Feline Leukemia
Erin O’Riley
Katie Colbrook
Feline Leukemia
• Usually abbreviated as FeLV
• First discovered in domestic cats in Scotland
• 1964
• Cross-species concern
• Domestic/feral cats(natural hosts) Wild Felids
• No reports of infection in humans
• Although human (and canine) tissue cultures grown in labs can be
infected with disease
Animals affected:
• Felids
• Both domestic and wild
• Seen in house cats, feral cat populations, Iberian lynx, captive
bobcats, Florida panthers and wild cougars
• Any age
• Biased towards males
• Virulent virus more common in domestic cats and wild felids of male
gender usually do to higher aggressiveness
FeLV Genetic/Virus Characteristics
• Carried in RNA
• Gammaretrovirus
• Is a genus of the retroviridae family
• Known for causing sarcomas and different
types of leukemia
• Total genome is about 9,600 base pairs
• This virus causes a disease which is a form
of cancer of blood cells called lymphocytes
Structure of FeLV Virus
Process of Infecting Host Cell
Transmission Dynamics
• Horizontal Transmission (Direct Contact)
• Saliva
• Cats are social animals constantly grooming each other
• Urine
• Blood
• Free floating in blood plasma so mechanical vectors (blood sucking
parasites) a possible concern
Stages of FeLV
There are 6 stages of FeLV infection:
• Stage One: The virus enters the cats system and infects the
epithelial cells then moves to different types of white blood
cells called lymphocytes and macrophages. These white blood
cells then move to the lymph nodes where the virus begins to
replicate.
• Stage Two: The virus enters the blood stream where it is
spread throughout the body.
• Stage Three: The virus enters the lymphoid system spreading
further though the felines body.
Stages Continued
• Stage Four: This is the main point of infection in the feline
where if the cat's immune system does not fight off the virus,
then it continues on to stage five
• Stage Five: The bone marrow becomes infected. When this
occurs the virus will stay with the cat for the rest of its life.
Then it is released from the bone marrow to further take over
the felines body.
• Stage Six: Feline becomes overwhelmed by infection and
mucous and glandular epithelial cells become infected. When
this occurs the virus can be easily transferred to other felines.
FeLV mortality
• Felids who contract FeLV have 3 possible outcomes:
• The cat produces neutralizing antibodies to eliminate virus
• The cat can remain latently infected
• The virus is virulent and the cat shows symptoms immediately
• No curative treatment
• Vaccine makes virus go into latency
• FeLV causes:
• Lymphoma
• Anemia
• Immunosuppression
• These secondary infections are typically
the cause of death
Signs of Infection
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Loss of appetite
Slow weight loss
Poor coat condition
Enlarged lymph nodes
Persistent fever
Pale and inflamed gums
Infections of the skin, urinary bladder, and upper respiratory
tract
Persistent diarrhea
Seizures, behavior changes, and other neurological disorders
A variety of eye conditions
Spontaneous abortions in pregnant females
FeLV Detection
• PCR
• Polymerase Chain Reaction
• Detects virulent and latent infection
• ELISA
• This tests for the antigen present when cats are infected
virulently with FeLV
Iberian Lynx
• FeLV was rarely reported and/or detected in wild felids until
the year 2007 when an outbreak occurred in the Iberian Lynx
population in Doñana (located in Spain).
• Even before the outbreak…
• The Iberian lynx is the most critically endangered felid species
in the world
• Due to predators losing population density because of:
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Human/wildlife conflict
Over harvesting
Prey decline
Habitat loss due to human encroachment
• Conservation measures were implemented to sustain the
species
Conservation of Iberian Lynx
• Since the Iberian lynx was known to be in trouble due to such
low densities (~160 individuals ) conservation efforts were
imposed
• Beginning of breeding season in ‘06-’07 in the CRS (Coto del Rey
subpopulation)
• 7 feeding stations were outfitted
• 12 drinking stations available
Before the Outbreak
• Positive for FeLV viremia Lynx discovered in December 2006
• Past knowledge of FeLV did not lead managers to find great risk in
releasing the infected individual
• Infection was probably due to contact with an infected feral cat
• Large populations of feral cats surround this area
Beginning of Outbreak (2007)
• Two more lynx were found dead and tested positive for FeLV
viremia
• This lead to construction of an FeLV Control Program specified
for the Iberian Lynx
FeLV Control Program
• Goals:
• 1. Control FeLV focus and stop spread across all of the Doñana
population
• 2. Remove virus from population
• 3. Minimize possibility of a new outbreak
• Objectives:
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1. Remove FeLV viremia positive lynx from wild
2. Give FeLV vaccine to all uninfected individuals
3. Modify management feeding/drinking stations
4. Reduce the feral cat population
FeLV Control Program
• Domestic cats were captured in lynx distribution areas
• ELISA tests done
• All viremic cats euthanized
• Cats not infected were returned to owners or rescue center after
being vaccinated
• All Lynxes were captured and transported to a clinic
• ELISA and PCR tests done
• If ELISA test was positive (conclusive to a viremic lynx) they were
moved to a rescue center until infection became latent
• All latent lynx returned to wild after being vaccinated
• Recapture and a second dose of vaccine was administered for as
many lynx as possible to achieve best results
Interpretation
• FeLV outbreak in the Doñana area probably due to interaction
of lynx with feral/domestic cats
• Spread of FeLV occurred because of
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Breeding season increases intraspecies contact
Feeding and Drinking stations increased intraspecies contact
High pathogenicity of the FeLV strain in the lynx
High density of the subpopulation
FeLV Prevention
• Decreasing interactions between domestic cats from wild
felids
• Side note: “green belt” areas made for wildlife should be farther
away from suburban areas to limit these interactions
• Should latent felids be released back into wild?
• Could cause new outbreak in future
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Vaccinate high risk populations of wild felids
Stricter vaccination policies of domestic cats
Don’t define threat level of a virus because its unpredictable
Critically think out conservation actions
• i.e. feeding stations that encourage saliva transfer
Sources
• Alexander, K.A. (2009). Successful intervention in a disease outbreak
in the endangered Iberian lynx: what can we learn? Animal
Conservation,12.183-4.
• Hardy, W.D., Old, L.J., Hess, P.W., Essex, M. and Cotter, S.
(1973).Horizontal Transmission of Feline Leukaemia
Virus.Nature,244.266-8.
• Hoopes, J., Baines B., Smyth, T., and Nugent, C. (2009). Overview of
feline leukemia virus and symptoms.
http://homepage.usask.ca/~vim458/virology/studpages2009/retrovi
ruses/plfelv.html
• Lopez, G., Lopez-Parr, M., Fernandez, L., Martinez-Granados, C.,
Martinez, F., Meli, M.L., Fil-Sanchez, J.M., Viqueira, N., Diaz-Portero,
M.A., Cadenas, R., Lutz, H., Vargas, A. and Simon, M.A. (2009).
Management measures to control a feline leukemia virus outbreak
in the endangered Iberian lynx. Animal Conservation, 12. 173-8.
Sources Continued
• Luaces, I., Domenech, A., Garcia-Montijano, M., Collado, V.M.,
Sanchez, J., Tejerizo, G., Galka, M., Fernandez, P. and GomezLucia, E. (2008). Detection of feline leukemia virus in the
endangered Iberian lynx. J Vet Diagn Invest 20, 381-5.