Emergence of new norovirus variants and genetic heterogeneity of noroviruses and sapoviruses in children admitted to hospital with diarrhea in Thailand

Abstract

Enteric caliciviruses, including noroviruses (NoVs) and sapoviruses (SaVs), are recognized as important etiologic agents of acute gastroenteritis with considerable genetic diversity. In this study, fecal specimens collected from 147 infants and young children admitted to hospital with acute gastroenteritis in 2005 in Chiang Mai, Thailand, were screened for NoVs and SaVs by reverse transcription-multiplex polymerase chain reaction (RT-multiplex PCR). Ten isolates (6.8%) belonged to NoV GII genogroup and five (3.4%) were positive for SaVs. GII/4 was the most predominant genotype of NoVs, followed by GII/15, GII/6, and GII/12. Surprisingly, NoVs GII/1, GII/2, GII/3, GII/7, and GII/16 genotypes, which were detected previously during the 2002-2004 survey, were not detected in 2005. Conversely, NoVs GII/6, GII/12, and GII/15 appeared in 2005 but were not detected during the 2002-2004 survey. The only genotype found to be common, as the most predominant genotype, in both surveys was NoV GII/4. Similar findings were also observed for SaVs, that is, the GI/2 and GIV detected during 2002-2004 were not detected in 2005, while GI/5 and GII/3 detected in 2005 were not detected previously during the 2002-2004 surveillance. In addition, comprehensive genetic evolutionary analysis of NoV GII/4 genotype demonstrated that the majority of GII/4 detected in this study (CMH002/05, CMH005/05, CMH042/05, and CMH083/05) were classified as new NoV variants and fell into subtype GII/4-d (Hunter'04-like cluster). Only one NoV GII/4 strain (CMH142/05) belonged to subtype GII/4-e. The data indicated heterogeneity and highly dynamic genotypic distribution of NoVs and SaVs circulating in children admitted to hospital with acute gastroenteritis in Chiang Mai, Thailand.