Feline Leukemia Virus or leucosis is a deadly viral disease. The virus can cause leukemia (tumors of the white blood cells), but this is not the disease that occurs most often after infection. The virus affects the cat’s immune system (immunosuppression), which makes them more susceptible to infections. The pathology of FeLV is, therefore, mainly caused by secondary infections.
After infection, the virus multiplies in the tonsils of the throat and spreads to the bone marrow, lymph vessels, and lymph nodes. The virus enters the blood, and from then on, it can be detected using a blood test. If the salivary gland is infected, the cat will excrete the virus. From now on, the cat is contagious for other cats!
Mainly saliva contains high concentrations of viruses. Saliva is also the primary way of transmission from one cat to another. FeLV is transmitted primarily by prolonged social contact with other cats. Think, for example of eating out of each other’s trays, or washing each other. Via saliva, blood, urine, and stools, the virus can be transmitted. A pregnant female cat can transmit the virus via the placenta to her kittens (and later via her mother’s milk). This can lead to abortion or congenital disabilities. Healthy born kittens will remain carriers of the virus.
FeLV is mainly transmitted by prolonged social contact, but also by a bite wound from fighting. In FIV, on the other hand, the main transmission occurs much more through a direct bite wound caused by fighting and to a much lesser extent through prolonged social contact.
Cats that live together in a group and do not fight among themselves also have a risk of infection if a cat is in the group with FeLV. However, not all cats that become infected with the virus become sick. Healthy, energetic cats with a good immune system can fight and overcome the virus. These cats don’t excrete the virus and don’t get sick.
Cats that can’t fight the virus, for example, due to reduced resistance, will excrete the virus. They are not sick yet but already contagious to other cats. They are, therefore, also called “carriers.” In the course of a few months to years (3 years), they will show symptoms of the disease.
- In young kittens, 70-100% will become sick.
- In kittens from 8-12 weeks old, 30-50% will become ill.
- In adult cats, 10-20% will become ill.