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Parents are often infected when their young children develop rotavirus diarrhea, but the parents usually are asymptomatic. Nevertheless, travelers diarrhea due to rotavirus has been described in adults (Ryder et al., 1981).

Pathogen Description

Rotavirus is a double-stranded RNA virus in the Reoviridae family, with a distinctive genome of 11 segments. Serological classification is somewhat confusing. Recent work finally has permitted separation of distinct serotypes based on outer capsid antigens detected by neutralization with hyperimmune sera (Wyatt et al., 1982). Four human serotypes have been described, and at least three additional distinct animal serotypes have been identified. Epidemiological studies are in progress to determine the prevalence of these serotypes in different parts of the world. The present data indicate that serotypes 1 and 2 are present worldwide and that serotype 3 may be less prevalent; serotype 4 has been found in only one or two outbreaks in Europe (Kapikian, personal communication, 1984). Some heterologous cross-reactivity has been reported between animal and human serotypes. The number and cross-reactivity of serotypes is obviously important for vaccine development.

Rotavirus subgroups exist in addition to serotypes. These involve inner capsid antigens detected by complement fixation, ELISA, or immune adherence assays (Kapikian, et al., 1981). Two well-defined subgroups, 1 and 2, also may be identified by differences in RNA patterns detected by electrophoresis in polyacrylamide-agarose gels (Kalica et al., 1981). A third subgroup may exist as well (Kapikian, personal communication, 1984). Serotype and subgroup determinations are controlled by different segments of the virus genome.

In vitro cultivation of human rotaviruses has been difficult. Strain Wa, the prototype serotype 1 rotavirus, originally was propagated in African green monkey kidney cells following 11 passages in newborn, germ-free piglets (Wyatt et al., 1980). Other strains, such as DS-1 (prototype of serotype 2), have been grown in vitro following rescue by genetic reassortment with readily grown bovine rotaviruses (Greenberg et al., 1981). Recently, many rotaviruses (up to 75 percent of stool isolates) have been cultivated in MA 104 cells, a primary embryonic cynomolgus monkey kidney line, following pretreatment of virus by trypsinization and low speed centrifugation (Sato et al., 1981; Urasawa et al., 1981).

Protective antigens have not been well defined. There is evidence of cross-protection between animal and human viruses, but the responsible determinants have not been identified (Wyatt et al., 1979).

Host Immune Response

Experimental studies in animals have demonstrated that feeding colostrum containing antibody to rotavirus during challenge is



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