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In March 2013, Shangahi, China, reported the first few cases of human infection with a novel avian-origin influenza A (H7N9) virus. The New England Journal of Medicine (NEJM) featured an article1 about the first three cases identified in a quest to understand the virology of this virus and its proposed mechanism of mutation. Although detailed information about this virus is not yet available, a preliminary report from the World Health Organization (WHO) warned that the “disease is of concern because most patients have been severely ill”2. The reported fatality rate in China seems high, with 10 deaths out of 38 confirmed cases, 19 of them were severe and 9 were mild cases. In addition, more than 760 close contacts of the confirmed cases are being closely monitored.2

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The first three confirmed infected cases were isolated from respiratory. Throat-swab and specimens were identified by means of real-time RT-PCR, viral isolation, and full genome sequencing. All three patients shared the same symptoms and they presented with fever, cough and dyspnea. Two patients had a history of recent exposure to poultry. Chest radiography showed diffuse consolidation. Acute respiratory distress syndrome and multi-organ failure were the most common complications identified. Unfortunately, all three patients subsequently died.

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The authors examined the virus and found a mutation that resulted from a deletion of five amino acids in the viral neuraminidase NA stalk has been observed in the novel H7N9 viruses. A similar deletion in the H5N1 avian virus has been shown to be responsible for the change in viral tropism to the respiratory tract, or to enhance viral replication, and it has been suggested that this deletion may be associated with adaptation and transmission in domestic poultry.

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As of yet, there is limited information about the burden of the disease or the fatality rate but it seems too soon to judge. In addition, most of the cases had the infection after being in contact with poultry, and there is no indication thus far that it can be transmitted between people. However, both animal-to-human and human-to-human routes of transmission are being actively investigated. In the meantime, WHO does not advise special screening at points of entry with regard to this event, nor does it recommend that any travel or trade restrictions be applied.

1. Gao R, Cao B, Hu Y, et al. Human Infection with a Novel Avian-Origin Influenza A (H7N9) Virus. N Engl J Med 2013. DOI: 10.1056/NEJMoa1304459.   [PubMed: 23577628]
2. World Health Organization. Human infection with influenza A(H7N9) virus in China – update. Available at: http://www.who.int/csr/don/2013_04_11/en/index.html. [Accessed April 12, 2013]

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