Feline Leukemia is caused by the FeLV retrovirus which affects the cat’s white blood cells (lymphocytes). It used to be the primary cause of death in cats in the past. The FeLV retrovirus is transmitted from one cat to another through saliva and direct contact (grooming, fights, shared litter box). It can also be passed from mother to kittens either through placenta or nursing. Prognosis in cats with feline leukemia is not encouraging. Only a small percent of infected cats can survive more than three years.
Feline Leukemia Prognosis
The prognosis for feline leukemia depends on a series of factors:
- The state of the immune system of the cat
- The length of exposure to the virus
- Whether the cat is vaccinated against FeLV
- The strength of the virus
Generally, 80% of the infected cats do not survive longer than 3 years from the moment when they get infected. Death usually occurs within 6 months from the detection of the virus.
However, the cat can react in different ways to the retrovirus. The reaction is difficult to predict. Generally, there are two ways the body responds to viruses: it may get infected or build immunity. In the case of FeLV, cats can also become immune carriers or have the virus in a latent state.
Immune Responses to FeLV
In 40% of cases of cats affected by FelV, the cat’s body can develop an immune response and fight the infection. When contracting the virus, the cat will exhibit some symptoms of the illness such as:
- Loss of appetite
- Lethargy and depression
- Fever
- Swelling of the lymph nodes around the neck
This period can last for up to 10 days. If the immune system can fight the disease and eliminate the infection, the symptoms disappear and the cat becomes immune to the retrovirus. Adult cats have more chances of fighting FeLV than kittens.
Infection with FeLV
Another possible outcome after contracting the FeLV is getting infected. In this case, the cat will exhibit the symptoms of infection for a period of time, but afterwards he will appear normal, even if he tested positive for FeLV. Infected cats generally die due to secondary diseases which the body cannot fight, as the immune system is suppressed by the FeLV.
Most common secondary conditions are infections. Antibiotics therapy can help with bacterial infections, but secondary viral infections can be deadly. Chylotorax (fluid accumulation in the chest) and chest tumors are also very frequent in cats with feline leukemia.
The expected lifespan of an infected cat ranges between 2 and 3 years. 15% of them can survive longer than 4 years. Vaccination does not help in infected cats.
Latency of FeLV
The retrovirus can enter the cat’s body and remain in a latent form. This means that it causes some genetic changes in the cat’s cells and remain undetected for a period up to 2 and a half years. The virus only tests positive within the first weeks, but afterwards it cannot be detected. The virus may start producing new FeLV cells and cause an infection which generally results in death. Latency can be experienced by around 30% of the cats that contracted the virus. In some cases, the cat’s immune system will destroy the abnormal cells, thus preventing infection.
Immune Carriers
Cats can have the FeLV, test positive for it, and not get infected. In these cases, the virus multiplies in the cat’s epithelial cells, but the immune system does not allow the disease to develop. This situation only occurs rarely (1%).