Most people have heard of feline distemper only because the distemper vaccine represents the core recommended regular immunization for pet cats. Because the vaccine is highly effective, most cat owners do not have a lot experience with the actual feline distemper infection. Feline distemper (more correctly called "panleukopenia") is caused by a “parvovirus” and represents a life-threatening disease. The feline distemper/panleukopenia virus is considered ubiquitous, meaning it is present in virtually every place that is not regularly disinfected. The infection is highly contagious among unvaccinated cats, usually kittens and young adult cats living in groups. Barn cats, feral colonies, animal shelter groups, pet stores, and rescue facilities are high risk for outbreaks. The following is a review of the virus and the disease it causes.
The feline distemper virus is a “parvovirus.” Many people are familiar with this term as parvovirus infection is a very real concern for dogs, especially puppies. In fact, canine parvovirus is very closely related to the feline distemper virus and much of the information regarding canine parvovirus holds true for feline distemper. The feline distemper virus, however, is more difficult to remove from the environment and more lethal in its victims than its canine counterpart.
INFECTION AND DISEASE
An infected cat sheds large amounts of virus in all body secretions including feces, vomit, urine, saliva, and mucus. The virus persists long after evidence of the original body secretion has faded away. The virus enters the victims body and proceeds to infect rapidly dividing cells. The lymph nodes of the throat are first and from there, over the next 2-7 days, the virus rushes to the bone marrow and intestine.
In the bone marrow, the virus suppresses production of the entire white blood cell line, hence the term “panleukopenia” (literally, “all-white-shortage”). The white blood cells are the immune cells that are needed to fight the infection and without them the victim is completely vulnerable to the advance of the virus.
In the intestine, the virus causes ulceration leading to diarrhea and life-threatening dehydration as well as bacterial infection as the barrier between the body and intestinal bacteria is lost. The patient dies from either dehydration or secondary bacterial infection.
Because most cats are exposed to this virus to some extent, it is unusual for a kitten to have no immunity whatsoever. Further, the vaccine is so effective that even one dose can provide long lasting protection. As a result, infection is largely limited to unvaccinated younger animals kept in groups (which corresponds to exposure to amounts of virus large enough to overwhelm their partial immunity). Mortality of the sick is typically considered 90%, though it has been said that a kitten that survives the first 5 days is likely to survive the infection.
DIAGNOSIS OF INFECTION
Any kitten with fever, appetite loss, diarrhea, and/or vomiting is a suspect for feline distemper. Classically, a white blood cell count shows almost no white blood cells; there are very few causes of white cell counts this low and the infection can be considered confirmed.
If a dead kitten is available for necropsy (“autopsy” in animals is called a “necropsy”), the infection is readily confirmed by biopsy as there are unique tissue findings in feline distemper.
Virus isolation, PCR testing, and antibody level measurement are also potential tests for feline distemper.
The infected cat can recover if he/she can be kept alive until his/her immune system recovers from the panleukopenia and can throw off the infection. This means that invading intestinal bacteria must be kept at bay with antibiotics and aggressive fluid therapy must control dehydration. This is essentially the same therapy as for canine parvovirus infection, though the feline experience seems to be more lethal. There is little chance of survival without hospitalization.
If a cat is lucky enough to recover from this infection, generally no permanent damage is retained and the cat goes on with lifetime immunity.
There is no way to adequately disinfect the environment; a new cat should simply be vaccinated.
Vaccination after age 12 weeks is generally effective in generating immunity against this infection, though immunity gained from mother’s milk may inactivate the vaccine through age 14-16 weeks. Most vaccine protocols call for at least two doses of vaccine to be given 2-4 weeks apart with the last dose being received at or after age 14 weeks.
Vaccination is generally given every 1-3 years depending on the protocol of the animal hospital. Vaccination can be given in a nasal form or in an injection (either modified live or killed virus vaccine) given in the right shoulder area. Killed virus vaccine has been associated with development of vaccination-associated fibrosarcoma (an aggressive cancer) in rare individuals. Research is continuing in this area.
Page last updated: 10/16/2011