Feline Leukemia Virus
The most common and destructive virus that infects cats is the Feline Leukemia
Virus (FeLV). It is extremely contagious and is usually spread by saliva during cat
fights, grooming or mating. The virus can also spread in blood, urine and feces.
Kittens can be infected in the womb, through the umbilical cord right after birth or
during nursing. 25% of the cats infected will die within one year, 75% will usually
die within three years.
There are three major disease categories associated with Feline Leukemia Virus;
1. Lekuemias, which are cancers of the blood cells.
2. Lymphosarcoma, which is a cancer beginning in the lymphatic system
(lymph nodes, spleen, etc.) and organ tissues.
3. Non-Cancerous Diseases such as anemia, abortion, arthritis, and
immune suppression. Chronic illness such as respiratory disease, eye
disease, skin disease, digestive tract disease, urinary tract infections,
infectious peritonitis, toxoplasmosis (contagious to humans), infections
of the mouth, gums and tongue and reproductive diseases are
common. Mild diseases may become fatal due to immune suppression.
There are four types of leukemia testing which may be used to detect a particular
virus protein in the cat. The blood ELISA test is used to detect FeLV at any stage
of infection but will not detect a latent virus. The IFA test will detect FeLV only
after the infection has progressed to a late stage. The tears/saliva ELISA test will
only indicate a positive in the late stage of infection. The very expensive PCR
test has recently become available to determine if the virus has become latent.
Once a cat has been exposed (not yet infected) to the Feline Leukemia Virus,
one of four outcomes is possible:
1. 40% of cats will develop immunity to the virus. Immunity is more likely
to develop in an adult cat than in a kitten.
2. 29% of cats will become permanently infected with the virus. These
cats are contagious to other cats.
3. 29% of cats will become latent with the virus. Feline Leukemia Virus
will insert a copy of genetic material (DNA) into the cat’s cells. These
cells will later either become cancerous or no longer function normally.
The genetic change will remain undetected for an average of 2 ½
years during which time the cat will appear normal. A false negative
will occur during testing except with the PCR test. These cats are
contagious to other cats.
4. 1-2% of cats will become immune carriers. The cat will appear normal
in every way but carries the virus hidden in the epithelial cells. The
virus continues to multiply in these cells but is not able to “infect”
because the cat is producing antibodies against the virus. These cats
are contagious to other cats.
Feline Leukemia Virus is not affected by treatment. The cat will always remain
infected by the virus. Relapse is possible and expected. While a healthy infected
cat may appear unaffected by the virus for years, they should be considered
infectious and dangerous to other cats. The vaccination against FeLV does not
offer 100% protection. A degree of risk occurs when a vaccinated cat is housed
with an infected cat.
Vaccination BEFORE exposure is the best means of preventing Feline
Leukemia. Annual boosters must be administered. Without vaccination, isolation
from other cats is the only means of prevention. To date, there is no cure for
FeLV. Because of the nature of the disease, most veterinarians will vaccinate
only those cats that have tested negative for FeLV. The vaccine is of little, or no,
value in and already infected animal.
Feline Leukemia Virus is relatively unstable outside an infected cat for an
appreciable length of time. The Cornell Feline Health Center recommends a
waiting period of at least 30 days after the removal of a FeLV positive cat before
a new cat is introduced. Disinfect all surfaces and bowls with a mixture of bleach
and water.
Euthanasia has been mentioned as the only effective means for preventing
further spread of Feline Leukemia Virus within the cat population at large.
Consult with your veterinarian for your individual case. If you own only one cat
that is FeLV positive, euthanasia is not necessary for controlling the virus as long
as you keep your cat confined inside and away from all other cats. Eventually,
your cat may contract a FeLV related illness and may have to be humanely
euthanized.
Once Feline Leukemia Virus infects a member of a feral cat colony, the total
removal of the colony is the only humane choice. Revaccination of non-infected
members is extremely difficult, if at all possible. False negative results can
hamper determining which cat has the virus or not. The feral colony becomes a
source of virus infection for any cat in the colony and in the surrounding area.