rus propagated in cell culture reported the diameter as A serotype 3 astrovirus was identified in stool 31 nm with 10 nm spikes (Risco et al., 1995). samples from an outbreak of acute gastroenteri-
The astrovirus genome is a single-strand positivetis that occurred among military recruits in sense RNA with three open reading frames (ORF), France. Sixteen stools samples and eight pairs ORF1a, ORF1b, and ORF2 (Jiang et al., 1993; Monroe of acute-and convalescent-phase serum were et al., 1993; Willcocks et al., 1994). ORF1a and ORF1b collected from affected individuals. Astrovirus encode putative protease and polymerase domains, the was detected in two stool samples by electron latter of which is expressed as a fusion protein synthemicroscopy and in four stool samples by reverse sized via a ribosomal frame-shift mechanism (Lewis transcriptase-polymerase chain reaction (RTand Matsui, 1995; Marczinke et al., 1994). ORF2 en-PCR). Seroconversion to the astrovirus present codes the viral capsid protein precursor (Lewis et al., in one stool was detected in seven patients by 1994). During astrovirus replication, a 2.7 kb subgenousing solid-phase immune electron microscopy mic RNA is synthesized in infected cells (Monroe et al., (SPIEM) and dot blot. For three patients, the sero-1993, 1991b). This subgenomic RNA, which includes logical results were consistent with the PCR re-ORF2, probably serves as an mRNA for the expression sults, indicating that astrovirus was a cause of of the capsid proteins during infection. gastroenteritis in these young adults. This study Seven serotypes of human astrovirus have been disdescribes the characterization of the serotype 3 tinguished by using immune EM (IEM) or immunofluoastrovirus associated with this outbreak. The virescence (Kurtz and Lee, 1984; Lee and Kurtz, 1994). rus has a buoyant density in cesium chloride of
In the United Kingdom, serotype 1 was reported to be 1.365 gm/ml and contains two proteins immunothe most prevalent type (Lee and Kurtz, 1994), and we precipitated with rabbit serum. Only the larger have recently confirmed and extended this finding by protein was recognized by immunoblotting using using collections from various regions of the world (Noel a convalescent-phase human serum. The protein et al., 1995). This study went on to show that nucleotide composition of this virus differs from that resequences in one part of ORF2 define seven genotypes ported for serotype 1 astrovirus, indicating heterothat are completely consistent with the serotypes detergeneity in the capsid composition among mined by EIA (Noel et al., 1995).