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Long-term impact on a closed household of pet cats of natural infection with feline coronavirus, feline leukaemia virus and feline immunodeficiency virus

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Abstract

A closed household of 26 cats in which feline coronavirus (FCoV), feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV) were endemic was observed for 10 years. Each cat was seropositive for FCoV on at least one occasion and the infection was maintained by reinfection. After 10 years, three of six surviving cats were still seropositive. Only one cat, which was also infected with FIV, developed feline infectious peritonitis (FIP). Rising anti-FCoV antibody titres did not indicate that the cat would develop FIP. The FeLV infection was self-limiting because all seven of the initially viraemic cats died within five years and the remainder were immune. However, FeLV had the greatest impact on mortality. Nine cats were initially FIV-positive and six more cats became infected during the course of the study, without evidence of having been bitten. The FIV infection did not adversely affect the cats' life expectancy.
PAPERS
&
ARTICLESU
Long-term
impact
on
a
closed
household
of
pet
cats
of
natural
infection
with
feline
coronavirus,
feline
leukaemia
virus
and
feline
immunodeficiency
virus
D.
D.
ADDIE,
J.
M.
DENNIS,
S.
TOTH,
J.
J.
CALLANAN,
S.
REID,
0.
JARRETT
A
closed
household
of
26
cats
in
which
feline
coronavirus
(FCoV),
feline
leukaemia
virus
(FeW)
and
feline
immunodeficiency
virus
(FIV)
were
endemic
was
observed
for
10
years.
Each
cat
was
seropositive
for
FCoV
on
at
least
one
occasion
and
the
infedion
was
maintained
by
reinfection.
After
10
years,
three
of
six
surviving
cats
were
still
seropositive.
Only
one
cat,
which
was
also
infected
with
FIV,
developed
feline
infectious
peritonitis
(FIP).
Rising
anti-Fcov
antibody
titres
did
not
indicate
that
the
cat
would
develop
FIP.
The
FeW
infection
was
self-limiting
because
all
seven
of
the
initially
viraemic
cats
died
within
five
years
and
the
remainder
were
immune.
However,
FeLv
had
the
greatest
impad
on
mortality.
Nine
cats
were
initially
FIV-
positive
and
six
more
cats
became
infected
during
the
course
of
the
study,
without
evidence
of
having
been
bitten.
The
FIV
infection
did
not
adversely
affect
the
cats'
life
expectancy.
Veterinary
Record
(2000)
146,
419-424
D.
D.
Addie,
PhD,
BVMS,
MRCVS,
S.
Toth,
PhD,
DVM,
S.
Reid,
PhD,
BVMS,
MRCVS,
0.
Jarrett,
PhD,
BVMS,
MRCVS,
FRSE,
Department
of
Veterinary
Pathology,
University
of
Glasgow
Veterinary
School,
Bearsden
Road,
Bearsden,
Glasgow
G61
IQH
J.
M.
Dennis,
BVMS,
MRCVS,
1
Homefield
Road,
Bromley
BRI
3AW
J.
J.
Callanan,
PhD,
MVB,
MRCVS,
MRCPath,
Department
of
Veterinary
Pathology,
University
College
Dublin,
Shelbourne
Road,
Dublin
4,
Ireland
THERE
have
been
many
publications
describing
the
effects
on
cats
of
infections
with
either
feline
immunodeficiency
virus
(FIV),
feline
leukaemia
virus
(FeLV)
or
feline
coronavirus
(FCoV)
individually,
and
cats
have
been
infected
with
combi-
nations
of
these
viruses
in
laboratory
settings.
However,
this
is
the
first
report
of
a
group
of
cats
naturally
infected
with
all
three
viruses
and
studied
over
a
long
period.
The
rate
of
infectivity
of
FIV
is
extremely
variable
with
reports
in
the
literature
stating
that
from
0
to
100
per
cent
(Table
1)
of
cats
in
contact
with
an
FIV-infected
cat
may
become
infected.
In
addition,
it
has
been
recognised
that
FIV-
infected
cats
kept
under
specific
pathogen-free
(SPF)
condi-
tions
can
survive
for
long
periods
after
being
first
diagnosed
(Kohmoto
and
others
1998).
However,
it
is
not
clear
whether
this
phenomenon
is
related
solely
to
cats
kept
in
an
artificially
disease-free
environment
or
whether
it
also
applies
to
cats
in
the
field.
Both
FIV
and
FeLV
are
immunosuppressive
agents,
but
there
is
little
information
about
their
ability
to
influence
each
other's
infectivity.
In
households
where
FCoV
is
endemic,
5
to
15
per
cent
of
infected
cats
may
develop
feline
infectious
peritonitis
(FIP),
and
cats
which
are
immunocompromised
by
a
simultaneous
retrovirus
infection
are
believed
to
be
at
greater
risk
(Poland
and
others
1996).
This
paper
describes
a
study
of
the
transmission
rates
of
FIV,
FeLV
and
FCoV
among
26
cats
in
a
closed
household
over
a
period
of
10
years.
The
viral
status
of
the
animals
and
their
survival
from
first
diagnosis
were
monitored,
and
their
causes
of
death
were
established
specifically
to
determine
whether
the
viruses
might
have
been
implicated.
MATERIALS
AND
METHODS
Husbandry
Twenty-six
pet
cats
kept
in
one
household
were
monitored
for
10
years.
The
cats
were
allowed
to
mix
with
each
other
but
none
was
allowed
to
roam
outside.
Only
one
cat
(cat
Z)
was
introduced
during
the
10
years;
it
was
the
only
pedigree
cat,
a
Persian,
and
had
been
rescued
in
May
1989
from
its
previ-
ous
owner
who
wished
it
to
be
euthanased
because
it
had
an
anti-FCoV
immunofluorescent
antibody
titre
of
1280.
None
of
the
cats
was
vaccinated
against
FeLV,
feline
panleucopenia
virus,
feline
calicivirus
or
feline
herpesvirus.
Virological
test-
ing
was
begun
in
March
1988,
because
three
cats
had
died
during
1987
after
developing
anaemia,
diarrhoea
and
sus-
pected
liver
failure.
Haemobartonellafelis
had
been
identified
in
one
of
the
three
cats.
The
cats
were
blood
tested
annually;
the
blood
samples
were
taken
and
any
postmortem
examinations
were
per-
formed
by
one
of
the
authors
(J.
D.).
The
blood
samples
and
selected
formalin-fixed
tissue
samples
were
examined
sero-
logically
and
histologically
at
the
Feline
Virus
Unit,
University
of
Glasgow.
Serology
and
virology
The
samples
were
initially
screened
for
FIV
antibodies
by
using
a
commercial
ELISA
(FIV
Petcheck;
Idexx)
and
positive
results
were
confirmed
by
Western
blotting
(Hosie
and
Jarrett
1990)
or
by
immunofluorescence
(IF)
(Pedersen
and
others
1987).
Samples
examined
after
1991
were
tested
by
IF.
FeLV
antigen
was
detected
by
using
an
ELISA
to
detect
p27
(FeLV
Petcheck;
Idexx,
or
Innochem;
C.
Lutz)
and
positive
results
were
con-
firmed
by
virus
isolation
(Jarrett
and
Ganiere
1996).
Virus
neutralising
antibody
titres
to
FeLV
were
measured
as
described
by
Jarrett
and
Ganiere
(1996).
Antibodies
to
FCoV
were
measured
by
IF
(Addie
and
Jarrett
1992),
and
faeces
and
saliva
were
monitored
for
FCoV
by
the
detection
of
FCoV
RNA
by
reverse
transcriptase-polymerase
chain
reaction
(RT-PCR)
by
the
method
described
by
Herrewegh
and
others
(1995).
Pathology
Postmortem
examinations
were
carried
out
on
15
of
the
19
cats
that
died.
Sections
of
formalin-fixed,
paraffin-embedded
tissue
were
cut
at
5
,um
and
stained
with
haematoxylin
and
eosin.
Selected
sections
were
also
stained
with
Giemsa
stain.
To
investigate
the
phenotype
of
lymphoid
tumours,
paraffin-
embedded
sections
were
immunostained
with
anti-cD79a
(mb-
1),
anti-CD3
and
MAC
387
(anti-macrophage/anti-neu-
trophil)
antibodies
by
the
methods
of
Callanan
and
others
(1996).
Statistical
analysis
To
compare
the
survival
of
the
cats
in
the
different
groups,
classified
according
to
their
viral
infection
status,
Kaplan-
Meier
product-limit
survival
curves
were
generated.
The
Tarone-Ware
statistic
was
used
to
assess
whether
any
observed
differences
were
statistically
significant
at
the
5
per
cent
level.
Where
necessary,
a
Cox
proportional
hazard
model
was
used
to
assess
the
hazard
function
associated
with
viral
status,
taking
into
account
age
at
testing
and
seroconversion;
again
The
Veterinary
Record,
April
8,
2000
419
PAPERS
&
ARTICLES
significance
was
set
at
the
5
per
cent
level.
The
longevity
of
the
cats
was
also
compared
by
using
the
Kaplan-Meier
product-
limit
method.
RESULTS
Table
2
shows
the
sex
and
age
of
the
cats
at
the
end
of
study
or
at
death,
and
the
causes
of
death.
Tables
3,4
and
5
give
the
serological
data
for
FCoV,
FeLV
and
FIV,
respectively.
FCoV
antibody
titres
and
FIP
Each
cat
had
anti-Fcov
antibodies
on
at
least
one
occasion
during
the
study
(Table
3).
The
percentage
of
seropositive
cats
decreased
from
92
per
cent
in
July
1988
to
39
per
cent
in
September
1989,
but
by
March
1990,
94
per
cent
of
the
cats
were
again
seropositive,
indicating
that
they
had
been
rein-
fected.
There
were
two
further
similar
cycles;
the
prevalence
of
seropositive
cats
decreased
to
50
per
cent
by
October
1993,
increased
to
88
per
cent
in