Objectives:

Rotaviruses are the major etiologic agents of infantile diarrhoea worldwide and the development of effective vaccines for rotavirus disease is considered a primary objective of the WHO. The main rotavirus serotypes G1, G2, G3 and G4 are the targets for vaccine development. However, unusual rotavirus serotypes, such as G5, G6, G8, G9 and G10 may acquire local relevance. The objective of the present study was to determine the antigenic specificities of the rotavirus strains spreading in Mantova (Italy), in 2003.

Methods:

A total of 134 stool samples were tested for the presence of rotavirus by an immuno-chromatographic assay during 2003. Sixteen rotavirus-positive samples (11.9%) were detected from children between 6 months and 9 years of age (median age of 2.56 years). A 14-point score system was used to summarise the clinical severity. Rotavirus RNA was analysed by reverse transcription-PCR, PCR genotyping and sequence analysis for determination of the G (VP7) and P (VP4) specificity. In order to evaluate the correlation between serotypes and pathogenicity, a statistical analysis was performed by the General Linear Model procedure (SAS 1990).

Results:

Eight samples were typed as G1, 4 as G4, 3 as G9 and one was not typeable. The VP7 genes of G9 strains revealed high genetic similarity to each other (about 100%) and to G9 strains identified recently in southern Italy (99.8%). Analysis of the VP4 gene revealed that all the strains (G1, G4 and G9) belonged to the P type P1A[8]. The severity of the disease was significantly higher for G9 rotavirus infections. The linear model fitted to pathogenicity score values was significant (P < 0.0289; R² = 0.54). Least square mean was 10.69 (standard error 1.20) for G9 rotaviruses and 6.32 (standard error 0.67) for the other serotypes.

Conclusions:

The rotavirus strains were characterised as P[8], G1, P[8], G4 and P[8], G9. The VP7 gene of the G9 strains revealed a high genetic similarity to other Italian G9 strains and to the globally spreading G9 lineage described recently worldwide. Interestingly, it was possible to find a statistically supported correlation between the rotavirus serotype and the severity of the rotavirus-associated disease, as the symptoms induced by rotavirus G9 infections were significantly more severe. The results described here emphasises the role of rotavirus G9 as an epidemiologically important serotype and the need to include the G9 specificity in candidate rotavirus vaccines.