cats immune response. 

Sadly, there is no effective treatment for FIP once it develops. 

And although research has been done into the development of a FIP vaccine, it is considered by veterinary immunologists to be ineffective, and many believe it may actually increase the risk of a cat developing FIP if it becomes infected by the enteric coronavirus. At our practice, we strongly recommend against the use of the FIP vaccination in cats. 

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