Detection and analysis of recombination in GII.4 norovirus strains causing gastroenteritis outbreaks in Alberta

- Two recombinant strains, Apeldoorn 2007 and Sydney 2012, circulated in Alberta.
- We identified a non recombinant evolutionary intermediate strain of Sydney 2012.
- This intermediate strain most likely evolved from an ancestor of New Orleans 2009.

Recombination is an important mechanism generating genetic diversity in norovirus (NoV) that occurs commonly at the NoV polymerase-capsid (ORF1/2) junction. The genotyping method based on partial ORF2 sequences currently used to characterize circulating NoV strains in gastroenteritis outbreaks in Alberta cannot detect such recombination events and provides only limited information on NoV genetic evolution. The objective of this study was to determine whether any NoV GII.4 strains causing outbreaks in Alberta are recombinants. Twenty stool samples collected during outbreaks occurring between July 2004 and January 2012 were selected to include the GII.4 variants Farmington Hills 2002, Hunter 2004, Yerseke 2006a, Den Haag 2006b, Apeldoorn 2007, New Orleans 2009, and Sydney 2012 based on previous NoV ORF2-genotyping results. Near full-length NoV genome sequences were obtained, aligned with reference sequences from GenBank and analyzed with RDPv4.13. Two sequences corresponding to Apeldoorn 2007, and Sydney 2012 were identified as recombinants with breakpoints near the ORF1/2 junction and putative parental strains as previously reported. We also identified, for the first time, a non-recombinant sequence resembling the ORF2-3 parent of the recombinant cluster Sydney 2012 responsible for the most recent pandemic. Our results confirmed the presence of recombinant NoV GII.4 strains in Alberta, and highlight the importance of including additional genomic regions in surveillance studies to trace the evolution of pandemic NoV GII.4 strains.