what is felv

Feline leukemia virus evolved from a virus of ancestral rats and cats. During the evolutionary process, three subgroups emerged. FeLV-A is the only subgroup that is contagious between cats, making it the most clinically significant. FeLV-B and FeLV-C are able to infect cats, but only if the cat is already infected with FeLV-A (4).

Feline leukemia virus is a virus that belongs to the
Retroviridae family, Oncovirinae subfamily. It is a gamma-
retrovirus. It has a genome comprised of a single strand of
viral RNA, surrounded by a protein core and encased within
an envelope (3).

THE FELINE LEUKEMIA VIRAL GENOME

Feline leukemia RNA codes for only a few proteins. The protein that is detected clinically is p27. This is a group-associated antigen (gag), indicating that all subgroups have the same protein. p27 is responsible for viral infectivity, virulence, and subsequent disease. Free p27 can be found in plasma, tears, and saliva. The polymerase (pol) gene codes for reverse transcriptase. Envelope (env) genes encode envelope proteins gp70 and p15e. gp70 defines the different subgroups. An anti-gp70 antibody is able to neutralize all three subgroups. Envelope protein p15e is responsible for immunosuppression in cats (3).

Retroviruses are unique from other viruses in that they carry with them an enzyme called reverse transcriptase (RT). Once the virus has infected a cell, the single-stranded viral RNA is released into the cellular cytoplasm. RT makes a DNA copy of the RNA. The DNA copy is called a provirus, which randomly inserts into the host cell’s DNA (6). As the host cell replicates its DNA, the viral DNA is replicated as well, followed by protein synthesis. The cell synthesizes its own cellular proteins along with viral proteins. The newly synthesized viral proteins come together to form new virions, each with a single strand of viral RNA inside them. FeLV leaves the cell by budding out (3). It takes a little bit of the cell’s plasma membrane and uses it to envelope itself. This process is non-cytopathic and the cell remains alive.