Simian rhesus rotavirus is a unique heterologous (non-lapine) rotavirus strain capable of productive replication and horizontal transmission in rabbits

Neonatal rhesus monkeys as an animal model for rotavirus infection

AIM

To establish a rotavirus (RV)-induced diarrhea model using RV SA11 in neonatal rhesus monkeys for the study of the pathogenic and immune mechanisms of RV infection and evaluation of candidate vaccines.

METHODS

Neonatal rhesus monkeys with an average age of 15-20 d and an average weight of 500 g ± 150 g received intragastric administration of varying doses of SA11 RV ( 10⁷ PFUs/mL, 10⁶ PFUs/mL, or 10⁵ PFUs/mL, 10 mL/animal) to determine whether the SA11 strain can effectively infect these animals by observing their clinical symptoms, fecal shedding of virus antigen by ELISA, distribution of RV antigen in the organs by immunofluorescence, variations of viral RNA load in the organs by qRT-PCR, histopathological changes in the small intestine by HE staining, and apoptosis of small intestinal epithelial cells by TUNEL assay.

RESULTS

The RV monkey model showed typical clinical diarrhea symptoms in the 10⁸ PFUs SA11 group, where we observed diarrhea 1-4 d post infection (dpi) and viral antigen shed in the feces from 1-7 dpi. RV was found in jejunal epithelial cells. We observed a viral load of approximately 5.85 × 10³ copies per 100 mg in the jejunum at 2 dpi, which was increased to 1.09 × 10⁵ copies per 100 mg at 3 dpi. A relatively high viral load was also seen in mesenteric lymph nodes at 2 dpi and 3 dpi. The following histopathological changes were observed in the small intestine following intragastric administration of SA11 RV: vacuolization, edema, and atrophy. Apoptosis in the jejunal villus epithelium was also detectable at 3 dpi.

CONCLUSION

Our results indicate that we have successfully established a RV SA11 strain diarrhea model in neonatal rhesus monkeys. Future studies will elucidate the mechanisms underlying the pathogenesis of RV infection, and we will use the model to evaluate the protective effect of candidate vaccines.

Rotavirus replication is correlated with S/G2 interphase arrest of the host cell cycle

In infected cells rotavirus (RV) replicates in viroplasms, cytosolic structures that require a stabilized microtubule (MT) network for their assembly, maintenance of the structure and perinuclear localization. Therefore, we hypothesized that RV could interfere with the MT-breakdown that takes place in mitosis during cell division. Using synchronized RV-permissive cells, we show that RV infection arrests the cell cycle in S/G2 phase, thus favoring replication by improving viroplasms formation, viral protein translation, and viral assembly. The arrest in S/G2 phase is independent of the host or viral strain and relies on active RV replication. RV infection causes cyclin B1 down-regulation, consistent with blocking entry into mitosis. With the aid of chemical inhibitors, the cytoskeleton network was linked to specific signaling pathways of the RV-induced cell cycle arrest. We found that upon RV infection Eg5 kinesin was delocalized from the pericentriolar region to the viroplasms. We used a MA104-Fucci system to identify three RV proteins (NSP3, NSP5, and VP2) involved in cell cycle arrest in the S-phase. Our data indicate that there is a strong correlation between the cell cycle arrest and RV replication.

Different virulence of porcine and porcine-like bovine rotavirus strains with genetically nearly identical genomes in piglets and calves

Direct interspecies transmissions of group A rotaviruses (RVA) have been reported under natural conditions. However, the pathogenicity of RVA has never been directly compared in homologous and heterologous hosts. The bovine RVA/Cow-tc/KOR/K5/2004/G5P[7] strain, which was shown to possess a typical porcine-like genotype constellation similar to that of the G5P[7] prototype RVA/Pig-tc/USA/OSU/1977/G5P9[7] strain, was examined for its pathogenicity and compared with the porcine G5P[7] RVA/Pig-tc/KOR/K71/2006/G5P[7] strain possessing the same genotype constellation. The bovine K5 strain induced diarrhea and histopathological changes in the small intestine of piglets and calves, whereas the porcine K71 strain caused diarrhea and histopathological changes in the small intestine of piglets, but not in calves. Furthermore, the bovine K5 strain showed extra-intestinal tropisms in both piglets and calves, whereas the porcine K71 strain had extra-intestinal tropisms in piglets, but not in calves. Therefore, we performed comparative genomic analysis of the K71 and K5 RVA strains to determine whether specific mutations could be associated with these distinct clinical and pathological phenotypes. Full-length sequencing analyses for the 11 genomic segments for K71 and K5 revealed that these strains were genetically nearly identical to each other. Two nucleotide mutations were found in the 5′ untranslated region (UTR) of NSP5 and the 3′ UTR of NSP3, and eight amino acid mutations in VP1-VP4 and NSP2. Some of these mutations may be critical molecular determinants for RVA virulence and/or pathogenicity.

Research priorities regarding rotavirus vaccine and intussusception: a meeting summary

Currently available rotavirus vaccines have been associated with a small increased risk of intussusception (~1-2 cases per 100,000 vaccinated infants) in some populations. In response to this newly emerging data on intussusception related to current rotavirus vaccines, a group of technical experts convened by the Program for Applied Technology in Health met to review the data, establish what gaps in knowledge exist, and identify what future research is needed. This manuscript outlines the evidence that is currently available and the research agenda that was generated during this meeting. It also highlights the need for countries that are using or considering introducing the rotavirus vaccine to evaluate both the benefits and risks of vaccination.

A feline rotavirus G3P[9] carries traces of multiple reassortment events and resembles rare human G3P[9] rotaviruses

The full-length genome sequence of a feline G3P[9] rotavirus (RV) strain, BA222, identified from the intestinal content of an adult cat, was determined. Strain BA222 possessed a G3-P[9]-I2-R2-C2-M2-A3-N1-T3-E2-H3 genomic constellation, differing substantially from other feline RVs. Phylogenetic analyses of each genome segment revealed common origins with selected animal and zoonotic human RVs, notably with rare multi-reassortant human G3P[9] RVs (Ita/PAI58/96 and Ita/PAH136/96). Altogether, the findings suggest that feline RVs are genetically diverse and that human RVs may occasionally originate either directly or indirectly (via reassortment) from feline RVs.

Intussusception and rotavirus vaccination: a review of the available evidence

Two live oral rotavirus vaccines (RotaTeq) and Rotarix) have recently been recommended by the WHO for inclusion into the national immunization programs of countries worldwide. Owing to the association of the withdrawn Rotashield vaccine with intussusception, these two new rotavirus vaccines underwent large clinical trials of over 60,000 infants each to assess safety with regard to this medical condition. For these two new vaccines, clinical trials and available postmarketing safety monitoring data do not indicate a risk of intussusception after vaccination, although a low-level risk cannot be excluded at present. We review these safety data for the new vaccines and for Rotashield to provide background information relevant for considering age recommendations for rotavirus vaccination.

Zoonotic aspects of rotaviruses

Rotaviruses are important enteric pathogens of humans and animals. Group A rotaviruses (GARVs) account for up to 1 million children deaths each year, chiefly in developing countries and human vaccines are now available in many countries. Rotavirus-associated enteritis is a major problem in livestock animals, notably in young calves and piglets. Early in the epidemiological GARV studies in humans, either sporadic cases or epidemics by atypical, animal-like GARV strains were described. Complete genome sequencing of human and animal GARV strains has revealed a striking genetic heterogeneity in the 11 double stranded RNA segments across different rotavirus strains and has provided evidence for frequent intersections between the evolution of human and animal rotaviruses, as a result of multiple, repeated events of interspecies transmission and subsequent adaptation.

Whole genome characterization of reassortant G10P[11] strain (N155) from a neonate with symptomatic rotavirus infection: identification of genes of human and animal rotavirus origin

BACKGROUND

Rotavirus G10P[11] strains have long been associated with asymptomatic neonatal infections in some parts of India. We have previously reported G10P[11] strains associated with both asymptomatic infections and severe gastrointestinal disease in neonates from Vellore in southern India, with >90% partial nucleotide and amino acid identity to the VP4, VP6, VP7 and NSP4 genes of the exclusively asymptomatic G10P[11] strain I321.

OBJECTIVES

In this study, the whole genome of a G10P[11] isolate (N155) from a neonate with severe gastrointestinal disease was characterized to determine whether there were significant differences in its genetic makeup in comparison to G10P[11] strain I321 and to establish the origin of the G10P[11] strains in Vellore.

STUDY DESIGN

PCR amplification and complete genome sequencing was carried out for all 11 gene segments of symptomatic G10P[11] rotavirus isolate N155. Nucleotide and amino acid sequence similarity with I321, other human and bovine strains for each gene segment were determined. The origin of each gene was determined based on the degree of identity to bovine or human rotavirus strains.

RESULTS

N155 was found to be a reassortant between human and bovine rotaviruses. With the exception of NSP2, gene sequences of strain N155 showed >90% identity to published sequences of I321. Gene segments encoding NSP1, 2 and 3 were of human rotavirus origin for both strains; however, phylogenetic analysis of NSP2 sequences indicated that the human parental strain that led to the origin of these bovine-human reassortant strains was different. There were no significant differences between NSP2 sequences of strains from symptomatic and asymptomatic neonates in the same setting.

CONCLUSIONS

The study shows that the difference in clinical presentations in neonates may not be due to the limited variability in the genome sequence of G10P[11] strains and that G10P[11] strains in different parts of India could have evolved through reassortment of different parental strains.

Full genomic analysis of human rotavirus strain B4106 and lapine rotavirus strain 30/96 provides evidence for interspecies transmission

The Belgian rotavirus strain B4106, isolated from a child with gastroenteritis, was previously found to have VP7 (G3), VP4 (P[14]), and NSP4 (A genotype) genes closely related to those of lapine rotaviruses, suggesting a possible lapine origin or natural reassortment of strain B4106. To investigate the origin of this unusual strain, the gene sequences encoding VP1, VP2, VP3, VP6, NSP1, NSP2, NSP3, and NSP5/6 were also determined. To allow comparison to a lapine strain, the 11 double-stranded RNA segments of a European G3P[14] rabbit rotavirus strain 30/96 were also determined. The complete genome similarity between strains B4106 and 30/96 was 93.4% at the nucleotide level and 96.9% at the amino acid level. All 11 genome segments of strain B4106 were closely related to those of lapine rotaviruses and clustered with the lapine strains in phylogenetic analyses. In addition, sequence analyses of the NSP5 gene of strain B4106 revealed that the altered electrophoretic mobility of NSP5, resulting in a super-short pattern, was due to a gene rearrangement (head-to-tail partial duplication, combined with two short insertions and a deletion). Altogether, these findings confirm that a rotavirus strain with an entirely lapine genome complement was able to infect and cause severe disease in a human child.

Molecular analysis of the VP7, VP4, VP6, NSP4, and NSP5/6 genes of a buffalo rotavirus strain: identification of the rare P[3] rhesus rotavirus-like VP4 gene allele

We report the detection and molecular characterization of a rotavirus strain, 10733, isolated from the feces of a buffalo calf affected with diarrhea in Italy. Strain 10733 was classified as a P[3] rotavirus, as the VP8* trypsin cleavage product of the VP4 protein revealed a high amino acid identity (96.2%) with that of rhesus rotavirus strain RRV (P5B[3]), used as the recipient virus in the human-simian reassortant vaccine. Analysis of the VP7 gene product revealed that strain 10733 possessed G6 serotype specificity, a type common in ruminants, with an amino acid identity to G6 rotavirus strains ranging from 88 to 98%, to Venezuelan bovine strain BRV033, and Hungarian human strain Hun4. Phylogenetic analysis based on the VP7 gene of G6 rotaviruses identified at least four lineages and an apparent linkage between each lineage and the VP4 specificity, suggesting the occurrence of repeated interspecies transmissions and genetic reassortment events between ruminant and human rotaviruses. Moreover, strain 10733 displayed a bovine-like NSP4 and NSP5/6 and a subgroup I VP6 specificity, as well as a long electropherotype pattern. The detection of the rare P[3] genotype in ruminants provides additional evidence for the wide genetic and antigenic diversity of group A rotaviruses.

Roles of outer capsid proteins as determinants of pathogenicity and host range restriction of avian rotaviruses in a suckling mouse model

We previously demonstrated that a pigeon rotavirus, PO-13, but not turkey strains Ty-3 and Ty-1 and a chicken strain, Ch-1, induced diarrhea in heterologous suckling mice. In this study, it was suggested that these avirulent strains, but not PO-13, were inactivated immediately in gastrointestinal tracts of suckling mice when they were orally inoculated. To determine which viral proteins contribute to the differences between the pathogenicitiy and the inactivation of PO-13 and Ty-3 in suckling mice, six PO-13 x Ty-3 reassortant strains that had the genes of the outer capsid proteins, VP4 and VP7, derived from the opposite strain were prepared and were orally inoculated to suckling mice. A single strain that had both PO-13 VP4 and VP7 with the genetic background of Ty-3 had an intermediate virulence for suckling mice. Three strains with Ty-3 VP7, regardless of the origin of VP4, rapidly disappeared from gastrointestinal tracts of suckling mice. These results indicated that the difference between the pathogenicity of PO-13 and that of Ty-3 was mainly dependent on both their VP4 and VP7. In particular, VP7 was found to be related to the inactivation of Ty-3 in gastrointestinal tracts of suckling mice.

Immunogenicity and protective efficacy of rotavirus 2/6-virus-like particles produced by a dual baculovirus expression vector and administered intramuscularly, intranasally, or orally to mice

Virus-like particles (VLPs) are being evaluated as a candidate rotavirus vaccine. Rotavirus VLPs composed of simian SA11 strain VP2 and VP6 proteins (homologous 2/6-VLPs) were produced by cloning the rotavirus simian SA11 genes 2 and 6 into a single baculovirus transfer vector (pAcAB4). The overall yield of homologous 2/6-VLPs produced with the dual recombinant baculovirus was at least 30-fold higher than that of VLPs composed of bovine RF strain VP2 and simian SA11 strain VP6 (heterologous 2/6-VLPs), produced with single recombinant baculoviruses. Adult mice were immunized intramuscularly twice with various doses of homologous or heterologous 2/6-VLPs in QS-21, orally with or without cholera toxin (CT), or intranasally with mutant Escherichia coli heat-labile enterotoxin (LT-R192G). Both homologous and heterologous 2/6-VLPs were immunogenic and induced protection from challenge, with those administered parenterally or intranasally affording the highest mean protection from challenge. The 2/6-VLPs did not induce serum neutralizing antibody (N-Ab) responses, but these VLPs primed for a broad heterotypic N-Ab response, which was elicited after rotavirus challenge. Heterotypic N-Ab responses were not observed in 2/6-VLP vaccinated mice that were > or =94% protected from challenge. After challenge, control mice immunized with adjuvant alone developed only homotypic serum N-Ab responses. Similar results were obtained after challenge of rabbits immunized parenterally or intranasally with heterologous 2/6-VLPs. These results suggest that 2/6-VLPs prime the immune system to enhance the production of heterotypic N-Ab responses, but the induction of heterotypic N-Abs requires that virus replication occurs after challenge. The use of 2/6-VLPs expressed from a single recombinant baculovirus simplifies production and would reduce the cost of a VLP-based vaccine.

The future of rotavirus vaccines

In 1998, a simian-human reassortant rotavirus vaccine was licensed and recommended for routine use in children. Within 1 year, however, the vaccine was found to be a cause of intussusception, estimated to be approximately 1 case per 10,000 immunized children, and the recommendations were withdrawn. Although the etiology and pathogenesis of vaccine-associated intussusception remain unclear, immunologic studies suggest several hypotheses. Development of new rotavirus vaccines necessitates the need for large, prelicensure, clinical trials to determine safety. Candidate vaccines currently in clinical trials include a bovine-human reassortant pentavalent vaccine and an attenuated human rotavirus monovalent vaccine. Important issues to be addressed include the acceptable, if any, degree of risk of developing intussusception and economic issues concerning the distribution of the vaccine in developing countries. The continuing interest of pharmaceutical companies in developing a safe and effective vaccine is encouraging, especially given the enormous burden of rotavirus disease in developing countries.

Group A rotavirus infection and age-dependent diarrheal disease in rats: a new animal model to study the pathophysiology of rotavirus infection

Group A rotaviruses are major pathogens causing acute gastroenteritis in children and animals. To determine if group A rotavirus replicates and induces disease in rats, antibody-negative Lewis neonatal or adult rats were inoculated orally with tissue culture-adapted human (Wa, WI61, and HAL1166), simian (rhesus rotavirus [RRV] and SA11), bovine (WC3), lapine (ALA), or porcine (OSU) rotavirus strains, wild-type murine (EC(wt)) rotavirus strain, or phosphate-buffered saline (PBS). Rotavirus infection in rats was evaluated by (i) clinical findings, (ii) virus antigen shedding or infectious virus titers in the feces or intestinal contents measured by enzyme-linked immunosorbent assay or fluorescent-focus assay, (iii) histopathological changes in the small intestine, (iv) distribution of rotavirus antigen in small-intestine sections by immunofluorescence, and (v) growth rate. Rotavirus infection of 5-day-old but not > or =21-day-old rats resulted in diarrhea that lasted from 1 to 10 days postinoculation. The severity of disease and spread of infection to naIve littermates differed depending on the virus strain used for inoculation. The duration of virus antigen shedding following infection was considerably prolonged (up to 10 days) in neonatal rats compared to that in 21-day-old rats (1 or 2 days). Based on lack of virus antigen shedding and disease induction, the murine EC(wt) rotavirus was the only strain tested that did not infect rats. Histopathological changes in the small-intestine mucosa of 5-day-old RRV-inoculated rats but not of PBS-inoculated rats was limited to extensive enterocyte vacuolation in the ileum. In RRV-inoculated neonatal rats, rotavirus antigen was detected in the epithelial cells on the upper half of the intestinal villi of the jejunum and ileum. In addition, infection of neonatal rats with RRV but not with PBS resulted in reduced weight gain. Rats infected with group A rotaviruses provide a new animal model with unique features amenable to investigate rotavirus pathogenesis and the molecular mechanisms of intestinal development, including physiological factors that may regulate age-dependent rotavirus-induced diarrhea.