Epidemiologic and molecular trends of "Norwalk-like viruses" associated with outbreaks of gastroenteritis in the United States.

Between July 1997 and June 2000, fecal specimens from 284 outbreaks of nonbacterial gastroenteritis were submitted to the Centers for Disease Control and Prevention for testing for "Norwalk-like viruses" (NLVs). Specimens were examined by reverse-transcription polymerase chain reaction and direct electron microscopy for the presence of NLVs. Adequate descriptive data were available from 233 of the outbreaks, and, of these, 217 (93%) were positive for NLVs. Restaurants and events with catered food were the most common settings, and contaminated food was the most common mode of transmission. Genogroup II (GII) strains were the predominant type (73%), with genogroup I strains causing 26% of all NLV-positive outbreaks. Certain GII clusters (GII/1,4,j) were more commonly associated with outbreaks in nursing home settings than with outbreaks in other settings. Strain diversity was great: one potential new sequence cluster was implicated in multiple outbreaks, and strains belonging to a tentative new genogroup were identified.

Prevalence and characterization of astroviruses in Argentinean children with acute gastroenteritis.

Among viral agents causing gastroenteritis, human astroviruses (HAstVs) take second or third place, after rotaviruses and caliciviruses, as the most frequent cause of illness. The aims of this study were to determine the prevalence of HAstV infection and to characterize the circulating HAstV strains in children with diarrhea under 3 years of age treated between 1995 and 1998 at out- or in-patient facilities of the children's hospital in Mendoza, Argentina. Reverse transcription-polymerase chain reaction (RT-PCR) and enzyme immunoassay (EIA) were used to detect HAstVs in stool specimens. Positive specimens were tested further by EIA and/or sequenced to type detected HAstV strains. HAstVs were detected in 40 (3.7%) of 1,070 samples that were rotavirus and calicivirus-negative: 14 (3.5%) of 402 from outpatients and 26 (3.9%) of 668 from inpatients. HAstV infection tended to be more severe in children during their first year of life: 18 (4.7%) of 383 HAstV-positive children 0-11 months old were hospitalized versus 8 (2.8%) of 285 children 1 year of age or older (P = 0.29). Type 1 (HAstV-1) was the most common type (41%), followed by HAstV-4 (25%), HAstV-2 (13%), HAstV-3 (13%), and HAstV-5 (8%). In this first epidemiological study of HAstV infection in this region, we confirmed HAstV to be a cause of severe gastroenteritis in children, more often among children younger than 12 months of age. HastV-4 caused 25% of HastV infections in Mendoza, although it has been detected commonly elsewhere. Distinct genetic lineages were apparent but their epidemiological significance remains to be demonstrated.

Inter- and intragenus structural variations in caliciviruses and their functional implications.

The family Caliciviridae is divided into four genera and consists of single-stranded RNA viruses with hosts ranging from humans to a wide variety of animals. Human caliciviruses are the major cause of outbreaks of acute nonbacterial gastroenteritis, whereas animal caliciviruses cause various host-dependent illnesses with a documented potential for zoonoses. To investigate inter- and intragenus structural variations and to provide a better understanding of the structural basis of host specificity and strain diversity, we performed structural studies of the recombinant capsid of Grimsby virus, the recombinant capsid of Parkville virus, and San Miguel sea lion virus serotype 4 (SMSV4), which are representative of the genera Norovirus (genogroup 2), Sapovirus, and Vesivirus, respectively. A comparative analysis of these structures was performed with that of the recombinant capsid of Norwalk virus, a prototype member of Norovirus genogroup 1. Although these capsids share a common architectural framework of 90 dimers of the capsid protein arranged on a T=3 icosahedral lattice with a modular domain organization of the subunit consisting of a shell (S) domain and a protrusion (P) domain, they exhibit distinct differences. The distally located P2 subdomain of P shows the most prominent differences both in shape and in size, in accordance with the observed sequence variability. Another major difference is in the relative orientation between the S and P domains, particularly between those of noroviruses and other caliciviruses. Despite being a human pathogen, the Parkville virus capsid shows more structural similarity to SMSV4, an animal calicivirus, suggesting a closer relationship between sapoviruses and animal caliciviruses. These comparative structural studies of caliciviruses provide a functional rationale for the unique modular domain organization of the capsid protein with an embedded flexibility reminiscent of an antibody structure. The highly conserved S domain functions to provide an icosahedral scaffold; the hypervariable P2 subdomain may function as a replaceable module to confer host specificity and strain diversity; and the P1 subdomain, located between S and P2, provides additional fine-tuning to position the P2 subdomain.