Naturally occurring serotype 2/subgroup II rotavirus reassortants in northern Brazil

Genetic variation of G4P[6] rotaviruses: evidence for novel strains circulating between the hospital and community

One hundred forty-six fecal specimens collected between 2007 and 2008 from infants with acute gastroenteritis were screened for rotavirus by ELISA with VP6-specific antibody. One hundred twenty-three of the samples (84.2%) were confirmed to be positive for group A rotavirus (community-acquired, n = 90 [73.2%] and nosocomial, n = 33 [26.8%]), and were typed subsequently using RT-PCR and sequence analysis methods. Determination of G- and P-type combinations showed that G4P[6] (78.9%) was the most common strain, followed by G3P[8] (7.3%), G1P[8] (6.5%), G2P[4] (0.8%), G2P[6] (0.8%), G1P[6] (0.8%), and G9P[8] (0.8%) strains. Of the 97 G4P[6] strains, 62 (63.8%) were responsible for community-acquired cases and 35 (36.1%) were hospital-acquired cases. Phylogenetic analysis of the VP7 gene from the G4P[6] strains revealed that both the community-acquired and nosocomial strains were segregated to the human rotaviruses circulating world-wide, including the prototype vaccinal strain, ST3, which constituted a novel sublineage in lineage 1. Owing to the recent emergence of G4P[6] rotaviruses within the hospital, as well as in the community, the findings from this study are important since they provide new information concerning the community and nosocomial spread of rotaviruses.

The relative frequencies of G serotypes of rotaviruses recovered from hospitalized children with diarrhea: A 10-year survey (1987-1996) in Japan with a review of globally collected data

Since rotavirus vaccines aim to protect children from severe diarrhea, knowledge of the prevailing G serotypes among rotaviruses from hospitalized children is essential. Thus, we determined the G serotypes of rotaviruses collected from children with acute diarrhea in a local referral hospital in Akita, Japan, over the 10-year period between January 1987 and December 1996. Based on the assumption that rotaviruses with an identical electropherotype possess the same G serotype, the G serotypes of 488 rotavirus-positive specimens that were classified into 63 electropherotypes were determined by enzyme-linked immunosorbent assay with a supplementary use of G typing by reverse transcription-PCR. The relative frequencies over the 10-year period were 77.0 (G1), 14.5 (G2), 2.7 (G3) and 5.3% (G4), leaving the possibility that only 0.4% had G serotypes uncommon to human rotaviruses. Of 24,050 rotaviruses extracted by reviewing 63 serotyping studies in literature, the relative frequencies of the four major G serotypes were 50.6 (G1), 9.3 (G2), 7.2 (G3) and 11.6% (G4). As to uncommon G serotypes, only 0.9% were described as serotypes other than G1-4, and our estimate for potential uncommon serotypes were at most 8.1%. Thus, both this long-term study focusing on the rotaviruses only from severe cases in a single hospital in Japan and the global review of G serotypes published to date indicate that the primary target of any rotavirus vaccines should be rotaviruses possessing serotypes G1-4.

[Rotavirus infection in Brazil: epidemiology and challenges for its control]

Worldwide, rotaviruses account for 600,000 to 870,000 deaths per year among infants and young children. In Brazil, rotaviruses were first seen in 1976 by scanning electron microscopy of stool samples from diarrheic infants in Belém, Pará. Hospital-based studies have shown that rotaviruses are associated with 12-42% of cases of acute diarrhea. In addition, community-based studies yielded an average of 0.25 rotavirus-related diarrheal episodes per child per year. G types 1 to 4 account for about two-thirds of circulating strains, but the (unusual) P[8],G5 genotype has been claimed to cause over 10% of rotavirus diarrheal episodes. It has been shown that over 70% of children develop rotavirus antibodies by the age of 4-5 years. The tetravalent rhesus-human rotavirus vaccine (RRV-TV) conferred 35% protection according to a two-year follow-up study in Belém, Pará, Brazil, but reached an efficacy of 60% during the first year of life. RRV-TV was also shown to be 75% protective against very severe gastroenteritis in northern Brazil. Vaccination with RRV-TV has been suspended recently in the United States because of the detection of intussusception as a side effect. Therefore, further vaccine trials in Brazil will probably involve rotavirus candidate vaccines other than RRV-TV.

Characterization of rotavirus P genotypes circulating among paediatric inpatients in northern brazil

Between November 1992 and August 1993, twenty-eight rotavirus-positive stool samples obtained from paediatric inpatients in Belem, Brazil, aged less than four years, were tested by RT-PCR to determine the P genotype specificities. With the exception of 7 non-diarrhoeic children, all patients were either diarrhoeic at admission or developed diarrhoea while in hospital. Rotavirus strains with the gene 4 alleles corresponding to P1B[4] and P1A[8] types (both of which bearing G2 specificity) predominated, accounting for 78.6% of the strains. While only one P2A[6] type strain - with (mixed) G1 and 4 type specificities - was detected, the gene 4 allele could not be identified in 4 (14.3%) of the strains. Most (81%) of the specimens were obtained from children during their first 18 months of life. Rotavirus strains bearing single P1B[4] type-specificity were identified in both diarrhoeic (either nosocomial, 28.6% or community-acquired diarrhoea, 28.6%) and non-diarrhoeic (42.8%) children. P1A[8] gene 4 allele, on the other hand, was detected only among diarrhoeic children, at rates of 57.1% and 42.9% for nosocomial- and- community acquired diarrhoea, respectively. Mixed P1A[8],1B[4] type infection was identified in only one case of community-acquired diarrhoea.

Molecular epidemiology of human rotaviruses: genogrouping by RNA-RNA hybridization

RNA-RNA hybridization performed under high stringency conditions allows rotavirus isolates to be grouped together based on the overall similarity of their genomic RNA constellation. Classification by this scheme has been termed "genogrouping". Genogrouping has advanced molecular epidemiology of human rotaviruses. Major observations include (i) Interspecies transmission occurs in nature and (ii) Intergenogroup reassortment occurs in nature with or without exchange of serotype-determining genes. Genogrouping is a particularly valuable asset for determining the gene constellation of unusual rotavirus isolates.

Preferential selection of specific rotavirus gene segments in coinfection and multiple passages with reassortant viruses and their parental strain

We previously reported non-random selections of human rotavirus (HRV) Wa genes 2 and 5 in reassortant formation between HRV strains Wa and HN126 under selection pressure with neutralizing monoclonal antibodies. In order to study whether or not these genes are preferentially selected in the genetic background of a parental strain HN126 in vitro without selection pressures, coinfection and multiple passage experiments were performed between HN126 and one of three reassortants, C1, C1T and C1F; C1 possessed genes 2 and 5 derived from Wa and the other genes derived from HN126, while C1T and C1F were single gene reassortants having Wa gene 2 or Wa gene 5 in the genetic background of HN126, respectively. When MA-104 cells were coinfected with the same infectious units of HN126 and C1, Wa genes 2 and 5 of reassortant C1 became predominant within 10 repeated passages, although Wa gene 5 was selected more preferably than Wa gene 2. Similar results were obtained under different experimental conditions in which different doses of parental strains or different type of cells were used. Also, in coinfections of MA-104 cells with HN126 and C1T, or HN126 and C1F, Wa gene 2 or Wa gene 5 became predominant at the sixth passage. Analysis of viral growth curves indicated that two reassortants, C1 and C1F, replicated to a titre higher than HN126, while no difference in viral growth was observed between C1T and HN126. These results indicated that in the genetic background of HN126, Wa gene 5 might provide viruses with a growth advantage compared with its HN126 counterpart, while Wa gene 2 might be preferentially selected into reassortant clones through its greater functional capacity for assortment during viral replication.

Recurrent circulation of single nonstructural gene substitution reassortants among human rotaviruses with a short RNA pattern

To determine the relative frequency of intergenogroup reassortants of rotavirus in nature, we analyzed the genetic composition of 22 electrophoretically distinct stool isolates which accounted for 95.2% of stool rotaviruses with a short RNA pattern collected during 10 rotavirus seasons. These strains all showed subgroup I and G2 specificities, but two distinct hybridization patterns were observed when the probes prepared from Wa (a member of the Wa genogroup) and KUN (a member of the DS-1 genogroup) were used. Genomic RNAs from 10 strains (accounting for 64% of the field rotaviruses with short RNA pattern) hybridized exclusively to the KUN probe, and thus belonged to the DS-1 genogroup. On the other hand, genomic RNAs of the remaining 12 strains (accounting for 36% of the field rotaviruses with short RNA pattern) formed one hybrid band with the Wa probe and 10 hybrid bands with the KUN probe. Thus, they were single gene substitution intergenogroup reassortants between members of the Wa and DS-1 genogroups. They had a similar genetic constellation in that a gene segment encoding either NS35 or NS34 from a Wa-like strain was introduced into a DS-1-like genome background.

Distinct yearly change of serotype distribution of human rotavirus in Thailand as determined by ELISA and PCR

A total of 241 group A rotavirus-positive stool samples collected from diarrhoeic patients in Thailand between July 1988 and June 1991 were characterized for their serotypes by enzyme-linked immunosorbent assay (ELISA) using serotype-specific monoclonal antibodies and by a polymerase chain reaction (PCR). In July 1988-June 1989, serotype 1 was the most prevalent (63.4%), followed by serotype 4 (11.0%) and serotype 2 (8.5%). In July 1989-June 1990, 59.8% were serotype 1, 24.3% were serotype 2, and 6.1% were serotype 3. In contrast, in July 1990-June 1991, serotype 3 was detected in the highest frequency (40.5%), 29.9% were serotype 1, and 27.3% were serotype 2. Thus, a distinct yearly change of serotype distribution of rotavirus in Thailand was observed in the three consecutive years. In particular, it was of note that the prevalence of serotype 3 greatly increased, in contrast to the previous studies in which almost no serotype 3 rotaviruses were detected in the years 1983-8 in Thailand.

Human rotavirus strain with unique VP4 neutralization epitopes as a result of natural reassortment between members of the AU-1 and Wa genogroups

Human rotavirus strain K8, which possesses unique VP4 neutralization epitopes, was examined by RNA-RNA hybridization to determine its genogroup. While it possessed four gene segments that formed hybrids with strain Wa (a prototype of the Wa genogroup), strain K8 possessed seven gene segments, including gene segment 4, that formed hybrids with strain AU-1 (a prototype of the AU-1 genogroup) which has been shown to share a unique gene 4 allele with feline rotaviruses. These results suggest that strain K8 is an intergenogroup reassortant formed in nature between a member of the Wa genogroup and a member of the AU-1 genogroup.

Cultivation and characterization of novel human group A rotaviruses with long RNA electropherotypes, subgroup II specificities, and serotype 2 VP7 genes

During an epidemiological study of human rotavirus infections in Bangladesh, three group A strains hybridized with a serotype 2 oligonucleotide probe, but they had long RNA electropherotypes. The three strains were collected from 8- to 20-month-old infants with acute diarrhea and moderate malnutrition. By a modified isolation procedure, two strains (T-B and T-C) were adapted in MA104 cell cultures. They were identified to be subgroup II specific by enzyme-linked immunosorbent assay with subgroup I- and II-specific monoclonal antibodies and were identified by a fluorescent focus reduction neutralization assay with hyperimmune antisera to be serotype 2 specific. Further characterization of these unusual rotavirus strains needs to be carried out.

Culture adaptation and characterization of group A rotaviruses causing diarrheal illnesses in Bangladesh from 1985 to 1986

Group A rotaviruses collected between 1985 and 1986 during comprehensive surveillance of treated diarrheal episodes occurring in a rural Bangladesh population were culture adapted and characterized by electropherotype, serotype, and subgroup. Of 454 episodes of rotavirus-associated diarrhea, rotaviruses were culture adapted from 381 (84%), and 335 contained 11 electrophoretically identical segments in unpassaged and cultured preparations. These 335 comprised 69 different electropherotypes with between 1 (32 isolates) and 79 representatives. The persistence of specific rotavirus strains within the study population, as defined by the detection of viruses with particular electropherotypes, was generally limited to a period of only a few months. All 335 isolates were serotyped by neutralization with hyperimmune antisera to prototype rotavirus strains representative of serotypes 1 to 4, i.e., Wa, DS-1, P, and ST-3. It was found that 80, 48, 119, and 88 isolates belonged to serotypes 1 to 4, respectively. The concentrations of hyperimmune antisera required to neutralize these isolates, however, were at least threefold greater than those needed to neutralize the homologous strains. Therefore, the isolates appeared to have altered neutralization epitopes from their prototype strains. Furthermore, the serotype 4 isolates were consistently shown to be much more closely related to the serotype 4B VA70 strain than the serotype 4A ST-3 strain. All but two isolates identified as serotypes 1, 3, or 4 had long electropherotypes and were subgroup II, and all but one serotype 2 isolate were subgroup I and had short electropherotypes. The three disparate strains appeared to be genetic reassortants. Evidence is presented that dual infections required for reassortant formation were not uncommon. Thus, formation of multiple reassortants may have been a cause for the observed rapid shift in viral strains within the study population.

Molecular evidence for naturally occurring single VP7 gene substitution reassortant between human rotaviruses belonging to two different genogroups

Twenty four stool rotaviruses that comprised 22 distinct electropherotypes were selected for genome analysis from the collection of diarrheal specimens obtained over an eight-year period. These 22 electropherotypes were found in 46% of the total electropherotypes identified during the previous studies and represented 328 (64%) of rotavirus specimens in the collection. When genomic RNAs from these stool rotaviruses were hybridized to the 32P-labeled transcription probes prepared from prototypes representing three human rotavirus genogroups, Wa, DS-1, and AU-1, any one of the isolates showed a high degree of homology only with one of the three probes, which data confirmed and extended our previous observation on the existence of three distinct genogroups among human rotaviruses. Two stool rotaviruses which had an unusual combination of serotype (G1), subgroup (I) and RNA pattern (an identical short electropherotype), however, yielded the hybridization pattern indicative of an intergenogroupic single VP7 gene substitution reassortant. When they were cell culture adapted and analyzed by RNA-RNA hybridization, molecular evidence was obtained indicating that their VP7 gene derived from viruses belonging to the Wa genogroup whereas the remaining 10 genes hybridized with viruses belonging to the DS-1 genogroup. Interestingly, these natural reassortants emerged in the midst of the rotavirus season in which G1 strains predominated.

Evidence for natural reassortants of human rotaviruses belonging to different genogroups

Of 335 rotavirus isolates associated with diarrheal disease in Bangladesh that were culture adapted and subsequently characterized for electropherotype, subgroup, and serotype, 9 had properties that suggested they may be natural reassortants between human rotaviruses belonging to different "genogroups." Two of these were examined in greater detail by RNA-RNA hybridization with prototype strains representative of each of the three proposed human rotavirus genogroups. One subgroup II isolate, 248, with a "long" electrophoretic pattern was neutralized by hyperimmune antisera to both serotype 2 and 4 strains. Consistent with these results, seven RNA segments of this isolate formed hybrids with human strains belonging to the Wa genogroup and four segments hybridized with strains belonging to the DS-1 genogroup. The second isolate examined, 456, belonged to subgroup II and had a long electrophoretic pattern but was found to be a serotype 2 strain. This isolate also appeared to be an intergenogroup reassortant because three of its segments formed hybrids with strains belonging to the Wa genogroup and eight hybridized with viruses of the DS-1 genogroup. On the basis of the relative migration rates of these RNA-RNA hybrids during gel electrophoresis, a suggested origin for each gene segment was proposed which was consistent with the results expected from electrophoretic, subgroup, and serotypic analyses.