The Thai Journal of Veterinary Medicine


Foodborne picornaviruses and human calicivirus have one molecule of linear, positive-sense, single-stranded RNA, covered by a capsid without a lipid envelope. These viruses have a spherical shape, a particle diameter of 27-40 nanometers and the triangulation (T=3) icosahedral symmetry of a capsid. The replication cycle of poliovirus (PV) and hepatitis A virus (HAV) occurs in the cytoplasm of the host cell. The viral proteins are synthesized by the translation of RNA after the virus particles attach and uncoat at the host cell membrane. Major translated proteins are structural protein (capsid protein) and functional proteins e.g. proteases and RNAdependent RNA polymerase. The capsids of PV and HAV comprise multiple capsid proteins (VPs), but there is only a single structural protein in the calicivirus capsid. A distinctive characteristic of the capsid architecture is the cup-shaped depressions of caliciviruses. The RNAs of Noroviruses (NV) and feline calicivirus are organized into three major open reading frames (ORFs). The HAV, PV and NV are transmitted enterically. These viruses are recognized as major causes of foodborne and waterborne disease in the U.S. The leading method of detection is reverse transcription polymerase chain reaction (RT-PCR) since the host cells of wild type HAV and NV are not available for an infectivity test. One may speculate that NV will become the leading cause of foodborne illness because as many as 35% of foodborne outbreaks of unknown etiology may fit the clinical and epidemiological criteria that are used to implicate NV.



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