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I was recently fortunate enough to be able to spend some time in the
labora-tory of Dr Niels Pedersen at the Uni-versity of California,
Davis.
These are his current feelings on FIP/Coro-na Virus infections and
the
serologi-cal testing thereof. As there is much controversy surrounding
this disease, the diagnosis and interpretation of serological results
and
also the advice that should be given to cat owners, I felt it important
to
share Dr. Peder-sen's view with practitioners. He says:
“The virus of FIP is genetically very similar to the common feline
coronaviruses (FECV) and we believe that it is a simple mutant that
occurs with some frequency during out-breaks of FECV infection.
The
FIP virus and FEC virus are so close that there are NO SEROLOGIC
TESTS THAT CAN DISTINGUISH ONE IN-FECTION FROM THE
OTHER. Therefore, all so-called serology merely measures antibodies
to
the entire group of coronaviruses. Although there is a
tendency for cats
with FIP to have higher antibody titres than cats infected only with
FECV, there is so much as TO NEGATE CORONA-VIRUS SEROLOGY
AS A PRIMARY DIAGNOSTIC TOOL FOR FIP”.
“FECV infection is endemic within virtually every cattery. The larger
the
cattery, the closer the confinement, and the more kittens that are
raised,
the more problems that vou will have with FECV. Although FECV
only
rarely causes severe diarrhoea, it does cause seroconversion.
Kittens
are infected with FECV at a very young age. Almost all kittens become
coronavirus seropositive. Cats that remain carriers and fecal
shedders of
the virus will usually maintain rela-tively high titres, while cats
that lose
the infection will have rapidly declin-ing titres.”
“Most cases of ElF occur because of two reasons”:
1) A high incidence of FECV in-fection within the
cattery, which
is usually a husbandry problem - too many cats,
too many
kittens, too poor sani-tation, too high density.
2) Genetic susceptibility or high stress. Many strains of
FIP virus
are of low pathogenici-ty. Cats infected with
such strains will
usually contain the infection in their body, and
most will
eventually get rid of it altogether. in others,
the infection will
persist and over a period of time the low grade
infection or
stress will grind down the cat's resis-tance and
allow the
infection to activate and kill the ani-mal.
However, I feel that
most cases of FIP are from en-dogenous rather than
exoge-nous
infections.
“Pathogenesis depends on an in-tact immune system”
i) A healthy immune system - no infection
ii) Partial cellular immunity -
dry form FIP
iii) Ineffectual cellular immunity - wet form FIP
“The reason why serology is no good is that, given the nature of FECV
infections in catteries, 70% or more cats will test positive with varying-
titres. Most of this seroconver-sion will have NOTHING to do
with FIP
infection. The so-called FIP test will NOT tell: (1) whether or not
there is
FIP in a cattery; it will only tell that there is FECV infection; (2)
whether a
seropositive cat is shedding FIP or FEC viruses; (3) whether a cat
will at
any time develop FIP during its life; or (4) whether or not a cattery
has
FIP at the time of testing. The only value of serology is to confirm
that
the cat-tery has FECV. This is of no value as most catteries have the
virus, -although it might indicate an over-crowded, over-stressed
catterv”.
“Cattery breeders should not stop breeding cats because they have core-
navirus seropositive animals. If they have no problems with FIP, their
ge-
netics, husbandry, etc., are probably good. I would also not
make
seroneg-ativity a criteria for going to a show, because this would
negate
virtually all showing. Owners should only be concerned when FIP losses
become frequent and high. Such a scenario would prompt a close
look at
the ge-netics of the cats and the husbandry. Virtually every breeder
will
occasion-ally lose a kitten from FIP if they breed enough cats, and
are in
the business long enough. If you are raising dozens of kittens
a year,
and only one in a hundred are dying of FIP, this is acceptable.
Catteries.
should not waste money on routine FIP serology, because serology
cannot be fully interpreted at the present time. If a veterinarian
suggests
that cats be tested, but cannot explain what to do with the results,
then
the veterinarian does not understand the disease and should not be
offering that service. Healthy cats should not be culled or killed
because
they are coronavirus seropositive. It has been stated with some
truthfulness that FIP serology may kill more cats than FIP”.
“If a cattery has a MAJOR out-break of FIP, stop ALL breeding for 6-12
months. Major outbreaks of FIP usually follow the introduction of a
certain new strain of FECV into a cattery. By stopping breeding,
you get
rid of the fuel (young kittens) that will sustain the infection. Also,
by
waiting you will allow the infec-tion to become endemic and for most
of
the older cats to become immune. This will limit the spread of the
vi-rus.
Periodic losses of a single kitten should be handled more conserva-
tively. Continue breeding as if noth-ing has happened and see what
occurs over the next year or so. If death losses slowly rise,
think about
making changes and/or husbandry. Male or female cats that frequently
produce affected kittens should be eliminated from the cattery.
The only
way to diagnose FIP is by clini-cal symptoms; even doing liver bi-opsies
will not help as this is like trying to catch a goldfish in a big dam
using a
spear gun”.
“The problem with the disease is that it is too complex to explain to
lay
people. That is why catterv -owners and veterinarians keep looking
for
the simple solution and this sim-ple solution inevitably involves se-
rology. I hope this information will be of help”.
I think that this article clarifies a great many problems that veterinari-ans
are often faced with and also serves as a guideline when answerin-g
questions posed by cat owners.
