RNA vaccines, DNA vaccines, recombinants … unless you have lived in a cave for three months, you should now be familiar with these scientific terminologies once reserved for a few experts! Among the vaccines developed to fight the Covid-19 pandemic, the Astrazeneca vaccine, with a viral vector, is a revolutionary drug. And yet! Veterinarians have been using this technology for over 20 years to protect cats from Feline Leukosis.
Feline Leukosis is a serious illness triggered by a retrovirus, Felv (Felin leukemia virus). This virus, from the same family as that of AIDS, was isolated for the first time in 1964. Leucosis is transmitted between cats, mainly by bites, mating or from mother to her kittens. The symptoms are varied; we often find anemia (decrease in the number of red blood cells) and cancers such as lymphoma or leukemia. At present, there is no treatment for this terrible pathology. Fortunately, several vaccines are available to veterinarians to effectively protect our little felines from Felv.
What vaccines against leukosis in cats?
There are different types of Felv vaccines depending on the lab.
Some use proven technologies such as inactivated virus vaccines. This consists of injecting the cat with a Felv virus which has been made to lose its virulence with a chemical treatment. In the animal’s body, it is now harmless but still recognized by the immune system. In case of infection with Leucosis, the sensitized lymphocytes will neutralize the virus. Other vaccines are composed only of the antigenic protein.
In the 2000s, the Merial laboratory (now Boehringer) launched an innovative vaccine against feline leucosis on the market; it uses the technology put forward today by Astrazeneca for its anti-covid vaccine: the viral vector vaccine or vector vaccine.
The technology of the vectorized vaccine consists in using not the Felv virus itself, but another (harmless) virus which will serve as a vector for Felv genes so that the cat’s immune system can recognize it and counter any possible infection.
The feline leukosis vaccine uses a canarypox. This is the virus that induces smallpox in canaries. It is not dangerous for the cat in which it can neither reproduce nor persist. Previously, this vector virus has been modified: two genes from Felv have been added to its genome (DNA). When canarypox is injected, it enters a cat’s cells to release its genetic information (this is the normal process of infection and multiplication of a virus). In cells, Felv genes are transformed into antigens (proteins) which are recognized by the cat’s immune system. This phenomenon activates the B lymphocytes (production of antibodies) and T (cellular memory) against these antigens specific to the feline leukemogenic virus.
The Astrazeneca vaccine against Covid-19 uses the same technique. It is a non-replicating or recombinant viral vector vaccine. The vector virus here is an adenovirus usually infecting chimpanzees and harmless to humans. Genes encoding the famous spike protein which allows SARS-Cov2 to attach to human cells have been integrated into its genome.
This viral vector virus technology is still underdeveloped in humans. Thanks to their recombinant vaccine against feline leucosis available for more than 20 years, cats are therefore a precursor!
This vaccine against Felv is safe and effective. The side effects are those usually encountered during vaccination: fever, pain at the injection site, a small lump at the injection site and exceptionally allergic reaction. In current practice, this vaccine has been shown to be very well tolerated, and looking back over 20 years has shown no new adverse effects compared to so-called traditional vaccines. The efficacy of this recombinant vaccine is very good and eliminates the need for adjuvants which are suspected to play a role in the appearance of post-injection fibrosarcomas.
Whatever vaccine your veterinarian has chosen, there are a few rules to follow so that your cat is well protected against Felv:
- Test your cat before vaccination: if your cat is already infected with the leukemogenic virus (as with AIDS, there may be a symptom-free phase of varying length), the vaccine will be ineffective. It may therefore be useful to test certain cats before vaccination if it is believed that they may have been in contact with the virus (kitten from a stray mother, brawling adult cat, etc.) in order to ensure that they are not already infected.
- Observe reminders: to be effective any vaccination requires reminders. At present, it is recommended to vaccinate kittens at 8, 12, 16 weeks and then at 1 year. You must then give a booster injection every year.
- Do not vaccinate a sick cat: the vaccination should not be carried out on a “woozy” animal, it might be less effective.
- Have him sterilized when he is 6 months old: both for the male and for the female, castration makes it possible to avoid certain close contacts, sources of contamination.
Scientists continue to amaze us. And when they work for the health of dogs and cats, they also give their humans a great gift. The vaccine against Feline Leukosis is not only a technological feat but also (above all) thousands of small felines saved!