Feline
infectious peritonitis (FIP) is a viral disease of cats that occurs throughout
the world and is almost invariably a fatal disease.
Causes
The disease is caused by
infection with a virus known as feline coronavirus. Infection with coronavirus
is actually very common in cats, but most of the time it does not cause any
problems, other than perhaps mild self-limiting diarrhoea.
Uncommonly, the virus mutates
(changes) to a strain of coronavirus which has the potential to cause disease.
This mutated strain is the cause of FIP.
In an affected cat, the virus
spreads throughout the body and can cause a wide range of different signs
(including peritonitis with the accumulation of fluid in the abdomen, but in
other cats fluid may accumulate in the chest cavity; in others the virus may
cause inflammation affecting the brain, eyes, liver, kidneys or elsewhere).
What are coronavirus infections?
Coronaviruses are a common group
of viruses that often infect the upper respiratory tract or gastrointestinal
tract in different animals. Different species of coronavirus are adapted to
cause disease in different animals. In humans, coronaviruses are one of the
frequent causes of the common cold.
Coronaviruses that infect cats
are called 'feline coronaviruses' or FCoV. In cats, FCoV most frequently causes
gastrointestinal infections, but in unusual cases (with a mutated form of the
virus) it can spread through the body and cause FIP.
How do cats get infected with coronavirus?
Coronavirus infection is
extremely widespread in cats, especially where large numbers of cats are kept
together. It is estimated that 25 to 40 per cent of household pet cats have
been infected with FCoV, but the infection rate increases to 80 - 100 per cent
for cats kept in multi-cat households or colonies.
The virus mainly infects the
intestinal tract, where it replicates. FCoV is shed in the faeces and may
survive in the environment for a short while (several days or a few weeks), but
is readily destroyed by common disinfectants. Infection is caused when a cat
ingests the virus (e.g., through licking). The relationship between the virus
and the cat is complex - some cats may remain persistently infected with FCoV
and shed virus in their faeces the whole time; others may be infected, develop
a strong immunity and be protected from future infections; and others may be
infected and manage to eliminate the virus, but then get recurrent infections.
In most cases, infection with
FCoV will cause mild signs of enteritis (mild, self-limiting diarrhoea), or
sometimes no signs at all. Diarrhoea is more likely to be seen in young cats,
but because it is mild and self-limiting a specific diagnosis of FCoV infection
is almost never made.
How does FCoV cause FIP?
Infections with FCoV are usually
limited to the intestinal tract, with very limited viral replication elsewhere.
Strains of FCoV causing these infections are referred to as feline enteric
coronavirus (or FECV). During infection, and while the virus replicates in the
intestine, it undergoes spontaneous mutations. This leads to the development of
different strains of the virus, and occasionally a strain may develop that has
dramatically altered disease-causing potential - this viral strain is referred
to as feline infectious peritonitis virus (FIPV). FIPV strains of FCoV differ
from FECV in that they no longer replicate well in the intestine, but rather
preferentially infect macrophages - one of the important cells of the immune
system. The virus spreads throughout the body, and if replication is not
contained by a good immune response, a cat will develop clinical signs of FIP.
In most cases, it appears that an
FIP-producing strain of FCoV probably arises within a cat already infected with
FCoV. In many (or even most) cases of FIP, the FIP-producing strains of the
virus are not shed in the faeces of a cat with FIP.
When an FIP-producing strain of
FCoV emerges, whether a cat will develop FIP or will remain healthy depends on
the quality of its immune response. A strong immune response (especially the
type of immunity termed 'cell mediated immunity') may enable the cat to control
the infection and prevent signs developing.
What are the clinical signs of FIP?
FIP can cause a very wide range
of clinical signs, and unfortunately none of these are unique for FIP – a
diagnosis cannot therefore be based on clinical signs alone.
Early signs of FIP are usually
very vague with a fluctuating fever, lethargy and inappetence being common.
After a period of several days or weeks (or sometimes even many months) other
signs usually develop. Two main forms of the disease are recognised known as
'wet' or 'effusive' disease, and 'dry' or 'non-effusive' disease. Many cats may
in fact have a mix of these two types:
'Wet'
or effusive FIP
In this form of disease there is
accumulation of fluid within the abdominal cavity (resulting in abdominal
distension) and/or the chest cavity (resulting in breathing difficulties). The
fluid accumulates because infection with FIPV causes damage to and inflammation
of blood vessels (called 'vasculitis') which results in fluid leaking from the
blood into the abdomen or chest. Cases that develop fluid accumulation in the
abdomen are responsible for the original name of this disease, 'peritonitis'
referring to the inflammation that occurs in the lining of the abdominal
cavity.
In effusive FIP, the fluid that
accumulates typically has a very high protein content, and is often a
clear-yellowish colour. However, other diseases (including some liver diseases
and neoplasia) can also cause a similar fluid accumulation.
'Dry' or non-effusive FIP
With non-effusive disease,
infection with FIPV predominantly causes chronic (long-standing) inflammatory
lesions to develop around blood vessels in many different organs and sites in
the body. The type of changes present is usually what is known as
'pyogranulomatous' inflammation.
This inflammation affects the
eyes in around 30% of cases and the brain in around 30% of cases, but can also
affect almost any tissues in the body including the liver, kidneys, lungs and
skin. Thus, a wide range of signs may be observed including neurological
disease (e.g., a wobbly and unsteady gait), bleeding in the eyes and other
vague signs of disease that may occur with lesions in the liver or other
internal organs.
In most cases of FIP, once
clinical signs have started, they tend to get progressively worse over time,
and in most cases (though not all) the time course for disease is rapid, with
cats deteriorating to the point that euthanasia is usually required within a
matter of days or weeks. It is thought that non-effusive cases of FIP are where
the cat has developed a partially effective immune response that helps to limit
viral replication - this may prevent development of effusions, but is not
sufficient to stop disease development.
In a number of cats, signs may
develop that are a combination of both effusive and non-effusive disease.
What cats are most often affected with FIP?
Although FIP can occur in cats of
any age, it is most often seen in young cats. Around 80% of cases diagnosed are
in cats less than 2 years old, and many cases are seen in kittens around 4-12
months old. FIP is also more common in cats kept in groups or colonies
(especially breeding households) as this is an environment where FCoV infections
are spread easily. A crowded environment may also contribute to stress, which
can be a factor in disease development as it compromises the cat's immune
response. There is evidence that genetics can also play a role in
susceptibility to disease, although this is complex.
How can FIP be diagnosed?
FIP is a very difficult disease
to deal with because there are no clinical signs that are specific for the
diagnosis of FIP, and no simple blood test to confirm a diagnosis. FIP may be considered more likely
when:
·
Cats are showing
clinical signs compatible with FIP
·
Cats are in a higher
risk category (e.g., younger cats, colony cats, etc.)
·
Typical changes are
seen on routine blood tests - these may include
o
Lymphopenia (low
numbers of lymphocytes, a type of white blood cell)
o
Neutrophilia
(increased numbers of neutrophils, a type of white blood cell)
o Anaemia
o
Elevated globulin
concentrations (one of the major groups of proteins in the blood)
o
Elevated liver
enzymes (eg, ALT, ALP)
o
Elevated bilirubin
(and jaundice or yellowing of the gums and eyes)
None of these blood changes are
specific for FIP, occurring with other diseases too, but if multiple changes
are seen in combination with appropriate signs, a diagnosis of FIP becomes more
likely. Many of these abnormalities may also not be present in the early stages
of the disease, but may become evident as the disease progresses. Thus some
tests that give normal results may have to be repeated later.
If an effusion is present in the
abdomen or chest cavity, obtaining a sample of the fluid and analysing the cell
and protein content can be extremely helpful. With FIP the fluid invariably has
a high protein content (greater than 35 g/l) and at least 50% of the proteins
are globulins. Because this test is very helpful, and because few other
diseases cause this type of fluid accumulation, when FIP is suspected a vet
will often take X-rays or do an ultrasound examination to see if fluid is
present so that a sample can be collected for analysis.
Other tests that can also sometimes
be helpful include:
·
Further analysis of
proteins in the blood (e.g., looking at globulin sub-types or measuring the
protein acid-1-alpha glycoprotein [AGP])
·
Evaluation of a
cerebrospinal fluid sample (the fluid that surround the brain and spinal cord)
in cases where there are neurological signs
Looking for the presence of
antibodies against the virus in a blood sample (coronavirus serology) is of
very limited value - antibodies against FCoV develop irrespective of the type
of virus infecting a cat and the antibody test cannot differentiate between
different strains of the virus. A very large number of perfectly healthy cats
are therefore positive on this test.
Confirming a diagnosis of FIP
The best test to confirm a
diagnosis of FIP is to collect a biopsy (usually done through a surgical
operation) from affected tissues. Typical FIP-type inflammation is usually
seen, which is highly suggestive, but the diagnosis can be confirmed using a
technique called 'immunohistochemistry' which will demonstrate the presence of
the virus itself within the damaged tissues.
With FIP, unfortunately, a cat
may be too sick for surgery to be performed, and so in many cases a definitive
diagnosis may only made on post-mortem examination (using immunohistochemistry,
as above).
The virus itself can also be
detected by the use of PCR (polymerase chain reaction, a molecular technique to
show the presence of the virus). This can be useful - for example if fluid is
present in the chest or abdomen which has typical characteristics of FIP (see
above), and if the fluid is also PCR positive for coronavirus, this is highly
suggestive that FIP is the underlying cause. However, because PCR cannot
distinguish different types of coronavirus (FIP-producing strains from
enteritis-producing strains), this test is not definitive.
Treatment for FIP
Once clinical signs of FIP
develop, it is generally an incurable and fatal disease. Supportive treatment
(e.g., anti-inflammatory drugs) may help relieve some signs and improve quality
of life temporarily but in most cases euthanasia is the most humane course of
action to avoid suffering. There are some reports of cats responding to therapy
with injectable interferon (recombinant feline interferon omega), but there is
currently no evidence for this being genuinely effective.
Prevention of FIP
A commercial vaccine is available
in some countries to help protect against FIP. However, this vaccine (while
showing some efficacy) can only be given to kittens over 16 weeks of age. The
major indication for using such a vaccine would be in breeding households,
especially with a history of FIP, but by the time a kitten can be vaccinated
(at 16 weeks) they would almost invariably have already been exposed to FCoV
infection and so the vaccine probably has little or no value.
Reducing the risk in breeding households
FIP is least common in household
pets. The risk can be minimised by obtaining cats from a source with relatively
few cats and by keeping cats in small stable groups (less than five cats in a
household).
In breeding catteries,
eradicating coronavirus infections is extremely difficult, as the virus is so
ubiquitous, and it is unsuitable in most situations to attempt this. A more
practical approach is to use measures to reduce the risk of FIP occurring, but recognising
that on occasions, this may happen even in the best run catteries. Good
practice to minimise the risk of FIP would include:
·
Avoid keeping large
groups of cats and having multiple litters of kittens at any one time
·
Keep cats in small
isolated groups (ideally no more than four cats in each group - this reduces
the risk of endemic FCoV infection)
·
Have at least one
litter box for every two cats, located in easy to clean and disinfect areas
·
Keep litterboxes away
from food and water bowls, and clean/disinfectant them regularly (at least
daily)
·
Avoid stress and
maintain good hygiene and preventive healthcare for all cats
Wherever FIP occurs is a problem
in a group of breeding cats:
·
Consider
preferentially breeding from older cats, as these will less likely be shedding
FCoV
·
Consider isolating
queens just before they give birth and keeping the queen and kittens isolated
from all other cats until the kittens are homed, as a means of reducing the
risk of FCoV spread to kittens
·
Stop breeding from
any queens or tom cats that repeatedly produce litters of kittens that develop
FIP as they may be passing on FCoV infection or may be passing on genetic
susceptibility to disease
·
Carefully review
management and hygiene policies
·
If faced with an
outbreak of FIP, stop all breeding for several months
Reducing the risk in rescue and rehoming facilities
Good hygiene and avoiding
overcrowding are essential strategies for minimising the risk of FIP. Cats
should ideally be housed individually, or if this is not possible, they should
be kept in small stable groups. Litter boxes and cleaning/disinfection should
be managed as in breeding households.
Source : http://www.icatcare.org/advice/cat-health/feline-infectious-peritonitis-fip
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