FELV.svgFeline Leukemia Virus Antigen Test (ELISA)

Feline Leukemia Virus (FELV) is caused by a retrovirus that can also cause non-neoplastic diseases in cats. These diseases include Lymphosarcoma, Myelogenous Leukemia, Non-Regenerative Anemia, and Panleukopenia. The immunosuppression caused by the virus can lead to serious secondary bacterial and viral infections. Many cats with FELV disease have concurrent (FIP) Feline Infectious Peritonitis disease.

FELV infection is most dangerous in cats that are less than 16-weeks of age. Cats older than 18-months appear to be fairly resistant to infection. There is a two-stage infection course, primary infection of the lymph nodes of the head and neck which can last for as long as twelve-weeks, then a viremia that can last for 2-years or more. Cats that are positive for the FELV ELISA Antigen test and are asymptomatic should be re-tested in 16-weeks. If they are still ELISA positive a buffy coat blood smear should be tested for FELV presence in the bone marrow. Cats that are FELV positive for more than 24-months have a 90% chance of suffering from FELV disease.

The FELV ELISA Antigen test consists of two monoclonal antibodies (to the P27 gag protein) one of which is bound to the plastic micro-well surface, the other is conjugated to horseradish peroxidase in a buffer solution. The patient serum sample is placed into a micro-well and the conjugated antibody is added to the well. If FELV antigen is present in the serum sample it will be captured by the monoclonal antibody bound to the plastic micro-well and also the second monoclonal conjugated to peroxidase forming a sandwich of, antibody – antigen – antibody – conjugate. Addition of a chromogenic substrate causes the development of a blue color in FELV positive samples. Absence of color means no FELV antigen is present.