Most people have heard of Panleukopenia (feline distemper) only because the distemper vaccine (FVRCP – Feline Viral Rhinotracheitis Calicivirus Panleukopenia) is the core recommended immunization for pet cats. Because the vaccine is highly effective, most cat owners do not have a lot of experience with the actual feline distemper infection. Kittens can develop immunity with a vaccination and a booster at or after 12 weeks of age. Adult cats can retain immunity through boosters provided every 3 years.
Feline distemper, caused by a parvovirus, is a life-threatening disease. The virus is found in virtually every place that is not regularly disinfected. The infection is highly contagious among unvaccinated cats, which are usually kittens and young adult cats living in groups. Barn cats, feral colonies, animal shelter groups, pet stores and rescue facilities are at high risk for outbreaks.
The feline distemper virus is very durable. It can last a year indoors at room temperature and survives freezing temperatures. It also survives treatment with common disinfectants like alcohol and iodine. Fortunately, it can be killed when exposed to a 10-minute soak in bleach (1 part bleach diluted in 32 parts water).
Virtually every cat will be exposed to this virus at some point. Infection occurs when the virus enters the body through the mouth or nose. Whether illness results or not depends on the cat’s immunity and the number of individual virus particles entering the body.
The feline distemper virus is a parvovirus. Many people are familiar with this term, as parvovirus infection is a concern for dogs, especially puppies. In fact, canine parvovirus is closely related to the feline panleukopenia 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 than its canine counterpart.
An infected cat sheds large amounts of the 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. When the virus enters a cat’s body, it proceeds to infect rapidly dividing cells. The lymph nodes in the throat are the first to be affected, and from there, over the next 2 to 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 (“all-white shortage”). The white blood cells are the immune cells needed to fight the infection, and without them, the victim is completely vulnerable to the progression of the virus.
In the intestine, the virus causes ulcerations, which lead to diarrhea, life-threatening dehydration and bacterial infection because the barrier between the body and intestinal bacteria is lost. The patient often dies from either dehydration or a 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. Furthermore, 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, as the virus exposure in large groups is high enough to overwhelm kittens’ partial immunity. Mortality of sick cats is typically considered 90%, though it has been said that a kitten who survives the first 5 days is likely to survive the infection.
A specific syndrome occurs if infection occurs during pregnancy. If infection occurs in mid or early pregnancy, the kittens simply abort. If the kittens are fairly far along, the cerebellum is involved, leading to cerebellar hypoplasia. The cerebellum is the part of the central nervous system that coordinates balance and movement, enabling one to walk or run on an uneven surface without consciously thinking about it. Without a normal cerebellum, a kitten is born with marked intention tremors: Whenever he focuses on purposeful movement, he tremors so much that normal movement is impossible.
Any kitten with a fever, appetite loss, diarrhea and/or vomiting is a suspect for feline distemper. Generally, a cat with distemper will have a white blood cell count that shows almost no white blood cells. There are few causes of white cell counts this low, so with an extremely low count, the infection can be considered confirmed.
An infected cat can recover if the cat can be kept alive until the immune system recovers from the panleukopenia and throws off the infection. This means that the 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 virus 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. The virus is shed for up to 6 weeks after recovery. There is no way to adequately disinfect the environment; a new cat should simply be vaccinated.