Feline Leukaemia Virus

Abstract

Feline leukaemia virus (FeLV) is a gammaretrovirus that causes a variety of fatal diseases including leukaemia and lymphoma in its host, the domestic cat, and occasionally in large cat species. Many cats become persistently infected and develop disease after an incubation period of several years, during which virus can be transmitted to other cats. Disease is often associated with the generation of FeLV variants with increased pathogenic potential that can arise by mutation of envelope sequences, duplication of transcriptional enhancer elements or recombination with host proto‐oncogene sequences. FeLV can also produce variants by recombination with endogenous proviruses related to FeLV that are found in the domestic cat and its close relatives. The prevalence of FeLV infection has been reduced in many cat populations by isolation of infected carriers and more recently by vaccines that augment the natural ability of most cats to control infection. Key Concepts: The outcome of infection by FeLV depends on the infectious dose, age and immunocompetence of the host. Many cats achieve lifelong control, if not elimination of infection. Cats that become persistently viraemic are at risk of a variety of FeLV‐related diseases after a latent period of up to several years. The common infectious form, FeLV‐A can acquire altered entry receptor specificity by envelope gene mutation (to FeLV‐C) or recombination with endogenous FeLV‐related proviruses (to FeLV‐B). FeLV envelope variants may induce fatal diseases of rapid onset including nonregenerative anaemia (FeLV‐C) or wasting and immunodeficiency (FeLV‐T). The oncogenic potential of FeLV can evolve by duplication of transcriptional enhancer control elements in the long‐terminal repeat or by transduction of host proto‐oncogene sequences. Although the immune parameters of vaccine protection remain unclear, FeLV demonstrates the feasibility of effective immunisation against the gamma retroviruses. Commercial FeLV vaccines in recent or current use include inactivated FeLV, infected cell extracts, recombinant envelope protein and live recombinant poxvirus vaccines.

Feline leukaemia virus infection: A practical approach to diagnosis

“…One case of focal infection is well documented in a queen, where the virus had been sequestered to the mammary glands; during a phase of negative free FeLV p27 antigen test results in the blood, the queen transmitted the virus to the kittens via the milk. 26,59 Focal infections with discordant test results have been reported under experimental conditions, 58,60,61 and have also been observed in up to 10% of naturally FeLV-infected cats. 26,56,57,59,62 In one study, about one-third of the cats with discordant FeLV test results were provirus PCR-positive and it was assumed that in these cats the bone marrow was infected.…”

“…However, some discordant antigenaemic but aviraemic cats have been described; as discussed, discordant results are mainly seen during the early phase of FeLV infection (see box on page 836), or with focal FeLV infection (see also Table 1 and above). 26,54–60 ,62…”

Measuring the Humoral Immune Response in Cats Exposed to Feline Leukaemia Virus

“…However, there is some evidence to suggest that these endogenous variants could be transmitted between cats [ 7 ]. The outcome following FeLV exposure is complex, unpredictable and dependent on many factors, including the route of infection, the age of the host at the time of infection, concurrent co-infections, stress and the dose of virus to which the host was exposed [ 8 , 9 , 10 , 11 ]. Cats that become infected following FeLV exposure can develop abortive, regressive or progressive infections, depending on their immune response to infection.…”

“…The antibody response to FeLV infection is directed mainly towards the viral surface unit (SU) glycoprotein (gp70) and p15E [ 10 ], although antibodies that recognise all major structural proteins have been detected in sera of cats with regressive infection [ 19 ]. Cats that develop virus neutralising antibodies (VNA) are protected from infection following exposure to the virus [ 20 ] and kittens that passively receive maternally derived antibodies are transiently protected from infection [ 10 , 21 ]. Most cats with regressive infection demonstrate high VNA titres; a high VNA titre is a good indicator of virus suppression such that clinical disease does not develop [ 22 , 23 ].…”

“…A total of 20 field cat plasma samples (samples[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] and two plasma samples from FeLV naïve specific pathogen free cats (samples21 & 22) were tested by immunoblotting to determine antibody reactivity to FeLV-A proteins. Each strip was probed individually with a cat plasma or antibody control.…”