In this paper published in the Journal of Veterinary Diagnostic Investigation, PhD-candidate Talita Resende from Dr. Vannucci’s lab, shares a novel diagnostic technique to detect various rotavirus species using newly developed markers.Continue reading “A new diagnostic test to differentiate rotavirus subtypes”
Our first publication of the year features the work of Frances Shepherd, a PhD student (who recently received an award at the CRWAD meeting) with Drs. Michael Murtaugh and Douglas Marthaler. The paper is in open access in the journal Pathogens and you can read it here.
In this experiment, 174 clinical samples from US and Canadian swine herds and positive for rotavirus B by PCR were used to sequence the gene for the protein VP7.
VP7 is a protein of interest in rotaviruses B because it is structural and can be found on the outer layer of the virus capsid. Along with VP4, they stimulate the creation of neutralizing antibodies in pigs.
Based on those sequences, 169 of the viruses were allocated to 8 defined genotypes: G8, G11, G12, G14, G16, G17, G18, and G20. However, five strains had less than 80% similarity with those genotypes and were assigned to the new genotypes G22, G23 (2 strains), G24, and G25. The G16 genotype was the most prevalent genotype each year. The predominant genotypes clustered geographically, with G12 being predominant on the east coast, G16 in the Midwest, and G20 within the Great Plains states.
Investigation of the variability within the VP7 proteins identified 8 variable regions. However, those regions did not align with the sites of high antigenicity detected in the predominant groups. Indeed, surface-exposed antigenic residues underwent negative selection more often than positive selection.
Rotavirus B (RVB) is an important swine pathogen, but control and prevention strategies are limited without an available vaccine. To develop a subunit RVB vaccine with maximal effect, we characterized the amino acid sequence variability and predicted antigenicity of RVB viral protein 7 (VP7), a major neutralizing antibody target, from clinically infected pigs in the United States and Canada. We identified genotype-specific antigenic sites that may be antibody neutralization targets. While some antigenic sites had high amino acid functional group diversity, nine antigenic sites were completely conserved. Analysis of nucleotide substitution rates at amino acid sites (dN/dS) suggested that negative selection appeared to be playing a larger role in the evolution of the identified antigenic sites when compared to positive selection, and was identified in six of the nine conserved antigenic sites. These results identified important characteristics of RVB VP7 variability and evolution and suggest antigenic residues on RVB VP7 that are negatively selected and highly conserved may be good candidate regions to include in a subunit vaccine design due to their tendency to remain stable.
Rotaviruses A are genetically diverse.
Rotaviruses are responsible for increased mortality in neonatal swine populations. They are different genetically and more studies are needed to characterize their diversity. This is the objective of this study coordinated by Dr. Marthaler’s lab focusing on rotaviruses strains found in Canada.
Viral proteins 7 and 4 are used for rotavirus A classification.
Rotaviruses are classified based on two viral proteins (VP) found on their outer capsid called respectively VP7 and VP4. Those two proteins are also essential to induce an efficient immune response against the virus. This project characterized VP7 and VP4 sequences in 136 Canadian samples and compared them with the strains used in a rotavirus commercial vaccine.
The VP7 (n=32) and partial VP4 (n=25) were analyzed, identifying the G3P, G5P, G5P[x], G9P, G9P, G9P, and G9P[x] genotypes.
Minimal differences in the antigenic epitopes for the G5, G9, and P strains were identified.
Major differences in the antigenic epitopes of the G3, P, and P may question the effectiveness of the ProSystems RCE RVA.
Surveillance of Rotavirus A (RVA) infections in North America swine populations are limited and not performed over a significant time period to properly assess the diversity of RVA strains in swine. The VP7 (G) and VP4 (P) genes of 32 Canadian RVA strains, circulating between 2009 and 2015 were sequenced, identifying the G3P, G5P, G9P, G9, and G9 genotype combinations. The Canadian RVA strains were compared to the RVA strains present in the swine ProSystems RCE rotavirus vaccine. The comparison revealed multiple amino acid differences in the G and P antigenic epitopes, regardless of the G and P genotypes but specifically in the Canadian G3, P and P genotypes. Our study further contributes to the characterization of RVA’s evolution and disease mitigation among swine, which may optimize target vaccine design, thereby minimizing RVA disease in this economically important animal population.
Our graduate students did a fantastic job at the 24th IPVS and we would like to congratulate them all for their hard work. Among them, Dr. Talita Resende won the IPVS award for best poster. Talita is a PhD candidate at the University of Minnesota under the supervision of Dr. Fabio Vannucci and she presented a poster on A novel diagnostic platform for in situ detection and subtyping of Rotaviruses and Influenza A in pigs.
A scientific paper published today in PLOS ONE reveals that based on three-level mixed-effects logistic regression models, the epidemiology of swine rotaviruses in North America is quite complex. The goal of the study led by Drs. Homwong, Perez, Rossow, and Marthaler from the University of Minnesota was to investigate the associations among age, rotavirus detection, and regions within the US swine production in samples submitted for diagnosis to the Minnesota Veterinary Diagnostic Laboratory.
Percentages of Rotavirus A (RVA), Rotavirus B (RVB), and Rotavirus C (RVC) samples by state. The color represented highest prevalence of the RV species (green represents RVA, purple represents RVB, blue represents RVC while pink represents equal percentages of RVA and RVC
Abstract: Rotaviruses (RV) are important causes of diarrhea in animals, especially in domestic animals. Of the 9 RV species, rotavirus A, B, and C (RVA, RVB, and RVC, respectively) had been established as important causes of diarrhea in pigs. The Minnesota Veterinary Diagnostic Laboratory receives swine stool samples from North America to determine the etiologic agents of disease. Between November 2009 and October 2011, 7,508 samples from pigs with diarrhea were submitted to determine if enteric pathogens, including RV, were present in the samples. All samples were tested for RVA, RVB, and RVC by real time RT-PCR. The majority of the samples (82%) were positive for RVA, RVB, and/or RVC. To better understand the risk factors associated with RV infections in swine diagnostic samples, three-level mixed-effects logistic regression models (3L-MLMs) were used to estimate associations among RV species, age, and geographical variability within the major swine production regions in North America. The conditional odds ratios (cORs) for RVA and RVB detection were lower for 1–3 day old pigs when compared to any other age group. However, the cOR of RVC detection in 1–3 day old pigs was significantly higher (p < 0.001) than pigs in the 4–20 days old and >55 day old age groups. Furthermore, pigs in the 21–55 day old age group had statistically higher cORs of RV co-detection compared to 1–3 day old pigs (p < 0.001). The 3L-MLMs indicated that RV status was more similar within states than among states or within each region. Our results indicated that 3L-MLMs are a powerful and adaptable tool to handle and analyze large-hierarchical datasets. In addition, our results indicated that, overall, swine RV epidemiology is complex, and RV species are associated with different age groups and vary by regions in North America.