Feline Leukemia Virus (FeLV) is a retrovirus that infects cats, affecting their immune system and increasing their vulnerability to various infections and illnesses. Unlike some viruses, a retrovirus can be incorporated into a cat’s genome and may persist over time. Affected cats may suffer from conditions such as anemia, cancer, and immune system suppression. Unfortunately, the disease tends to progress over time and is often fatal.

Uninfected cats can be exposed to the virus through direct contact with infected fluids (urine, saliva, feces, and milk), mutual grooming, sharing litter boxes and food dishes, and through fighting, particularly via bite wounds. Young kittens have the highest risk of infecting the virus, while adults may have some inherent protection. Cats of all ages can catch the virus and develop the disease.

Symptoms:

In the initial phases of infection, cats often show no symptoms. As time passes, an infected cat's health may gradually decline, and the cat may experience a variety of disorders. The symptoms of feline leukemia can be broad, as the FeLV virus affects the immune system, triggering various other diseases.

Anemia is a frequent symptom. Cats with anemia often display weakness, lethargy, and an increased respiratory rate. Intestinal inflammation, neurologic disorders, and stomatitis may also appear. Some cats infected with FeLV may develop cancer, especially lymphoma and leukemia. These disorders can be worsened by the presence of other infectious diseases, such as feline panleukopenia or calicivirus.

Outcomes:

After being infected with the feline leukemia virus, a cat’s body can react in three different ways: abortive infection, regressive infection, and progressive infection.

Abortive infection: a cat can generate a robust immune response against the virus and eradicating it prior to the virus integrates into the cat’s genome. These cats develop antibodies against FeLV, conferring immunity to the disease.

Regressive infection: When the immune system and the virus are evenly matched, the immune system has a partially effective immune response but cannot completely eliminate it. The virus can undergo reactivation and resume replication, particularly if the cat experiences immunosuppression due to illness or medications. During such reactivation, the cat becomes infectious to other cats and faces an increased risk of developing clinical illness.

Progressive infection: After viral infection, the body lacks sufficient immunity to prevent viral replication. The survival time of cats with progressive FeLV infection is shorter compared to those with regressive infections, often resulting in death from FeLV-related diseases within a few years of infection.

Diagnosis:

Currently, there are three types of blood tests that are commonly used to diagnose FeLV: Enzyme-Linked Immunosorbent Assay (ELISA), Immunofluorescence Assay (IFA), and quantitative Polymerase Chain Reaction (qPCR). Unfortunately, there is no cure for feline leukemia virus. For infected cats, early diagnosis and treatments should be started as soon as possible. It is recommended to see the veterinarian immediately if you notice any sign of infection or illness in your cats.