ABSTRACT
The family Picobirnaviridae includes several animal and human picobirnaviruses (PBVs) that are a group of nonenveloped spherical, small viruses 35-40 nm in diameter with simple core capsid and bisegmented double stranded RNA linear genome approximately 4-4.5 kb in size [1]. The size of segment 1 varies from 2.2 to 2.7 kb whereas segment 2 varies from 1.2 to 1.9 kb. To date, human PBVs have been characterized with either large genome prole or small genome prole, based on the relative migration of the two genomic segments (Figure 69.1). Picobirnaviruses with small genome prole have two genomic segments of dsRNA with highly consistent RNA electropherotype of 1.75 kb and 1.55 kb for segment 1 and 2, respectively (Figure 69.2). Apart from protein (ORF2), the larger segment 1 also encodes a polyprotein (ORF1) that self cleaves to yield the mature coat protein and a large peptide. The smaller segment 2 encodes RNAdependent RNA polymerase [2,3]. The virions of picobirnaviruses are icosahedral with T = 3 symmetry, having buoyant density of 1.38-1.4 g/ml [4]. Owing to the lack of a suitable cell culture system, the method of choice for detection and characterization of PBVs is polyacrylamide gel electrophoresis (PAGE) and partial genomic segment amplication by reverse transcription-polymerase chain reaction (RT-PCR) with genogroup I (Chinese strain CHN-97) and genogroup II (Atlanta strain 4GA-91) specic primers, or more recently complete genomic segment amplication using single primer followed by nucleotide sequencing [5,6].
