#12,872
One of the recurring themes in this blog is that when we talk about a specific influenza subtype - like H7N9, or H5N1 - we aren't talking about a singular viral threat, but rather a group of viruses that share common (or similar) HA and NA genes.
Subtypes are divided into clades (and further into subclades) based on their HA gene, while differences in their internal genes (due to reassortment) can produce multiple genotypes. And even within each specific genotype, there can be many variants due to amino acid changes.This viral diversity likely explains why HPAI H5N1 has caused hundreds of deaths in places like Indonesia, Vietnam, Egypt, and China - and yet in places like India - where hundreds of outbreaks have occurred, no human infections have ever been reported.
As you might expect, the longer a virus stays in circulation, the more diverse it tends to become. Since H5N1 re-emerged back in 2003, the WHO has had to select three dozen different H5N1 candidate vaccine viruses (CVVs) for development.
Tracking the evolution of H7N9 in China, while of much shorter duration, is no less challenging.Last year, in addition to the rapid emergence of a new (Yangtze River Delta) lineage of LPAI H7N9, we saw the emergence of an HPAI strain as well. Last week, in Cell Research: Another Cautionary H7N9 Study Out Of China, the authors reported:
Here, we evaluated the evolution of H7N9 viruses isolated from avian species between 2013 and 2017 in China and found 23 different genotypes, 7 of which were detected only in ducks and were genetically distinct from the other 16 genotypes that evolved from the 2013 H7N9 viruses.Today we've another study, published yesterday in the EID Journal, that looks again at this growing diversity among H7N9 viruses in China. Specifically they isolated 3 different H7N9 viruses found to be co-circulating in chickens between June 2016 and January 2017 in Gaungdong Province, China.
All three proved to be HPAI - and all replicated well and transmitted easily among chickens. One was a triple reassortment (of H5, H7, H9) and two were double reassortments (of H7 & H9).While it isn't surprising to find this much diversity arise so quickly among this new HPAI strain of H7N9, this is the first detailed analysis I've seen.
As the authors note, all three of these viruses possess traits that `could cause a pandemic among poultry and humans in China.'I've only included some excerpts, so follow the link to read the report in its entirety.
Research Letter
Avian Influenza (H7N9) Viruses Co-circulating among Chickens, Southern China, 2016–2017
Nianchen Wang1, Minhua Sun1, Wenqing Wang1, Guowen Ouyang, Zuxian Chen, You Zhang, Bingbing Zhao, Siyu Wu, Jianni Huang, Hailiang Sun, Ming Liao, and Peirong Jiao
Abstract
During 2016–2017, three avian influenza (H7N9) viruses were isolated from chickens in southern China. Each virus had different insertion points in the cleavage site of the hemagglutinin protein compared to the first identified H7N9 virus. We determined that these viruses were double or triple reassortant viruses.
Since its first documentation on March 30, 2013, through March 16, 2017, avian influenza (H7N9) virus has caused 5 epidemic waves of infection among humans in China, resulting in 1,307 laboratory-confirmed clinical cases and 489 deaths (1). According to reports of H7N9 virus outbreaks among humans in China, the virus clustered into the Yangtze River Delta lineage and the Pearl River Delta lineage (2). As with most low-pathogenicity avian influenza viruses, the early H7N9 avian influenza virus produced mild symptoms in domestic poultry and was therefore generally only detected through active virologic surveillance (3,4).
During June 2016–January 2017, H7N9 viruses (isolates A/chicken/Guangdong/Q1/2016, A/chicken/Guangdong/Q26/2017, and A/chicken/Guangdong/Q39/2017, hereafter Q1, Q26, and Q39) were isolated from lung samples collected from chicken carcasses in Guangdong, China. We sequenced all 8 genes of these viruses to trace the origin and clarify the genetic properties. The nucleotide sequences are available from GenBank (accession nos. MF280181–204).
(SNIP)
The biological features of H7N9 virus and its pandemic potential have caused global concern (8). The early H7N9 viruses lacked the basic HA cleavage site, exhibited low pathogenicity, and caused mild or no disease in poultry (9). The cleavage site in HA protein of the isolates we analyzed were KGKRTAR↓G and KRKRTAR↓G. They had high pathogenicity and replication in chickens and could transmit among chickens by contact. Therefore, these new H7N9 viruses could cause a pandemic among poultry and humans in China.
Molecular evolution showed that Q1 was a triple reassortant virus (H5, H7, and H9 subtypes) consisting of Yangtze River Delta A and B lineages of H7N9 and GSGD96 lineage of H5N1. The Q26 and Q39 viruses were both double reassortant avian influenza viruses (H7 and H9 subtype), as was the early H7N9 virus (Figure; Technical Appendix[PDF - 1.39 MB - 9 pages] Table 1, Figure)
Therefore, the 3 H7N9 viruses we isolated have 2 kinds of insertions in the cleavage sites and were likely derived from different lineages of H7N9 viruses, or even from different subtypes that were co-circulating in southern China during 2016–2017.
Mr. Wang is a student in the Master of Science program in the College of Veterinary Medicine, South China Agricultural University. His primary research interest is the epidemiology and pathogenesis of avian influenza viruses.
