Feline Infectious Peritonitis
Feline infectious peritonitis (FIP)
is an infectious, life threatening disease of primarily young
cats, with all ages of cats being susceptible. The death losses
usually begin shortly after weaning and peak at 8-18 months
of age. Progression of FIP may be facilitated by concurrent
infection with feline leukemia virus or feline immunodeficiency
virus.
The causative agent is a coronavirus
which can be of two types; feline infectious peritonitis virus
(FIPV) or feline enteric coronavirus (FECV). Depending on
which virus is involved, the clinical signs may range from
asymptomatic, to gastrointestinal disease or two widespread
multi-organ disease. FIPV and FECV have been referred to as
biotypes because they are morphologically and antigenically
identical except for the disease potential.
Entry of FIPV can be initiated by respiratory,
fecal-oral (predominantly), or intra- uterine route. The virus
replicates in epithelial cells of oropharynx or intestine.
Antibodies are elicited and virus-antibody complex is formed.
Virus-antibody complexes can be engulfed by monocytes or macrophages
and also circulate until deposited in the small blood venules
on the serosal or pleural surface, meninges, ependyma, and
uveal tissue. This results in disseminated immune-mediated
vasculitis and perivasculitis leading to vascular endothelial
damage, leakage of fibrin and immunoglobulin, and pyogranulomatous
lesions. If severe damage occurs, clotting abnormalities,
thrombocytopenia, increased fibrin degradation products (FDP's),
decreased clotting times, and development of DIC may be inevitable.
Feline infectious peritonitis can be
catergorized into effusive (wet) and non-effusive (dry) forms.
The effusive form may present with nonspecific signs (fever,
anorexia, weight loss, etc.), but the most noticeable sign
is the progressive abdominal distention or ascities. Pleural
effusion can occur and leads to respiratory distress, decreased
exercise tolerance, dyspnea, and muffled heart and lung sounds.
Peritoneal or pleural fluid is secondary to vasculitis and
leakage of fluid from the vasculature. The fluid is usually
a "straw colored" pyogranulomatous inflammatory exudate with
diffuse granular fibrinous exudation covering serosal surfaces
or floating in the effusion. The non-effusive form lacks specific
clinical signs, but may be associated with specific organ
dysfunction resulting from pyogranulomatous inflammation.
Clinical signs range from fever, weight loss, anorexia, respiratory
distress to renal, hepatic, pancreatic, CNS, or ocular disease.
Kidneys may be enlarged as "lumpy-bumpy" kidneys due to pyogranulomatous
lesions in the cortex and the cat may have polyuria, polydypsia,
lethargy, vomiting, proteinuria, and azotemia. The liver may
have focal necrotizing pyogranulomatous inflammation involving
hepatic capsule and adjacent hepatic parenchyma. Affected
animals may have increased ALT, GGT, alkaline phosphatase,
or hyperbilirubinemia. The brain and spinal cord may have
meningoencephalitis and myelitis, with vasculitis. Central
vestibular signs, seizures, ataxia, depression, nystagmus,
or personality changes may be evident. The eyes may have bilateral
anterior uveitis, keratitis, iritis, aqueous flare, corneal
edema, fundic pyogranulomas, and engorgement of retinal vessels
with perivascular cuffing. Lungs may have granulomatous pleuritis
and pneumonia. Microscopic lesions consist of multiple foci
of necrosis and pyogranulomatous inflammation, usually extending
from and incorporating the wall of a blood vessel. The lesions
appear to be a primary vasculitis and the evidence suggests
that it is mediated through circulating immune complexes.
Clinical pathology laboratory findings
include normocytic, normochromic anemia, leukocytosis with
neutrophilia and lymphopenia. Changes in clinical chemistry
panel depend on which organ(s) are involved. Peritoneal or
pleural fluid can be clear, slightly opaque to pale yellow,
or golden with fibrin strands and flakes. Cellularity usually
ranges between 1600 to 25,000 cells per microliter. Cells
are mostly a mixture of nondegenerate neutrophils, macrophages
and lymphocytes.
Clinical diagnosis is made by history,
physical examination, laboratory findings, and coronavirus
antibody titers. Tissue biopsy with pyogranulomatous inflammation
is still the preferred diagnostic procedure that will definitely
confirm FIP. Serum tests include virus isolation, IFA, ELISA,
and agar gel immunodiffusion. Care needs to be taken when
evaluating antibody titer results. Coronavirus titers have
been found in serum of apparently healthy cats, in cats with
FIP, and in cats with a disease other than FIP. The antibody
titers do not identify the strain of coronavirus responsible
for seroconversion, so the presence of a titer only indicates
that the cat has been infected with a coronavirus such as
FIP, FECV, canine coronavirus, TGE, or bovine or human coronavirus.
Most healthy cats with a positive titer probably have been
infected, but it is impossible to predict accurately the long-term
prognosis. In general, a high titer (>1:3200) and clinical
signs point to the diagnosis of FIP, but this is not absolute.
And if a cat is healthy, symptom free and has a negative titer,
it does not mean that the cat does not have FIP. A few cats
with histopathologically confirmed FIP have been seronegative.
Possible reasons include disappearance of the virus in advanced
stages; formation of immune complexes that leave little or
no free coronavirus antibodies to react with the test or the
test is not sensitive enough.
Most treatments center on supportive
care, such as antibiotics to decrease secondary infection,
IV fluids, nutritional support, and systemic corticosteroids
to decrease disseminated antibody-mediated vasculitis. Antiviral
and immunosuppressive agents have not been effective. Prognosis
for cats with definitively diagnosed FIP is extremely poor.
It is recommended that all cats with
signs of FIP be isolated, cats that are infected with FeLV
and FIV be removed, overcrowding does not occur, improvement
of hygiene and nutrition, proper removal of feces and admitting
only cats that have negative coronavirus antibody titers.
Removal of health cats with positive coronavirus antibody
titers from multiple-cat residences is justified only if there
is strong evidence that the cat is a source of FIP infection
for the other cats. The litter box should be shared by no
more than two cats, cleaned and disinfected regularly, and
should be kept away from the feeding area. Vaccinations are
available but are not universally recommended and should only
be used in cats that are at risk, which include multi-cat
households or catteries with confirmed FIP problems.
- by Mark Schlatter, Class of 1998
- edited by Tsang Long Lin, DVM, PhD
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