Page 1516 - Small Animal Internal Medicine, 6th Edition

1488 PART XIV Infectious Diseases

FELINE CORONAVIRUS and respiratory tract infection increase the risk for FIP, sug-
gesting that the immune status of the host is important in
Etiology and Epidemiology
VetBooks.ir Coronaviruses causing disease in cats include feline infec- determining the development of clinical disease. Cats con-
currently infected with FIV shed 10 to 100 times more FECV
tious peritonitis virus (FIPV) and feline enteric coronavirus
inducing feline coronaviruses before challenge with viru-
(FECV). The virology and immunopathogenesis of feline in stool than FIV-naive cats. Previous exposure to non-FIP-
coronaviruses has been reviewed (Pedersen et al., 2014a). lent FIPV can result in acceleration of the disease process
Enteric infection generally results in mild gastrointestinal (Pedersen et al., 2014c). Experimentally infected, coronavi-
signs; systemic infection can induce a clinical syndrome with rus seropositive kittens can develop accelerated FIP com-
diverse manifestations commonly referred to as feline infec- pared with seronegative kittens when exposed to FIPV. This
tious perinotitis (FIP). Most current work suggests that the antibody-dependent enhancement of virus infectivity occurs
mutations associated with the FIPV strains are in the 3c because macrophages are more effectively infected by virus
and spike protein genes (Bank-Wolf et al., 2014; Lewis et al., complexed with antibody than by virus alone, but this phe-
2015; Rottier et al., 2005). Enteric coronaviruses are com- nomenon appears to be rare in naturally infected cats.
monly shed in feces and are highly contagious. By RT-PCR
testing, coronaviruses can be detected in feces as early as 3 Clinical Features
days after infection. In studies of FECV-infected, closed cat Enteric replication of coronaviruses commonly results in
colonies, almost every cat becomes infected. In one study of fever, vomiting, and mucoid diarrhea. With FECV infec-
155 pet cats with naturally occurring FECV infection, viral tion, clinical signs are self-limiting and generally respond
RNA was shed continuously (n = 18) or intermittently (n = to supportive care within days. Fulminant FIP can occur in
44) in the feces of some cats (Addie et al., 2001). Others were cats of any age but is generally recognized in cats younger
initially shedding viral RNA and then ceased shedding (n = than 5 years; most cases are younger than 1 year. Intact
56), and some were resistant to infection (n = 4). The cats males are over-represented in some studies. In cattery out-
that stopped viral shedding were susceptible to reinfection. breaks, usually only one or two kittens in a litter are clini-
Viral RNA was detected in the ileum, colon, and rectum of cally affected. This may relate to poor transmissibility of
cats with persistent shedding. strains capable of inducing FIP. Anorexia, weight loss, and
Most cases of FIP develop in multiple-cat households or general malaise are common presenting complaints (Box
catteries. Theoretically, the effusive form of disease develops 96.1). Icterus, ocular inflammation, abdominal distension,
in cats with poor cell-mediated immune responses; the nonef- dyspnea, or CNS abnormalities are occasionally noted by
fusive form (“dry”) develops in cats with partial cell-mediated the owner.
immunity. The effusive form of disease is an immune complex Fever and weight loss are common. Pale mucous mem-
vasculitis characterized by leakage of protein-rich fluid into branes or petechiae are noted in some cats. FIP is one of the
the pleural space, the peritoneal cavity, the pericardial space, most common causes of icterus in cats younger than 2 years;
and the subcapsular space of the kidneys. In the noneffusive liver size can be normal or enlarged, and the margins are
form pyogranulomatous or granulomatous lesions develop usually irregular. Abdominal distension is common, a fluid
in multiple tissues, particularly the eyes, brain, kidneys, wave can often be balloted, and occasionally masses (pyo-
omentum, and liver. Some affected cats have characteristics granulomas or lymphadenopathy) can be palpated in the
of both forms of FIP. Using reverse transcriptase quantitative omentum, mesentery, or intestines. A solitary ileocecocolic
PCR (RT-qPCR) assay and immunohistochemical staining, or colonic mass, resulting in obstruction leading to vomiting
it was shown that experimentally inoculated cats have FIPV and diarrhea, occurs in some cats (Harvey et al., 1996).
genomic RNA mainly in macrophages in diseased tissues and Kidneys can be small (chronic disease) or large (acute disease
effusions (Pedersen et al., 2015). or subcapsular effusion); renal margins are usually irregular.
Clinical disease associated with FIP virus may be influ- Pleural effusion can result in dyspnea and a restrictive
enced by a number of factors, including the virulence of breathing pattern (shallow and rapid), as well as muffled
the strain, the dose of the virus, the route of infection, the heart and lung sounds. Male cats sometimes have scrotal
immune status of the host, genetically determined host enlargement from fluid accumulation.
factors, the presence of other concurrent infections, and Anterior uveitis and chorioretinitis occur most frequently
whether the cat had been previously exposed to a corona- with the noneffusive form of the disease and can be its only
virus. Some breeds, including British Shorthair, Devon Rex, manifestation. Pyogranulomatous disease can develop any-
and Abyssinian, appear to be predisposed to the development where in the CNS, leading to a variety of neurologic signs
of FIP in some studies (Pedersen et al., 2014a; Pesteanu- that include seizures, posterior paresis, and nystagmus.
Somogyi et al., 2006; Worthing et al., 2012;). However, it has Seizures secondary to FIP are a poor prognostic indicator
been difficult to determine the genetic basis for increased (Timmann et al., 2008).
susceptibility or resistance (Pedersen et al., 2014c). In a study Feline coronaviruses have been suggested as a cause
of 40 of 111 cats that survived experimental inoculation with of failure to conceive, abortion, stillbirth, and congenital
FIPV, there was no sex association, but resistance increased defects, as well as the fading kitten syndrome (kitten mortal-
after 6 months of age (Pedersen et al., 2014c). FeLV infection ity complex). However, one epidemiologic study failed to