Emerging Novel GII.P16 Noroviruses Associated with Multiple Capsid Genotypes

Area of Science:

• Virology
• Molecular Epidemiology
• Public Health

Background:

• Noroviruses are a leading cause of acute gastroenteritis outbreaks globally.
• Viral evolution through recombination and antigenic drift drives norovirus emergence.
• A novel GII.P16-GII.4 Sydney recombinant strain emerged in the US in 2015.

Purpose of the Study:

• To investigate the unique characteristics of the novel GII.P16 norovirus recombinant strain.
• To understand the impact of this recombinant strain on norovirus outbreaks in the US.
• To identify genetic changes associated with the novel GII.P16 polymerase.

Main Methods:

• Dual-typing of 1807 norovirus-positive samples.
• Sequencing of 124 samples to obtain near-complete genomes.
• Integration of molecular data with outbreak surveillance records (CaliciNet, NORS) and GenBank data.

Main Results:

• The novel GII.P16 polymerase extended GII.4 Sydney predominance and increased GII.2 outbreaks in the US.
• Introduction of novel GII.P16 noroviruses did not correlate with unique VP1 changes, altered disease severity, or affected populations.
• Unique amino acid changes were identified in immune-antagonistic proteins (NS1/2, NS4, VP2) and the RNA-dependent RNA polymerase (RdRp).

Conclusions:

• Recombination involving the novel GII.P16 polymerase significantly impacted norovirus epidemiology in the US.
• Specific genetic alterations in non-structural and structural proteins may contribute to the success of emerging recombinant noroviruses.
• Molecular surveillance of norovirus genomes is crucial for understanding viral evolution and informing vaccine and antiviral development.