Subgroup and serotype distributions of human, bovine, and porcine rotavirus in Thailand

Rotavirus associated gastroenteritis in Thailand

Group A rotavirus is the leading cause of severe diarrhea in infants and young children, and in young animals of many species worldwide. Rotavirus is also the major cause of deaths of children younger than 5 years of age, particularly, in developing countries in Asia and Africa. In Thailand, the burden of rotavirus infection rate in children admitted to the hospitals with acute gastroenteritis ranged from 28.4 to 44.5 %. The seasonality of rotavirus gastroenteritis in Thailand was detected all-year-round with the peak from November to April of the following year. The distributions of G genotypes in pediatric patients during twelve-year surveillances of 2000-2011 were G1, G2, G3, G4, G9, and G12. The G9 was detected as the most predominant genotype in 2000-2004 while G1 and G3 were predominated in 2005-2009 and 2009-2011, respectively. The G4 was detected only in 2001-2003 and G12 only in 2007-2009 but was not detectable in any other years of surveillances. For P genotype, P[8] was the only P genotype that always existed as the most predominant with high prevalence. The G-P combination of human rotavirus strains circulated in Thailand were G1P[8], G2P[4], G2P[8], G3P[3], G3P[8], G3P[9], G3P[10], G3P[19], G9P[8], G12P[6], and G12P[8]. The G1P[8] was the most predominant strain followed by G9P[8], G2P[4], G3P[8], G12P[8], G3P[9], G3P[10], G3P[3], G2P[8], G3P[19], and G12P[6]. The studies of animal rotaviruses were performed mainly on porcine rotaviruses and a wide variety of porcine rotavirus strains have been reported, including G2P[27], G3P[6], G3P[13], G3P[19], G3P[23], G4P[6], G4P[13], G4P[19], G4P[23], G5P[6], G5P[13], G9P[7], G9P[13], and G9P[19]. Several unusual strains of human rotaviruses that carried the genes with nucleotide sequences closely related to those of animal rotaviruses have been described in Chiang Mai, Thailand which provided evidences for interspecies transmission of rotaviruses between humans and animals, and also animals to animals are occurring in nature.

Genomic diversity among group A rotaviruses from diarrheic children, piglets, buffalo and cow calves of Madhya Pradesh

Diarrheal disease continues to be a global health problem, particularly among young ones in developing nations. Amongst several viral and non-viral agents associated with diarrhea, group A rotavirus has been recognized as the major etiological agent of childhood gastroenteritis in human infants as well as several animal species throughout the world. During this study, a total of 181 diarrheic stool samples collected from children, piglets, buffalo and cow calves of Madhya Pradesh, central India were analyzed by electrophoretic mobilities of the 11 segments of dsRNA by polyacrylamide gel electrophoresis (PAGE). This technique revealed prevalence of rotavirus among different species (human-26.09%, pig-25.71%, buffalo-23.61% and cattle-21.43%). Prevalence of existence of circulating 8 different electropherotypes of group A rotaviruses indicated high genomic diversity among rotaviruses in this geographical region. Majority of the electropherotypes from humans and animals were of long pattern (75%) than short electropherotypes (9.09%). Same electropherotype was found to exist either only in a single species or in more than one species implicating the possibility of cross species transmission of the rotavirus strains. As it was found that certain animal rotavirus strains had electropherotypic similarities to some human strains, speculation increased about whether animals play a role as a source of rotavirus infection in humans or vice-versa. There is a need for further detailed study on the molecular characterization of rotaviruses which would have important implication in vaccine evaluation program.

Detection of rare G3P[19] porcine rotavirus strains in Chiang Mai, Thailand, provides evidence for origin of the VP4 genes of Mc323 and Mc345 human rotaviruses

Among 175 fecal specimens collected from diarrheic piglets during a surveillance of porcine rotavirus (PoRV) strains in Chiang Mai, Thailand, 39 (22.3%) were positive for group A rotaviruses. Of these, 33.3% (13 of 39) belonged to G3P[19], which was a rare P genotype seldom reported. Interestingly, their VP4 nucleotide sequences were most closely related to human P[19] strains (Mc323 and Mc345) isolated in 1989 from the same geographical area where these PoRV strains were isolated. These P[19] PoRV strains were also closely related to another human P[19] strain (RMC321), isolated from India in 1990. The VP4 sequence identities with human P[19] were 95.4% to 97.4%, while those to a porcine P[19] strain (4F) were only 87.6 to 89.1%. Phylogenetic analysis of the VP4 gene revealed that PoRV P[19] strains clustered with human P[19] strains in a monophyletic branch separated from strain 4F. Analysis of the VP7 gene confirmed that these strains belonged to the G3 genotype and shared 97.7% to 98.3% nucleotide identities with other G3 PoRV strains circulating in the regions. This close genetic relationship was also reflected in the phylogenetic analysis of their VP7 genes. Altogether, the findings provided peculiar evidence that supported the porcine origin of VP4 genes of Mc323 and Mc345 human rotaviruses.

Isolation and characterization of dually reactive strains of group a rotavirus from hospitalized children

Seven rotavirus strains dually reactive to serotype G1- and G2-specific monoclonal antibodies (MAbs) from hospitalized children with rotavirus diarrhea were culture adapted. Six strains were neutralized with G1 antiserum to a higher titer than that of G2, and one was neutralized with G1 and G2 antisera to equal titers. Of these, four strains were also neutralized with G6 antiserum. Five strains with short RNA pattern could not be serotyped, and the remaining two strains with long RNA pattern were serotyped as G1 strains. In addition, two strains showing dual reactivity to G2 and G4 MAbs and one G2-like strain from a nontypeable specimen were isolated. The dual reactivity of the isolates could not be attributed to mixed infections.

Detection of a human rotavirus with G12 and P[9] specificity in Thailand

G12 rotavirus has not been detected anywhere in the world since the first detection of a human strain, L26 (G12, P1B[4]), in the Philippines in 1990. In this study, we isolated a human rotavirus (strain T152) with a VP7 of G12 specificity from the stool of an 11-month-old diarrheic patient in Thailand. The strain T152 exhibited a long RNA pattern and subgroup I specificity. In the comparison of the nucleotide and amino acid sequences of the VP7 gene of strain T152 with those of rotaviruses with different G type specificities, strain T152 showed the highest identity, 90.9 and 93.9%, respectively, to G12 prototype strain L26. In contrast, the VP4 gene of strain T152 showed the highest identity with P[9] specificity of human strains K8 and AU-1 and feline strains Cat2 and FRV-1, with homologies of 89.3 to 90.6% at the nucleotide level and 93.9 to 95.6% at the amino acid level. Thus, strain T152 was found to be a natural reassortant strain with G12 and P[9] specificities.

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.

Epidemiology of rotavirus infection in Thailand

Rotavirus is a major cause of acute severe diarrhea in children worldwide and an important cause of death among young children in developing countries. Group A rotaviruses are antigenically complex and multiple serotypes infect humans. Reassortant rotavirus vaccines are now available which offer protection against severe illness caused by rotavirus serotypes G1-4. Before vaccines are introduced into target populations, it is necessary to establish the baseline data of the epidemiology of rotavirus infection in those countries. The purpose of the present study is to provide information related to the epidemiology of rotavirus infection in Thailand. All rotavirus studies performed in Thailand were found through Medline and Thai Index Medicus searches. A total of 26 of the most relevant studies published in international and national journals are reviewed. Most studies reported that the prevalence of rotavirus infection in Thailand was 27-34%, although a few studies have reported a prevalence above this range. The peak seasonal distribution of rotavirus infection among children hospitalized with diarrhea in Thailand was seen in the dry cool seasons: October to February. The prevalence of rotavirus infection was most frequently found in children aged 6-11 months up to 2 years. G1 was the most prevalent serotype in Thailand, followed by G2, G4 and G3, respectively. At least three G serotypes, mostly G1, G2 and G4, are seen to coexist in Thailand each epidemic year and in some studies all four G-serotypes were reported in the same epidemics. In a 1996-1997 study, G9 was the third prevailing serotype after G1 and G2, respectively. These results indicate that rotavirus epidemics occur in Thailand every year and children are the most affected population. In Thailand, although G1-G4 have been reported, G1 is the most prevalent serotype in each epidemic and G9 is becoming increasingly common.

Isolation of serotype G8, P6[1] bovine rotavirus from adult cattle with diarrhea

Two electrophoretically identical strains of group A rotavirus were isolated from diarrheic cows aged 3, 4, and 7 years on a dairy farm in Japan. They had a rare serotype combination of G8 and P6[1] and were shown by RNA-RNA hybridization to be most closely related to bovine strain NCDV-Lincoln (G6P6[1]).

Serotype of Nigerian rotavirus strains

Three hundred and fourteen stool samples collected from children < 5 years between December 1993 and August 1995 were analysed by PAGE, ELISA, PCR and Dot-blot hybridization technique for electropherotype and serotype distribution of rotavirus infection among Nigerian paediatric patients. 14.3% of the children were positive for rotavirus antigen. Children aged 6-9 months were most often infected, accounting for 35.6% of all positive samples, 91.1% of rotavirus-positive samples could be serotyped. Serotypes G2, G4 and G8 were not detected. Serotype G3 predominated (62.5%) in southern Nigeria, while mixed infection specificity was more widespread (63.6%) in northern Nigeria. The presence of some untypeable samples may indicate serotypes which the serotype-specific primers and cDNA probes used could not detect. Electropherotypes of 26 (57.7%) of the positive samples were determined. Two and 3 migration patterns were observed among the short and long-pattern electropherotypes, respectively. Implications for vaccine development and utilization in the country are discussed.

Nondefective rotavirus mutants with an NSP1 gene which has a deletion of 500 nucleotides, including a cysteine-rich zinc finger motif-encoding region (nucleotides 156 to 248), or which has a nonsense codon at nucleotides 153-155

We isolated two nondefective bovine rotavirus mutants (A5-10 and A5-16 clones) which have nonsense mutations in the early portion of the open reading frame of the NSP1 gene. In the NSP1 gene (1,587 bases long) of A5-10, a nonsense codon is present at nucleotides 153 to 155 just upstream of the coding region (nucleotides 156 to 230) of a cysteine-rich Zn finger motif. A5-16 gene 5 (1,087 bases long) was found to have a large deletion of 500 bases corresponding to nucleotides 142 to 641 of a parent A5-10 NSP1 gene and to have a nonsense codon at nucleotides 183 to 185, which resulted from the deletion. Expression of gene 5-specific NSP1 could not be detected in MA-104 cells infected with the A5-10 or A5-16 clone or in an in vitro translation system using the plasmids with gene 5 cDNA from A5-10 or A5-16. Nevertheless, both A5-10 and A5-16 replicated well in cultured cells, although the plaque size of A5-16 was extremely small.

Serological and genomic characterization of porcine rotaviruses in Thailand: detection of a G10 porcine rotavirus

A total of 557 fecal specimens collected from piglets with diarrhea in Thailand were examined for rotavirus RNA by polyacrylamide gel electrophoresis. Twenty-three, one, and two samples were positive for group A, group B, and group C rotaviruses, respectively. Two samples exhibited two segments found in picobirnavirus RNA. RNA electropherotyping of 23 group A rotaviruses showed that they were classified into five patterns. By serotyping by enzyme-linked immunosorbent assay and PCR, viruses in 3 and 14 specimens were found to be serotype G3 and serotype G10, respectively. For one specimen, containing a serotype G10 virus (strain P343), virus was isolated in MA-104 cells, and the nucleotide sequences of the VP7 and VP4 genes were determined. Comparative sequence analysis and cross-neutralization tests showed that strain P343 has B223-like G10 and UK-like P7 serotype (or VP4 genotype 5) specificities. Rotaviruses having such antigenic specificities have not been detected in piglets. Thus, the interspecies transmission of rotaviruses between cows and pigs was suggested.

Epidemiology of symptomatic human rotaviruses in Bangalore and Mysore, India, from 1988 to 1994 as determined by electropherotype, subgroup and serotype analysis

Epidemiology of symptomatic rotaviruses from Bangalore and Mysore in Southern India was investigated. While serotype G3 predominated throughout the 7-year study period from 1988 to 1994 in Bangalore, serotype G1 was more predominant than serotype G3 in Mysore during 1993 and 1994. Serotype G2 strains were either not detected or infrequently observed in both the cities. However, several strains with subgroup I and 'short' RNA pattern that exhibited high reactivity with typing MAbs specific for serotype 2 as well as other serotypes were detected throughout the period. Among the nonserotypeable strains from both cities, several exhibited dual subgroup (SGI + II) or subgroup I specificity and 'long' RNA pattern indicating their probable animal origin. Notably, a gradual, yet highly significant reduction in rotavirus gastroenteritis, from 45.3% in 1988 to 1.8% during 1994, was observed in Bangalore in stark contrast to the consistently high (about 34%) incidence of asymptomatic infections among neonates by I321-like G10P11 type strains during the same period. Moreover, I321-like asymptomatic strains were not detected in children with diarrhea.

Structure and function of rotavirus NSP1

Studies on the structure and function of the nonstructural proteins (NSP1-NSP5) of rotaviruses are important for dissection of the morphogenesis and replication processes of rotavirus. Above all, NSP1, the product of gene 5, has several interesting features, such as extreme sequence diversity, a highly conserved cysteine-rich region, RNA-binding activity, accumulation on the cytoskeleton, and non-random segregation in reassortment. Recently, comparable NSP1 sequence analysis has been performed on a number of rotavirus strains from various species. Furthermore, characterization of mutants with rearranged NSP1 genes has helped to elucidate the structure-function interaction of NSP1. We isolated and characterized two interesting mutants which have a large deletion including the cysteine-rich region or a nonsense codon at the early portion in the open reading frame (ORF) of the NSP1 gene. In this report, we summarize the structure and function of NSP1.

Serotypic differentiation of rotaviruses in field samples from diarrheic pigs by using nucleic acid probes specific for porcine VP4 and human and porcine VP7 genes

Of 216 fecal and intestinal samples collected from nursing or weaned diarrheic pigs in the United States and Canada, 57 were identified as group A rotavirus positive by RNA electrophoresis and silver staining. Fifty-seven and 52 rotavirus-positive samples were analyzed by hybridization with Gottfried and OSU PCR-derived gene 9 and 4 probes, respectively. Only 17 samples were identified with either homologous VP4 (P)- or VP7 (G)-coding genes or both. One rotavirus identified as G4 and P7 was similar to the previously characterized interserotype rotavirus, SB-1A. Additional hybridization analyses were performed with PCR-derived probes prepared from gene 9 cDNA of the human rotaviruses Wa (G1), DS-1 (G2), and P (G3) and of the porcine rotavirus YM (G11). Eleven of 52 samples collected and analyzed from swine in Ohio, California, and Nebraska were identified as G11. No samples with G1-, G2-, or G3-type specificities were detected among the 25 of 57 rotavirus-positive samples analyzed with human rotavirus-derived probes. Further investigations with a PCR-derived gene 4 probe prepared from porcine rotavirus YM revealed hybridization specificities similar to those of the OSU gene 4 probe.

Rotavirus vaccines and vaccination potential

The development of a successful rotavirus vaccine is a complex problem. Our review of rotavirus vaccine development shows that many challenges remain, and priorities for future studies need to be established. For example, the evaluation of administration of a vaccine with OPV or breast milk might receive less emphasis until a vaccine is made that shows clear efficacy against all virus serotypes. Samples remaining from previous trials should be analyzed to determine epitope-specific serum and coproantibody responses to clarify why only some trials were successful. Detailed evaluation of the antigenic properties of the viruses circulating and causing illness in vaccinated children also should be performed for comparisons with the vaccine strains. In future trials, sample collection should include monitoring for asymptomatic infections and cellular immune responses should be analyzed. The diversity of rotavirus serotype distribution must be monitored before, during, and after a trial in the study population and placebo recipients must be matched carefully to vaccine recipients. Epidemiologic and molecular studies should be expanded to document, or disprove, the possibility of animal to human rotavirus transmission, because, if this occurs, vaccine protection may be more difficult in those areas of the world where cohabitation with animals occurs. We also need to have an accurate assessment of the rate of protection that follows natural infections. Is it realistic to try to achieve 90% protective efficacy with a vaccine if natural infections with these enteric pathogens only provide 60% or 70% protection? Subunit vaccines should be considered to be part of vaccine strategies, especially if maternal antibody interferes with the take of live vaccines. The constraints on development of new vaccines are not likely to come from molecular biology. The challenge remains whether the biology and immunology of rotavirus infections can be understood and exploited to permit effective vaccination. Recent advances in developing small animal models for evaluation of vaccine efficacy should facilitate future vaccine development and understanding of the protective immune response(s) (Ward et al. 1990b; Conner et al. 1993).

Serological and genomic characterization of two porcine rotaviruses with serotype G1 specificity

Two porcine rotavirus strains, C60 and C95, which had been previously shown to be reactive in an enzyme-linked immunosorbent assay with serotype G1-specific monoclonal antibodies, were classified as G1 by cross-neutralization tests and on the basis of the homology of the sequenced VP7 gene. This report confirms that porcine rotavirus strains with a G1 serotype occur in nature.

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.

Serotype analysis of rotaviruses from different locations in Malaysia

The distribution of rotavirus G (VP7) serotypes circulating in four locations in Malaysia, representing three geographical areas, was evaluated in 341 RNA-positive stool specimens obtained discontinuously between 1977 and 1988 from infants and young children under the age of five years who were hospitalized with acute gastroenteritis. A total of 306 specimens (256 stool suspensions and 50 that were adapted to growth in tissue culture) that were rotavirus positive by the confirmatory enzyme-linked immunosorbent assay (ELISA) were examined for serotype by ELISA utilizing monoclonal antibodies to rotavirus G serotype 1, 2, 3, 4, or 9. One hundred eighty (59%) of the 306 specimens could be serotyped; of these 180 specimens, 71% were serotype 4, 15% were serotype 1, 4% were serotype 2, and 4% were serotype 3. Serotype 9 rotavirus was not detected. Most (71%) of the specimens tested were obtained in 1988, when serotype 4 predominated in three locations in West Malaysia; no single serotype was predominant in a limited number of specimens from East Malaysia.

Identification of human and bovine rotavirus serotypes by polymerase chain reaction

The use of the polymerase chain reaction (PCR) for identifying serotypes of human and bovine rotaviruses was examined. In the identification of 115 human rotavirus samples in stools, results with PCR showed excellent agreement with results of serotyping by an enzyme-linked immunosorbent assay (ELISA) using serotype-specific monoclonal antibodies. Furthermore, the PCR showed a much higher sensitivity (93%) than the ELISA test (82.6%). The PCR method could also be applied for identifying the serotype of bovine rotaviruses.

Distribution of serotypes of human rotavirus in different populations

Serotyping is a useful tool to study the epidemiologic characteristics of rotaviruses in large populations and to assess the need for a vaccine to protect against all strains. By using an enzyme immunoassay with serotype-specific monoclonal antibodies to the four most common rotavirus serotypes, we analyzed 1,183 rotavirus-positive specimens from 16 stool collections in eight countries on four continents that were obtained from 1978 to 1989. Of the 926 strains (78%) that could be serotyped, 48% were serotype 1, 8% were serotype 2, 15% were serotype 3, and 7% were serotype 4. Twenty-two percent had insufficient numbers of double-shelled virus particles to react with the monoclonal antibody of the VP4 rotavirus protein and therefore could not be serotyped. Our results indicate that vaccines being developed must provide the greatest coverage against serotype 1 and that the serotype distribution cannot be predicted currently by the geographic area or prevalence in the preceding year.

Isolation and characterization of two distinct human rotavirus strains with G6 specificity

Two new human rotavirus (HRV) strains, PA151 and PA169, with subgroup I specificity and a long RNA pattern, yet with a serotype G (VP7) specificity different from those of any of the six well-established HRV serotypes (G1 to G4, G8, and G9), were isolated 3 months apart from two children with acute gastroenteritis in Sicily, southern Italy, in the winter season of 1987 and 1988. The HRV isolates were adapted to growth in cell cultures and were then characterized by neutralization and RNA-RNA (Northern blot) hybridization. Cross-neutralization studies with type-specific immune sera to RV serotypes 1 to 10 showed the antigenic relatedness of the two strains with serotype 6 bovine strains UK and NCDV. Monoclonal antibodies to VP7 of UK were able to recognize UK and NCDV strains as well as both HRV isolates. Cross-hybridization studies showed a genetic relatedness of PA151 and PA169 to bovine strains for all genes except gene 4. Gene 4 of PA151 appeared to be genetically related to that of AU228 (a human strain of subgroup I and with serotype G3 specificity that belongs to a feline genogroup), whereas gene 4 of PA169 appeared to be unique, yet it was related to gene 4 of two recently reported subgroup I HRV strains, one (PA710) with serotype G3 specificity and the other (HAL1271) with serotype G8 specificity. The new HRV strains must be taken into consideration when deciding strategies for the development of an effective RV vaccine.

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.

Epidemiology of rotavirus serotypes in Melbourne, Australia, from 1973 to 1989

Fecal rotavirus strains collected between 1973 and 1989 from 943 children admitted with acute diarrhea to one hospital in Melbourne, Australia, were serotyped by using an enzyme-linked immunosorbent assay. The assay incorporated neutralizing monoclonal antibodies specific for VP7 of the four major human serotypes (1 through 4). A serotype could be assigned to 690 of 943 specimens (73.2%). Typeable strains comprised serotype 1 (72.5%), serotype 2 (6.8%), serotype 3 (2.9%), or serotype 4 (15.4%). Monotypes 1a and 1c comprised 52 and 44%, respectively, of serotype 1 strains. All serotypes and monotypes exhibited polymorphic genomic RNAs. Specimens reacting as mixed serotypes were rare (3.2%) and included intertypic strains (0.7%) and mixed infections (1.0%). Nontypeable strains for which an electropherotype could be determined appeared to be identical with typeable strains present concurrently in the community. Serotypes exhibited various epidemiological patterns. Serotype 1 strains were dominant except during three successive winters when 60 to 90% of the disease was caused by serotype 2. Serotype 4 strains showed an episodic pattern of appearance, recurring at peak incidence approximately every 3 years. Fecal rotavirus strains collected from 145 newborn babies housed in Melbourne obstetric hospitals between 1974 and 1986 were also serotyped. All 135 typeable strains (93.1%) belonged to serotype 3. It is hypothesized that endemic infection with serotype 3 rotaviruses in nurseries for the newborn influenced the epidemiology of rotavirus serotypes responsible for severe clinical disease in young children in the same community.

Reactivities of serotyping monoclonal antibodies with culture-adapted human rotaviruses

Rotaviruses collected in Bangladesh during 1985 to 1986 were culture adapted and used in a comparative serotyping study with three groups of monoclonal antibodies, all of which reacted with the major neutralization protein (VP7) of serotype 1, 2, 3, or 4. The goals were to determine which monoclonal antibodies most accurately predicted the serotype and why large variations in serotyping efficiencies have occurred with these monoclonal antibodies in previous studies. The 143 rotavirus isolates used in this study belonged to 69 different electropherotypes; and 44, 23, 21, and 55 isolates were identified as serotype 1 through 4, respectively, by neutralization with serotype-specific hyperimmune antisera. Serotyping specificity by enzyme-linked immunosorbent assay with monoclonal antibodies was 100% consistent with results found by neutralization with polyclonal antisera, but large differences were observed in the sensitivities of the different monoclonal antibodies. Monoclonal antibodies 5E8 (serotype 1), 1C10 (serotype 2), 159 (serotype 3), RV3:1 (serotype 3), ST-3:1 (serotype 4), and ST-2G7 (serotype 4) reacted with all the isolates of the corresponding serotype for which there were sufficient infectious particles. Monoclonal antibody 2F1 (serotype 2) was much less sensitive and reacted with only five serotype 2 isolates, but these were among those with the highest titers. Monoclonal antibodies RV4:2 (serotype 1), KU6BG (serotype 1), RV5:3 (serotype 2), and S2-2G10 (serotype 2), on the other hand, failed to react with between one and three isolates of the corresponding serotypes which had high titers, apparently because of epitope changes in these isolates. Effects of epitope variation were, however, most apparent with monoclonal antibodies 2C9 (serotype 1) and YO-1E2 (serotype 3), which reacted with one and no isolates of the corresponding serotypes, respectively. Cross-neutralization of escape mutants indicated that the serotype 1 monoclonal antibodies 5E8, 2C9, and RV4:2 reacted with different but probably overlapping epitopes, as did serotype 2 monoclonal antibodies 2F1, 1C10, and RV5:3, finding that were consistent with the enzyme-linked immunosorbent assay data. Because of epitope variations between rotavirus strains, serotyping with several monoclonal antibodies directed at different epitopes may increase the sensitivity of the method.

Diversity of rotavirus serotypes in Mexican infants with gastroenteritis

One hundred thirty-two stool specimens from infants with rotavirus gastroenteritis hospitalized in two Mexican cities (Mexico City and Mérida) were examined by serotype- and subgroup-specific enzyme immunoassays. Among them, 38 (29%) were serotype 1, 15 (11%) were serotype 2, 13 (10%) were serotype 3, 22 (17%) were serotype 4, none was serotype 5 or 6, and 44 (33%) could not be serotyped. By subgrouping, 121 specimens were characterized as follows: 24 (18%) were subgroup 1, 97 (74%) were subgroup 2, and none had both subgroup specificities. While serotype 1 rotavirus predominated in the Mexico City area for 4 consecutive years (1984 to 1987), serotype 4 predominated in Mérida during the single epidemic season studied (1985). These data demonstrate that all four primary human rotavirus serotypes circulated in Mexico, with serotype 1 being the most prevalent. The seroneutralization responses of 14 of the 22 patients infected with serotype 4 strains had been previously studied. Of these 14 infants, 11 appeared to have primary infections, as indicated by absence of neutralizing antibodies in the acute-phase sera and their young age (8 months on average) at the time of illness. Seven patients seroresponded to serotypes 1 and 4; two seroresponded to serotypes 1, 3, and 4; three seroresponded to serotype 1; and two had low-level seroresponses to serotype 3 or 4. These data indicate that heterotypic neutralizing antibody responses occur frequently following infection with serotype 4 rotaviruses.

Porcine rotaviruses antigenically related to human rotavirus serotypes 1 and 2

Fecal samples from rotavirus-infected piglets were characterized by a serotyping enzyme-linked immunosorbent assay (ELISA) by using monoclonal antibodies (MAbs) specific to human serotypes 1, 2, 3, and 4 (D. O. Matson, M. K. Estes, J. W. Burns, H. B. Greenberg, K. Taniguchi, and S. Urasawa, submitted for publication). Rotavirus in 19 of 25 specimens tested from two herds of pigs from Buenos Aires province, Argentina, were classified antigenically as follows: one serotype 1, four serotype 2, two serotype 3, and no serotype 4. Six specimens reacted with both serotype 1 and 2 MAbs, and viruses in six specimens probably belonged to other serotypes because they reacted only with a VP7 common epitope MAb. Two porcine rotavirus fecal samples found to contain both serotype 1 and 2 viruses by the MAb-based test and one found to contain a serotype 2 virus were grown in tissue culture. When plaque-purified preparations of these tissue culture-adapted viruses were analyzed in the serotyping ELISA, the C60 and C86 preparations reacted only as serotype 1 viruses, indicating that the original fecal samples, which showed multiple VP7 reactivities, were heterogeneous and apparently contained two types of viruses. Testing of plaque-purified C134 virus confirmed its serotype 2 reactivity. The MAb-based serotype designations of these viruses also were confirmed by using a neutralization immunoperoxidase focus reduction assay. This is the first report of the occurrence of serotype 1 and 2 rotaviruses in animals. The MAbs originally developed to serotype human rotaviruses can be utilized to type animal rotaviruses.