Development of a high resolution melting analysis for detection and differentiation of human astroviruses

Simultaneous detection and differentiation of DuCV-1 and DuCV-2 by high-resolution melting analysis

Birds infected with duck circovirus (DuCV) can potentially cause immunosuppression by damaging lymphoid tissues, causing great losses in the duck breeding industry. Duck circovirus can be divided into two genotypes (DuCV-1 and DuCV-2), but simultaneous detection and differentiation of DuCV-1 and DuCV-2 by high-resolution melting (HRM) analysis is still lacking. Here, we designed specific primers according to the sequence characteristics of the newly identified ORF3 gene and then established a PCR-HRM method for the simultaneous detection and differentiation of DuCV-1 and DuCV-2 via high-resolution melting analysis. Our data showed that the established PCR-HRM assay had the advantages of specificity, with the lowest detection limits of 61.9 copies/μL (for DuCV-1) and 60.6 copies/μL (for DuCV-2). The melting curve of the PCR-HRM results indicated that the amplification product was specific, with no cross-reaction with common waterfowl origin pathogens and a low coefficient of variation less than 1.50% in both intra-batch and inter-batch repetitions, indicating the advantages of repeatability. We found that the percentage of DuCV-2-positive ducks was higher than that of DuCV-1-positive ducks, with 8.62% rate of DuCV-1 and DuCV-2 coinfection. In addition, we found DuCV-2-positive in geese firstly. In conclusion, this study provides a candidate PCR-HRM assay for the detection and accurate differentiation of DuCV-1 and DuCV-2 infection, which will help us for further epidemiological surveillance of DuCVs.

Discrimination of human papillomavirus genotypes using innovative technique nested-high resolution melting

The prompt detection of human papillomavirus and discrimination of its genotypes by combining conventional methods in new molecular laboratories is essential to achieve the global call of eliminating cervical cancer. After predicting the melting temperature of an approximately 221 bp region of the L1 gene from different HPV genotypes by bioinformatics software, an innovative technique based on the nested- high resolution melting was designed with three approaches and using conventional PCR, qPCR, and diagnostic standards. HPV-positive samples identified by microarray along with diagnostic standards were evaluated by qPCR-HRM and discordant results were subjected to sequencing and analyzed in silico using reference types. In addition to screening for human papillomavirus, nested-qPCR-HRM is one of the modified HRM techniques which can discriminate some genotypes, including 6, 16, 18, 52, 59, 68 and 89. Despite the differences in diagnostic capabilities among HRM, microarray and sequencing, a number of similarities between HRM, and sequencing were diagnostically identified as the gold standard method. However, the bioinformatics analysis and melting temperature studies of the selected region in different HPV genotypes showed that it could be predicted. With numerous HPV genotypes and significant genetic diversity among them, determining the virus genotype is important. Therefore, our goal in this design was to use the specific molecular techniques with several specific primers to increase sensitivity and specificity for discriminating a wide range of HPV genotypes. This approach led to new findings to evaluate the ability of different approaches and procedures in accordance with bioinformatics.

Emergence of Multiple Novel Inter-Genotype Recombinant Strains of Human Astroviruses Detected in Pediatric Patients With Acute Gastroenteritis in Thailand

Objective: Human astrovirus (HAstV) is recognized as an important cause of acute gastroenteritis in children. Recombination between different genotypes of HAstV can contribute to diversity and evolution of the virus. This study aimed to investigate the emergence of HAstV recombinant strains in pediatric patients hospitalized with acute gastroenteritis in Chiang Mai, Thailand, spanning 2011–2020.

Methods: A total of 92 archival HAstV strains collected from pediatric patients with acute gastroenteritis during 2011–2020 were further characterized to identify the recombinant strains. The ORF1b and ORF2 junction region of each strain was amplified and sequenced. The obtained sequences were analyzed in comparison with the reference sequences retrieved from GenBank database. Their genotypes were assigned using MEGA X software based on the partial ORF1b (RdRp) and ORF2 (capsid) regions, and the recombination breakpoints of recombinant strains were determined by SimPlot and RDP4 analyses.

Results: Five inter-genotype recombinant strains with three recombination patterns of ORF1b/ORF2 of classic HAstV, HAstV8/HAstV1, HAstV8/HAstV3, and HAstV3/HAstV2, were detected. The recombination breakpoints of all strains were located at the 3′-end region of ORF1b close to the ORF1b/ORF2 junction.

Conclusion: Several novel inter-genotype recombinant strains of classic HAstV genotypes were detected in pediatric patients with acute gastroenteritis in Chiang Mai, Thailand, during the period of 10 years from 2011 to 2020.

An HRM Assay to Differentiate Sheeppox Virus Vaccine Strains from Sheeppox Virus Field Isolates and other Capripoxvirus Species

Sheep poxvirus (SPPV), goat poxvirus (GTPV) and lumpy skin disease virus (LSDV) affect small ruminants and cattle causing sheeppox (SPP), goatpox (GTP) and lumpy skin disease (LSD) respectively. In endemic areas, vaccination with live attenuated vaccines derived from SPPV, GTPV or LSDV provides protection from SPP and GTP. As live poxviruses may cause adverse reactions in vaccinated animals, it is imperative to develop new diagnostic tools for the differentiation of SPPV field strains from attenuated vaccine strains. Within the capripoxvirus (CaPV) homolog of the variola virus B22R gene, we identified a unique region in SPPV vaccines with two deletions of 21 and 27 nucleotides and developed a High-Resolution Melting (HRM)-based assay. The HRM assay produces four distinct melting peaks, enabling the differentiation between SPPV vaccines, SPPV field isolates, GTPV and LSDV. This HRM assay is sensitive, specific, and provides a cost-effective means for the detection and classification of CaPVs and the differentiation of SPPV vaccines from SPPV field isolates.

Next-generation amplicon sequencing identifies genetically diverse human astroviruses, including recombinant strains, in environmental waters

Human astroviruses are associated with gastroenteritis and known to contaminate water environments. Three different genetic clades of astroviruses are known to infect humans and each clade consists of diverse strains. This study aimed to determine the occurrence and genetic diversity of astrovirus strains in water samples in different geographical locations, i.e., influent and effluent wastewater samples (n = 24 each) in Arizona, U.S., and groundwater (n = 37) and river water (n = 14) samples collected in the Kathmandu Valley, Nepal, using next-generation amplicon sequencing. Astrovirus strains including rare types (types 6 and 7 classical human astroviruses), emerging type (type 5 VA-astroviruses), and putative recombinants were identified. Feline astrovirus strains were collaterally identified and recombination between human and feline astroviruses was suggested. Classical- and VA-astroviruses seemed to be prevalent during cooler months, while MLB-astroviruses were identified only during warmer months. This study demonstrated the effectiveness of next-generation amplicon sequencing for identification and characterization of genetically diverse astrovirus strains in environmental water.

A novel HRM assay for the simultaneous detection and differentiation of eight poxviruses of medical and veterinary importance

Poxviruses belonging to the Orthopoxvirus, Capripoxvirus and Parapoxvirus genera share common host species and create a challenge for diagnosis. Here, we developed a novel multiplex PCR method for the simultaneous detection and differentiation of eight poxviruses, belonging to three genera: cowpox virus (CPXV) and camelpox virus (CMLV) [genus Orthopoxvirus]; goatpox virus (GTPV), sheeppox virus (SPPV) and lumpy skin disease virus (LSDV) [genus Capripoxvirus]; orf virus (ORFV), pseudocowpox virus (PCPV) and bovine papular stomatitis virus (BPSV) [genus Parapoxvirus]. The assay is based on high-resolution melting curve analysis (HRMCA) of PCR amplicons produced using genus specific primer pairs and dsDNA binding dye. Differences in fragment size and GC content were used as discriminating power. The assay generated three well separated melting regions for each genus and provided additional intra-genus genotyping allowing the differentiation of the eight poxviruses based on amplicon melting temperature. Out of 271 poxviral DNA samples tested: seven CPXV, 25 CMLV, 42 GTPV, 20 SPPV, 120 LSDV, 33 ORFV, 20 PCPV and two BPSV were detected; two samples presented co-infection with CMLV and PCPV. The assay provides a rapid, sensitive, specific and cost-effective method for the detection of pox diseases in a broad range of animal species and humans.

A comparison of PCR assays for beak and feather disease virus and high resolution melt (HRM) curve analysis of replicase associated protein and capsid genes

Beak and feather disease virus (BFDV) threatens a wide range of endangered psittacine birds worldwide. In this study, we assessed a novel PCR assay and genetic screening method using high-resolution melt (HRM) curve analysis for BFDV targeting the capsid (Cap) gene (HRM-Cap) alongside conventional PCR detection as well as a PCR method that targets a much smaller fragment of the virus genome in the replicase initiator protein (Rep) gene (HRM-Rep). Limits of detection, sensitivity, specificity and discriminatory power for differentiating BFDV sequences were compared. HRM-Cap had a high positive predictive value and could readily differentiate between a reference genotype and 17 other diverse BFDV genomes with more discriminatory power (genotype confidence percentage) than HRM-Rep. Melt curve profiles generated by HRM-Cap correlated with unique DNA sequence profiles for each individual test genome. The limit of detection of HRM-Cap was lower (2×10^-5ng/reaction or 48 viral copies) than that for both HRM-Rep and conventional BFDV PCR which had similar sensitivity (2×10^-6ng or 13 viral copies/reaction). However, when used in a diagnostic setting with 348 clinical samples there was strong agreement between HRM-Cap and conventional PCR (kappa=0.87, P<0.01, 98% specificity) and HRM-Cap demonstrated higher specificity (99.9%) than HRM-Rep (80.3%).

Wastewater Analysis Indicates that Genetically Diverse Astroviruses, Including Strains Belonging to Novel Clades MLB and VA, Are Circulating within Japanese Populations

Human astroviruses (HAstVs) are a common etiological agent of infantile gastroenteritis. Recent studies revealed that novel astrovirus (AstV) strains of the MLB clade (MLB-AstVs) and VA clade (VA-AstVs), which are genetically distinct from the classic HAstVs, are circulating in the human population. In the present study, we quantified classic HAstVs as well as carried out a genetic analysis of classic and novel HAstVs in wastewater in Japan. The concentration of classic HAstVs in the influent water samples ranged from 10(4) to 10(5) copies per liter, and the amount removed by wastewater treatment was determined to be 2.4 ± 0.3 log10. Four types of classic HAstV strains (HAstV types 1, 2, 5, and 4/8) as well as novel AstV strains belonging to the MLB-2, VA-1, and VA-2 clades were identified using reverse transcription-PCR (RT-PCR) assays, including assays newly developed for the detection of strains of the MLB and VA clades, followed by cloning and nucleotide sequencing. Our results suggest that genetically diverse AstV strains are circulating among the human population in Japan. The newly developed (semi)nested RT-PCR assays for these novel AstV clades are useful to identify and characterize the novel AstVs in environmental waters.