Human rotavirus (HRV) type 1 or 2, adenovirus, or non-cultivatable 27 nm virus-like particles were demonstrated by electron microscopy and/or rotavirus ELISA in fecal samples from 45.5% of 604 gastroenteritis inpatients, 25.0% of 200 gastroenteritis outpatients and 6.0% of 812 control subjects, all sampled at Children's Hospital National Medical Center. Washington, DC. Rotaviruses were the most common pathogens detected as 39% and 22% of gastroenteritis inpatients and outpatients, respectively, shed HRV. About three-fourths of the rotaviruses were type 2, which was prevalent during five successive epidemic years from January, 1974, through June, 1978. HRV type 1 was detected in the last four successive epidemic years and represented nearly half of the HRV infections observed among gastroenteritis inpatients during the year 1977--1978. Both rotavirus serotypes were detected most often in the month of January, when 71% of 123 gastroenteritis inpatients and 62% of 34 gastroenteritis outpatients shed one of these viruses. Uncultivatable adenoviruses were detected significantly more frequently in stools from patients with gastroenteritis (3.9%) than from control subjects (0.6%), suggesting that these viruses played a role in acute enteric disease. The frequency of detection of 27 nm particles was not significantly different in gastroenteritis and control patients. Numerically, HRV infection was detected most often in gastroenteritis inpatients who were 10 through 12 months of age. The group of gastroenteritis inpatients with the highest percentage of HRV infection was 13 through 15 months of age. The excess of type 2 HRV infection relative to type 1 infection was especially large in those aged 7 through 24 months. Lower socioeconomic status or greater crowding appeared to be associated with the occurrence of rotavirus infection earlier in life and earlier in the epidemic year.

A series of reassortants was isolated from coinfection of cell cultures with a wild-type animal rotavirus and a "noncultivatable" human rotavirus. Wild-type bovine rotavirus (UK strain) was reassorted with human rotavirus strains D, DS-1, and P; wild-type rhesus rotavirus was reassorted with human rotavirus strains D and DS-1. The D, DS-1, and P strains represent human rotavirus serotypes 1, 2, and 3, respectively. Monospecific antiserum (to bovine rotavirus, NCDV strain) or a set of monoclonal antibodies to the major outer capsid neutralization glycoprotein, VP7 (of the rhesus rotavirus), was used to select for reassortants with human rotavirus neutralization specificity. This selection technique yielded many reassortants which received only the gene segment coding for the major neutralization protein from the human rotavirus parent, whereas the remaining genes were derived from the animal rotavirus parent. Single human rotavirus gene substitution reassortants of this sort represent potential live vaccine strains.

The ribonucleic acid migration patterns of 7 subgroup 1 and 16 subgroup 2 human rotaviruses recovered from four geographic areas were compared. The subgroup 1 ribonucleic acid patterns had strikingly slower-moving segments 10 and 11, suggesting a correlation between the ribonucleic acid pattern and the subgroup specificity.

An immune adherence hemagglutination assay (IAHA) and a modified enzyme-linked immunosorbent assay for antigenic characterization of human rotaviruses were developed. The designations of type 1 and type 2 were identical to those established previously by specific complement fixation, enzyme-linked immunosorbent assay, and immune electron microscopy. By IAHA (and modified enzyme-linked immunosorbent assay) certain animal rotaviruses were found to be closely related to human rotavirus type 1. The pattern of IAHA reactivity and the cell culture neutralization serotype were found to be distinct properties. The separation of neutralization and IAHA reactivity was apparent when animal rotaviruses which were distinguishable from each other by neutralization assays were found to share IAHA specificity. Further evidence for the dissociation of the neutralization and IAHA specificities was found in studies of human and bovine rotaviruses which underwent genetic reassortment during coinfection. Thus, it appeared that the IAHA and neutralization antigens were coded for by different genes. In view of these findings, we suggest that the term serotype be reversed to identify the antigen that reacts with neutralizing antibodies as is customary for other viruses and that the term subgroup (instead of serotype) be used for the specificity detected by specific complement fixation, enzyme-linked immunosorbent assay, and now IAHA.

The neutralization epitopes of human and simian rotavirus protein VP7 were studied by producing six neutralizing monoclonal antibodies (N-MAbs) and using these N-MAbs to select antigenic mutants that resisted neutralization by the N-MAbs used for their selection. Cross-neutralization tests between the N-MAbs and the antibody-selected antigenic mutants identified one cross-reactive and five distinct serotype-specific neutralization epitopes which operationally overlapped one another and constituted a single antigenic site. In addition, the amino acid substitutions in human rotavirus VP7 that are responsible for the antigenic alterations in the mutants selected with anti-VP7 cross-reactive or serotype-specific N-MAbs were identified. All the amino acid substitutions in the antigenic mutants occurred in one of two variable regions: amino acids 87 to 101 and 208 to 221.