Evolution Of H7N9 Viruses Research Articles

Analysis of the Codon Usage Pattern of HA and NA Genes of H7N9 Influenza A Virus.

Novel H7N9 influenza virus transmitted from birds to human and, since March 2013, it has caused five epidemic waves in China. Although the evolution of H7N9 viruses has been investigated, the evolutionary changes associated with codon usage are still unclear. Herein, the codon usage pattern of two surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA), was studied to understand the evolutionary changes in relation to host, epidemic wave, and pathogenicity. Both genes displayed a low codon usage bias, with HA higher than NA. The codon usage was driven by mutation pressure and natural selection, although the main contributing factor was natural selection. Additionally, the codon adaptation index (CAI) and deoptimization (RCDI) illustrated the strong adaptability of H7N9 to Gallus gallus. Similarity index (SiD) analysis showed that Homo sapiens posed a stronger selection pressure than Gallus gallus. Thus, we assume that this may be related to the gradual adaptability of the virus to human. In addition, the host strong selection pressure was validated based on CpG dinucleotide content. In conclusion, this study analyzed the usage of codons of two genes of H7N9 and expanded our understanding of H7N9 host specificity. This aids into the development of control measures against H7N9 influenza virus.

Delayed peak of human infections and ongoing reassortment of H7N9 avian influenza virus in the newly affected western Chinese provinces during Wave Five

ObjectivesEight additional provinces in western China reported human infections for the first time during the fifth wave of human H7N9 infections. The aim of this study was to analyze the epidemiological and virological characteristics of this outbreak. MethodsThe epidemiological data of H7N9 cases from the newly affected western Chinese provinces were collected and analyzed. Full-length genome sequences of H7N9 virus were downloaded from the GenBank and GISAID databases, and phylogenetic, genotyping, and genetic analyses were conducted. ResultsThe peak of human infections in the newly affected western Chinese provinces was delayed by 4 months compared to the eastern Chinese provinces, and both low pathogenic (LP) and highly pathogenic (HP) H7N9-infected cases were found. The LP- and HP-H7N9 virus belonged to 10 different genotypes (including four new genotypes), of which G11 and G3 were the dominant genotypes, respectively. Almost all of these viruses originated from eastern and southern China and were most probably imported from neighboring provinces. Genetic characteristics of the circulating viruses were similar to those of the viruses from previously affected provinces during Wave Five. ConclusionsA delayed peak of human infections was observed in the newly affected western Chinese provinces, and reassortment has been ongoing since the introduction of H7N9 viruses. This study highlights the importance of continued surveillance of the circulation and evolution of H7N9 virus in western China.

Development of a quadruple qRT-PCR assay for simultaneous identification of highly and low pathogenic H7N9 avian influenza viruses and characterization against oseltamivir resistance

BackgroundDuring the fifth wave of human H7N9 infections, a novel highly pathogenic (HP) H7N9 variant emerged with an insertion of multiple basic amino acids in the HA cleavage site. Moreover, a neuraminidase inhibitor (NAI) resistance (R292K in NA) mutation was found in H7N9 isolates from humans, poultry and the environment. In this study, we set out to develop and validate a multiplex quantitative reverse transcript polymerase chain reaction (qRT-PCR) to simultaneously detect the presence of H7N9 and further identify the HP and NAI-resistance mutations.MethodsA quadruple qRT-PCR to simultaneously detect the presence of H7N9 and further identify the HP and NAI-resistance mutations was designed based on the analyses of the HA and NA genes of H7N9. This assay was further tested for specificity and sensitivity, and validated using clinical samples.ResultsThe assay was highly specific and able to detect low pathogenic (LP)- or HP-H7N9 with/without the NAI-resistance mutation. The detection limit of the assay was determined to be 50 genome-equivalent copies and 2.8 × 10− 3 50% tissue culture infectious doses (TCID50) of live H7N9 per reaction. Clinical validation was confirmed by commercial kits and Sanger sequencing with ten clinical samples.ConclusionsWe developed and validated a rapid, single-reaction, one-step, quadruple real-time qRT-PCR to simultaneously detect the presence of H7N9 and further identify the HP- and NAI-resistance strains with excellent performance in specificity and sensitivity. This assay could be used to monitor the evolution of H7N9 viruses in the laboratory, field and the clinic for early-warning and the prevention of H7N9 infections.

Co-circulation of multiple genotypes of influenza A (H7N9) viruses in eastern China, 2016-2017.

Five epidemic waves of human infection with influenza A (H7N9) virus have emerged in China since spring 2013. We previously described the epidemiological characterization of the fifth wave in Jiangsu province. In this study, 41 H7N9 viruses from patients and live-poultry markets were isolated and sequenced to further elucidate the genetic features of viruses of the fifth wave in Jiangsu province. Phylogenetic analysis revealed substantial genetic diversity in the internal genes, and 18 genotypes were identified from the 41 H7N9 virus strains. Furthermore, our data revealed that 41 isolates from Jiangsu contained the G186V and Q226L/I mutations in their haemagglutinin (HA) protein, which may increase the ability of these viruses to bind the human receptor. Four basic amino acid insertions were not observed in the HA cleavage sites of 167 H7N9 viruses from Jiangsu, which revealed that highly pathogenic avian influenza (HPAI) H7N9 viruses did not spread to Jiangsu province in the fifth wave. These findings revealed that multiple genotypes of H7N9 viruses co-circulated in the fifth wave in Jiangsu province, which indicated that the viruses have undergone ongoing evolution with genetic mutation and reassortment. Our study highlights the need to constantly monitor the evolution of H7N9 viruses and reinforce systematic influenza surveillance of humans, birds, and pigs in China.

Epidemiology and Evolution of Influenza A/H7N9

The World Health Organization (WHO) has reported a first human infection by H7N9 virus from China in March 2013. Cases continued to be reported throughout April till now. There were four imported cases in Taiwan and one of them died. It has been established that many of the human cases of H7N9 appear to have a link to live bird markets except few cases. Due to the increasing travel frequency between Taiwan and Mainland China, it is needed to strengthen monitoring of the H7N9 virus and its epidemics. This study focuses on the epidemiology, genetics and evolution of H7N9 virus. The results showed that influenza tends to strike during the winter months, and the second wave which began in October 2013, although the mortality rate from H7N9 infection is less than the first wave, however, the age and geographic distribution is broader. According to the genetic analysis data, the amino acids composition of this virus makes it easier to replicate and to infect human. To prevent the H7N9 epidemic in this winter period, any traveler visiting China and has influenza-like illness symptoms developed upon arriving in Taiwan, such as fever and cough, please put on a surgical mask and seek immediate medical attention. Moreover, physicians and medical workers should pay attention to patient's recent travel history; include visiting live poultry markets, direct contacting with poultry and birds or their droppings/dead bodies, to facilitate the diagnosis and treatment.