FeLV, or Feline Leukemia Virus, is one of the most common infectious diseases in cats.

The disease is caused by a retrovirus of the Oncornavirus genus. They are fragile and unstable viruses in the environment, but they have the ability to seriously affect the immune system of infected cats - leaving them more susceptible to infections and secondary diseases.

Transmission of the virus between cats occurs during grooming habits, play or by sharing objects - through bodily secretions such as saliva, nasal and tear secretions, urine and feces of cats infected with the feline leukemia virus (FeLV).

Infected females can also transmit the virus to offspring during pregnancy or lactation.

The evolution of the disease in cats can assume different stages. After infection by FeLV, immunocompetent cats can fight and eliminate the virus, not developing the disease. However, animals with a weaker immune system remain infected.

As with the feline immunodeficiency virus (FIV), there may be a period when the animal is sick but shows no clinical signs, until it eventually develops a series of systemic problems (including neoplasms).

In cats with FeLV, clinical signs are related to depression of the immune system and secondary infections and include: bad breath (halitosis), skin problems, diarrhea, respiratory infections, blood disorders and neoplasms.

Cats carrying FeLV and without symptoms can transmit the virus to other animals, thus being sources of contagion.

The treatment is prolonged and sometimes difficult to follow. The best way to prevent infection is through vaccination of susceptible animals.

Vaccination against FeLV is recommended for cats older than 6 months (after testing for the disease), coming from the street or having access to the street and in contact with unprotected cats.