Feline leukemia virus is a retrovirus that infects cats. FeLV can be transmitted from infected cats when the transfer of saliva or nasal secretions is involved.
Feline leukemia (or FeLV) is the leading viral killer of cats. It weakens the immune system, increases susceptibility to other diseases, causes blood disorders and is the most common cause of cancer in cats.

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Symptoms of Feline Leukemia Virus. Cats infected with FeLV may exhibit one or more of the following symptoms: Pale gums. Yellow color in the mouth and whites of eyes. Enlarged lymph nodes. Bladder, skin, or upper respiratory infections.

Feline Leukemia Virus (FeLV) is a common but preventable virus that can affect almost all cats. Dr. Boldan shares how FeLV weakens a cat's immune system, symptoms, and how the feline leukemia virus vaccine can be life-saving.

Feline leukemia symptoms stem from the weakening of the immune system as the virus attacks the blood cells, and cats may take time to become symptomatic. In early infections, most cats are asymptomatic, Rutherford says.
Feline leukemia is a disease caused by feline leukemia virus (FeLV), which suppresses a cat's immune system. This virus directly targets a cats white blood cells, resulting in a decrease of defenses.