Feline Leukemia Virus (FeLV)

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Product Description

Feline Leukemia Virus (FeLV)

Feline leukemia virus (FeLV) is a γ-retrovirus belonging to group of retroviruses, together with FIV. It causes a serious incurable infectious disease in cats. Four subgroups of FeLV, namely FeLV-A, -B, -C, and -T, have been identified. Specifically, FeLV-A viruses represent the naturally occurring, horizontally transmissible subgroup spread cat-to-cat in nature. FeLV-B, C and T are thought not to be horizontally transmissible in nature, but arise de novo within the infected animal by mutation of FeLV-A and/or by recombination between FeLV-A and endogenous FeLV-related elements in the cat genome. FeLV-B bears greater risk for developing lymphomas, and FeLV-C and –T for anemia and immunodeficiency, respectively. Generally, FeLV-infected are 62-times more likely to develop lymphoma or leukemia than non-infected cats.

Sample: 0,5 ml EDTA-blood

Modes of transmission

The largest source of FeLV infection are persistently viremic asymptomatic cats. FeLV is highly transmissible through saliva and nasal secretions as well as through coitus and vertical transmission from queen to kitten.

Clinical signs

There is a long asymptomatic phase, in which cats do not show clinical signs. After infection, the virus starts initially to replicate in the local lymphoid tissue in the oropharyngeal area. In some immunocompetent cats viral replication may be terminated because of high levels of neutralizing antibodies. In this case we are talking about abortive infection.

In regressive infection, there is an effective immune response and the virus is duplicated in infected lymphocytes and monocytes. After about three weeks of viremia, bone marrow cells become infected. Viremia can be terminated within weeks or months. Regressively infected cats do not shed FeLV and are not infectious to others, but regressive infection can be reactivated.

In cats with progressive infection extensive virus replication occurs, first in the lymphoid tissues, followed by the bone marrow and mucosal and glandular epithelial tissues. Progressively infected cats remain persistently viremic. They are infectious to other cats for the remainder of their life.

Clinical signs associated with FeLV infection can be classified as tumors, immunosuppression, enteritis, hematologic disorders (anemia, neutropenia, thrombocytopenia, aplastic anemia), immune-mediated diseases, and neurological other syndromes. Various co-infections are common, especially with FIV and FIP, and secondary infections due to immunosuppression.


There is no treatment for FIV, so it is mainly based on treating associated conditions. Currently, there are no effective antivirals or immunomodulators available.


Prevention is consisted of separating infected cats from healthy ones, keeping cats indoors and vaccination of high-risk populations.


FeLV infection decreases life expectancy, but with proper care cats with FeLV can live for years.


Prevalence of FeLV infection is about 2% in healthy cats and up to about 30% in high-risk or sick cats in the USA. Similarly, animal-to-animal contact contributes to the different rates of FeLV infection in single cat households (4%–11%) compared to multicat households whose prevalence has been reported to be as high as 70%.


Bolin, L.L., and Levy, L.S. (2011). Viral Determinants of FeLV Infection and Pathogenesis: Lessons Learned from Analysis of a Natural Cohort. Viruses 3, 1681–1698.

Greggs, W.M., Clouser, C.L., Patterson, S.E., and Mansky, L.M. (2011). Broadening the use of antiretroviral therapy: the case for feline leukemia virus. Ther Clin Risk Manag 7, 115–122.

Hartmann, K. (2012). Clinical Aspects of Feline Retroviruses: A Review. Viruses 4, 2684–2710.

Tandon, R., Cattori, V., Gomes-Keller, M.A., Meli, M.L., Golder, M.C., Lutz, H., and Hofmann-Lehmann, R. (2005). Quantitation of feline leukaemia virus viral and proviral loads by TaqMan® real-time polymerase chain reaction. Journal of Virological Methods 130, 124–132.