Sites of persistence of feline calicivirus

Various tissues were collected from eight cats persistently infected with feline calicivirus (FCV) strain 255 to determine the sites of viral persistence. Tissues were tested by virus isolation and an immunohistochemical technique in which infected cells were detected in formalin-fixed, paraffin-embedded tissue sections using rabbit antiserum to FCV 255, a biotinylated second antibody and streptavidin-peroxidase. Virus was detected by one or both techniques in tonsillar tissues of each animal, and not in other samples. Infected cells were detected in samples from six of eight kittens, and in each animal were few in number, and were cells of the superficial tonsillar epithelium or the stratum germinativum of the adjacent fossa mucosa. Transmission electron microscopic examination of tissues from three of the cats revealed calicivirus-like particles in cells similar to those identified immunohistochemically. These results confirm that the tonsillar region is the major site of FCV persistence and indicate that virus replication during persistence is confined to the surface epithelium of the tonsil and adjacent fossa mucosa.