varies in cats,
depending on immune status of the cat, virulence of the virus, and dose
of virus the
several stages in the disease process:
INITIAL ORONASAL INFECTION
The virus replicates in
oropharyngeal lymphoid tissue.
happens next depends on the cat’s immune system:
cat uses its cell-mediated immunity to
inhibit further viral
eliminate it from the body. The cat
develops high levels of neutralizing
antibody so the virus cannot
blood is tested, FeLV is
not detected, but high levels of anti-FeLV antibody are found. These cats are called REGRESSOR cats (3). They
are free of infection and are now immune
to further FeLV infection.
cat cannot prevent viral replication and the infection becomes systemic
virus traveling in lymphocytes and monocytes through the circulation. A blood sample will reveal detectable FeLV
p27 protein (3).
cat with systemic virus is
viremic. This occurs 2-4 weeks
post-infection. The virus is carried to
the thymus, spleen, lymph nodes, and salivary glands.
At this stage, the cat shows signs of
malaise, fever and lymphadenomegaly (5).
has a transient viremia, the virus can
be removed completely from
within 3-6 weeks on average (maximum of 16 weeks).
While the cat’s immune system is trying to
remove the virus, cats are infectious and shed the virus (3).
The virus has not yet infected the bone
marrow at this stage.
of infected cats show transient viremia.
Once it is cleared, they are
immune to recurrent infection of
4) BONE MARROW INFECTION
viremia persists, the harder it is to
When the virus infects hematopoietic cells of the bone marrow at
weeks, the condition worsens. All
granulocytes are infected as well as
platelets because the
are precursors for these cell lines (5).
still remove the viremia at this stage,
but they cannot completely
virus since the provirus has inserted
into the bone marrow stem cell
DNA. They end up with a latent
infection. No virus is produced at
this time because the
proviral DNA is not translated, so the cats will test negative for FeLV
(5). Latent infections are not really
significant to the veterinarian because these cats cannot spread the
infections can eventually be eliminated at 9 – 16 months.
If not eliminated, a latent infection can
reactivate under various stimuli such as stress, glucocorticoid
immunosuppressive drugs (3). Upon
reactivation, the cat becomes viremic
once again and sheds the
The longer the virus remains latent, the
harder it is to reactivate because the provirus
is slowly being deleted
from the precursor blood cells (5).
cats, the viremia persists for longer
than 16 weeks.
It is not cleared and so becomes a persistent
viremia. Cats are unable to mount a
good enough immune response to remove the virus. This
is a permanent and eventually fatal
condition within 3 years of initial infection.
They die of FeLV-related diseases.
These cats remain infectious throughout life and only have low
circulating neutralizing antibodies. A
cat exposed to the virus once has a low chance of developing persistent
viremia. A cat that is continually being
contagious cats has an increased risk of developing persistent viremia
spreads to epithelium of lacrimal glands, salivary glands, intestine,
urinary bladder at 3-4 weeks. At this
cats can have up to 1 million virus particles per milliliter of saliva