Rotavirus disease, but not infection and development of intestinal histopathological lesions, is age restricted in rabbits

Reduction in Severity of All-Cause Gastroenteritis Requiring Hospitalisation in Children Vaccinated against Rotavirus in Malawi

Rotavirus is the major cause of severe gastroenteritis in children aged <5 years. Introduction of the G1P[8] Rotarix® rotavirus vaccine in Malawi in 2012 has reduced rotavirus-associated hospitalisations and diarrhoeal mortality. However, the impact of rotavirus vaccine on the severity of gastroenteritis presented in children requiring hospitalisation remains unknown. We conducted a hospital-based surveillance study to assess the impact of Rotarix® vaccination on the severity of gastroenteritis presented by Malawian children. Stool samples were collected from children aged <5 years who required hospitalisation with acute gastroenteritis from December 2011 to October 2019. Gastroenteritis severity was determined using Ruuska and Vesikari scores. Rotavirus was detected using enzyme immunoassay. Rotavirus genotypes were determined using nested RT-PCR. Associations between Rotarix® vaccination and gastroenteritis severity were investigated using adjusted linear regression. In total, 3159 children were enrolled. After adjusting for mid-upper arm circumference (MUAC), age, gender and receipt of other vaccines, all-cause gastroenteritis severity scores were 2.21 units lower (p < 0.001) among Rotarix®-vaccinated (n = 2224) compared to Rotarix®-unvaccinated children (n = 935). The reduction in severity score was observed against every rotavirus genotype, although the magnitude was smaller among those infected with G12P[6] compared to the remaining genotypes (p = 0.011). Each one-year increment in age was associated with a decrease of 0.43 severity score (p < 0.001). Our findings provide additional evidence on the impact of Rotarix® in Malawi, lending further support to Malawi's Rotarix® programme.

An Investigation of the Relationship between Cyniclomyces guttulatus and Rabbit Diarrhoea

Cyniclomyces guttulatus is usually recognised as an inhabitant of the gastrointestinal (GI) tract in rabbits. However, large numbers of C. guttulatus are often detected in the faeces of diarrhoeic rabbits. The relationship of C. guttulatus with rabbit diarrhoea needs to be clearly identified. In this study, a C. guttulatus Zhejiang strain was isolated from a New Zealand White rabbit with severe diarrhoea and then inoculated into SPF New Zealand white rabbits alone or co-inoculated with Eimeriaintestinalis, another kind of pathogen in rabbits. Our results showed that the optimal culture medium pH and temperature for this yeast were pH 4.5 and 40-42 °C, respectively. The sequence lengths of the 18S and 26S ribosomal DNA fragments were 1559 bp and 632 bp, respectively, and showed 99.8% homology with the 18S ribosomal sequence of the NRRL Y-17561 isolate from dogs and 100% homology with the 26S ribosomal sequence of DPA-CGR1 and CGDPA-GP1 isolates from rabbits and guinea pigs, respectively. In animal experiments, the C. guttulatus Zhejiang strain was not pathogenic to healthy rabbits, even when 1 × 10⁸ vegetative cells were used per rabbit. Surprisingly, rabbits inoculated with yeast showed a slightly better body weight gain and higher food intake. However, SPF rabbits co-inoculated with C. guttulatus and E. intestinalis developed more severe coccidiosis than rabbits inoculated with C. guttulatus or E. intestinalis alone. In addition, we surveyed the prevalence of C. guttulatus in rabbits and found that the positive rate was 83% in Zhejiang Province. In summary, the results indicated that C. guttulatus alone is not pathogenic to healthy rabbits, although might be an opportunistic pathogen when the digestive tract is damaged by other pathogens, such as coccidia.

Heterogeneous susceptibility to rotavirus infection and gastroenteritis in two birth cohort studies: Parameter estimation and epidemiological implications

Cohort studies, randomized trials, and post-licensure studies have reported reduced natural and vaccine-derived protection against rotavirus gastroenteritis (RVGE) in low- and middle-income countries. While susceptibility of children to rotavirus is known to vary within and between settings, implications for estimation of immune protection are not well understood. We sought to re-estimate naturally-acquired protection against rotavirus infection and RVGE, and to understand how differences in susceptibility among children impacted estimates. We re-analyzed data from studies conducted in Mexico City, Mexico and Vellore, India. Cumulatively, 573 rotavirus-unvaccinated children experienced 1418 rotavirus infections and 371 episodes of RVGE over 17,636 child-months. We developed a model that characterized susceptibility to rotavirus infection and RVGE among children, accounting for aspects of the natural history of rotavirus and differences in transmission rates between settings. We tested whether model-generated susceptibility measurements were associated with demographic and anthropometric factors, and with the severity of RVGE symptoms. We identified greater variation in susceptibility to rotavirus infection and RVGE in Vellore than in Mexico City. In both cohorts, susceptibility to rotavirus infection and RVGE were associated with male sex, lower birth weight, lower maternal education, and having fewer siblings; within Vellore, susceptibility was also associated with lower socioeconomic status. Children who were more susceptible to rotavirus also experienced higher rates of rotavirus-negative diarrhea, and higher risk of moderate-to-severe symptoms when experiencing RVGE. Simulations suggested that discrepant estimates of naturally-acquired immunity against RVGE can be attributed, in part, to between-setting differences in susceptibility of children, but result primarily from the interaction of transmission rates with age-dependent risk for infections to cause RVGE. We found that more children in Vellore than in Mexico City belong to a high-risk group for rotavirus infection and RVGE, and demonstrate that unmeasured individual- and age-dependent susceptibility may influence estimates of naturally-acquired immune protection against RVGE.

Differences in susceptibility can help explain why some individuals, and not others, acquire infection and exhibit symptoms when exposed to infectious disease agents. However, it is difficult to distinguish between differences in susceptibility versus exposure in epidemiological studies. We developed a modeling approach to distinguish transmission intensity and susceptibility in data from cohort studies of rotavirus infection among children in Mexico City, Mexico, and Vellore, India, and evaluated how these factors may have contributed to differences in estimates of naturally-acquired immune protection between the studies. Given the same exposure, more children were at high risk of acquiring rotavirus infection, and of experiencing gastroenteritis when infected, in Vellore than in Mexico City. The probability of belonging to this high-risk stratum was associated with well-known individual factors such as lower socioeconomic status, lower birth weight, and incidence of diarrhea due to other causes. We also found the risk for rotavirus infections to cause symptoms declined with age, independent of acquired immunity. These findings can, in part, account for estimates of lower protective efficacy of acquired immunity against rotavirus gastroenteritis in high-incidence settings, mirroring estimates of reduced effectiveness of live oral rotavirus vaccines in low- and middle-income countries.

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.

Naturally Acquired Immunity Against Rotavirus Infection and Gastroenteritis in Children: Paired Reanalyses of Birth Cohort Studies

Background

Observational studies in socioeconomically distinct populations have yielded conflicting conclusions about the strength of naturally acquired immunity against rotavirus gastroenteritis (RVGE), mirroring vaccine underperformance in low-income countries. We revisited birth cohort studies to understand naturally acquired protection against rotavirus infection and RVGE.

Methods

We reanalyzed data from 200 Mexican and 373 Indian children followed from birth to 2 and 3 years of age, respectively. We reassessed protection against RVGE, decomposing the incidence rate into the rate of rotavirus infection and the risk of RVGE given infection, and tested for serum antibody correlates of protection using regression models.

Results

Risk for primary, secondary, and subsequent infections to cause RVGE decreased per log-month of age by 28% (95% confidence interval [CI], 12%-41%), 69% (95% CI, 30%-86%), and 64% (95% CI, -186% to 95%), respectively, in Mexico City, and by 10% (95% CI, -1% to 19%), 51% (95% CI, 41%-59%) and 67% (95% CI, 57%-75%), respectively, in Vellore. Elevated serum immunoglobulin A and immunoglobulin G titers were associated with partial protection against rotavirus infection. Associations between older age and reduced risk for RVGE or moderate-to-severe RVGE given infection persisted after controlling for antibody levels.

Conclusions

Dissimilar estimates of protection against RVGE may be due in part to age-related, antibody-independent risk for rotavirus infections to cause RVGE.

Seroprevalence of Rotavirus infection in pig population of Arunachal Pradesh

AIM

This study was conducted to find out the seroprevalence of Rotavirus(RV) infection among the pig population of Arunachal Pradesh.

MATERIALS AND METHODS

Serums samples were collected from piglets of age ranging from 1 week to 6 months and the sows associated with the piglets that were reared under organized and unorganized system of management in six different districts of Arunachal Pradesh. The prevalence of RV specific antibodies was detected using a polyclonal antibody-based indirect enzyme-linked immunosorbent assay (i-ELISA).

RESULTS

The study revealed that out of 394 serum samples, 255 (64.72%) samples were found to be positive for RV-specific antibody in i-ELISA. Considering the samples from different districts, Papumpare district of Arunachal Pradesh showed highest numbers of seropositive animals (68.75%) followed by upper Subansiri (64.91%) while West Siang district showed lowest positivity rate (61.22%).

CONCLUSION

As considerable seropositivity was recorded among pig population of Arunachal Pradesh in this study, there is urgent need to establish high-impact and cost-effective public health intervention tools, key among them being the introduction of strict hygiene practice and RV vaccination program, to greatly reduce the number of deaths due to diarrheal diseases. To the authors' knowledge, this is the first report on the prevalence of RV infection from pigs of Arunachal Pradesh.

Avian rotavirus enteritis - an updated review

Rotaviruses (RVs) are among the leading causes of enteritis and diarrhea in a number of mammalian and avian species, and impose colossal loss to livestock and poultry industry globally. Subsequent to detection of rotavirus in mammalian hosts in 1973, avian rotavirus (AvRV) was first reported in turkey poults in USA during 1977 and since then RVs of group A (RVA), D (RVD), F (RVF) and G (RVG) have been identified around the globe. Besides RVA, other AvRV groups (RVD, RVF and RVG) may also contribute to disease. However, their significance has yet to be unraveled. Under field conditions, co-infection of AvRVs occurs with other infectious agents such as astroviruses, enteroviruses, reoviruses, paramyxovirus, adenovirus, Salmonella, Escherichia coli, cryptosporidium and Eimeria species prospering severity of disease outcome. Birds surviving to RV disease predominantly succumb to secondary bacterial infections, mostly E. coli and Salmonella spp. Recent developments in molecular tools including state-of-the-art diagnostics and vaccine development have led to advances in our understanding towards AvRVs. Development of new generation vaccines using immunogenic antigens of AvRV has to be explored and given due importance. Till now, no effective vaccines are available. Although specific as well as sensitive approaches are available to identify and characterize AvRVs, there is still need to have point-of-care detection assays to review disease burden, contemplate new directions for adopting vaccination and follow improvements in public health measures. This review discusses AvRVs, their epidemiology, pathology and pathogenesis, immunity, recent trends in diagnostics, vaccines, therapeutics as well as appropriate prevention and control strategies.

The gastrointestinal frontier: IgA and viruses

Viral gastroenteritis is one of the leading causes of diseases that kill ~2.2 million people worldwide each year. IgA is one of the major immune effector products present in the gastrointestinal tract yet its importance in protection against gastrointestinal viral infections has been difficult to prove. In part this has been due to a lack of small and large animal models in which pathogenesis of and immunity to gastrointestinal viral infections is similar to that in humans. Much of what we have learned about the role of IgA in the intestinal immune response has been obtained from experimental animal models of rotavirus infection. Rotavirus-specific intestinal IgA appears to be one of the principle effectors of long term protection against rotavirus infection. Thus, there has been a focus on understanding the immunological pathways through which this virus-specific IgA is induced during infection. In addition, the experimental animal models of rotavirus infection provide excellent systems in which new areas of research on viral-specific intestinal IgA including the long term maintenance of viral-specific IgA.

Viral infections of rabbits

Viral diseases of rabbits have been used historically to study oncogenesis (e.g. rabbit fibroma virus, cottontail rabbit papillomavirus) and biologically to control feral rabbit populations (e.g. myxoma virus). However, clinicians seeing pet rabbits in North America infrequently encounter viral diseases although myxomatosis may be seen occasionally. The situation is different in Europe and Australia, where myxomatosis and rabbit hemorrhagic disease are endemic. Advances in epidemiology and virology have led to detection of other lapine viruses that are now recognized as agents of emerging infectious diseases. Rabbit caliciviruses, related to rabbit hemorrhagic disease, are generally avirulent, but lethal variants are being identified in Europe and North America. Enteric viruses including lapine rotavirus, rabbit enteric coronavirus and rabbit astrovirus are being acknowledged as contributors to the multifactorial enteritis complex of juvenile rabbits. Three avirulent leporid herpesviruses are found in domestic rabbits. A fourth highly pathogenic virus designated leporid herpesvirus 4 has been described in Canada and Alaska. This review considers viruses affecting rabbits by their clinical significance. Viruses of major and minor clinical significance are described, and viruses of laboratory significance are mentioned.

Astroviruses in rabbits

A novel astrovirus was found more frequently in rabbits with enteric disease than in asymptomatic animals.

By screening rabbits with enterocolitis or enteritis complex and asymptomatic rabbits, we identified a novel astrovirus. The virus was distantly related (19.3%–23.7% aa identity) in the capsid precursor to other mammalian astroviruses within the Mamastrovirus genus. By using real-time reverse transcription PCR, with specific primers and probes and targeting a conserved stretch in open reading frame 1b, we found rabbit astrovirus in 10 (43%) of 23 samples from animals with enteric disease and in 25 (18%) of 139 samples from asymptomatic animals in Italy during 2005–2008. The mean and median titers in the positive animals were 10²× and 10³× greater, respectively, in the symptomatic animals than in the asymptomatic animals. These findings support the idea that rabbit astroviruses should be included in the diagnostic algorithm of rabbit enteric disease and animal experiments to increase information obtained about their epidemiology and potential pathogenic role.

Analyses of clinical, pathological and virological features of human rotavirus strain, YO induced gastroenteritis in infant BALB/c mice

Experimental studies of human rotavirus infections in mice are limited and there is lack of information on the quantitative assessment of rotaviral replication and its relationship with histological changes. In the present study, consequences of human rotavirus strain, YO induced gastroenteritis in infant BALB/c mice were analyzed for the occurrence of clinical symptoms, histopathology and virological events. The infected animals developed diarrhea and dehydration and showed accumulation of vacuolated enterocytes with lodging of the rotavirus antigens and shortening of villi in the intestine over a period of 5 days. The ileum was identified as the most susceptible and supportive part of small intestine for perpetuation of rotavirus infection in mice. Rotaviral antigen/RNA in stool and RNA in intestine were detected throughout the clinical disease period. At 48-72 h post inoculation, diarrhea was at the peak (90-95%) in the infected animals with increased load of viral RNA and intense pathological lesions suggesting it as the critical time point in the course of infection. The rising titers of antirotavirus neutralizing antibodies ascertained the replication of human rotavirus strain, YO in mice. These data may contribute to the understanding of pathophysiological, immunological and virological characteristics of rotavirus infections in mice.

Molecular characterization of equine rotavirus in Ireland

Group A rotaviruses are important causative agents of severe, acute dehydrating diarrhea in foals. A total of 86 rotavirus-positive fecal samples, collected from diarrheic foals from 11 counties in three of the four provinces of Ireland, were obtained from the Irish Equine Centre in Kildare during a 7-year (1999 to 2005) passive surveillance study and were characterized molecularly to establish the VP7 (G type) and VP4 (P type) antigenic specificities. Fifty-eight samples (67.5%) were found to contain G3 viruses, while in 26 samples (30.2%) the rotaviruses were typed as G14 and in 2 samples (2.3%) there was a mixed infection, G3 plus G14. All samples except for two, which were untypeable, were characterized as P[12]. Fifty-eight percent of the samples were obtained from County Kildare, the center of the Irish horse industry, where an apparent shift from G3P[12] to G14P[12] was observed in 2003. By sequence analysis of the VP7 protein, the G3 Irish strains were shown to resemble viruses of the G3A subtype (H2-like) (97.1 to 100% amino acid [aa] identity), while the G14 Irish strains displayed 93.9 to 97.1% aa identity to other G14 viruses. In the VP8* fragment of the VP4 protein, the P[12] Irish viruses displayed high conservation (92.3 to 100% aa) with other equine P[12] viruses. Worldwide, G3P[12] and G14P[12] are the most prevalent equine rotavirus strains, and G3P[12] vaccines have been developed for prevention of rotavirus-associated diarrhea in foals. Investigations of the VP7/VP4 diversity of the circulating equine viruses and the dynamics of strain replacement are important for better assessing the efficacies of the vaccines.

Anti-NSP4 antibody can block rotavirus-induced diarrhea in mice

BACKGROUND

Rotavirus infection is the most common cause of infectious diarrhea and gastroenteritis among children worldwide. The viral proteins (VP), especially VP4- and VP7-induced neutralizing antibodies, were considered to be critical in protective immunity to rotavirus disease. However, whether the antibody to rotavirus nonstructural protein 4 (NSP4) protects against rotavirus-induced diarrhea directly is not completely clear, especially for the protective time course.

MATERIALS AND METHODS

To obtain direct evidence, 12-day-old ICR mice were treated with NSP4 and entire rotavirus to induce diarrhea.

RESULTS

Both NSP4 and rotavirus-treated mice developed diarrhea, which was accompanied by histological changes in the small intestine compared to age-matched control mice. Anti-NSP4 antibody demonstrated protection against both entire rotavirus-induced diarrhea and NSP4-induced diarrhea. The histological changes in the small intestinal were reversible. These data show that early intervention with anti-NSP4 antibody can prevent rotavirus-induced diarrhea in mice; late intervention with anti-NSP4 antibody could halt diarrhea progression in mice.

CONCLUSIONS

Our findings demonstrate for the first time that administration of anti-NSP4 antibody is effective both prior to and during the time course of rotavirus infection. These observations extend our knowledge of rotavirus infection and its therapeutic options.

Rotavirus infection is not associated with small intestinal fluid secretion in the adult mouse

In contrast to humans, adult but not infant small animals are resistant to rotavirus diarrhea. The pathophysiological mechanism behind this age-restricted diarrhea is currently unresolved, and this question was investigated by studying the secretory state of the small intestines of adult mice infected with rotavirus. Immunohistochemistry and histological examinations revealed that rotavirus (strain EDIM) infects all parts of the small intestines of adult mice, with significant numbers of infected cells in the ilea at 2 and 4 days postinfection. Furthermore, quantitative PCR revealed that 100-fold more viral RNA was produced in the ilea than in the jejuna or duodena of adult mice. In vitro perfusion experiments of the small intestine did not reveal any significant changes in net fluid secretion among mice infected for 3 days or 4 days or in those that were noninfected (37 +/- 9 microl . h(-1) . cm(-1), 22 +/- 13 microl . h(-1) . cm(-1), and 33 +/- 6 microl . h(-1) . cm(-1), respectively) or in transmucosal potential difference (4.0 +/- 0.3 mV versus 3.9 +/- 0.4 mV), a marker for active chloride secretion, between control and rotavirus-infected mice. In vivo experiments also did not show any differences in potential difference between uninfected and infected small intestines. Furthermore, no significant differences in weight between infected and uninfected small intestines were found, nor were any differences in fecal output observed between infected and control mice. Altogether, these data suggest that rotavirus infection is not sufficient to stimulate chloride and water secretion from the small intestines of adult mice.

Examination of the applicability of a commercial human rotavirus antigen detection kit for use in laboratory rabbits

The applicability of a commercial human rotavirus detection kit for the detection of lapine rotavirus in laboratory rabbits was examined. Rotavirus antigen positive samples determined by the kit were shown to include lapine rotavirus by reverse transcriptional polymerase chain reaction and restriction endonuclease analysis. The kit was confirmed to be adequate for the detection of lapine rotavirus by these results. The kit is suggested to be useful for the management of laboratory rabbits because of its ability to detect rotavirus antigen excretion which occurs in the early stage of the infection. It will contribute to minimizing the loss of rabbits in the event of an outbreak.

Identification of the novel lapine rotavirus genotype P[22] from an outbreak of enteritis in a Hungarian rabbitry

Application of improved molecular techniques in the detection and characterization of rotavirus strains has led to the recent description of several new combinations, specificities, and genetic variants of the outer capsid genes, VP7 and VP4. In spite of the enormous diversity of mammalian rotavirus strains, the few lapine rotaviruses characterized to date, appear to carry a narrow range of such antigen combinations; only P[14], G3 and, based on a more recent study, P[22], G3 rotaviruses have proved to be epidemiologically important in rabbits. In the present study, we characterized a lapine group A rotavirus with a super-short electropherotype detected in an outbreak of fatal enteritis in a Hungarian commercial rabbitry. Based on sequence and phylogenetic analysis of the VP7, VP4, and NSP4 genes, our lapine strain is a P[22], G3 rotavirus that carries the NSP4 genotype shared by most lapine rotaviruses. Although the P[22] VP4 specificity has been newly identified, the relatively high sequence variation between our strain and those identified in Italy (89.1-90.4% nucleotide identity; region VP8*) implies that these strains diversified far before they were described for the first time, strongly suggesting that this genotype may have circulated in rabbitries or in nature without prior detection. We conclude that genotype P[22] lapine rotaviruses show a wider geographical dispersal than previously thought, although understanding their true epidemiological significance needs further investigation.

Lapine rotaviruses of the genotype P[22] are widespread in Italian rabbitries

An epidemiological survey was carried out to investigate the distribution of the VP7 and VP4 specificities of lapine rotaviruses (LRVs) in rabbitries from different geographical regions of Italy. Almost all the strains were characterized as P[22],G3, confirming the presence of the newly-recognized rotavirus P[22] VP4 allele in Italian rabbits. Only one P[14],G3 LRV strain was identified and two samples contained a mixed (P[14] + [22],G3) rotavirus infection. All the LRV strains analyzed exhibited a genogroup I VP6 specificity and a long dsRNA electropherotype. However, one of the P[14],G3 strains possessed a super-short pattern. Altogether, these data highlight the epidemiological relevance of the P[22] LRVs in Italian rabbitries.

Experimental infection of pigtailed macaques with a simian rotavirus, YK-1

Experimental rotavirus infection was investigated in pigtailed macaques to study the infectivity, immunity, and pathogenesis of rotavirus. A challenge virus, YK-1, was administered intragastrically to four seronegative macaques (age: 11-16 months). Although none of the monkeys developed diarrhea, an active infection occurred with high titers of rotavirus antigen detected in stools 2-10 days after challenge. These animals developed rotavirus-specific antibody responses similar to those seen following primary exposure to rotavirus. YK-1 was then inoculated in four seropositive macaques (age: 14-16 months). All animals shed viral antigen in their stool, but the titers and duration were significantly less when compared to seronegative macaques. When rechallenged 28 days after initial YK-1 challenge, the macaques demonstrated significant protection against reinfection. All seropositive animals developed a rise in rotavirus-specific serum and fecal antibodies during YK-1 challenge and rechallenge. To independently assess the role of age and preexisting IgG titers to rotavirus, a 4-month-old seronegative and 6-month-old seropositive macaque were inoculated with YK-1. The seronegative macaque shed high titers of virus for 9 days, while the seropositive macaque shed only 3 days and in low titer. These data suggest that a primate model of rotavirus infection using the YK-1 strain may be useful in examining the immune response and protection from infection in pigtailed macaques and indicate that levels and duration of shedding may provide a good measure of protection from natural infection and from that induced by oral or parenteral vaccines.

Viral diseases of the rabbit

Viral disease in the rabbit is encountered infrequently by the clinical practitioner; however, several viral diseases were reported to occur in this species. Viral diseases that are described in the rabbit primarily may affect the integument, gastrointestinal tract or, central nervous system or maybe multi-systemic in nature. Rabbit viral diseases range from oral papillomatosis, with benign clinical signs, to rabbit hemorrhagic disease and myxomatosis, which may result in significant clinical disease and mortality. The wild rabbit may serve as a reservoir for disease transmission for many of these viral agents. In general, treatment of viral disease in the rabbit is supportive in nature.

Rotavirus infection stimulates the Cl- reabsorption process across the intestinal brush-border membrane of young rabbits

Rotavirus is a major cause of infantile gastroenteritis worldwide. However, the mechanisms underlying fluid and electrolyte secretion associated with diarrhea remain largely unknown. We investigated the hypothesis that loss of Cl(-) into the luminal contents during rotavirus infection may be caused by a dysfunction in the chloride absorptive capacity across the intestinal brush-border membrane (BBM). The luminal Cl(-) concentrations in the entire small intestine of young rabbits infected with lapine rotavirus decreased at 1 and 2 days postinfection (dpi), indicating net Cl(-) absorption. At 7 dpi, luminal Cl(-) concentrations were slightly increased, indicating a moderate net Cl(-) secretion. By using a rapid filtration technique, (36)Cl uptake across BBM was quantified by modulating the alkali-metal ion, electrical, chloride, and/or proton gradients. Rotavirus infection caused an identical, 127% +/- 24% increase in all Cl(-) uptake activities (Cl(-)/H(+) symport, Cl(-) conductance, and Cl(-)/anion exchange) observed across the intestinal BBM. The rotavirus activating effects on the symporter started at 1 dpi and persisted up to 7 dpi. Kinetic analyses revealed that rotavirus selectively affected the capacity parameter characterizing the symporter. We report the novel observation that rotavirus infection stimulated the Cl(-) reabsorption process across the intestinal BBM. We propose that the massive Cl(-) reabsorption in villi could partly overwhelm chloride secretion in crypt cells, which possibly increases during rotavirus diarrhea, the resulting imbalance leading to a moderate net chloride secretion.

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.

Protective immunity and antibody-secreting cell responses elicited by combined oral attenuated Wa human rotavirus and intranasal Wa 2/6-VLPs with mutant Escherichia coli heat-labile toxin in gnotobiotic pigs

Two combined rotavirus vaccination regimens were evaluated in a gnotobiotic pig model of rotavirus infection and disease and were compared to previously tested rotavirus vaccination regimens. The first (AttHRV/VLP2x) involved oral inoculation with one dose of attenuated (Att) Wa human rotavirus (HRV), followed by two intranasal (i.n.) doses of a rotavirus-like particle (2/6-VLPs) vaccine derived from Wa (VP6) and bovine RF (VP2) rotavirus strains. The 2/6-VLPs were coadministered with a mutant Escherichia coli heat-labile toxin, LT-R192G (mLT) adjuvant. For the second regimen (VLP2x/AttHRV), two i.n. doses of 2/6-VLPs+mLT were given, followed by one oral dose of attenuated Wa HRV. To compare the protective efficacy and immune responses induced by the combined vaccine regimens with individual rotavirus vaccine regimens, we included in the experiments the following vaccine groups: one oral dose of attenuated Wa HRV (AttHRV1x and Mock2x/AttHRV, respectively), three oral doses of attenuated Wa HRV (AttHRV3x), three i.n. doses of 2/6-VLPs plus mLT (VLP3x), three i.n. doses of purified double-layered inactivated Wa HRV plus mLT (InactHRV3x), mLT alone, and mock-inoculated pigs. The isotype, magnitude, and tissue distribution of antibody-secreting cells (ASCs) in the intestinal and systemic lymphoid tissues were evaluated using an enzyme-linked immunospot assay. The AttHRV/VLP2x regimen stimulated the highest mean numbers of intestinal immunoglobulin A (IgA) ASCs prechallenge among all vaccine groups. This regimen induced partial protection against virus shedding (58%) and diarrhea (44%) upon challenge of pigs with virulent Wa HRV. The reverse VLP2x/AttHRV regimen was less efficacious than the AttHRV/VLP2x regimen in inducing IgA ASC responses and protection against diarrhea (25% protection rate) but was more efficacious than VLP3x or InactHRV3x (no protection). In conclusion, the AttHRV/VLP2x vaccination regimen stimulated the strongest B-cell responses in the intestinal mucosal immune system at challenge and conferred a moderately high protection rate against rotavirus disease, indicating that priming of the mucosal inductive site at the portal of natural infection with a replicating vaccine, followed by boosting with a nonreplicating vaccine at a second mucosal inductive site, may be a highly effective approach to stimulate the mucosal immune system and induce protective immunity against various mucosal pathogens.

Avian-to-mammal transmission of an avian rotavirus: analysis of its pathogenicity in a heterologous mouse model

It has been suggested that group A avian rotaviruses can be transmitted to mammals, but there is no direct evidence that such viruses induce disease in mammals. Suckling mice were orally inoculated with two avian rotaviruses. A pigeon rotavirus, PO-13, was found to induce diarrhea, but a turkey rotavirus, Ty-3, did not. The diarrhea induced by PO-13 was dependent on the age of the mouse. In histopathological examinations, antigens of PO-13 were sporadically detected in absorptive cells in the ileum, and lesions were observed as ballooning degenerations of absorptive cells in a region from the duodenum to the ileum. However, the rotavirus antigen was not detected in the majority of these degenerative cells. These results indicated that PO-13 could infect and induce diarrhea in suckling mice. This is the first evidence of an avian rotavirus being experimentally transmissible to a mammal.

Intranasal administration of 2/6-rotavirus-like particles with mutant Escherichia coli heat-labile toxin (LT-R192G) induces antibody-secreting cell responses but not protective immunity in gnotobiotic pigs

We investigated the immunogenicity of recombinant double-layered rotavirus-like particle (2/6-VLPs) vaccines derived from simian SA11 or human (VP6) Wa and bovine RF (VP2) rotavirus strains. The 2/6-VLPs were administered to gnotobiotic pigs intranasally (i.n.) with a mutant Escherichia coli heat-labile toxin, LT-R192G (mLT), as mucosal adjuvant. Pigs were challenged with virulent Wa (P1A[8],G1) human rotavirus at postinoculation day (PID) 21 (two-dose VLP regimen) or 28 (three-dose VLP regimen). In vivo antigen-activated antibody-secreting cells (ASC) (effector B cells) and in vitro antigen-reactivated ASC (derived from memory B cells) from intestinal and systemic lymphoid tissues (duodenum, ileum, mesenteric lymph nodes [MLN], spleen, peripheral blood lymphocytes [PBL], and bone marrow lymphocytes) collected at selected times were quantitated by enzyme-linked immunospot assays. Rotavirus-specific immunoglobulin M (IgM), IgA, and IgG ASC and memory B-cell responses were detected by PID 21 or 28 in intestinal and systemic lymphoid tissues after i.n. inoculation with two or three doses of 2/6-VLPs with or without mLT. Greater mean numbers of virus-specific ASC and memory B cells in all tissues prechallenge were induced in pigs inoculated with two doses of SA11 2/6-VLPs plus mLT compared to SA11 2/6-VLPs without mLT. After challenge, anamnestic IgA and IgG ASC and memory B-cell responses were detected in intestinal lymphoid tissues of all VLP-inoculated groups, but serum virus-neutralizing antibody titers were not significantly enhanced compared to the challenged controls. Pigs inoculated with Wa-RF 2/6-VLPs (with or without mLT) developed higher anamnestic IgA and IgG ASC responses in ileum after challenge compared to pigs inoculated with SA11 2/6-VLPs (with or without mLT). Three doses of SA 11 2/6-VLP plus mLT induced the highest mean numbers of IgG memory B cells in MLN, spleen, and PBL among all groups postchallenge. However, no significant protection against diarrhea or virus shedding was evident in any of the 2/6-VLP (with or without mLT)-inoculated pigs after challenge with virulent Wa human rotavirus. These results indicate that 2/6-VLP vaccines are immunogenic in gnotobiotic pigs when inoculated i.n. and that the adjuvant mLT enhanced their immunogenicity. However, i.n. inoculation of gnotobiotic pigs with 2/6-VLPs did not confer protection against human rotavirus challenge.

Rotavirus infection impairs intestinal brush-border membrane Na(+)-solute cotransport activities in young rabbits

The mechanism of rotavirus diarrhea was investigated by infecting young, specific pathogen-free, New Zealand rabbits with a lapine rotavirus, strain La/RR510. With 4-wk-old animals, virus shedding into the intestinal lumen peaked at 72 h postinfection (hpi), and a mild, watery diarrhea appeared at 124 hpi. No intestinal lesions were seen up to 144 hpi, indicating that diarrhea does not follow mucosal damage but can precede it, as if cell dysfunction were the cause, not the consequence, of the histological lesions. Kinetic analyses with brush-border membrane vesicles isolated from infected rabbits revealed strong inhibition of both Na(+)-D-glucose (SGLT1) and Na(+)-L-leucine symport activities. For both symporters, only maximum velocity decreased with time. The density of phlorizin-binding sites and SGLT1 protein antigen in the membrane remained unaffected, indicating that the virus effect on this symporter is direct. Because SGLT1 supports water reabsorption under physiological conditions, the mechanism of rotavirus diarrhea may involve a generalized inhibition of Na(+)-solute symport systems, hence, of water reabsorption. Massive water loss through the intestine may eventually overwhelm the capacity of the organ for water reabsorption, thereby helping the diarrhea to get established.

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

Simian rhesus rotavirus (RRV) is the only identified heterologous (non-lapine) rotavirus strain capable of productive replication at a high inoculum dose of virus (>10(8) p.f.u.) in rabbits. To evaluate whether lower doses of RRV would productively infect rabbits and to obtain an estimate of the 50% infectious dose, rotavirus antibody-free rabbits were inoculated orally with RRV at inoculum doses of 10(3), 10(5) or 10(7) p.f.u. Based on faecal virus antigen or infectious virus shedding, RRV replication was observed with inoculum doses of 10(7) and 10(5) p.f.u., but not 10(3) p.f.u. Horizontal transmission of RRV to one of three mock-inoculated rabbits occurred 4-5 days after onset of virus antigen shedding in RRV-infected rabbits. Rabbits infected at 10(7) and 10(5), but not 10(3), p.f.u. of RRV developed rotavirus-specific immune responses and were completely (100%) protected from lapine ALA rotavirus challenge. These data confirm that RRV can replicate productively and spread horizontally in rabbits. In attempts to elucidate the genetic basis of the unusual replication efficacy of RRV in rabbits, the sequence of the gene encoding the lapine non-structural protein NSP1 was determined. Sequence analysis of the NSP1 of three lapine rotaviruses revealed a high degree of amino acid identity (85-88%) with RRV. Since RRV and lapine strains also share similar VP7s (96-97%) and VP4s (69-70%), RRV might replicate efficiently in rabbits because of the high relatedness of these three gene products, each implicated in host range restriction.