Feline leukemia virus (FeLV)

Test code: S0111 - Ultrasensitive qualitative detection of feline leukemia virus by real time polymerase chain reaction.  This assay detects but does not differentiate proviral DNA of feline leukemia virus types A, B and C.

S0111 is included on P0021 - Feline Bloodborne Panel

Feline leukemia virus (FeLV) infection is one of the leading causes of death in cats. In the United States, 2% to 3% of all cats are infected with FeLV.

FeLV is a retrovirus which infects domestic cats and some wild felines. There are three types: FeLV-A, FeLV-B and FeLV-C. Cats can be infected with one, two or all three types simultaneously. Infection with FeLV-A can result in severe immunosuppression. When infected with FeLV-B, cats develop neoplastic disease (ie tumors and other abnormal tissue growths) more readily than cats infected only with FeLV-A. FeLV-C is seen in only about 1% of FeLV-infected cats and causes severe anemia.

After initial infection, the virus replicates in the tonsils and pharyngeal lymph nodes. It spreads via the bloodstream to other parts of the body, especially other lymph nodes, bone marrow and intestinal tissue, where it continues to replicate. Viremia, the presence of virus in the blood, usually begins 2 to 4 weeks after the initial infection.

There are several risk factors for FeLV infection. Ill cats are four times more likely than healthy cats to become infected with FeLV. Researchers estimate that about 50% of cats with severe bacterial infections and 75% of cats with toxoplasmosis also have FeLV infections. Outdoor cats are more likely than indoor cats to be infected with FeLV. Less than 1% of healthy indoor cats in the United States are infected with FeLV, compared to 1% to 2% of healthy outdoor cats, and more than 13% of ill stray cats.

FeLV can easily be transmitted via saliva. It can also spread through infected urine, tears and feces, and to kittens during gestation and nursing. Twenty percent of FeLV-positive mothers pass the virus to their kittens. Other modes of transmission include bites from infected cats, blood transfusions, mutual grooming, nose-to-nose contact, shared food dishes and water bowls, shared litter trays and sneezing.

FeLV vaccination does not provide absolute protection against FeLV infection, so chronically ill cats should be tested for FeLV even if vaccinated.

Serological diagnosis of FeLV has been used to diagnose FeLV-infected cats. However, cats with weakened immune response due to other infections or diseases will not be reliably detected by serological methods. Molecular detection by PCR overcomes this problem, because PCR detects the presence of the pathogen itself rather than the host animal’s immune response. PCR is rapid, highly sensitive and specific. A recent study (Gomes-Keller et al., 2006) has shown that FeLV proviral DNA detection in blood by PCR provides significantly higher sensitivity, specificity and positive and negative predictive values than serology.

Utilities:

• Confirm the disease causing agent
• Shorten the time required to confirm a clinical diagnosis of FeLV infection
• Ensure that feline populations are free of FeLV
• Early prevention of spread of this virus among a feline population
• Minimize human exposure to this virus

Reference:
Gomes-Keller, M.A., Gönczi, E., Tandon, R., Riondato, F., Hofmann-Lehmann, R.,Meli, M.L. and Lutz, H. (2006) Detection of feline leukemia virus RNA in saliva from naturally infected cats and correlation of PCR results with those of current diagnostic methods. J. Clin. Microbiol. 44:916-22.

Specimen requirement: 0.5 ml whole blood in EDTA (purple top) or ACD (yellow top) tube, shipped overnight at room temperature.

For specimen types other than those listed here, please call to confirm specimen acceptability and shipping instructions.

For all specimen types, if there will be a delay in shipping, or during very warm weather, refrigerate specimens until shipped and ship with a cold pack unless more stringent shipping requirements are specified. Frozen specimens should be shipped so as to remain frozen in transit. See shipping instructions for more information.

Turnaround time: 2 business days

Methodology: Real time PCR

Normal range: Nondetected