Cause

The causative agent is feline leukaemia virus (FeLV) an oncornavirus belonging to the retrovirus group. It consists of a single strand of RNA protected by an envelope. Based on nucleotide studies it is believed to have evolved from a virus prevalent in an ancestor of the rat.

This virus does not kill cells that it infects, and it replicates by budding. During budding the viral particles assume some host antigen and so are protected from the hosts immune system because they are recognised as "self". The bone marrow, salivary gland and epithelium of the respiratory tract are just some of the tissues in which this virus can replicate.

Signs
Initial signs of FeLV infection include:

• general dullness and 
• enlargement of lymph nodes (called lymphadenopathy). The lymphatics form part of the cats's immune system, and this enlargement is part of the immune response to the presence of the virus in the body. If the immune system is unable to eliminate the infection the virus migrates to bone marrow where it affects blood cell production.

Later signs include :

• weight loss
• recurrent infections

a) The development of cancer - lymphoma - often involving the intestine or the thymus region of the chest

b) Cancer of the blood cells (Leukaemia) - white cells and red cells

c) Anaemia due to bone marrow suppresssion

d) Reproductive abnormalities - including infertility, abortion, resorption

e) Osteochondromas (cancer of cartilage)

 

Transmission

Close contact is needed and transmission from one cat to another occurs mainly via saliva. Apparently healthy cats can live for years and yet have FeLV virus in their blood (called viraemia) and shed virus all the time. Other routes of transmission are much less likely - in urine, faeces, other secretions , via flea bites, from contaminated hypodermic needles, surgical instruments, blood transfusions, infected environmental materials because in the environment the virus only survives up to 48 hours.

Feline leukaemia virus is not highly contagious , so infected individuals can be kept in a hospital environment - provided direct contact with other cats is prevented, and reasonable hygiene is practices - such a snot sharing feeding utensils, and washing hands by personnel after handling each individual cat.

Transplacental transmission does take place , and transmission can also occur in the immediate post-natal period when the infected queen grooms them. Kittens are more susceptible to infection than adults.

Long term problems