Feline Leukemia Virus (FeLV) is one of the most common feline retrovirus that causes feline leukemia. FeLV DNA is a provirus that is a copy of reverse transcribed FeLV RNA built into the genome of the host (cat). The most common symptoms of the disease are apathy, loss of appetite, weight loss due to anemia. As the disease develops, the cat becomes susceptible to recurrent respiratory and digestive infections. The first symptoms of the disease may appear even several years after infection. Isolation of infected cats and vaccination effectively prevent the spread of the disease.