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Cavanaugh, Mike cavanam at HESKA.COM
Fri Aug 7 17:46:41 EST 1998

Dear Michele Mura,

Regarding the results you've found with the HESKA=D4 Solo Step=D4 FH, we =
not surprised that you have found 20% of the cats tested to be positive.
 Before the Heska antibody test was developed, there was not a good way
of identifying cats with heartworm infection.  Many veterinarians used
in-clinic antigen tests which were originally introduced to diagnose
canine heartworm, but were subsequently approved for use in cats.  Any
antigen tests will miss many feline infections because they lack the
ability to detect male-only infections.  Cats have small worm burdens
and hence have a much higher likelihood of single-sex infections than
dogs do.  Therefore, you now have the ability to detect the infections
in more cats than you did before.  Do all 20% of the cats have worms
present in the heart?  Probably not.  Not all cats infected with
heartworms end up with adult worms in the heart and/or pulmonary
vasculature.  From the minute cats get infected, their immune system is
working to try to clear the infection.  When the infection is cleared,
anti-heartworm antibodies will remain in their system and they will test
positive on the antibody test for a period of time.  It is unknown how
long those antibodies persist, because the only way to know for sure
would be to necropsy every infected cat at specified time to see when
the worms are gone vs. when the antibodies are undetectable.  You can do
echocardiography to help confirm the diagnosis.  Drs. Genchi and Venco
from Italy has done some very interesting work with echocardiographic
diagnosis of heartworm infection in cats and in the same study they
found very good correlation between cats being echo positive for
heartworms and testing positive on Heska's test.

In terms of reading the test, if you are using serum or plasma, read the
test at 5 minutes.  If  you are using anticoagulated whole blood, read
results at 5 to 10 minutes.  If you have no red line at that time, the
test is negative. Do not read the test after 10 minutes.  The blue
procedural control line should always come up.  If it does not,
something has gone wrong and you need to re-run the sample. =20

Our distributor in Italy is FATRO.  Their technical services number in
Bologna is 051-791-517.  They should be able to help you with anything
you perceive to be a problem.   You may also contact Heska's website at

Thanks you for your interest in Heska products.

Dr. Mike Cavanaugh
Director,  Medical and Technical Consultation
Heska Corporation
Ft. Collins, CO

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