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Endogenous Feline Leukemia Virus Entered the Jungle Cat Genome Hundreds of Thousands of Years Ago

Wild jungle cat walking beside dry vegetation in India
Research · Genetics & genomics

A genomic study has strengthened evidence that inherited DNA from feline leukemia virus entered the jungle cat (Felis chaus) genome long after the species split from other members of the genus Felis. Published on 21 April 2026 in Annals of the New York Academy of Sciences, the study dated integration of the endogenous virus sequences in the jungle cat lineage to approximately 320,000–801,000 years ago.

Feline leukemia virus is a retrovirus that can cause immunosuppression, anaemia and tumours in cats. The sequences studied here were not evidence of a current infection. They were endogenous retroviral DNA: remnants of an ancient virus that entered germ cells, became part of the host genome and was then inherited by later generations. The researchers searched 17 felid genomes for this endogenous form, known as enFeLV. For domestic cat (Felis catus), black-footed cat (Felis nigripes) and jungle cat they used long-read genome assemblies, which read much longer continuous stretches of DNA and therefore make repeated viral insertions easier to place accurately in the genome.

The jungle cat genome contained 27 typical enFeLV copies, significantly more than the other long-read genomes examined. Unlike older, more degraded viral remnants that may persist only as isolated long terminal repeats (LTRs), none of the jungle cat copies had been reduced to a solo LTR. All 27 insertions were estimated to have occurred within the last million years, and ten still retained uninterrupted protein-coding regions across the viral genome. Together, this indicates that the jungle cat copies are relatively young and structurally well preserved. The authors also note that no circulation of the exogenous, infectious form of FeLV is known in jungle cats or black-footed cats.

Evidence of Ancient Hybridisation

The evolutionary position of the jungle cat sequences differed from what would be expected if the viral DNA had simply been inherited continuously from the common ancestor of the Felis species. Jungle cats diverged from the rest of the genus at least about two million years ago, whereas the estimated integration of enFeLV occurred much later. The researchers therefore found the timing incompatible with straightforward inheritance from the ancestral lineage.

Instead, their genomic results support an earlier hypothesis that enFeLV entered the jungle cat germline through introgression after hybridisation with another Felis species. Introgression means that DNA from one species enters another species’ gene pool through hybridisation and subsequent breeding. Earlier genetic tests of gene flow cited by the authors point to the sand cat (Felis margarita) as the most likely source, although the donor species has not yet been established with certainty.

Hypotheses for enFeLV evolution in Felis species
Three hypotheses for the viral sequences’ history: inheritance alone (A), gene transfer between species (B), and loss of parts of the earlier genomic record (C). Panel B illustrates the proposed introgression into jungle cat. Figure 5, Mouta et al. (2026), CC BY 4.0.

The jungle cat copies were highly similar to one another and formed their own strongly supported evolutionary group. Their similarity, structural completeness and young insertion dates are consistent with the viral DNA spreading to multiple genomic locations after introgression. The authors describe this as a possible example of “genomic shock”: newly introduced mobile genetic elements—DNA sequences able to copy or move within a genome—can proliferate rapidly before the host genome and the elements settle into a more stable relationship.

Sources and image credit

  1. Mouta, R., Cavalcante, L. T. de F., Soares, M. A., Schrago, C. G., D’arc, M., Moreira, F. R. R., & dos Santos, A. F. A. (2026). Evolutionary dynamics of endogenous feline leukemia virus in the Felis genus through the lens of genomics. Annals of the New York Academy of Sciences, 1558(1), e70278.

Image: Dr. Raju Kasambe — wild jungle cat photographed at Ambazari Lake, Nagpur, Maharashtra, India, 6 December 2018; Wikimedia Commons; representative wild jungle cat, not an individual whose genome was analysed in the 2026 enFeLV study · CC BY-SA 4.0 · Source

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