FeLV infection

(15.08.2009) ABCD recommends FeLV prevaccination testing - but to be “interpreted with care”

The European Advisory Board on Cat Diseases (ABCD) published the first European prevention and treatment guidelines for feline leukaemia virus (FeLV) infection.

FeLV occurs worldwide and is mainly transmitted during close, ‘friendly’ contact such as mutual grooming and using the same bowl, although it may also be transmitted by biting. The general prevalence of the infection in most European countries is low (around or below 1%), although in some regions it exceeds 20%.

Young cats particularly susceptible

Risk factors include young age, high population density (multi-cat households and shelters), outdoor access (contact with infected cats) and a high local prevalence of infection.

“A healthy immune system may overcome the infection, but under crowded conditions, up to one in three cats may become persistently viraemic”, explains Professor Hans Lutz (Zurich Veterinary Faculty), ABCD member and internationally recognised specialist on feline retroviruses.

“This may lead to a wide variety of clinical signs, with immune suppression, anaemia and lymphoma being the most prominent. Most of these cats will die within two years after diagnosis.” Young cats are particularly susceptible, as resistance develops with age.

Vaccination: only if at risk

FeLV vaccines are the only anti-retrovirus vaccines available today in Europe, human medicine included. Vaccination is recommended for cats at risk, certainly for young cats with outdoor access and contact to other cats, in areas with a high prevalence of infection. Kittens should receive their initial vaccinations at 9 and 12 weeks of age, followed by annual boosters.

Considering the lower susceptibility of older cats, the ABCD recommends boosters to be given not more often than every two to three years to cats of three years or older – and only if at risk.

Pre-vaccination testing: interpret with care

If the cat’s history is unknown, it should be tested for the presence of FeLV antigen in the blood before vaccination, as vaccination of a viraemic cat is useless. However, positive results obtained with in-house test kits should be interpreted with caution, in particular in healthy cats and in areas where the prevalence is low: the possibility of a false positive result increases as the local prevalence drops. Therefore, the ABCD recommends that an unexpected positive result in a healthy cat should always be confirmed, preferably using provirus PCR offered by a reliable laboratory.

Furthermore, true positive results may indicate a transient viraemia, which occurs in around 30-40% of cats, which are generally not at risk of developing a FeLV-related disease.

Management of FeLV infected cats

Persistently viraemic FeLV-infected cats should be kept isolated to prevent transmission to other cats. For their own benefit, FeLV-infected cats should be kept separate from cats suffering from other infectious diseases and should receive regular clinical check-ups, complete blood counts (CBC), biochemistry profiles, and urinalyses. Treatment of sick, viraemic cats with feline interferon omega was shown to improve clinical signs and extend survival time, even though it did not ’cure’ them of viraemia.

For further details and downloads of the full-text ABCD Feline Leukaemia Guidelines, please visit www.abcd-vets.org. There you will also find recommendations for specific situations, such as breeding catteries and cats undergoing corticosteroid treatment.

The guidelines on FeLV were adopted at the sixth meeting of the ABCD, held in Munich (Germany) on 24-26 October 2007. At the meeting, the panel also discussed feline immunodeficiency (FIV) and rabies in cats, for which guidelines are currently in preparation.