Emergence of new variant rotavirus G3 among infants and children with acute gastroenteritis in Japan during 2003-2004.

A total of 402 fecal specimens from infants and children with acute gastroenteritis in five places (Tokyo, Maizuru, Saga, Sapporo, and Osaka) in Japan from July 2003 to June 2004 were collected and then tested for the presence of rotavirus by RT-PCR. Of these, 83 were positive for rotavirus and this accounted for 20.6%. Rotavirus was further characterized to G-types (VP7 genotypes) and P-types (VP4 genotypes). Interestingly, an emergence of rotavirus G3 was identified with an exceptionally high prevalence (97.5%; 81 of 83), followed by rotavirus G2 (2.5%; 2 of 83). The P-types of 19 rotavirus strains, which could not be typed by RT-PCR, were determined as P[8] with multiple point mutations at the VP4 primer-binding site by sequencing analysis. The predominant genotype was G3P[8] (95.2%, 79 of 83), followed by a number of unusual combinations G3P[4] (2.4%, 2 of 83), and G2P[8] (2.4%, 2 of 83). Another interesting feature of the study was the demonstration of a great genetic diversity in new variant rotavirus G3 strains circulating in Japan. In comparison with rotavirus G3 strains circulating in 1990-1995 in Japan, a wide range of amino acid substitutions (up to 16) of new variant rotavirus G3 VP7 genes was identified. Of note, the changes at positions 96, 99, and 100 were revealed to be located in the antigenic region A, and 213 in the antigenic region C. To the best of our knowledge, this is the first reporting of an emergence of new variant rotavirus G3 together with a sudden disappearance of G1, G4, and G9 in infants and children with rotavirus infection-associated gastroenteritis in Japan.

Detection and genetic characterization of norovirus strains circulating among infants and children with acute gastroenteritis in Japan during 2004-2005.

A total of 752 fecal specimens collected during the period of July 2004 to June 2005 from infants and children with acute gastroenteritis from four different regions (Maizuru, Tokyo, Sapporo, and Osaka) of Japan were tested for the presence of norovirus by RT-PCR. It was found that 139 (18.5%) fecal specimens were positive for norovirus. Norovirus infection was detected almost all year round with the highest prevalence in January. Norovirus GII was the most predominant genogroup (98.6%; 137 of 139). The genotypes detected in this study were GI/1, GII/1, GII/3, GII/4, and GII/6. Of these, NoV GII/4 (known as the Lordsdale virus cluster) was re-emerging and became the leading genotype (77.7%). Meanwhile, the incidence of NoV GII/3 (known as the Arg320 virus cluster) has dropped rapidly, accounting for only 15.8%. Another interesting feature of the study was the identification of Picton03/AU-like recombinant NoV for the first time in Japan. Based on the genetic analysis, it was interesting to note that NoV GII/4 in 2004-2005 made a distinct cluster in comparison to other NoV GII/4 circulating in 2002-2003 and 2003-2004. Of note, "new recombinant variant designated GIIb" within NoV GII/3, which was first detected in Saga City, Japan in 2003-2004 in only one case, had increased, spreading widely in Japan and representing 45.5% (10 of 22). Further epidemiological studies should be conducted to determine whether this new recombinant variant strain will be dominant in Japan in the coming year.

Viral diarrhea in Japanese children: results from a one-year epidemiologic study.

A total of 557 fecal specimens from infants and children with acute gastroenteritis in five places (Maizuru, Tokyo, Sapporo, Saga and Osaka) in Japan from July 2002 to June 2003 were tested for the presence of diarrheal viruses by RT-PCR, PRHA, RNA-PAGE and latex agglutination methods. Of these, 56.4% (314) were found positive for diarrheal viruses. Among them, group A rotavirus was the most prevalent (43.6%, 137 of 314) followed by norovirus (29.9%, 94 of 314), adenovirus (7.6%, 24 of 314), group C rotavirus (6.4%, 20 of 314), sapovirus (5.1%, 16 of 314) and astrovirus (1.6%, 5 of 314), respectively. A high rate (7.4%, 19 of 314) of viral mixed infections, including one triple infection (adenovirus, norovirus and astrovirus) was demonstrated. Norovirus infection that usually has a peak during November and January in Japan was detected year-round and highest in September in our study. Norovirus was subjected to molecular genetic analysis by sequencing. The results clearly indicated that norovirus group II was a dominant genogroup (94.3%, 100 of 106). It is noteworthy that noroviruses detected in this study were classified into 8 genotypes (GI/1, GI/4, GII/2, GII/3, GII/4, GII/5, GII/6 and GII/12). Of these, NVGII/4 was the predominant genotype, followed by NVGII/6, and these presented 75.6% (80 of 106) and 11.3% (12 of 106), respectively. Another interesting feature in our study was the sudden appearance and disappearance of SaitamaU16-like strains belonging to NVGII/6 in the short period (January 2003 to June 2003). Our findings confirmed the presence of many diarrheal viruses co-circulating among Japanese infants and children and showed the great genetic diversity among norovirus.

Genetic heterogeneity, evolution, and recombination in noroviruses.

Norovirus is one of the most common causes of nonbacterial gastroenteritis in humans. A total of 603 fecal specimens collected from sporadic pediatric cases of acute gastroenteritis in Japan from 2004 to 2005 were tested for the presence of norovirus by RT-PCR. It was found that 51 (8.5%) specimens were positive for norovirus. The norovirus genotypes detected in this study were GII/1, GII/2, GII/3, GII/4, GII/6, and GII/7. Of these, GII/3 was the most predominant (52.9%), followed by GII/4 (37.2%) and others. It was noticed that four distinct types of recombinant noroviruses were co-circulating and the variant norovirus GIIb suddenly emerged to be the leading strain in Japan for the first time. A novel norovirus nomenclature was proposed, in which worldwide noroviruses were classified into seven distinct genogroups (I-VII). Norovirus GI and GII consisted of 16 genotypes with 32 subgenotypes and 23 genotypes with 34 subgenotypes, respectively. Of note, human and porcine noroviruses had a close genetic relationship within GII. Interestingly, multiple short amino acid motifs located at N terminus, S domain, P1 domain, P2 domain, and C terminus of capsid gene correctly defined the phylogenetic norovirus genogroups, genotypes, and subgenotypes. Another interesting feature of the study was the identification of eight hitherto unreported recombinant noroviruses. It was noteworthy that three different types (intergenogroup, intergenotype, and intersubgenotype) of recombination in noroviruses were also found. This is the first report to demonstrate the existence of intergenogroup and intersubgenotype recombinations in noroviruses and highlights a possible route of zoonoses in humans because porcine, bovine and murine noroviruses belong to genogroups II, III, and V, respectively.

Changing distribution of norovirus genotypes and genetic analysis of recombinant GIIb among infants and children with diarrhea in Japan.

A total of 402 fecal specimens collected during July 2003-June 2004 from infants and children with acute gastroenteritis, encompassing five localities (Maizuru, Tokyo, Sapporo, Saga, and Osaka) of Japan, were tested for the presence of norovirus by RT-PCR. It was found that 58 (14.4%) fecal specimens were positive for norovirus. Norovirus infection was detected throughout the year with the highest prevalence in December. Norovirus GII was the most predominant genogroup (98.3%; 57 of 58). The genotypes detected in this study were GI/4, GII/2, GII/3, GII/4, and GII/6. Of these, NoV GII/3 (known as the Arg320 virus cluster) was the most predominant genotype (43.9%), followed by NoV GII/4 (the Lordsdale virus cluster; 35.1%) and others. Two norovirus strains clustered with a "new variant designated GIIb" and a "new variant of GII/4" were found circulating in Japan for the first time. It was interesting to note that NoV GIIb and NoV GII/3 appeared to be the recombinant strains and the recombination site was demonstrated at the overlap of ORF1 and ORF2. The majority (96%) of the dominant norovirus strains were identified as the recombination of GII/3 capsid and GII/12 polymerase. The recombination in the NoV GIIb capsid gene at the breakpoint located at P1 domain was also identified. Obviously, NoV GIIb isolate in Japan had double recombination. This is the first report demonstrating the existence of different "new variants" co-circulating in Japanese infants and children with acute gastroenteritis.