Feline leukaemia – to vaccinate or not PDF Print E-mail
News - Rubrieke
Monday, 22 February 2016 18:46
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Dr Liesel van der Merwe is a small animal medicine specialist. Send her your questions: This e-mail address is being protected from spambots. You need JavaScript enabled to view it .


Dr Liesel van der Merwe

I was working a weekend shift a few weeks ago and a client from the Mooikloof area asked why we didn’t routinely vaccinate against feline leukaemia virus, as many cats in her area were infected or had died from it. So, this brought a discussion to the fore of the infection and core and non-core vaccines.

FeLV is the most common cause of cancer in cats, as well as causing many blood disorders and immune deficiency, resulting in opportunistic infections that are responsible for many of the diseases associated with FeLV.

Infection and susceptibility
Cats persistently infected with FeLV serve as sources of infection. Viraemic cats shed the virus in very high quantities from the saliva, nasal secretions, faeces and milk. Risk factors are young age, high population density and poor hygiene.

Transmission occurs mainly through friendly contacts, such as grooming, as well as biting and rarely through shared feed bowls and litter trays. Transmission can also take place from an infected mother cat to her kittens, either before they are born or while they are nursing.

Feline leukaemia virus does not survive for long outside the host and is readily inactivated by disinfectants, soap, heating and drying. 

Cats at the greatest risk of infection are those exposed to infected cats, for example multi-cat households with unknown status cats, cats allowed outdoors unsupervised (95% of South African cats I would presume) and kittens born to infected mothers. Young cats are much more susceptible to infection than adult cats.

Stages
There are two stages of FeLV infection: primary viraemia is the first wave of infection after exposure. During this stage some cats have an effective immune response, eliminate the virus from the bloodstream, and halt progression to the second stage.

The secondary viraemic stage is characterized by persistent infection of the bone marrow and other tissue. The majority of cats with secondary viraemia will be infected for the rest of their lives.

Examining the odds of what will happen to a cat exposed to FeLV in a multi-cat household without control of FeLV infection, the following percentages are found: 30-40% of the cats will develop persistent viraemia; 30-40% will become latently infected; and 20-30% will never be detectably viraemic. 

The cats which become latently infected may reactivate if they experience immune suppression or chronic stress. Latently infected cats do not shed the virus.

Related disease
During the early stages of infection, it is common for cats to exhibit no signs of disease. However, over time the cat's health may progressively deteriorate or it may develop recurrent illness.

Signs can include loss of appetite, slow but progressive weight loss, followed by severe wasting late in the disease process, poor coat condition, enlarged lymph nodes, persistent fever, pale gums and other mucus membranes, inflammation of the gums (gingivitis) and mouth (stomatitis), infections of the skin, urinary bladder and upper respiratory tract, persistent diarrhoea, seizures, behaviour changes, and other neurological disorders. Prognosis in these cats is poor, and most will die within three years of diagnosis.

Diagnosis
Infection is diagnosed using an in-house ‘Snap Test’ which usually tests for FeLV and FIV at the same time. The test kit has an antibody to recognise certain protein parts of the actual FeLV and is called an antigen test.

It can detect a virus in both the first and second stage of disease. It is, however, the interpretation of this result which is important. As the incidence of a disease decreases, there are more false positive results in a test. So, you have to look at the whole picture and not just read a result.

If the test is just a pre-vaccine screen of a healthy cat, then the animal may overcome the infection and test negative three to four months later. The ‘Snap Test’ cannot pick up a latent infection. If the test is positive in a sick, an anaemic or a thin cat, then the result is more reliable and likely to represent stage two disease.

Prevent 
The only sure way to protect your cat from getting the disease is to prevent exposure to FeLV-infected cats. Adopt only infection-free cats into households with uninfected cats, house infection-free cats separately from infected cats, and don't allow infected cats to share food and water bowls or litter boxes with uninfected cats.

Consider FeLV vaccination of uninfected cats. FeLV vaccines are widely available, but since not all vaccinated cats will be protected, preventing exposure remains important even for vaccinated pets.

FeLV vaccines will not cause cats to receive false positive results on ELISA, IFA or any other available FeLV tests.

Vaccinations are divided into two groups: the core vaccines and the non-core vaccines. Core vaccines are recommended for all cats either because the disease the vaccine protects against is extremely severe and/or is especially common, or the disease is a threat to humans. Non-core vaccines are recommended only for cats whose life-styles or living situations place them at risk for the disease.

Core
For cats, core vaccines include feline panleukopaenia, feline calicivirus and rhinotracheitis (also known as feline snuffles) and rabies. Non-core vaccinations for cats include vaccinations for diseases such as FeLV.

The need for these vaccinations is determined on a case by case basis. All cats at risk of exposure should be vaccinated – kittens at the age of eight or nine weeks and again at 12 weeks, together with core vaccine components.

To avoid “vaccine failures” all cats should be tested for infection before vaccination. Boosters can be given every two to three years after three years of age as natural resistance increases.

 

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