Weifeng Shi

Origin and diversity of novel avian influenza A H7N9 viruses causing human infection: phylogenetic, structural, and coalescent analyses

BACKGROUND On March 30, 2013, a novel avian influenza A H7N9 virus that infects human beings was identified. This virus had been detected in six provinces and municipal cities in China as of April 18, 2013. We correlated genomic sequences from avian influenza viruses with ecological information and did phylogenetic and coalescent analyses to extrapolate the potential origins of the virus and possible routes of reassortment events. METHODS We downloaded H7N9 virus genome sequences from the Global Initiative on Sharing Avian Influenza Data (GISAID) database and public sequences used from the Influenza Virus Resource. We constructed phylogenetic trees and did 1000 bootstrap replicates for each tree. Two rounds of phylogenetic analyses were done. We used at least 100 closely related sequences for each gene to infer the overall topology, removed suspicious sequences from the trees, and focused on the closest clades to the novel H7N9 viruses. We compared our tree topologies with those from a bayesian evolutionary analysis by sampling trees (BEAST) analysis. We used the bayesian Markov chain Monte Carlo method to jointly estimate phylogenies, divergence times, and other evolutionary parameters for all eight gene fragments. We used sequence alignment and homology-modelling methods to study specific mutations regarding phenotypes, specifically addressing the human receptor binding properties. FINDINGS The novel avian influenza A H7N9 virus originated from multiple reassortment events. The HA gene might have originated from avian influenza viruses of duck origin, and the NA gene might have transferred from migratory birds infected with avian influenza viruses along the east Asian flyway. The six internal genes of this virus probably originated from two different groups of H9N2 avian influenza viruses, which were isolated from chickens. Detailed analyses also showed that ducks and chickens probably acted as the intermediate hosts leading to the emergence of this virulent H7N9 virus. Genotypic and potential phenotypic differences imply that the isolates causing this outbreak form two separate subclades. INTERPRETATION The novel avian influenza A H7N9 virus might have evolved from at least four origins. Diversity among isolates implies that the H7N9 virus has evolved into at least two different lineages. Unknown intermediate hosts involved might be implicated, extensive global surveillance is needed, and domestic-poultry-to-person transmission should be closely watched in the future. FUNDING China Ministry of Science and Technology Project 973, National Natural Science Foundation of China, China Health and Family Planning Commission, Chinese Academy of Sciences.

Performance of criteria for selecting evolutionary models in phylogenetics: a comprehensive study based on simulated datasets.

BackgroundExplicit evolutionary models are required in maximum-likelihood and Bayesian inference, the two methods that are overwhelmingly used in phylogenetic studies of DNA sequence data. Appropriate selection of nucleotide substitution models is important because the use of incorrect models can mislead phylogenetic inference. To better understand the performance of different model-selection criteria, we used 33,600 simulated data sets to analyse the accuracy, precision, dissimilarity, and biases of the hierarchical likelihood-ratio test, Akaike information criterion, Bayesian information criterion, and decision theory.ResultsWe demonstrate that the Bayesian information criterion and decision theory are the most appropriate model-selection criteria because of their high accuracy and precision. Our results also indicate that in some situations different models are selected by different criteria for the same dataset. Such dissimilarity was the highest between the hierarchical likelihood-ratio test and Akaike information criterion, and lowest between the Bayesian information criterion and decision theory. The hierarchical likelihood-ratio test performed poorly when the true model included a proportion of invariable sites, while the Bayesian information criterion and decision theory generally exhibited similar performance to each other.ConclusionsOur results indicate that the Bayesian information criterion and decision theory should be preferred for model selection. Together with model-adequacy tests, accurate model selection will serve to improve the reliability of phylogenetic inference and related analyses.

Genetic diversity and evolutionary dynamics of Ebola virus in Sierra Leone

A novel Ebola virus (EBOV) first identified in March 2014 has infected more than 25,000 people in West Africa, resulting in more than 10,000 deaths. Preliminary analyses of genome sequences of 81 EBOV collected from March to June 2014 from Guinea and Sierra Leone suggest that the 2014 EBOV originated from an independent transmission event from its natural reservoir followed by sustained human-to-human infections. It has been reported that the EBOV genome variation might have an effect on the efficacy of sequence-based virus detection and candidate therapeutics. However, only limited viral information has been available since July 2014, when the outbreak entered a rapid growth phase. Here we describe 175 full-length EBOV genome sequences from five severely stricken districts in Sierra Leone from 28 September to 11 November 2014. We found that the 2014 EBOV has become more phylogenetically and genetically diverse from July to November 2014, characterized by the emergence of multiple novel lineages. The substitution rate for the 2014 EBOV was estimated to be 1.23 × 10−3 substitutions per site per year (95% highest posterior density interval, 1.04 × 10−3 to 1.41 × 10−3 substitutions per site per year), approximating to that observed between previous EBOV outbreaks. The sharp increase in genetic diversity of the 2014 EBOV warrants extensive EBOV surveillance in Sierra Leone, Guinea and Liberia to better understand the viral evolution and transmission dynamics of the ongoing outbreak. These data will facilitate the international efforts to develop vaccines and therapeutics.

Dynamic reassortments and genetic heterogeneity of the human-infecting influenza A (H7N9) virus

Influenza A (H7N9) virus has been causing human infections in China since February 2013, raising serious concerns of potential pandemics. Previous studies demonstrate that human infection is directly linked to live animal markets, and that the internal genes of the virus are derived from H9N2 viruses circulating in the Yangtze River Delta area in Eastern China. Here following analysis of 109 viruses, we show a much higher genetic heterogeneity of the H7N9 viruses than previously reported, with a total of 27 newly designated genotypes. Phylogenetic and genealogical inferences reveal that genotypes G0 and G2.6 dominantly co-circulate within poultry, with most human isolates belonging to the genotype G0. G0 viruses are also responsible for the inter- and intra-province transmissions, leading to the genesis of novel genotypes. These observations suggest the province-specific H9N2 virus gene pools increase the genetic diversity of H7N9 via dynamic reassortments and also imply that G0 has not gained overwhelming fitness and the virus continues to undergo reassortment.

Two novel reassortants of avian influenza A (H5N6) virus in China.

Eight avian influenza A (H5N6) viruses were isolated from live poultry markets (LPMs) in Sichuan and Jiangxi Provinces in China in 2014, including those close to the county where the human H5N6 infection occurred. Genetic and phylogenetic analyses revealed that these H5N6 viruses were novel reassortants between H5N1 clade 2.3.4 and H6N6 viruses, and had evolved into two distinct lineages (Sichuan and Jiangxi). Moreover, the human H5N6 virus was closely related to the avian-source viruses of Sichuan lineage. Notably, H5N6 viruses contained a T160A substitution in the haemagglutinin protein and an 11 aa deletion in the neuraminidase stalk, which may aid in enhancing viral affinity for human-like receptors and virulence in mammals. As the H5N1 virus infects humans through direct contact, infection with the novel H5N6 virus raised significant concerns that the H5 subtype was a likely candidate for a pandemic. Therefore, extensive and long-term surveillance of avian influenza viruses in LPMs is essential.

Origin and molecular characterization of the human-infecting H6N1 influenza virus in Taiwan

In June 2013, the first human H6N1 influenza virus infection was confirmed in Taiwan. However, the origin and molecular characterization of this virus, A/Taiwan/2/2013 (H6N1), have not been well studied thus far. In the present report, we performed phylogenetic and coalescent analyses of this virus and compared its molecular profile/characteristics with other closely related strains. Molecular characterization of H6N1 revealed that it is a typical avian influenza virus of low pathogenicity, which might not replicate and propagate well in the upper airway in mammals. Phylogenetic analysis revealed that the virus clusters with A/chicken/Taiwan/A2837/2013 (H6N1) in seven genes, except PB1. For the PB1 gene, A/Taiwan/2/2013 was clustered with a different H6N1 lineage from A/chicken/Taiwan/ A2837/2013. Although a previous study demonstrated that the PB2, PA, and M genes of A/Taiwan/2/2013 might be derived from the H5N2 viruses, coalescent analyses revealed that these H5N2 viruses were derived from more recent strains than that of the ancestor of A/Taiwan/2/2013. Therefore, we propose that A/Taiwan/2/2013 is a reassortant from different H6N1 lineages circulating in chickens in Taiwan. Furthermore, compared to avian isolates, a single P186L (H3 numbering) substitution in the hemagglutinin H6 of the human isolate might increase the mammalian receptor binding and, hence, this strain’s pathogenicity in humans. Overall, human infection with this virus seems an accidental event and is unlikely to cause an influenza pandemic. However, its co-circulation and potential reassortment with other influenza subtypes are still worthy of attention.

Epidemiology, Genetic Recombination, and Pathogenesis of Coronaviruses

Human coronaviruses (HCoVs) were first described in the 1960s for patients with the common cold. Since then, more HCoVs have been discovered, including those that cause severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), two pathogens that, upon infection, can cause fatal respiratory disease in humans. It was recently discovered that dromedary camels in Saudi Arabia harbor three different HCoV species, including a dominant MERS HCoV lineage that was responsible for the outbreaks in the Middle East and South Korea during 2015. In this review we aim to compare and contrast the different HCoVs with regard to epidemiology and pathogenesis, in addition to the virus evolution and recombination events which have, on occasion, resulted in outbreaks amongst humans.

Sequence embedding for fast construction of guide trees for multiple sequence alignment

BackgroundThe most widely used multiple sequence alignment methods require sequences to be clustered as an initial step. Most sequence clustering methods require a full distance matrix to be computed between all pairs of sequences. This requires memory and time proportional to N2 for N sequences. When N grows larger than 10,000 or so, this becomes increasingly prohibitive and can form a significant barrier to carrying out very large multiple alignments.ResultsIn this paper, we have tested variations on a class of embedding methods that have been designed for clustering large numbers of complex objects where the individual distance calculations are expensive. These methods involve embedding the sequences in a space where the similarities within a set of sequences can be closely approximated without having to compute all pair-wise distances.ConclusionsWe show how this approach greatly reduces computation time and memory requirements for clustering large numbers of sequences and demonstrate the quality of the clusterings by benchmarking them as guide trees for multiple alignment. Source code is available for download from http://www.clustal.org/mbed.tgz.

Poultry carrying H9N2 act as incubators for novel human avian influenza viruses

www.thelancet.com Vol 383 March 8, 2014 869 1 Chinese Center for Disease Control and Prevention. Weekly updates human infection with avian infl uenza A(H7N9) virus in China . http://www.chinacdc.cn/en/ (accessed Feb 11, 2014). 2 Chen H, Yuan H, Gao R, et al. Clinical and epidemiological characteristics of a fatal case of avian infl uenza A H10N8 virus infection: a descriptive study. Lancet 2014; published online Feb 5. DOI: 10.1016/S01406736(14)60111-2. 3 Liu D, Shi W, Shi Y, et al. Origin and diversity of novel avian infl uenza A H7N9 viruses causing human infection: phylogenetic, structural, and coalescent analyses. Lancet 2013; 381: 1926–32. 4 Shi W, Li W, Li X, et al. Phylogenetics of varied subtypes of avian infl uenza viruses in China: potential threat to humans. Protein Cell (in press). 5 Cui L, Liu D, Shi W, et al. Dynamic reassortments and genetic heterogeneity of the human-infecting infl uenza A (H7N9) virus. Nat Commun 2014; 5: 3142. Both H7N9 and H10N8 viruses possess internal gene cassettes recruited from poultry H9N2 virus. Long-term surveillance of poultry in China and east Asia shows that H9N2 virus is widely spread. Phylogenetics analyses suggest that diff erent subtypes of avian infl uenza viruses cocirculated with H9N2 and have reassorted their internal genes (fi gure). Although the contribution of H9N2 genes to infection in human beings needs to be determined, these genes probably enable H7N9 virus to survive and be transmitted within poultry, because dynamic reassortments of H7N9 with H9N2 genes have been observed, suggesting that H7N9 virus evolved in poultry to become a virus that infects human beings. Hence, reassortment between the prevalent poultry H9N2 viruses (providing genetic segments) and the infl uenza virus from wild birds could make the influenza evolve to adapt to domestic hosts. Poultry, especially in live markets, would have a pivotal role during the emergence of a novel infl uenza virus of avian origin. Several subtypes of avian infl uenza viruses in poultry are capable of infecting human beings, and the next avian infl uenza virus that could cause mass infections is not known. Therefore, slaughter of poultry carrying H9N2—the incubators for wild-bird-origin influenza viruses— would be an effective strategy to prevent human beings from becoming infected with avian infl uenza. We call for either a shutdown of live poultry markets or periodic thorough disinfections of these markets in China and any other regions with live poultry markets.

Hepatitis B virus subgenotyping: History, effects of recombination, misclassifications, and corrections

Hepatitis B virus (HBV) has evolved into phylogenetically separable genotypes and subgenotypes. Accurately assigning the subgenotype for an HBV strain is of clinical and epidemiological significance. In this paper, we review the recommendations currently employed for HBV subgenotyping, the history of HBV subgenotyping, the effects of recombination on HBV subgenotyping, misclassifications in HBV subgenotyping, and suggestions are made to correct the misclassifications. Finally, proposals are made to guide future HBV subgenotyping.