Leukemia Virus in Cats

Leukemia virus in cats (FeLV) is a retrovirus that was first discovered in 1964 in a cat Leukemia Virus in Catswith leukemia.  The virus is associated with a number of different types of illnesses in addition to cancer, including anemia and immunodeficiency.  Although it is called the feline leukemia virus, it is more commonly associated with other types of diseases in cats than it is with leukemia, which is a relatively uncommon type of cancer in cats.  FeLV infection is estimated to affect 1-8% of healthy cats worldwide and 3-4 times more likely to be detected in cats with clinical signs of illness.  Due to testing and vaccination programs, the prevalence of the virus has declined since it was initially discovered.

Genetic features of leukemia virus in cats

FeLV is a retrovirus, which means that its genetic material is transmitted to the cat as RNA.  In a cell, the RNA is converted to DNA and become inserted randomly into the cat’s DNA.  The virus encodes three major protein groups: group-specific proteins or antigens (gag), a reverse transcriptase (which allows the RNA to be converted to DNA), and envelope proteins.  One of the gag proteins called p27 is abundant in the blood plasma of infected cats and cytoplasm of infected cells, which most tests for FeLV in cats are designed to detect.  The envelope protein gp70 defines the virus subgroup and appears to be important for inducing an immune response by the cat.  Most commercial vaccines for FeLV are designed with this thought in mind and induce virus-neutralizing antibodies specific for gp70.

Subgroups of leukemia virus in cats

There are three subgroups of FeLV called A, B and C, which vary in the disease they cause in cats.  Subgroup A is the most common isolate in 100% of cases and is passed horizontally, meaning from cat to cat.  Subgroup B occurs when the FeLV A virus envelope gene combines with endogenous retroviral sequences.  This occurrs in approximately 50% of infected cats, and is associated with immune suppression and tumors in cats.  Subgroup C is rare in approximately 1% of infected cats and occurs when a mutation in the envelope gene sequences occurs.  Subgroup C is most commonly associated with the development of fatal anemia in cats.

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