Feline Enteric Coronavirus
Feline enteric coronavirus (FECV) is an enveloped, single-stranded RNA virus that is highly prevalent worldwide in domestic cats. Infection is often subclinical or characterized by transient, mild GI illness in kittens. Mutation of FECV to a biotype capable of infection and replication within macrophages is responsible for development of feline infectious peritonitis (FIP), a highly fatal, multisystemic disease.
Fecal shedding of feline enteric coronavirus begins within 1 week of initial infection and persists at high levels for 2–10 months, followed by an extended period (up to 24 months) of lower level, potentially intermittent, viral shedding. At least 13% of infected cats shed the virus indefinitely.
Cats become infected through ingestion or inhalation of virus-containing feces or through contact with contaminated fomites (eg, litter boxes, mutual grooming, housing, personnel). FECV is relatively fragile but can survive in dry environments for up to 7 weeks. Close contact between cats (eg, catteries and multicat households) facilitates transmission. Vertical transmission from infected queens to kittens does occur. Kittens generally do not begin to shed virus before 9–10 weeks of age, although viral shedding as early as 4 weeks of age has been reported. Soon after infection, virus may replicate in oropharyngeal tissue, resulting in transient (hours to days) salivary shedding. FECV infects and replicates in mature apical epithelial cells of the intestinal villi, causing brush border shortening and destruction.
Most feline enteric coronavirus infections are clinically inapparent or characterized by mild, self-limiting gastroenteritis. Occasionally, vomiting and diarrhea can be acute and severe or chronic and unresponsive to treatment. Although diarrhea is the most common clinical sign of infection in kittens, upper respiratory tract signs have also been reported.
The viral DNA of feline enteric coronavirus can be detected in feces by RT-PCR. Because chronic carriers of FECV tend to be asymptomatic, FECV can be assumed to be the cause of the diarrhea only after other causes (eg, infectious, dietary, inflammatory bowel disease, neoplasia, etc) have been excluded. The clinical utility of serologic evaluation for antibodies to FECV is questionable. Positive coronavirus antibody titers are detected in up to 40% of pet cats and in up to 90% of cats in catteries or multicat households. Positive FECV antibody titers are indicative only of exposure to the virus and are not suggestive of the etiology of the current disease, do not correlate with the risk of developing FIP, and are not diagnostic for FIP. Histologic lesions suggestive of FECV enteritis include intestinal villous fusion, atrophy, or sloughing. Because these lesions are nonspecific, definitive diagnosis requires immunohistochemical or immunofluorescent detection of viral antigen in intestinal epithelial cells.
The mild, transient clinical signs of feline enteric coronavirus are unlikely to require therapy. Treatment, if required, is symptomatic and supportive (ie, fluid therapy, oral electrolyte solutions, antiemetics). There is no specific antiviral therapy. Death due to the FECV-associated gastroenteritis is uncommon.
Control and prevention of FECV are usually a concern only in breeding catteries and rescue shelters. Ingestion of virus-contaminated fecal particles should be prevented as much as possible. Fecal contamination of the environment can be minimized with sufficient litter box numbers, daily litter box cleaning, weekly litter box disinfection, and clipping/cleaning fur from the hind end of long-haired cats. FECV can survive indoors for up to 7 weeks under dry conditions but is readily inactivated by most commercial disinfectants.
Ideally, cats should be housed in small (three or four cats), closed groups. The room, cages, bedding, and litter boxes should be disinfected between groups. Although impractical in a shelter situation, cats should be housed in groups according to their antibody (immunofluorescent antibody test seropositive or seronegative) and virus shedding (based on fecal PCR) status. Seropositive cats can be retested every 3–6 months and moved into seronegative groups as their antibody titer decreases. In a rescue or shelter situation, cats should be housed singly. Identification of FECV carrier cats requires nine monthly, consecutive positive fecal RT-PCR tests, whereas identification of a cat that has eliminated FECV infection requires five consecutive negative fecal RT-PCR tests.
Seropositive cats should be mated only to other seropositive cats, and seronegative cats to other seronegative cats. Kittens born of seropositive matings or to a seropositive queen are protected from infection by maternally derived immunity until about 6 weeks of age. Kittens weaned from seropositive queens by 6 weeks of age are unlikely to acquire infection from the queen. Serologic testing of kittens should be delayed until 10–11 weeks of age, by which time seroconversion is likely.
New cats should be serologically tested before introduction into a cattery or breeding program. Only seronegative and virus-free (fecal PCR) cats should be introduced into an FECV-free cattery or a cattery attempting to eliminate the virus. Seropositive cats are less likely to develop FIP than seronegative cats when introduced to an FECV-endemic environment. Vaccination with an intranasal, temperature-sensitive FECV mutant is not generally recommended but can be considered in seronegative cats >16 weeks old introduced into an FECV-endemic environment. Vaccination will lead to seroconversion and does not completely protect cats previously exposed to FECV from developing FIP.