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A Winn Foundation Health Article
On ...
Feline Infectious Peritonitis
NEW! - Purchase the Winn Feline Foundation CD summarizing the latest in
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Feline
Infectious Peritonitis - updated information for breeders
Susan Little DVM, Diplomate ABVP (Feline)
One of the most poorly understood and enigmatic feline viruses is the
feline coronavirus - the virus responsible for feline infectious
peritonitis (FIP). It is no exaggeration to say that this is one of the
most feared diseases in catteries. Many catteries that remain operative
for several years will have a brush with FIP. Despite the fact that
this disease is a shared experience in the cat fancy, affected
catteries are wrongly feared and ostracized. All breeders need to make
efforts to understand this disease and how to control it.
While the first description of feline infectious peritonitis was
reported by Dr. Jean Holzworth in 1963, there are reports of clinical
cases that are likely FIP going back to1914. Even though we have known
about this virus for a long time, we know frustratingly little about
it. However, much new research has been done in the past 5 years that
is slowly shedding more light on this ever-present feline health
problem. This article is designed to present some of the newer
information and change some of the older ideas still found in print and
other media.
Feline coronavirus operates differently from any other feline virus in
several important ways: a) systemic antibodies have no protective
function for the cat and may play a role in the disease FIP itself b)
antibody titres are meaningless for diagnosis of FIP or prognosis c) a
vaccine is available, but there is no consensus on its efficacy or
safety
First, some notes on terminology.
* FIP is the term for clinical disease associated
with feline coronavirus infection.
* The common benign form of feline coronavirus is
referred to as FECV (feline enteric coronavirus).
* When FECV has mutated into a disease-causing form,
it is then referred to as FIPV (feline infectious peritonitis virus).
* Feline coronaviruses in general are referred to as FCoV.
FECV is a very common, highly infectious feline virus. It belongs to
the genus Coronavirus, which has members that infect other species
(man, swine, cattle, birds, dogs). The majority of cats with FECV
(about 95% or more) remain healthy. But in a small number of cases,
FECV infection is the first step in a chain of events leading to FIP.
This happens because coronaviruses are made of large numbers of
nucleotides, the basic unit of genetic material, and they are very
prone to mutations. As a virus reproduces itself, errors are made in
copying these nucleotides. The more nucleotides, the more errors are
possible. While most of these errors are harmless, some will have the
effect of giving FECV the ability to cause disease. These mutant FECV
strains are called FIPV.
Recent research has shown that mutant FECVs arise within an individual
cat. Thus, we now know that the vast majority of cats do not "catch"
FIP, but they develop it themselves from their own mutant FECV.
Transmission of FIP from cat to cat is considered to be rare. This fact
has caused leading FIP researchers to state that cats who are ill with
FIP are unlikely to be a risk to other cats and thus do not need to be
isolated.
It has been estimated that in multi-cat households where FECV has been
introduced, 80-90% of all the cats will be infected. Catteries are
especially likely to be FECV positive since traffic of cats and kittens
in and out of the establishment is common. However, the incidence of
cases of FIP is quite low in comparison. Generally, most catteries
experience far less than 10% losses to FIP over the years. Rare
instances have been documented where an apparent epidemic of FIP is
associated with mortality rates of over 10% in a short period of time.
One possible factor in these epidemics is the shedding of virulent
virus, an uncommon situation. Usually, losses are sporadic and
unpredictable. The peak ages for losses to FIP are from 6 months to 2
years old (with the highest incidence at 10 months of age).
Age-associated immunity to FIP appears to be possible. Transmission of
FIP from a queen to her unborn kittens has not been shown to occur.
What are the factors that predispose a small percentage of cats with
FECV to the development of FIP? Research is currently trying to find
more answers to this question, but some facts are becoming clear. Dr.
Janet Foley and Dr. Niels Pedersen of the University of California at
Davis have identified three key risk factors: genetic susceptibility,
the presence of chronic FECV shedders, and cat-dense environments that
favour the spread of FECV.
A genetic predisposition to the development of FIP was identified by
Drs. Foley and Pedersen in 1996. They examined pedigree and health data
from 10 generations of cats in several purebred catteries and found
that the heritability of susceptibility to FIP could be very high
(about 50%). It is likely a polygenetic trait rather than a simple
dominant or recessive mode of inheritance. Inbreeding, by itself, is
not a risk factor. Selecting for overall disease resistance is a
helpful tool for breeders. The likely defect in immunity to FIP is in
cell-mediated immunity. Therefore cats that are susceptible to FIP are
also likely susceptible to some other infections as well, especially
fungal and viral infections. This finding gives breeders the ability to
achieve success in reducing the risk of FIP by using pedigree analysis
to select breeding cats from family backgrounds that have strong
resistance to FIP and other infectious diseases.
Research has shown that there are two main patterns that occur with
FECV infection. Most cats will become infected and recover, but will
not be immune. They are susceptible to reinfection the next time they
contact the virus. A small number of cats become infected but do not
recover. They become persistent shedders of FECV in the cattery and are
the source of reinfection for the other cats. Therefore, the key to
eliminating FECV (and thus the risk of FIP) in a cattery would be the
identification and removal of chronic shedders. Currently, however,
there is no easy way to determine which cats in a cattery are
persistent shedders. The traditional antibody titre for FECV cannot be
used to determine which cats are chronic shedders. The most effective
and practical tool is PCR analysis of feces for the presence of FECV, a
test which is not yet widely available.
In addition to selecting disease-resistant breeding stock, breeders can
initiate husbandry practices that discourage the spread of FECV and
development of FIP. Cat-dense environments favour the transmission of
the highly contagious FECV. Dr. Diane Addie of the University of
Glasgow, Scotland, recommends that the ideal way to house cats in
catteries is individually. However, since this is not always possible,
she recommends that they be kept in stable groups of no more than 3 or
4. Kittens should remain in groups of similar ages and not be mixed
with adults in the cattery. Any measures that reduce environmental and
social stress in the cattery population will have a beneficial effect.
FECV is spread primarily by the fecal-oral route and, to a lesser
degree, through saliva or respiratory droplets. The virus can persist
in the environment in dried feces on cat litter for 3 to 7 weeks, so
scrupulous cleaning of cages and litter pans is important to reduce the
amount of virus in the environment. It is important to have adequate
numbers of litter pans available and that they be scooped at least
daily and dumped and disinfected at least weekly. Litter pans should be
kept away from food bowls and spilled litter should be regulary
vacuumed up from the floor.
Dr. Addie has also described a method for early weaning and isolation
of kittens born to FECV positive queens. It involves rigorous barrier
nursing techniques to prevent the spread of the highly contagious FECV,
and so is not for every breeder or cattery. The procedure involves
first isolating the pregnant queen in a separate area to have the
kittens. When they are 5-6 weeks old (at the time when their maternal
immunity to FECV is waning), the kittens are removed from the queen and
isolated by themselves. Some of the difficulties with this method
involve the strict infection control procedures needed and possible
difficulties in socializing kittens. When properly practiced, not only
can FECV-negative kittens can be produced, but the kittens are often
less prone to respiratory diseases and other common kitten ailments.
As with so many aspects of FIP, testing remains problematic. To date,
there is no way to screen healthy cats for the risk of developing FIP.
Antibody titres are poorly correlated with risk of FIP and should not
be used to screen cats. As well as problems with interpretation of
these antibody tests, there are problems with laboratory quality
control. There are newer DNA-based tests offered by a few labs that are
purported to be FIP-specific. However, these tests are considered
unvalidated by experts as they have not been subjected to scientific
scrutiny by researchers outside of the labs that offer them. In
addition, there are no published studies that have identified the
genetic difference between FECV and FIPV. An article was published by
the Cornell Feline Health Center in 1998 warning that the so-called
FIP-specific ELISA tests are based on insufficient data and the assays
are not yet validated.
The fact remains that we have no screening test for FIP in well cats.
Neither do we have a fool-proof way to diagnose FIP in a sick cat. The
gold standard remains a biopsy or findings at necropsy. Recently, Dr.
Andrew Sparkes and his colleagues at the University of Bristol,
England, have suggested that combining several test results (globulin
levels, lymphocyte counts) with clinical findings and antibody titre
can help rule in or rule out FIP with some degree of certainty. It
remains true, however, that a negative antibody titre does not rule out
FIP. Neither does a positive antibody titre rule in FIP as a diagnosis.
One benefit of the new DNA-based tests may be their use on body fluids,
such as effusions from the chest or abdomen of a sick cat. If virus is
found in these fluids, it strongly supports the presumptive diagnosis
of FIP.
Probably one of the most controversial areas in any discussion of FIP
is Primucell FIP, the vaccine made by Pfizer Animal Health, available
since 1991. The vaccine is a modified-live termperature-sensitive viral
mutant licensed for intranasal use in cats at least 16 weeks of age.
The manufacturer recommends annual revaccination although no duration
of immunity studies are available. The vaccine stimulates local
immunity and will also produce an antibody titre. Evaluation of the
risks and benefits associated with this vaccine is a difficult venture
and has engendered much controversy.
Since FIP is a severe and fatal disease, the safety of any vaccine is a
paramount consideration. Dr. Fred Scott of the Cornell Feline Health
Center, concluded in a recently published paper, that the risks
associated with the Primucell FIP vaccine are minimal in most
situations. He notes that the vaccine has been in use for 7 years with
no increase in the incidence of FIP. Troubling reports of a phenomenon
called "antibody-dependent enhancement" (ADE) of infection arose from
several labs, where cats vaccinated with FIP vaccines and challenged
experimentally with virus developed accelerated disease instead of
being protected. It is not known whether the phenomenon of ADE occurs
in the real world and there is no easy way to find out. If it does
occur, it is likely an uncommon event, but the possibility remains
troubling.
On the other side of the issue, the benefits of the Primucell FIP
vaccine appear to be small. The best reported efficacy for the vaccine
is seen when FCoV negative cats at least 16 weeks old were vaccinated
twice (3 weeks apart), in a study by Dr. Nancy Reeves published in
1995. In this study, FCoV antibody-negative cats were vaccinated before
entering a large cat shelter where FIP was endemic. The vaccinated cats
experienced a significantly lower mortality rate than unvaccinated
cats. The efficacy of the vaccination was calculated to be 75%
(preventable fraction).
In catteries where FIP is endemic, studies have shown the vaccine had
no effect on the incidence of disease. One reason may be that most
kittens in catteries are infected between 6 and 10 weeks of age, long
before the 16 weeks of age the vaccine is licensed for. Once a cat is
infected with FCoV, the vaccine has no benefit. Some cattery owners
have been using the vaccine at ages younger than 16 weeks to get around
this problem. Dr. Johnny Hoskins has outlined a vaccination protocol
for catteries experiencing FIP losses in kittens under 16 weeks of age.
He recommends giving the vaccine at 9, 13 and 17 weeks with annual
revaccination afterward. Use of this protocol must be made with the
knowledge that no controlled studies have been done on kittens under 16
weeks of age and that this is an off label use. It would appear that
the use of the vaccine according to the manufacturer’s directions is
limited to the vaccination of FCoV antibody-negative cats entering high
risk situations, such as catteries and shelters.
Recommended Reading
1. Addie DD. The control of feline coronavirus and feline
infectious peritonitis in cat colonies. Feline Focus (European Society
of Feline Medicine newsletter) 5 (Summer): 5-7, 1997
2. Cornell Feline Health Center. Is the FIP-specific ELISA
test specific? Feline Health Topics for Veterinarians, Vol 13(2): 7,
1998.
3. Foley JE, Pedersen NC. The inheritance of
susceptibility to feline infectious peritonitis in purebred catteries.
Fel Pract 24(1): 14-22, 1996
4. Foley JE et al. Patterns of feline coronavirus
infection and fecal shedding from cats in multiple-cat environments. J
Amer Vet Med Assoc 210(9): 1307-1312, 1997
5. Foley JE et al. Risk factors for feline infectious
peritonitis among cats in multiple-cat environments with endemic feline
enteric coronavirus. J Amer Vet Med Assoc 219(9): 1313-1318, 1997
6. Horzinek MC. Update on feline infectious peritonitis.
Feline Focus (European Society of Feline Medicine newsletter) 5
(Summer): 1-4, 1997
7. Hoskins JD. FIP vaccination. Feline Focus (European
Society of Feline Medicine newsletter) 5 (Summer): 4-5, 1997
8. Legendre AM. Feline infectious peritonitis - an update.
Proc 16th Amer Coll Vet Intern Med Forum, San Diego CA, 1998.
9. Norsworthy GD. Feline infectious peritonitis, in
Norsworthy GD et al (ed): The Feline Patient: Essentials of Diagnosis
and Treatment, Williams and Wilkins, Baltimore, 1998, pp. 200-203
10. Pedersen NC, Addie DD, Wolf A. Recommendations from working
groups of the international feline enteric coronavirus and feline
infectious peritonitis workshop. Fel Pract 23(3): 108-111, 1995
11. Scott FW. Evaluation of risks and benefits associated with
vaccination against coronavirus infections in cats. Advances Vet Med
41:347-358, 1999
12. Sparkes AH, Gruffydd-Jones TJ, Harbour DA. An appraisal of
the value of laboratory tests in the diagnosis of feline infectious
peritonitis. J Amer Anim Hosp Assoc, Vol 30:345-350, 1994.
13. Various authors. Report from the International FIP/FECV
Workshop, University of California, Davis CA, Feline Practice Vol
23(3): 1995
14. Weiss RC. Feline infectious peritonitis and other
coronaviruses, in Sherding RG (ed): The Cat: Diseases and Clinical
Management, second edition, WB Saunders Co., Philadelphia, 1994, pp.
449-477
Related Links:
* Updates on Feline Infectious Peritonitis - Winn
Feline Foundation
* New Tests Being Commercially Marketed for FIP
Detection - Winn Feline Foundation
* Feline Infectious Peritonitis - Virus Shedding and
Infection - The British Experience (Virus Excretion of Feline
Coronavirus) - Winn Feline Foundation
* Feline Infectious Peritonitis - Virus Shedding and
Infection - The American Experience - WInn Feline Foundation
* FIP Frequently Asked Questions - UC Davis