Rotavirus-Like, Calicivirus-Like, and 23-nm Virus-Like Particles Associated with Diarrhea in Young Pigs

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Abstract
Virus particles morphologically similar to caliciviruses and rotaviruses were detected by EM in the intestinal contents of a 27-day-old diarrheic nursing pig. A 3rd small spherical 23-nm virus-like particle was also observed. Calicivirus-like particles averaged 33 nm in diameter. Similar to rotaviruses, rotavirus-like particles were present as single-capsid 55-nm forms or double-capsid 70-nm particles. Most gnotobiotic pigs orally exposed to samples containing these 3 viruses developed diarrhea and villous atrophy of the small intestine, and all shed the 3 viruses in their intestinal contents. Attempts to propagate these viruses in cell culture were unsuccessful. The antigenic relationship of the rotavirus-like particles to known rotaviruses were explored by immune EM and immunofluorescent staining. By these techniques, the rotavirus-like particles did not cross-react with antisera to porcine, bovine or human rotativurses or to reovirus type 3. Antisera from gnotobiotic pigs exposed to all 3 viruses had enzyme-linked immunosorbent assay and virus neutralization titers of < 4 against porcine rotavirus. Previous infection of gnotobiotic pigs with the mixture containing rotavirus-like particles failed to protect them against a subsequent challenge with porcine rotavirus. The antigenic relationship of the calicivirus-like particles to known caliciviruses was investigated by immune EM and virus neutralization. By these tests, the calicivirus-like particles did not react with antisera against feline calicivirus strain 255 or M-8. In a study conducted at Plum Island Animal Disease Center [Greenport, New York, USA], antiserum against the 3 combined agents did not specifically neutralize any serotype of swine vesicular exanthema virus.

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