FELINE PANLEUKOPENIA VIRUS
Species:Feline panleukopenia virus
Also called feline infectious eneritis, feline “distemper”, and feline ataxia or incoordination. Examples of other viruses belonging to the same genus as Feline panleukopenia virus include Canine parvovirus type 2, Porcine parvovirus, Mink enteritis virus, and Raccoon enteritis virus.
Feline panleukopenia virus (FPV) is a small (20 nm) autonomous , non -enveloped, icosahedral, single-stranded DNA virus that is approximately 5,120 nucleotides in legnth. The genome encodes for two genes which each form two proteins by alternative mRNA splicing. The non-enveloped capsid is assembled from 60 copies of a combination of the overlapping capsid proteins VP1 and VP2. The virus contains three capsid proteins. The capsids normally enter cells by clathrin-mediated endocytosis. Replication of the virus in the host occurs in cells that are rapidly dividing. FPV can survive in pH ranging from 3 to 9. The virus is highly resistant to most disinfectants (ether, chloroform, acid, alcohol, and heat), but is susceptible to Clorox bleach.
History and Natural Biology of Feline Panleukopenia Virus:
Feline panleukopenia is endemic to cats worldwide. The virus has been identified since the early 20th century. The virus is so severe that it was referred to as “cat plague” in earlier times when infections worldwide nearly wiped out cat populations in certain geographic areas. Now FPV rarely occurs in domestic populations in which vaccination is routinely practiced. There is a seasonality to the occurrence of FPV that usually coincides with the production of new populations of susceptible kittens. This seasonal effect may vary according to geographic location. In the northeastern United States, most cases of FPV are seen in the summer and early fall. However, outbreaks of FPV may occur at any time of the year. It is thought that feral domestic cat populations are a natural resevior for Feline panleukopenia virus.
Clinical Features and Viral Pathogenesis:
All members of the cat family (Felidae) are susceptible to infection with feline panleukopenia virus (FPV), as are raccoons, and minks, in the family Procyoniclae. Three major body sytems are affected by FPV. FPV specifically depresses the white blood cells and thus the immune system of the host, it attacks the rapidly reproducing cells lining the gut, and FPV affects the reproducing cells of the cerebellum and the retina of the eye when they are in their developing stage. The system it chooses depends on the age of the cat at the time of infection. The severity of the clinical signs exhibited also depends on the cat’s age, and varies tremendously from case to case. Many cats show no signs of infection at all; the only method of diagnosis is the detection of FPV antibody in the blood. Mild clinical infections can be seen as a borderline drop in white blood cell count, mild temperature elevation, and slight inappetence. In a “typical” case of FPV, the clinical signs develop suddenly. Vomiting and severe diarrhea may develop within twenty-four hours of infection. During this time the cat’s temperature may elevate to 104oF or greater. Severe dehydration and electrolyte imbalances occur as a result of ongoing vomiting and diarrhea. The hair coat becomes dull and there is a loss of elasticity of the skin due to severe dehydration. The lymph nodes in the abdomen become enlarged, and the digestive tract contains excessive amounts of gas and liquid. By this time the cat’s abdomen is painful, and touching it will elicit a pain response. The mortality rate in an outbreak of FPV may vary from 25 to 80 percent. Death commonly occurs within the first five days of illness, but can occur later by subsequent complications by other problems. Signs in kittens infected in utero, often go unnoticed before sudden death. Ataxia, or incoordination, will sometimes occur within two weeks of birth due to the viruses tropism for the rapidly dividing cells of the cerebellum and retina. There is no treatment for ataxia, the damage has been done at this point. When a susceptible host is exposed to an infected animal, or with the feces or urine of an infected animal, FPV enters the oropharynx and replicates in regional lymphoid tissue and intestine. Within twenty-four hours of infection, virus is present in the blood, which distributes it throughout the body. After two days of infection, nearly every body tissue contains significant amounts of the virus. As circulating antibodies appear, the amount of virus present gradually decreases. The longer the animal survives with the virus the greater the chances that it will overcome the virus.
Treatment and Control of Feline Panleukopenia virus:
Feline panleukopenia virus normally has a high mortality rate, but with supportive care for the symptoms the mortality rate can often be reduced. Strict isolation of the infected cat is essential to reduce the environmental contamination. The main objective is to keep the affected animal alive and in relative good health until the natural defenses take over. Antibodies usually appear about three or four days after the first signs of illness; two to three days later a sharp rebound in white blood cell number can be expected to occur. Thus, if the infected cat can be supported for five to seven days after onset of the disease, the chances of recovery usually are good. To combat the loss of nutrient due to vomiting and diarrhea, supplementation of specific amounts of vitamin B and A is administered. Antiemetics may be given to reduce vomiting, and intravenous fluid administration may be necessary to correct any electrolyte imbalances. Sometimes plasma or whole blood transfusions may be necessary to replace white blood cells. Since there is no specific treatment for FPV infection, preventing viral infection by vaccination is recommended. There are several excellent vaccines available to immunize cats against FPV. Both inactivated and modified-live vaccines are commercially marketed and effective in preventing FPV. Immunization using the inactivated vaccine should be initiated by the veterinarian when the kittens are eight to ten weeks old. A second vaccination should be given four weeks later. A third vaccination is recommended in areas where prevalence of infection is high. The modified-live vaccines provide the quickest protection and only require one vaccination. MLV’s however should not be administered to kittens under four weeks of age, or immunocompromised animals. In conclusion, feline panleukopenia virus causes a severe, highly contagious, multisytematic disease that is endemic in the cat population. Prevention of disease by adequate vaccination is important because there is no specific treatment for FPV. The remarkable resistance of FPV to environmental conditions requires thorough cleansing and disinfection of the premesis with bleach before the introduction of new cats. Once FPV has infected a premises, the infectious virus, left untreated with bleach, may persist for months to years.