Enteric Coronavirus

Enteric replication of coronaviruses may result in fever, vomiting, and mucoid diarrhea in some kittens. However, most kittens have subclinical infections. Unfortunately, making an antemortem diagnosis of enteric coronavirus-associated illness is impossible with currently available assays. For example, a recent study failed to show an association between fecal scores and the presence of coronavirus RNA in feces (Gingrich et al, 2010).

Feline Infectious Peritonitis

Fulminant effusive FIP can occur in cats of any age but generally is recognized in cats younger than 5 years; most cases are younger than 1 year. Anorexia, weight loss, and general malaise are common presenting complaints. Icterus, ocular inflammation, abdominal distention, dyspnea, or CNS abnormalities occasionally are noted by the owner. In cats with effusive disease, abdominal distention is common and a fluid wave often can be balloted. Pleural effusion can result in dyspnea and a restrictive breathing pattern (shallow and rapid) as well as muffled heart and lung sounds. Male cats sometimes have scrotal enlargement from fluid accumulation.

Fever and weight loss are common with the effusive and noneffusive forms of the disease. Pale mucous membranes or petechiae are noted in some cats. FIP is one of the most common causes of icterus in cats younger than 2 years; liver size can be normal or enlarged, and the margins are usually irregular. Occasionally masses (pyogranulomas or lymphadenopathy) can be palpated in the omentum, mesentery, or intestines. A solitary ileocecocolic or colonic mass, resulting in obstruction leading to vomiting and diarrhea, occurs in some cats. Kidneys can be small (chronic disease) or large (acute disease or subcapsular effusion); renal margins are usually irregular. Anterior uveitis and chorioretinitis occur most frequently with the noneffusive form of the disease and can be its only manifestation. Pyogranulomatous disease can develop anywhere in the CNS, leading to a variety of neurologic signs that include seizures, posterior paresis, and nystagmus. Seizures secondary to FIP are a poor prognostic indicator (Timmann et al, 2008).

Enteric Coronavirus

As discussed, no assay is available to determine whether enteric coronaviruses are associated with diarrhea in cats. Cats with coronavirus RNA in feces should be evaluated for other causes of diarrhea.

Feline Infectious Peritonitis

Diagnostic tests for diagnosis of FIP have been reviewed (Giori et al, 2011; Hartmann et al, 2003). Cats with effusion disease are usually easy to confirm because the fluid is fairly characteristic. The fluid is sterile, appears colorless to straw colored, may contain fibrin strands, and may clot when exposed to air. The protein concentration on fluid analysis commonly ranges from 3.5 g/dl to 12 g/dl and is generally higher than that associated with other diseases. Mixed inflammatory cell populations of lymphocytes, macrophages, and neutrophils occur most commonly; neutrophils predominate in most cases, but in some cats macrophages are the primary cell type seen. In some cats the coronavirus antibody titers are greater in the effusion than in serum. Measurement of protein concentrations in effusions and calculation of the albumin/globulin ratio can aid in the diagnosis of effusive FIP. In one study an albumin/globulin ratio of 0.5 had a positive predictive value of 89%, and an albumin/globulin ratio of 1.0 had a negative predictive value of 91% (Hartmann et al, 2003). Coronavirus antigens commonly are detected by direct immunofluorescence in the effusions of cats with FIP but not in the effusions of cats with other diseases. In addition, viral RNA can be amplified detected by reverse transcriptase polymerase chain reaction (RT-PCR) in effusions and is unlikely to be in effusions from other causes.

Multiple hematologic, serum biochemical, urinalysis, diagnostic imaging, and CSF abnormalities develop in cats with noneffusive FIP. Several authors have assessed the predictive values of individual and combinations of tests (Giori et al, 2011; Hartmann et al, 2003). Other than histopathology, the positive predictive values of tests used to aid in the diagnosis of FIP are less than 100%, including the amplification of mRNA from blood. A presumptive diagnosis of noneffusive FIP usually is based on the combination of clinical and clinicopathologic findings and excluding other causes of the presenting clinical syndromes. Definitive diagnosis can be made by documenting appropriate histopathologic findings and coronavirus in tissues with immunohistochemistry.