An isolated epizootic of hemorrhagic-like fever in cats caused by a novel and highly virulent strain of feline calicivirus

An isolated epizootic of a highly fatal feline calicivirus (FCV) infection, manifested in its severest form by a systemic hemorrhagic-like fever, occu rred over a 1-month period among six cats owned by two different employees and a client of a private veterinary practice, The infection may have start ed with an unowned shelter kitten that was hospitalized during this same pe riod for a severe atypical upper respiratory infection. The causative agent was isolated from blood and nasal swabs from two cats; the electron micros copic appearance was typical for FCV and capsid gene sequencing showed it t o be genetically similar to other less pathogenic field strains, An identic al disease syndrome was recreated in laboratory cats through oral inoculati on with tissue culture grown virus. During the course of transmission studi es in experimental cats, the agent was inadvertently spread by caretakers t o an adjoining room containing a group of four normal adult cats. One of th e four older cats was found dead and a second was moribund within 48-72 h i n spite of symptomatic treatment; lesions in these animals were similar to those of the field cats but with the added feature of severe pancreatitis, The mortality in field cats, deliberately infected laboratory cats, and ina dvertently infected laboratory cats ranged from 33-50%. This new isolate of calicivirus, named FCV-Ari, was neutralized at negligible to low titer by antiserum against the universal FCV-F9 vaccine strain, Cats orally immunize d with FCV-F9, and then challenge-exposed shortly thereafter with FCV-Ari, developed a milder self-limiting form of disease, indicating partial protec tion. However, all of the held cars, including the three that died, had bee n previously immunized with parenteral FCV-F9 vaccine. FCV-Ari caused a dis ease that was reminiscent of Rabbit Hemorrhagic Disease, a highly fatal cal icivirus infection of older rabbits. (C) 2000 Elsevier Science B.V. All rig hts reserved.