Characterization of influenza A (H7N9) viruses isolated from human cases imported into Taiwan
Ji-Rong Yang1, Chuan-Yi Kuo1, Hsiang-Yi Huang1
1Center for Research, Diagnostics and Vaccine Development, Centers for Disease Control, Taipei, Taiwan, ROC.
Abstract:
A novel avian influenza A (H7N9) virus causes severe human infections and was first identified in March 2013 in China. The H7N9 virus has exhibited two epidemiological peaks of infection, occurring in week 15 of 2013 and week 5 of 2014. Taiwan, which is geographically adjacent to China, faces a large risk of being affected by this virus. Through extensive surveillance, launched in April 2013, four laboratory-confirmed H7N9 cases imported from China have been identified in Taiwan. The H7N9 virus isolated from imported case 1 in May 2013 (during the first wave) was found to be closest genetically to a virus from wild birds and differed from the prototype virus, A/Anhui/1/2013, in the MP gene. The other three imported cases were detected in December 2013 and April 2014 (during the second wave). The viruses isolated from cases 2 and 4 were similar in the compositions of their 6 internal genes and distinct from A/Anhui/1/2013 in the PB2 and MP genes, whereas the virus isolated from case 3 exhibited a novel reassortment that has not been identified previously and was different from A/Anhui/1/2013 in the PB2, PA and MP genes. The four imported H7N9 viruses share similar antigenicity with A/Anhui/1/2013, and their HA and NA genes grouped together in their respective phylogenies. In contrast with the HA and NA genes, which exhibited a smaller degree of diversity, the internal genes were heterogeneous and provided potential distinctions between transmission sources in terms of both geography and hosts. It is important to strengthen surveillance of influenza and to share viral genetic data in real-time for reducing the threat of rapid and continuing evolution of H7N9 viruses.
Insights
Novel avian influenza A (H7N9) virus poses a severe threat. Surveillance in Taiwan identified four imported cases, revealing genetic diversity in internal genes, highlighting the need for real-time data sharing.
Area of Science:
- Virology
- Epidemiology
- Public Health
Background:
- A novel avian influenza A (H7N9) virus emerged in China in March 2013, causing severe human infections.
- The virus exhibited two distinct epidemiological peaks in 2013 and 2014.
- Taiwan's proximity to China posed a significant risk for H7N9 importation.
Purpose of the Study:
- To investigate the genetic characteristics of H7N9 virus imported into Taiwan.
- To understand the genetic evolution and reassortment of H7N9 strains.
- To inform public health strategies for influenza surveillance.
Main Methods:
- Extensive influenza surveillance in Taiwan initiated in April 2013.
- Laboratory confirmation and genetic sequencing of four imported H7N9 cases.
- Phylogenetic analysis of viral genes (HA, NA, and internal genes).
Main Results:
- Four imported H7N9 cases were identified, with three cases occurring during the second epidemiological wave.
- Viruses from imported cases showed genetic variations, particularly in internal genes (PB2, PA, MP), compared to the prototype A/Anhui/1/2013 strain.
- A novel reassortment was identified in one imported H7N9 virus.
- The HA and NA genes displayed limited diversity, while internal genes were heterogeneous, suggesting different transmission sources.
Conclusions:
- Imported H7N9 viruses in Taiwan exhibit genetic diversity, especially in internal genes, indicating complex transmission dynamics.
- Real-time sharing of viral genetic data is crucial for effective surveillance and control of evolving influenza strains.
- Strengthening influenza surveillance systems is essential to mitigate the threat of H7N9 and other novel influenza viruses.
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