Abstract
The surface envelope (SU) protein determines the cell tropism and consequently the pathogenesis of the feline leukemia virus (FeLV) in felids. Recombination of exogenous FeLV (exFeLV) with endogenous retroviruses (enFeLV) allows the emergence of more pathogenic variants. Currently, phenotypic testing through interference assays is the only method to distinguish among subgroups—namely, FeLV-A, -B, -C, -E, and -T. This study proposes a new method for FeLV classification based on molecular analysis of the SU gene. A total of 404 publicly available SU sequences were used to reconstruct a maximum likelihood tree. However, only 63 of these sequences had available information about phenotypic tests or subgroup assignments. Two major clusters were observed: (a) clade FeLV-A, which includes FeLV-A, FeLV-C, FeLV-E, and FeLV-T sequences, and (b) clade enFeLV, which includes FeLV-B and enFeLV strains. We found that FeLV-B, FeLV-C, FeLV-E, and FeLV-T SU sequences share similarities to FeLV-A viruses and most likely arose independently through mutation or recombination from this strain. FeLV-B and FeLV-C arose from recombination between FeLV-A and enFeLV viruses, whereas FeLV-T is a monophyletic subgroup that has probably originated from FeLV-A through combined events of deletions and insertions. Unfortunately, this study could not identify polymorphisms that are specifically linked to the FeLV-E subgroup. We propose that phylogenetic and recombination analysis together can explain the current phenotypic classification of FeLV viruses.
Highlights
Feline leukemia virus (FeLV) is an exogenous gammaretrovirus horizontally transmitted among domestic and wild felids and is known to cause a range of diseases, including lymphadenopathy, anemia, bone marrow suppression, immune suppression, lymphoma, leukemia, and death [1,2,3,4]
Four hundred and fifteen FeLV surface envelope (SU) sequences met our criteria for data quality and were downloaded from the GenBank (1368 base pairs, Supplementary Table S1)
Even though the exclusion does not preclude phylogenetic analyses, the reduced number of sequences may interfere with the extent of conclusions regarding FeLV evolution
Summary
Feline leukemia virus (FeLV) is an exogenous gammaretrovirus horizontally transmitted among domestic and wild felids and is known to cause a range of diseases, including lymphadenopathy, anemia, bone marrow suppression, immune suppression, lymphoma, leukemia, and death [1,2,3,4]. FeLV is shed in saliva, nasal secretions, urine, feces, and milk of infected cats and is mainly transmitted horizontally through saliva, blood, and other body fluids by close contact between cats. FeLV has the highest case fatality rate in domestic cats out of all major feline viruses in spite of remaining one of the few retroviral diseases with an available effective vaccine [6,7]. FeLV remains one of the most common viral agents in countries where vaccination is not a common practice [8]
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