Astrovirus serotype 4 has increased in relative prevalence in the Oxford, UK area in 1993. The structural gene of human astrovirus serotype 4 has been sequenced and the results indicate that this protein differs substantially from serotypes 1 and 2. In particular, conservation at the C terminus is greatly reduced. However, amino acid substitutions in this region show a strong conservation in character suggesting that structural or functional constraints operate in this region.

We have developed a microimmunofluorescence test (IF) which uses cells infected with a recombinant baculovirus which expresses the capsid proteins of astrovirus types 1 or 6. The IF test was sensitive and specific and the results for human astrovirus type 1 (HAst-1) were comparable to those obtained by immune electronmicroscopy and radioimmunoassay. Application of the test to a panel of 273 sera collected from patients and staff at two childrens hospitals in London showed that over 50% of the population were infected by HAst-1 between the age of 5 and 12 months rising to 90% by 5 years, whereas human astrovirus type 6 (HAst6) was relatively uncommon (10-30%) in all age groups.

Astroviruses (genus Astrovirus) are assigned to a newly established virus family, the Astroviridae. The molecular biology of these agents reveals many features unique amongst the non-enveloped animal viruses and resembles that of members of certain plant virus families. In particular, their possession of a serine protease and use of ribosomal frameshifting to express the RNA polymerase are similar to the luteoviruses. Many aspects of the astrovirus replication strategy are still unclear, but replication may involve a nuclear step and non-structural proteins may influence host cell range. 278 LLCMK.