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Viral Disease - Feline Coronavirus

Definition and Cause

Feline coronavirus (FCoV) causes either subclinical infection or mild, transient diarrhea in exposed cats.

Spontaneous mutation of enteric FCoV may lead to clinical FIP, which is associated with very high morbidity and mortality.

FCoV is an SS-RNA virus of the family Coronaviridae.

Pathophysiology

FCoV is highly contagious via fecal-oral transmission, but salivary, urinary, and transplacental sources of exposure are uncommon.

Most infected cats shed the virus intermittently and then stop shedding, although some shed persistently.

FCoV that has mutated to an FIP-causing form is seldom shed in feces, so epizootics are rare.

Although inactivated by most disinfectants, FCoV may persist in the environment.

Enteric infection results in villous atrophy and mild, self-limiting diarrhea.

With FIP, a history of recent stress or illness may precede the disease.

  • » Mutated FCoV invades intestinal epithelium and enters macrophages, resulting in disseminated spread of mutated viral particles.
  • » Immunological response is ineffective and pathologic changes occur.
  • » Two forms of FIP are recognized.

a) Effusive (wet) form

  • » Immune complexes circulate and are deposited in endothelia.
  • » A vasculitis ensues with exudation of protein rich fluid into body cavities.
  • » The wet form is usually more rapidly progressive than the dry form.

b) Non effusive (dry) form

  • » An ineffective cell-mediated immune response is mounted against the virus.
  • » Pyogranulomatous inflammation in a variety of tissues results in disease.
  • » The dry form may become effusive in its terminal stages.

Clinical Signs

Enteric FCoV: often subclinical or mild diarrhea

FIP

  • » Young (<2 years) and elderly cats more commonly affected
  • » Sexually intact and purebred cats more commonly affected
  • » Effusive FIP

    • » Common: fever, pale mucous membranes, dyspnea, abdominal distention
    • » Variable: abdominal masses, abdominal organomegaly, icterus

  • » Non effusive FIP

    • » Development of clinical signs is often insidious.
    • » Signs reflect the body system affected.

Hepatomegaly, icterus, abdominal masses, renomegaly

Pathologic ocular findings: uveitis, chorioretinitis

CNS signs, dyspnea

Fever and weight loss common

Diagnosis

Enteric FCoV infection

  • » Definitive diagnosis is seldom necessary.
  • » Antibody titers suggest prior exposure, but do not reflect fecal shedding or active infection.
  • » Viral particles identified in fecal specimens by PCR or EM have few, if any, implications for the health of an individual cat.

FIP infection

  • » General diagnostics tests
  • » Hematological findings: non regenerative anemia, neutrophilia - left shift
  • » Supportive biochemical findings

    • » Hyperglobulinemia with a low albumin:globulin ratio
    • » Other potential findings: icterus, elevated liver enzymes, azotemia

  • » Serum electrophoresis: polyclonal gammopathy
  • » Fluid analysis

    • » Clear to straw-colored, viscous effusion with low to moderate cellularity, and high protein content
    • » Contains lymphocytes, macrophages, and nondegenerate neutrophils

  • » Radiography: body cavity effusions- organo-megaly, pulmonary infiltrates
  • » Ultrasonography: nodular lesions within organs, organomegaly, effusions (pleural, peritoneal, pericardial, retroperitoneal)

Coronavirus-specific serological tests

  • » Detection of serum Ab identifies exposure to FCoV, but is not diagnostic of FIP.
  • » Titers cannot distinguish exposure to enteric FCoV from exposure to the mutated virus causing FIP.
  • » Titers cannot distinguish exposure to corona viruses of other species from exposure to FCoV.
  • » Most healthy cats with Abs to FCoV never develop FIP.
  • » Positive FCoV Ab titers do not suggest that the cat is shedding virus.
  • » Cats with FIP occasionally have negative titers, especially during terminal stages of disease.
  • » In cats with signs suggestive of FIP, high Ab titers support a diagnosis of FIP.

PCR tests for coronavirus

  • » PCR may identify FCoV in cats with either FIP or enteric FCoV.
  • » It cannot distinguish between enteric FCoV and the FIP-causing mutated forms.
  • »The test result may be negative in a significant number of cats with confirmed FIP.
  • »Positive PCR results from body effusions support a diagnosis of FIP.
  • »A fecal PCR test identifies viral shedding; although persistent viral shedding does not increase the risk for development of FIP, it can be a source of exposure for other cats.

Histopathologic findings

  • » Histopathologic evaluation remains the best method to diagnose FIP.
  • » Affected tissues exhibit pyogranulomatous inflammation with vasculitis and perivascular cuffing with mononuclear cells, macrophages, lymphocytes, and neutrophils.
  • » FA and immune histo-chemical testing of tissue specimens from biopsy (ultrasound-guidance or surgically obtained hepatic or renal tissue) or necropsy may confirm FIP.

Differential Diagnosis

Enteric FCoV infection with diarrhea: feline pan leukopenia, parasites, dietary indiscretion, protozoal infections, bacterial infections, foreign body, and inflammatory bowel disease

Effusive FIP: peritonitis, pyothorax, chylothorax, neo - plasia, heart failure, cholangiohepatitis, and disseminated fungal or bacterial infections

Non effusive FIP: toxoplasmosis, fungal infection, neo - plasia, and cholangiohepatitis

Treatment

Enteric FCoV with diarrhea

  • » Because the disease is usually subclinical or self-limiting, specific therapy is not often necessary.
  • » No known therapy reduces the small chance that FCoV-infected cats will develop FIP.

Feline infectious peritonitis

  • » Treatment is unsuccessful because the disease is usually fatal.
  • » Spontaneous remissions occur rarely.
  • » Supportive care with nutritional supplementation, relief of effusions that impair respiration, blood transfusions, parenteral fluid therapy, and antibiotic therapy for secondary infections may help prolong life.
  • » Immunosuppressive or immune modulatory therapy may benefit a small number of cats.

Prednisone 2 to 4 mg/kg PO BID

Cyclophosphamide 2.2 mg/kg PO 4 days/week or chlorambucil 20 mg/m2 PO every 2 to 3 weeks

Human-recombinant interferon-a 30 U PO SID on alternating weeks

Pentoxifylline: suggested therapy but data insufficient

Clinical studies of other proposed treatments (e.g., vitamins E, A, C) are not available.

Monitoring and Prevention

I. Catteries and multicat households

Control exposure to feces and disinfect fomites.

Ab tests identify exposed cats but do not predict fecal shedding or propensity to develop FIP, so do not euthanize healthy cats based on positive Ab test results.

Fecal PCR identifi es chronic shedders; segregation may reduce exposures.

Strategy to eradicate FCoV is as follows:

  • » Obtain negative (zero) titers on new cats.
  • » Segregate positive cats in the facility from negative cats.
  • » Keep all cats indoors
  • » Remove kittens from seropositive queens at 5 to 6 weeks of age.

II. Vaccination

The available intranasal vaccine appears safe when used as directed.

  • » Temperature-sensitive vaccine virus replicates only in respiratory epithelium, inducing mucosal immunity.
  • » Vaccine efficacy is 50% to 75% for previously unexposed cats.
  • »It is not indicated in low-risk cats, such as adults or cats in single-cat households.
  • »At-risk kittens possibly benefit from vaccination, with two doses given 3 to 4 weeks apart and followed by yearly booster vaccinations.
  • »Currently, the vaccine is not recommended for routine use (Table 112-3).

Vaccination does not prevent mutation of FCoV in an infected cat.


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