Download Feline Leukaemia Virus (FeLV)

Feline Leukaemia Virus (FeLV)
Classified as a retrovirus, it is a common infection in cats. Worldwide, it is the cause of more cat
deaths, directly or indirectly, than any other organism and is widespread in the cat population.
The virus incorporates itself within cells and when they divide the daughter cells also contain the
virus. It can result in immune system failure, bone marrow suppression (myelodysplasia) and neoplasia
(cancer). It occurs as 3 subtypes that can cause slightly differing disease presentations, but all 3 forms are
diagnosed with existing test and prevented with current vaccines.
Clinical signs
There is a long pre-clinical phase, so it is often diagnosed on a routine test, in an otherwise healthy cat.
Once cats are ill due to the infection, they commonly present with mass loss, or signs of immune
suppression like diarrhoea, big lymph nodes, dehydration, fever, abscess’s, nasal and ocular discharge
(snuffles). Any organ can be affected and facial skin lesions are another unusual presenting sign.
Approximately 1/3 of cats with immune mediated attacks on their blood are FELV positive, and cats that are
persistently FeLV positive have a sixtyfold increased risk of developing a cancer called lymphoma. If they
have developed bone marrow failure and a low blood count or cancer, they often present with weakness,
lethargy or poor appetite. Cancer within the chest causes increased breathing (dyspnoea) effort or
struggling to get air in.
When FeLV localizes in specific organs, signs attributed to that location, for e.g. infection in the brain
causes weak back legs, and causes cats to be off balance or blind. FeLV in the queen often causes
abortions and “fading kittens” that die within 2-3 weeks of being born.
Disease Transmissions
FeLV can be transmitted in several ways:
I.
II.
III.
IV.
V.
Oro-nasal route – via the saliva of infected cats, thereby, contaminating the eye, mouth and nose
mucous membranes of non-infected cats via licking and grooming.
Via bite wounds
Via faces
In infected blood to non-infected cats
From mother to foetuses (developing kittens) during pregnancy – Note it is NOT infective to dogs or
people!!
Post exposure Disease Progression
Older studies - showed that young cats < 1 year of age, are more likely to become persistently viraemic, and that
2/3 of older infected / exposed cats eliminate the virus and become immune
Newer studies with m ore sensitive testing for the virus show that most cats are more likely to remain infected for life.
This has led to 2 main forms of the disease being recognized post exposure:Progressive infection: These cats are persistently viraemic and usually succumb to FeLV related diseases
as they do not develop immunity to virus
Regressive Infection: - An effective immune response limits viral replication and although virus is detected
in blood for 2-3 weeks post infection, it then disappears 2-8 weeks later.
In those cats that do not develop immunity, the virus spreads to the bone marrow. Diseases may occur in
any of the tissues invaded by the virus, or the virus may be directly responsible for other illnesses because
of its immunosuppressive effect.
Cats with latent (regressive infections are thought to be intermittently capable of transmitting the disease in
saliva, tears and urine. If a stressful event reactivates the viraemia, some of these latent carriers will
become clinically ill and these ostensibly recovered FeLV provirus-positive cats may act as a source of
infection but seldom get ill from the presence of FeLV RNA in their cells.
Diagnostic Tests
The diagnosis is made by testing the cat’s blood for the presence of the virus itself. This can be done inhouse with a snap test (Eliza or IFA test) or at a lab with a very sensitive molecular test called a PCR test.
As cats can “self cure”, 2 positive tests, 2 months apart are needed to confirm a diagnosis of FeLV
infection.
Latent carriers – will unfortunately remain negative on ELIZA and IFA tests.
Note: Vaccinations does not cause IFA, ELIZA or PCR tests to give false positive results
Kittens may be tested at any age. However infection in newborn kittens may not be detected until
weeks to months after birth. Therefore, several FeLV tests during the first 6 months of life may be
necessary to feel completely “safe” about a negative test result.
Summarizing outcomes following exposure to FeLV
FeLV Ag in blood
Viral Blood Culture
Positive PCR for
FeLV in blood
FeLV-associated
Disease
Positive infection
Positive
Positive
Positive
Likely
Regressive Infection
Transient ►then
Negative
Transient ► then
Negative
Transient ►then
Negative
Unlikely
Cats with known exposure to FeLV – All kittens or adult cats tested after a known or suspected
exposure to FeLV that tested negative on the ELISA screening, should be retested to rule out possible
negative results obtained during incubation of the FeLV virus. Although the majority of cats will test positive
within several weeks, final retest of negative cats should be sooner than 90 days post-exposure.
Other tests may be needed to look for signs that the infection may be local/localized in an organ, or that the
other problems have occurred 2nd to the virus. These may include blood chemistry, full blood counts, xrays, bone marrow aspiration, lumber puncture, eye exam and specialized antibody tests.
Treatment
There is no effective treatment for the myeloproliferative (bone marrow) form of leukaemia. Treatment is
mainly supportive, and my require cortisone, antibiotics, chemotherapy and blood transfusions. These cats
must become 100% indoor cats to prevent spread of the virus and to prevent exposure of these cats to
infectious agents that will hasten their demise.
FeLV cancer (lymphoma) has a better response to therapy than bone marrow failure (myeloproliferative
daisies) and has the same response to chemo as do FeLV negative cases.
Monitoring
As there is no therapy and a long sub clinical phase can occur, we advise:
1. Keep these cats indoors to prevent exposure to infectious diseases
2. Full bloods and urine checks with chest x-rays every 4-6 months to pick up the disease changes
early
3. Routine vaccinations of FeLV cats should be maintained (on a yearly and NOT 2-3 Yearly basis)
using killed virus vaccines only
Prognosis
Without therapy of secondary problems, 85% of cats with persistent FeLV infection (positive tests 2 moth
apart), are dead within 3 years of the diagnosis. However, with proper monitoring and care much longer
longevity can be acquired.
Which casts are at RISK? – These are high risk exposure to FeLV:
Includes outdoor cats, indoor/outdoor cats, stray/feral cats, open multi-cat households, FeLV positive
households, and households with unknown FeLV status.
Low risk of exposure to FeLV would include indoor cats and closed multi-cat households that have
tested negative.
PREVENTION OF FeLV
There are several preventative measures that can be taken to decrease the risk of contracting FeLV. The
vaccine has good efficacy, but no vaccine is 100% so vaccination should NOT be used as a substitute for
testing, identifying and isolating infected cats.
1. Vaccination of at risk cats: Cats should be FeLV tested, and then vaccinated if
they are negative
Kittens – first vaccination at > 8 weeks of age with a booster vaccine after 1 month and then
annually till at least 4 years of age.
Older cats – initial vaccination with a 1 month booster then annually.
Duration of immunity from a single vaccination may vary from fifteen weeks to three years
Positive cats should be isolated from other cats and re-tested after 2 months and if negative ►
VACCIANATE THEM!!!!
In FeLV-negative cats -Vaccinations may also be associated with adverse events and duration
of immunity may vary from fifteen weeks to three years.
In FeLV positive cats – vaccinations of
infected cats does not affect the carrier
state, the capacity to infect other cats, or
the development of disease in the
infected cats. Rather test all cats prevaccination
2.In large catteries: - a test and removal programme can be instituted
3.Multi-cat households with FeLV positive cats should be maintained as a closed
colony:
Kindly note the following:
There a number of modified live FeLV vaccines. They are either all killed or recombinant
types. Retroviruses are unstable, live for only minutes outside the cat’s body, and are
readily destroyed by most disinfectants. Because the FeLV is so unstable, handlers of cats
are very unlikely to spread the disease between cats. This implies that a new healthy cat(s)
can be brought safely into a recently “contaminated” house within days of the departure of a
FeLV infected cat.
The following vaccine sites are recommended
RF ► Right shoulder – as low down as practical
Panleucpaenia; Herpes; calicivirus (+/Chlamydia)
LR ►Left rear leg – as far down as practical
Leukaemia virus (+/- other Antigens except Rabies)
RR ►Right leg:
Rabies Ag (antigen) + (any other antigen)
(RR – Rabies Right)
LF ►left shoulder - or left side of the body
Animal Clinic Brackenfell
Western Cape, South Africa
Other intramuscular injections should be administered
avoiding the right rear leg. Other Sub cut injections
should be administered on a side of the body or over
the Left Shoulder (LF).
Between the shoulder blades and over the top of
the back should be avoided for all injections