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What is feline infectious peritonitis (FIP)?
Feline infectious peritonitis (FIP) is a disease caused by a
coronavirus infection. Many different strains of
coronavirus are capable of infecting cats, but most do not
produce serious disease. FIP-producing strains are
distinguished by their ability to invade and grow in
certain white blood cells. The infected cells transport the
virus throughout the cat's body. An intense inflammatory
reaction occurs in the tissues where these virus-infected
cells locate. It is this interaction between the body's own
immune system and the virus that is responsible for the
disease.
Infected cats shed coronavirus in their saliva and feces.
Most cats become infected by inhaling or ingesting the
virus, either by direct contact with an infected cat, or by
contact with virus-contaminated surfaces like clothing,
bedding, feeding bowls, or toys.
Although the virus can survive for a number of weeks in
the environment, it is rapidly inactivated by most
household detergents and disinfectants. An inexpensive
and effective disinfectant is one part of household bleach
in thirty-two parts of water (4 ounces of bleach per gallon
of water).
FIP and feline leukemia are caused by different viruses.
Some cats that have FIP may also be infected by the
feline leukemia virus, but the diseases are two separate
entities.
Initial exposure to the FIP virus usually results in no
obvious clinical disease, although some cats may
experience a mild upper respiratory disease that is
characterized by sneezing, watery eyes, and watery nasal
discharge. Some cats may experience a mild intestinal
disease. Most cats that undergo the primary infection
completely recover, although some of them may become
virus carriers. Only a small percentage of exposed cats
develop the lethal disease: weeks, months, or perhaps
years after primary infection.
This disease has two major manifestations. The first is
called the "dry form". In the dry form the white blood
cells are involved, and cause an inflammatory reaction
to the internal organs. These organs do not function
normally because of this inflammation, and eventually
will fail as the disease progresses
The other manifestation of this disease is called the "wet
form", and is where the original name of "peritonitis"
(inflammation of the lining of the abdominal cavity) came
from. It is called this because fluid accumulates in the
abdomen or the chest. The fluid that appears in the wet form is
straw colored to yellow in appearance, and has a relatively
high protein content. The fluid originates from small blood
vessels that have been affected by the immune systems
response to the virus. This immune response damages these
blood vessels, causing them to leak fluid into the abdominal
cavity usually, or thoracic cavity less often.
The virus can also infect the brain or spinal cord. This form
of the disease can sometimes be diagnosed by an eye exam.
Changes can be noted in the back of the eye, especially the
retina. (video)
The onset of clinical signs of lethal FIP may be sudden
(especially in kittens), or the signs may gradually
increase in severity over a period of weeks. Many cats
have nonspecific signs such as intermittent inappetence,
depression, rough hair coat, weight loss, and fever.
The major forms of lethal FIP are effusive (wet) FIP,
noneffusive (dry) FIP, and combinations of both. The
most characteristic sign of effusive FIP is the
accumulation of fluid within the abdomen and/or chest.
When fluid accumulation becomes excessive, it may
become difficult for the cat to breathe normally.
Cats that have FIP will have physical exam findings similar to
other feline diseases. In the wet form the fluild buildup in the
abdomen becomes apparent as time goes on.
One of the ways we check for fluid during an exam is to look for a
fluid wave. (video)
The fluid that builds up in the wet form of FIP is called ascites
when it occurs in the abdomen, and pleural effusion when it
occurs in the thorax. The fluid is sticky and usually light yellow to
golden color, with a relatively large amount of protein.
This is what the fluid looks like just after is has been removed from
the body.
This is an x-ray of a normal cats thorax. This cat is laying on its right
side, the head is towards the left. You can see the heart and the black
lung tissue in the shape of a triangle. The diaphragm (arrows) is the
vertical line that separates the thorax on the left from from the
abdomen on the right. The liver resides in the abdomen.
This cat has a significant amount of fluid in the thorax (pleural
effusion), making it difficult to identify normal organs. You cannot
see the heart or diaphragm, and the lung tissue is greatly reduced
because of all the fluid. The lungs are unable to expand fully
causing significant difficulty in breathing. This pet is very ill and
has minimal breathing reserve. It needs immediate removal of the
fluid.
After some of the fluid was removed it is possible to visualize more
of the organs. There is more lung tissue present and the top of the
diaphragm is now visible.
The onset of noneffusive FIP is usually slower. Fluid
accumulation is minimal, although weight loss,
depression, anemia, and fever are almost always present.
Signs of kidney failure (increased water consumption and
urination), liver failure (jaundice), pancreatic disease
(vomiting, diarrhea, diabetes), neurologic disease (loss of
balance, behavioral changes, paralysis, seizures),
enteritis (vomiting, diarrhea), or eye disease
(inflammation, blindness) may be seen in various
combinations. FIP is often a difficult disease to diagnose
because each cat can display different signs that are
similar to those of many other diseases.
Young cats (less than two years of age), older cats (over
ten years old), cats in poor physical condition, and cats
undergoing concurrent infections or stress are more
susceptible to FIP. It is a relatively uncommon disease in
the general cat population, probably affecting fewer than
one percent of the cats brought to a veterinarian's office
for treatment. In multiple-cat populations such as some
shelters and catteries the disease rate can be much
higher, affecting up to 10 to 20 percent of the susceptible
population over a period of several months.
The KELA, ELISA, IFA, and virus-neutralization tests
detect the presence of coronavirus antibodies in a cat. A
positive test result only means the cat has had a prior
exposure to a coronavirus -- not necessarily one that
causes FIP -- and has developed antibodies against that
virus. If the test is negative, it means the cat has not
been exposed to a coronavirus.
The number, or titer, that is reported is the highest serum
dilution that still produced a positive reaction. Low titers
indicate a small amount of coronavirus antibodies in the
serum, while high titers indicate greater amounts of
antibodies. A healthy cat with a high titer is not
necessarily more likely to develop FIP or be a carrier of
an FIP-causing coronavirus than a cat with a low titer. It
also is not necessarily protected against future FIP virus
infection.
Recently, two new tests have been developed that can
detect parts of the virus itself. The immunoperoxidase
test can diagnose FIP more accurately than traditional
histopathologic examination because it detects virusinfected cells in the tissue. A biopsy of affected tissue is
necessary for evaluation. Another antigen test utilizes
polymerase chain reaction (PCR) to detect viral genetic
material in tissue or body fluid. Although this test shows
promise, PCR is presently only capable of detecting
coronaviruses in general, not necessarily those that cause
FIP.
There are two primary situations where the determination
of coronavirus-antibody titers can be useful to the cat
owner or breeder and the veterinarian:
1.As a screening test, to determine the presence or
absence of antibodies in a previously untested
household and to detect potential virus carriers or
shedders when introducing new cats into households
or catteries that are negative for coronavirus
antibodies
2.As an aid (and nothing more than an aid) in the
clinical diagnosis of a diseased cat that has signs
suggestive of FIP.
Unfortunately, many laboratories use different antigens
prepared in different ways, and their interpretation of the
assay can differ. False results can occur from nonspecific
reactions unless the tests are meticulously controlled. The
test can be difficult to interpret, since it usually depends
on a subjective decision made by the person reading the
test.
A presumptive diagnosis of FIP can usually be made on
the basis of clinical signs, routine laboratory tests, and
evaluation of abdominal or chest fluid. Some cases,
however, present a diagnostic challenge, since the signs
of illness are not distinct for FIP. In all cases, a tissue
biopsy is the only way to absolutely confirm a diagnosis
of FIP.
Currently, FIP is considered to be a routinely fatal disease
once a positive diagnosis has been made. Unfortunately,
no cure yet exists. The basic aim of therapy is to provide
supportive care and to alleviate the self- destroying
inflammatory response of the disease. Some treatments
may induce short-term remissions in a small percentage
of patients. A combination of corticosteroids, cytotoxic
drugs, and antibiotics with maintenance of nutrient and
fluid intake may be helpful in some cases. In the future,
combining immune-modulating drugs with effective
antiviral medications may prove to be beneficial for
treatment of FIP.
The first FIP vaccine (Primucell FIP by Pfizer Animal
Health) was introduced in 1991. It is a temperaturesensitive, modified-live vaccine. The vaccine is licensed
for intranasal vaccination of cats at 16 weeks of age, with
boosters in 3 to 4 weeks, and then yearly. Once a cat is
vaccinated, its serum may have a positive coronavirus
antibody titer. This could be a problem for cattery owners
who use serologic testing to maintain a coronavirus-free
population.
The vaccine appears to be safe, but various studies have
yielded different estimates of vaccine efficacy. The role
that Primucell FIP will ultimately play in protecting cats
from FIP is not yet known; for the time being, discussions
with your veterinarian should help you decide if your cat
should be vaccinated.
Once clinical signs appear, cats with the effusive (wet)
form of FIP will live a few days to a few weeks, although
some adult cats may linger for six to eight months. Cats
with the dry form of FIP usually die within a few weeks,
but survival for up to a year or more is possible.
Providing good nursing care and feeding a balanced,
highly nutritious diet will make your cat more comfortable
in the terminal stages of the disease. Your veterinarian
may prescribe medications to reduce the discomfort
associated with the disease or provide more-specific
supportive therapy.
FIP has not been documented in any species other than
those of the cat family. FIP is not known to constitute any
health risk for human beings. However, FIP virus is
similar to a common virus of dogs - canine coronavirus,
that produces enteritis in dogs.