Molecular characterization by RNA-RNA hybridization of a serotype 8 human rotavirus with "super-short" RNA electropherotype

Serotype diversity and reassortment between human and animal rotavirus strains: implications for rotavirus vaccine programs

The development of rotavirus vaccines that are based on heterotypic or serotype-specific immunity has prompted many countries to establish programs to assess the disease burden associated with rotavirus infection and the distribution of rotavirus strains. Strain surveillance helps to determine whether the most prevalent local strains are likely to be covered by the serotype antigens found in current vaccines. After introduction of a vaccine, this surveillance could detect which strains might not be covered by the vaccine. Almost 2 decades ago, studies demonstrated that 4 globally common rotavirus serotypes (G1-G4) represent >90% of the rotavirus strains in circulation. Subsequently, these 4 serotypes were used in the development of reassortant vaccines predicated on serotype-specific immunity. More recently, the application of reverse-transcription polymerase chain reaction genotyping, nucleotide sequencing, and antigenic characterization methods has confirmed the importance of the 4 globally common types, but a much greater strain diversity has also been identified (we now recognize strains with at least 42 P-G combinations). These studies also identified globally (G9) or regionally (G5, G8, and P2A[6]) common serotype antigens not covered by the reassortant vaccines that have undergone efficacy trials. The enormous diversity and capacity of human rotaviruses for change suggest that rotavirus vaccines must provide good heterotypic protection to be optimally effective.

Close relationship between G8-serotype bovine and human rotaviruses isolated in Nigeria

A bovine rotavirus, NGRBg8, isolated from the feces of a calf with diarrhea in Nigeria was characterized by reverse transcription-PCR, nucleotide sequence analysis, and Northern blot hybridization. The nucleotide sequence of the VP7 gene of the strain was most closely related to that of a Nigerian human G8-serotype strain, HMG035 (99.9%). The NSP1 gene of strain NGRBg8 is highly related (99.4%) to that of a Thai G8 bovine strain, A5-10. Northern blot hybridization revealed a high overall genomic relatedness of bovine strain NGRBg8 with human strain HMG035; all 11 RNA segments hybridized to each other. Thus, the results show the close relationship between G8 bovine and human rotaviruses in Nigeria.

Molecular and serologic characterization of novel serotype G8 human rotavirus strains detected in Blantyre, Malawi

During a 2-year study of diarrhea among children in Blantyre, Malawi, greater than 50% of rotavirus strains genotyped by using reverse transcription-polymerase chain reaction possessed previously unrecognized combinations of the neutralization proteins VP7 and VP4. Serotype G8 rotaviruses, which have been identified recently in several African countries, were found to possess P[4] or P[6] VP4 genotype specificity. Two of these short electropherotype rotaviruses were further investigated: these comprised a P[6], G8 representative strain (MW23) and a P[4], G8 representative strain (MW333). The VP7 gene sequences of both strains exhibited greatest homology to human and animal serotype G8 rotaviruses. Sequence analysis of the VP4 gene of MW23 indicated closest identity to the P2A[6], G9 strain US1205 from the United States. The VP4 gene of MW333 was most closely related to the P[4], G12 strain L26 isolated in the Philippines and the Australian P[4], G2 strain RV-5. The NSP4 gene sequences of both strains were classified in NSP4 genetic group I. RNA-RNA hybridization demonstrated that each of these two strains is related to the DS-1 genogroup of human rotaviruses. Subgroup analysis and virus neutralization confirmed complete antigenic characterization of MW23 as subgroup I, P2A[6], G8 and MW333 as subgroup I, P1B[4], G8. The similarity of the VP7 gene sequences of the prototype strains described in this report to bovine serotype G8 rotaviruses suggests that they may represent human/bovine reassortant viruses.

Comparative studies of human rotavirus serotype G8 strains recovered in South Africa and the United Kingdom

Epidemiological studies on the VP7 serotype prevalence of human rotaviruses in South Africa and the United Kingdom identified several strains which could not be serotyped as G1-G4 by monoclonal antibodies. Further analysis of these strains with a G8-specific monoclonal antibody and with probes for human rotaviruses confirmed them as G8 rotaviruses. These G8 strains exhibited a high degree of sequence identity when compared with each other and with other rotavirus G8 strains. Five South African strains were further characterized as VP6 subgroup I, but with a long RNA electropherotype, which is similar to the G8 strains previously isolated in Finland. In the UK strains, one was VP6 subgroup II with a long RNA electropherotype (similar to the Italian G8 strain). The other two were subgroup I with a short RNA electropherotype. None of these strains exhibited the super-short RNA electropherotype described in the prototype G8 strains recovered from Indonesia (69M).

Epidemiological study of the G serotype distribution of group A rotaviruses in Kenya from 1991 to 1994

An epidemiological study on the G serotype distribution of group A rotaviruses (GARV) isolated in Kenya was carried out in one urban hospital in Nairobi and in two rural hospitals in Nanyuki and Kitui to clarify the prevalent G serotypes before future introduction of the ready licensed rotavirus vaccine in Kenya. A total of 1,431 stool specimens were collected from children, who were mainly outpatients, aged from 0 to 6 years old with acute gastroenteritis from August 1991 to July 1994. Samples positive for GARV by conventional ELISA were then analyzed by subgrouping and serotyping ELISA and by PAGE. To ascertain the G serotypes of viruses in samples that were unable to be typed by serotyping ELISA, polymerase chain reaction was also attempted. The prevalence of GARV was 28.4% in the urban hospital, 22.5% in Nanyuki, and 13.7% in Kitui. Among rotavirus-positive samples, subgroup II rotaviruses were detected in 63.1%, and subgroup I rotaviruses were 25.9%. Serotype G4 was most prevalent, accounting for 41.6% followed by 23.3% of serotype G1, 17.0% of serotype G2, and serotype G3 was rarely isolated. Seven strains of serotype G8/P1B rotavirus was detected for the first time in Kenya by RT-PCR. Eleven specimens with an unusual composition of subgroup, serotype, and electropherotype were atypical GARV in which the P-serotype was P1A, P1B, or P2. Although uncommon GARV serotype G8/P1B and atypical GARV were detected, the four major GARV serotypes, G1 through G4, should be targeted at this moment for vaccination to control this diarrheal disease in Kenya. Continuous monitoring of the G- and P-serotype distribution of GARV should provide important information about the impact of rotavirus vaccination in Kenya.

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]).

Species-specific and interspecies relatedness of NSP1 sequences in human, porcine, bovine, feline, and equine rotavirus strains

We have sequenced gene 5 encoding NSP1 for three human, two porcine, two bovine, one feline, and five equine rotavirus strains, and compared the nucleotide and deduced amino acid sequences with the published sequences for other various strains. Subgroup I human strains L26, 69M, and DS-1 were found to have a similar NSP1 sequence despite their different G serotypes, VP4 genotypes, and RNA patterns. The NSP1 sequence of the human strain K8 showed a high degree of homology to those of porcine strains OSU and YM. A high degree of homology was found among three equine strains (H2, FI-14, and FI23), but they differed from the other equine strains L338 and H1. The strain H1 was similar to the porcine strains. The feline strain Cat2 showed a high homology to bovine strains UK, RF, and A44. Thus, species-specific and interspecies relatedness of NSP1 sequences among human, porcine, bovine, feline and equine rotaviruses was found. Overall genomic relatedness of strains L26 and YM to various human and animal strains was also examined by RNA-RNA hybridization assay. The present and previous hybridization results showed that there is a good correlation in most strains between overall genomic property (or genogroup) and NSP1 sequence homology.

Comparative nucleotide and deduced amino acid sequence analysis of VP7 gene of the NCDV Cody (I-801) strain of group A bovine rotavirus

The prevalent G serotypes of group A bovine rotavirus (BRV) reported are G6, G10, and less commonly, G8. Neonatal Calf Diarrhea Virus (NCDV), Lincoln and Cody strains were first isolated from diarrheic calves in Nebraska. The NCDV Lincoln strain is the currently used U.S. vaccine strain and has a G6 serotype. In this study, the complete nucleotide sequence of the VP7 gene of NCDV Cody (I-801 strain) was determined using the primer extension method. The VP7 gene nucleotide sequence homologies between Cody I-801 and established G8 rotaviruses, A5 (Thailand BRV), 678 (UK BRV), B37 (human RV) and 69M (human RV) were 84.7%, 86.4%, 84.7% and 85.9%, respectively. The deduced VP7 amino acid sequence of Cody I-801 was similar to that of A5, 678, B37 and 69M (93.6%, 95.7%, 92.6% and 95.1%, respectively). The VP7 gene nucleic acid sequence homologies between NCDV Cody (I-801) and NCDV Lincoln or B223 (G10) was 76.2% and the deduced VP7 amino acid sequence homologies between Cody I-801 and NCDV Lincoln or B223 were 82.5% and 81.3%, respectively. Thus, our sequence data suggests that the VP7 gene of Cody I-801 strain of BRV is genetically most similar to G8 rotaviruses and unrelated to the NCDV Lincoln G6 rotavirus strain.

Detection of rotavirus serotypes G1, G2, G3, and G11 in feces of diarrheic calves by using polymerase chain reaction-derived cDNA probes

On the basis of antigenic variability in the VP7 outer capsid glycoprotein, at least 14 G serotypes exist for group A rotaviruses. Serotypic diversity exists among bovine rotaviruses (BRV), with serotypes G1, G6, G8, and G10 reported for cattle. Although G1 and G8 rotaviruses were originally described for humans, the recent isolation of G6 and G10 rotaviruses from humans further emphasizes the serotypic similarity between human and bovine rotaviruses and the possible zoonotic potential of rotaviruses. Results of our previous studies have indicated that more than 24% of BRV-positive field samples from diarrheic calves were nonreactive with cDNA probes or monoclonal antibodies to serotypes G6, G8, and G10. In this study, cDNA probes were prepared by polymerase chain reaction amplification of the hyperdivergent regions of the VP7 genes (nucleotides 51 to 392) from human (G1, G2, and G3) and porcine (G4, G5, and G11) rotaviruses. These probes were used in a dot blot hybridization assay to further characterize the G types of 59 BRV strains (fecal samples from diarrheic calves in Ohio, Nebraska, Washington, and South Dakota) that were nonreactive with cDNA probes to G6, G8, and G10. Rotaviruses belonging to serotypes G1 (n = 7), G2 (n = 1), G3 (n = 2), and G11 (n = 3) were identified among the BRV field samples. The BRV associated with these G types accounted for 22% of the samples tested; the other 78% of these samples remained untypeable with these probes. To our knowledge, this is the first report in the United States of the identification among BRV isolates of rotavirus serotypes G1, G2, G3, and G11.

Antigenic analysis of avian rotavirus VP6 using monoclonal antibodies

Monoclonal antibodies (MAbs) were prepared to analyze antigens on the major inner capsid protein, VP6 of avian group A rotavirus. Based on the results of a competitive binding assay using 15 MAbs directed against VP6 of the PO-13 rotavirus strain, isolated from a pigeon in Japan, it was found that VP6 of avian rotavirus possesses at least four spatially distinct antigenic sites. Two antigenic sites (I and II) were topologically distinct from the other two (III and IV), which were in close proximity. From the reaction of MAbs in indirect immunofluorescent antibody tests to a series of known rotaviruses, epitopes representing common antigens of all group A rotavirus including avian rotavirus were localized in sites II and III. One epitope in site IV appeared to have a subgroup antigenic specificity that reacted only with rotaviruses belonging to subgroup I. Interestingly, avian rotaviruses isolated from turkeys and chickens in Northern Ireland also reacted only with these subgroup I specific MAbs, but not with subgroup II specific MAb. This indicates that avian rotavirus has subgroup I specific antigen, which is antigenically similar to that of other mammalian rotavirus strains.

Characterization of field strains of group A bovine rotaviruses by using polymerase chain reaction-generated G and P type-specific cDNA probes

Dot and Northern blot hybridization assays were used to analyze field strains of group A bovine rotaviruses (BRVs) by using nucleic acid probes representing P and G type specificities. The probes were prepared by polymerase chain reaction amplification of hyperdivergent regions of the cloned VP4 (nucleotides 211 to 686) and VP7 (nucleotides 51 to 392) genes from four serotypically distinct (in P or G types) strains of rotaviruses: NCDV (G6, P1), IND (G6, P5), 69M (G8, P10), and Cr (G10, P11). The P and G type cDNA probes were radiolabeled with [32P]dCTP and hybridized with RNA extracted from reference cell culture-passaged rotavirus strains or the field samples. The field samples were obtained from young diarrheic calves from Ohio, Nebraska, Washington State, and Canada. The cDNA probes were specific for their respective G or P types on the basis of analysis of known P and G type reference strains. The G typing analysis of 102 field samples revealed that 36.3% (37 of 102) were G6, 2.9% (3 of 102) were G8, 12.7% (13 of 102) were G10, and 23.5% (24 of 102) were untypeable. The P typing results for 93 samples indicated that 2.2% (2 of 93) were P1 (NCDV-like), 20.4% (19 of 93) were P5 (UK-like), 9.3% (10 of 93) were P11 (B223-like), and 40.8% (38 of 93) were untypeable. This is the first report of the identification among BRV strains in North America of a G type other than G6 or G10. Our report further confirms that G6, P5 rotaviruses are predominant among the BRV field strains that we examined, and the P types of these strains differ from that of the BRV vaccine strain used in the United States (G6, P1). The large number of untypeable G (23.5%) and P (40.8%) types suggests that other or new P and G types exist among BRV field strains.

A liquid-hybridization method for typing the Vp4 and Vp7 genes of bovine rotaviruses

A simple liquid-hybridization assay was developed which allows assessment of the degree of hybridization between the two serotype-determining genes of the bovine rotavirus strain UK and the homologous genes of the isolate under test. 32P-labelled transcription probes were produced from cloned complementary DNA (cDNA) copies of UK gene segments 4 and 8 and hybridized to double stranded RNA (dsRNA) extracted from rotavirus-positive field samples. Subsequent treatment with ribonuclease A (RNase A), separation of the RNase A-resistant hybrid fragments by polyacrylamide gel electrophoresis (PAGE) and autoradiography yielded a specific, reproducible banding pattern for each isolate. A total of 74 field samples was tested by both the hybridization assay and by an enzyme-linked immunosorbent assay (ELISA) using serotype-specific monoclonal antibodies (Mabs). The results obtained were in excellent agreement and confirmed that serotype G6 rotaviruses predominated. Hybridization of these G6 viruses with the gene 4 probe suggested that viruses with Vp4s related to that of UK rotavirus are also common. The hybridization assay was more sensitive than the ELISA.

Exclusive asymptomatic neonatal infections by human rotavirus strains having subgroup I specificity and "long" RNA electropherotype

A large number of stool specimens, of healthy newborn infants, collected from various hospitals and clinics in Bangalore City, India, have been examined for the presence of asymptomatic rotaviral excretion. Out of 370 samples analysed during a three year period from 1988 to 1991, 133 specimens (36%) were positive for rotavirus RNA. All these asymptomatic neonatal strains, without exception, showed "long" RNA pattern, but subgroup I specificity. Serotype analysis by ELISA or by hybridization with serotype-specific probes indicated that these strains probably represent a new serotype in newborn children. We find an exclusive association of human rotaviruses having "long" RNA pattern and subgroup I specificity with asymptomatic neonatal infections in contrast to the earlier observations of association of such unusual strains with acute gastroenteritis in young children.

Human and bovine serotype G8 rotaviruses may be derived by reassortment

The origin of, and relationship between human and bovine serotype G8 rotaviruses were investigated by genomic hybridisation. Radiolabelled mRNAs of human G8 rotaviruses 69M (isolated in Indonesia) and HAL1271 (isolated in Finland), and bovine rotaviruses KK3 (G10) and NCDV (G6), were used as probes. The products of liquid hybridisation between the probes and the genomic RNA of human and bovine rotaviruses, including bovine G8 rotavirus 678 (isolated in Scotland) and two other Finnish human G8 rotaviruses HAL1166 and HAL8590, were examined by separation in polyacrylamide gels. The genomes of Finnish human G8 rotaviruses were similar to those of bovine G6 and G10 rotaviruses. Neither Indonesian human G8 nor bovine G8 viruses had high levels of similarity to each other or to other bovine and human rotaviruses. Thus these three epidemiologically distinct G8 rotaviruses have different origins and may be derived by reassortment with rotaviruses of a third, as yet unknown, host species. The similarity between the Finnish isolates and the bovine isolate NCDV suggests that they have diverged recently and that these human G8 rotaviruses may be derived from a zoonotic infection, or alternatively, from the live rotavirus vaccine of bovine origin which has been used to vaccinate Finnish children.

Presence of three P types (VP4 serotypes) and two G types (VP7 serotypes) among bovine rotavirus strains

Cross neutralization tests with a panel of rotavirus strains representing previously described nine VP7 (G) serotypes revealed that bovine rotavirus strain KK-3, a prototype Japanese bovine serotype 2, belonged to a new serotype (G10), confirming and extending the recent report of Snodgrass et al. [J. Clin. Microbiol. 28: 504-507 (1990)] which showed that hyperimmune serum to the KK-3 strain neutralized the B223 strain, a proposed type strain of G10. Further antigenic characteristics of the KK-3 strain, as well as the 0510 strain (a G6 strain isolated in Japan), were examined in terms of their VP4 (P) specificity. For the characterization of P types, we employed genetic reassortants that possess VP4 gene for UK and VP7 gene for D (G1), VP4 gene for NCDV and VP7 gene for SA11 (G3), or VP4 gene for SA11 and VP7 gene for NCDV (G6) in the plaque reduction neutralization assay with hyperimmune sera against these two Japanese strains and the prototype bovine rotavirus NCDV strain. While the 0510 strain had UK-like P and NCDV-like G types, the KK-3 strain had a distinct set of P and G types. Thus, at least three P types (NCDV-, UK-, and KK-3-like) and two G types (G6 and G10) are present among bovine rotavirus strains.