A variant serotype G3 rotavirus isolated from an unusually severe outbreak of diarrhoea in piglets

Detection and genetic diversity of porcine rotavirus A, B and C in eastern Australian piggeries

Rotaviruses (RV) have a high prevalence in piggeries worldwide and are one of the major pathogens causing severe diarrhoea in young pigs. RV species A, B, and C have been linked to piglet diarrhoea in Australian pig herds, but their genetic diversity has not been studied in detail. Based on sequencing of the structural viral protein 7 (VP7) RVA G genotypes G3, G4 and G5, and RVC types G1, G3, G5, and G6 have been identified in Australian piggeries in previous studies. Although occurrence of RVB was reported in Australia in 1988, no further genetic analysis has been conducted. To improve health management decisions in Australian pig herds, more information on RV prevalence and genetic diversity is needed. Here, 243 enteric samples collected from 20 pig farms within Eastern Australia were analysed for the presence of RV in different age groups using a novel PCR-based multiplex assay (Pork MultiPath™ enteric panel). RVA, RVB, and RVC were detected in 10, 14, and 14 farms, respectively. Further sequencing of VP7 in selected RV-positive samples revealed G genotypes G2, G5, G9 (RVA), G6, G8, G14, G16, G20 (RVB), and G1, G3, G5, G6 (RVC) present. RVA was only detected in young (<10 weeks old) pigs whereas RVB and RVC were also detected in older animals (>11 weeks old). Interestingly, RVB and RVC G-type occurrence differed between age groups. In conclusion, this study provides new insights on the prevalence and diversity of different RV species in pig herds of Eastern Australia whilst demonstrating the ability of the Pork MultiPath™ technology to accurately differentiate between these RV species.

Outbreak of diarrhoea in piglets caused by novel rotavirus genotype G4P[49] in north-western district of Bangladesh, February 2014

Group A rotavirus (RVA) associated diarrhoea in piglets represents one of the major causes of morbidity and mortality in pig farms worldwide. A diarrhoea outbreak occurred among nomadic piglets in north-western district of Bangladesh in February 2014. Outbreak investigation was performed to identify the cause, epidemiologic and clinical features of the outbreak. Rectal swabs and clinical information were collected from diarrhoeic piglets (n = 36). Rectal swabs were tested for RVA RNA by real-time reverse transcription polymerase chain reaction (rRT-PCR) using NSP3-specific primers. The G (VP7) and P (VP4) genes were typed by conventional RT-PCR and sanger sequencing and full genome sequences were determined using next-generation sequencing. We found the attack rate was 61% (50/82) among piglets in the nomadic pig herd, and the case fatality rate was 20% (10/50) among piglets with diarrhoea. All study piglets cases had watery diarrhoea, lack of appetite or reluctance to move. A novel RVA strain with a new P[49] genotype combined with G4 was identified among all piglets with diarrhoea. The genome constellation of the novel RVA strains was determined to be G4-P[49]-I1-R1-C1-M1-A8-N1-T7-E1-H1. Genetic analysis shows that the novel G4P[49] strain is similar to Indian and Chinese porcine or porcine-like G4 human strains and is genetically distant from Bangladeshi human G4 strains. Identification of this novel RVA strain warrants further exploration for disease severity and zoonotic potential.

Porcine Rotaviruses: Epidemiology, Immune Responses and Control Strategies

Rotaviruses (RVs) are a major cause of acute viral gastroenteritis in young animals and children worldwide. Immunocompetent adults of different species become resistant to clinical disease due to post-infection immunity, immune system maturation and gut physiological changes. Of the 9 RV genogroups (A–I), RV A, B, and C (RVA, RVB, and RVC, respectively) are associated with diarrhea in piglets. Although discovered decades ago, porcine genogroup E RVs (RVE) are uncommon and their pathogenesis is not studied well. The presence of porcine RV H (RVH), a newly defined distinct genogroup, was recently confirmed in diarrheic pigs in Japan, Brazil, and the US. The complex epidemiology, pathogenicity and high genetic diversity of porcine RVAs are widely recognized and well-studied. More recent data show a significant genetic diversity based on the VP7 gene analysis of RVB and C strains in pigs. In this review, we will summarize previous and recent research to provide insights on historic and current prevalence and genetic diversity of porcine RVs in different geographic regions and production systems. We will also provide a brief overview of immune responses to porcine RVs, available control strategies and zoonotic potential of different RV genotypes. An improved understanding of the above parameters may lead to the development of more optimal strategies to manage RV diarrheal disease in swine and humans.

An outbreak of diarrhoea in one-week-old piglets caused by group A rotavirus genotypes P[7],G3 and P[7],G5

Thirty-two group A isolates of rotavirus detected in faecal samples from diarrhoeic piglets, were selected for P and G genotyping using a Multiplex RT-PCR. Ten isolates, from animals less than 8 days old, characterized an outbreak of diarrhoea caused by group A rotavirus in animals. P[7],G3 (CRW8-like) and P[7],G5 (OSU-like) genotypes were detected in 5 animals each. Isolates of a group A rotavirus of genotypes compatible with the OSU prototype were those most frequently identified in single infections in older animals (20/32 strains). In addition to these, 20 isolates from piglets with diarrhoea caused by group A rotavirus, collected between May 1998 and June 1999, but not from the outbreak month, were analysed. These isolates were used to compare the types observed on the farm outside the outbreak in May 1999 and the CRW8-like genotype was found in none of these faecal samples. P[7],G5 was the most frequent genotype (10/20 strains). No outbreak of diarrhoea caused by rotavirus in 1-week-old piglets was found in any other period during the 13 months of this study.

Survey of porcine rotavirus G and P genotype in Poland and the United States using RT-PCR

Porcine rotaviruses are a common cause of gastroenteritis. Several serotypes have been detected based on the two surface proteins VP4 (P-types) and VP7 (G-types). However, limited studies have been performed on the relative frequency of rotavirus types in diarrhetic pigs primarily because of the lack of availability of suitable methods. In this study, we describe a reverse transcriptase-polymerase chain reaction (RT-PCR) method for the typing of P and G types of rotavirus. This method allowed to detect G and P types in 96.8 and 87.1% of isolates collected in the United States, respectively and in 54.5 and 38.6% of isolates collected in Poland, respectively. Within the US specimens the G3, G4, G5, G9 and G10 types were detected in combination with P6 and P7 types while among Polish specimens only G3, G4 and G5 types in combination with P6 and P7 types were identified. In both instances the G4 and G5 were the most prevalent types. These studies show that a RT-PCR typing method is suitable for molecular epidemiological studies and that there is more diversity among porcine rotavirus than previously reported.

Nucleotide sequence variation of the VP7 gene of two G3-type rotaviruses isolated from dogs

The sequence of the VP7 gene of two rotaviruses isolated from dogs in southern Italy was determined and the inferred amino acid sequence was compared with that of other rotavirus strains. There was very high nucleotide and amino acid identity between canine strain RV198/95 and other canine strains, and to the human strain HCR3A. Strain RV52/96, however, was found to have about 95% identity to the G3 serotype canine strains K9, A79-10 and CU-1 and 96% identity to strain RV198/95 and to the simian strain RRV. Therefore both of the canine strains belong to the G3 serotype. Nevertheless, detailed analysis of the VP7 variable regions revealed that RV52/96 possesses amino acid substitutions uncommon to the other canine isolates. In addition, strain RV52/96 exhibited a nucleotide divergence greater than 16% from all the other canine strains studied; however, it revealed the closest identity (90.4%) to the simian strain RRV. With only a few exceptions, phylogenetic analysis allowed clear differentiation of the G3 rotaviruses on the basis of the species of origin. The nucleotide and amino acid variations observed in strain RV52/96 could account for the existence of a canine rotavirus G3 sub-type.

Single point mutations may affect the serotype reactivity of serotype G11 porcine rotavirus strains: a widening spectrum?

A panel of single and double neutralization-resistant escape mutants of serotype G11 porcine rotavirus strains A253 and YM, selected with G11 monotype- and serotype-specific neutralizing monoclonal antibodies (MAbs) to VP7, was tested in neutralization assays with hyperimmune sera raised against rotavirus strains of different serotypes. Escape mutants with an amino acid substitution in antigenic region A (amino acids [aa] 87 to 101) resulting in a residue identical or chemically similar to those present at the same positions in serotype G3 strains, at positions 87 for strain A253 and 96 for strain YM, were significantly more sensitive than the parental strains to neutralization with sera against some serotype G3 strains. Also, one YM antigenic variant (YM-5E6.1) acquired reactivity by enzyme-linked immunosorbent assay with MAbs 159, 57/8, and YO-1E2, which react with G3 strains, but not with the serotype G11 parental strain YM. Cross-adsorption studies suggested that the observed cross-neutralization by the G3-specific sera was due to the sera containing antibodies reactive with the parental strain plus antibodies reactive with the epitope(s) on the antigenic variant that mimick the serotype G3 specific one(s). Moreover, antibodies reactive with antigenic region F (aa 235 to 242) of VP7 might also be involved since cross-reactivity to serotype G3 was decreased in double mutants carrying an additional mutation, which creates a potential glycosylation site at position 238. Thus, single point mutations can affect the serotype reactivity of G11 porcine rotavirus strains with both monoclonal and polyclonal antibodies and may explain the origin of rotavirus strains with dual serotype specificity based on sequence divergence of VP7.

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

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

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.

Comparative amino acid sequence analysis of the major outer capsid protein (VP7) of porcine rotaviruses with G3 and G5 serotype specificities isolated in Venezuela and Argentina

Seven porcine group A rotavirus strains isolated in Venezuela were shown to be antigenically related to serotype G3 (five strains) or to serotype G5 (two strains), whereas two strains isolated in Argentina were classified as serotype G5. The serological classification of eight of these strains was confirmed by sequence analysis of the gene encoding the VP7 glycoprotein. A high degree of homology was observed among strains belonging to the same G serotype, although some variations in the serotype-specific regions were detected among different strains. Comparison with the published VP7 amino acid sequences of serotype G3 indicated that most porcine rotavirus strains are more closely related to each other and to human rotavirus strains than to rotavirus strains isolated from other species. Amino acid sequence comparison among serotype G5 porcine strains revealed that Venezuelan porcine isolates were more closely related to the American strain OSU, while the Argentinian strains had a higher similarity to the Australian strain TRF-41. This report confirms the worldwide distribution of these G serotypes among the porcine population.