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About FIV (Feline
Immunodeficiency Virus)
The
incidence of FIV infection is 1-3% in healthy appearing cats
and up to 15% of sick cats. An excellent expose about this disease
is available at the Cornell
Feline Health Center.
FIV Testing and FIV
Vaccination
Cats
that are vaccinated with the new FIV vaccine develop antibodies to
subtypes (strains) A and D that are present in the vaccine. All
commercially available tests are based on finding FIV antibodies
in the serum. This means that vaccinated cats will show a positive
result on these tests, including the Western Blot, used as a
confirming test when the patient initially tests positively. Cats
that test negative for antibodies are very likely truly negative.
There are questions regarding efficacy. The vaccine efficacy studies used only subtype A to
challenge the vaccinated cats. Subtype B is actually more common
in the east coast of the United States. Given the virus' ability
to mutate and a lack of information on Subtype B challenge, can we
be confident this vaccine will "work" in our region? We
certainly cannot assume that all vaccinated cats are fully
protected.*
Consequences of the diagnostic confusion
between vaccinated cats and FIV infected cats are listed here-
1.
Until a test is readily available to differentiate FIV vaccinated
and FIV infected cats, it will be impossible to tell
vaccinated cats from infected cats or infected AND vaccinated
cats.
2.
Reducing virus transmission by testing and isolating positive cats
will be less effective.
3.
It will be more confusing to bring a positive testing cat into
households with uninfected cats, even if the others are
vaccinated. It is unrealistic to expect all vaccinated cats to be
protected.
4.
Kittens born to vaccinated cats will likely test positive until
about 8 weeks of age, according to the manufacturer.
5.
Perhaps the most tragic possibility is the situation where a
vaccinated house cat escapes, is picked up by a shelter, rescue
group, or other well meaning person. The animal is tested
and shows positive for FIV on a combo test (leukemia/FIV in office
kit). The cat is then euthanized (put to death).
Until a test is developed that can distinguish between infected
and vaccinated cats, we at Ebenezer Animal Hospital prefer to
offer this vaccine only in very special circumstances.
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