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The IDSA’s Journal of Infectious Diseases published a pair of new studies on the H7N9 virus yesterday that don’t exactly break new ground, but do add to what we’ve learned from earlier studies.
While full access to these studies requires a subscription, we can glean the basics from their abstracts.
The first looks at the transmissibility and pathogenicity of the H7N9 virus in ferrets, and finds (as we’ve seen previously in Nature: Limited Airborne Transmission Of H7N9 Between Ferrets & Science: H7N9 Transmissibility Study In Ferrets) that this emerging avian flu virus could be transmitted between ferrets (albeit at low levels) via respiratory droplets.
The Novel Avian-Origin Human A (H7N9) Influenza Virus Could be Transmitted between Ferrets via Respiratory Droplets
Lili Xu1,†, Linlin Bao1,†, Wei Deng1,†, Libo Dong3,†, Hua Zhu1, Ting Chen1, Qi Lv1, Fengdi Li1, Jing Yuan1, Zhiguang Xiang1, Kai Gao1, Yanfeng Xu1, Lan Huang1, Yanhong Li1, Jiangning Liu1, Yanfeng Yao1, Pin Yu1, Xiyan Li2, Weijuan Huang2, Xiang Zhao2, Yu Lan2, Junfeng Guo2, Weidong Yong1, Qiang Wei1, Honglin Chen3, Lianfeng Zhang1 and Chuan Qin1,*
Abstract
The outbreak of human infections caused by the novel avian-origin H7N9 subtype influenza viruses in China since March 2013 underscores the need to better understand the pathogenicity and transmissibility of these viruses in mammals.
In a ferret model, the H7N9 influenza virus was found to be less pathogenic than a H5N1 virus but was comparable with the 2009 pandemic H1N1 virus, based on the clinical signs, mortality, virus dissemination, and histopathological analyses. The H7N9 virus could replicate in the upper and lower respiratory tract, heart, liver, and olfactory bulb.
It is worth noting that the H7N9 virus exhibited low level of transmission between ferrets via respiratory droplets. There were four mutations in the virus isolated from the contact ferret which were D678Y in PB2, R157 K in HA(H3 numbering), I109T in NP, and T10I in NA. These data emphasized that the avian-origin H7N9 subtype influenza virus has the ability to transmit between mammals, highlighting the potential of human-to-human transmissibility.
The second study looks for the source of human infection with the H7N9 virus, and finds – as we’ve seen suggested before (see OIE Statement On Live Markets And H7N9) – that live market birds appear to be the major contributing factor.
Relationship between domestic and wild birds in live poultry market and a novel human H7N9 virus in China
Chengmin Wang1,*, Jing Wang2,*, Wen Su1, Shanshan Gao1, Jing Luo1, Min Zhang1, Li Xie2,*, Shelan Liu3, Xiaodong Liu4, Yu Chen4, Yaxiong Jia4, Hong Zhang1, Hua Ding2 and Hongxuan He1,#†
Abstract
To trace the source of the avian H7N9 viruses, we collected 99 samples from 4 live poultry markets and the family farms of 3 patients in Hangzhou city of Zhejiang province, China.
We found almost all positive samples came from chickens and ducks in live poultry markets. These results strongly suggest that the live poultry markets are the major source of recent human infections with H7N9 in Hangzhou city, Zhejiang province of China.
Therefore, control measures are needed, not only in the domestic bird population, but also in the live poultry markets to reduce human H7N9 infection risk.
Although the vast majority of positive H7N9 bird and environmental samples have come from live bird markets - not poultry farms - there remain many questions over how this virus could have spread so rapidly and across such a wide swath of China, only via live market birds.
Many observers still believe we are missing pieces to this epidemiological puzzle.
If the virus makes a return visit this fall, nailing down (and hopefully, interrupting) the source of transmission will be the top priority for public health authorities.
