Three people have been infected with an H7N9 subtype of influenza virus in the last two month in central China. Two, an 87 year-old man and a 27 year-old man, became infected in February and died within a week. A third case, a 35 year-old woman, became infected March 9th and is recovering in the hospital.
88 close contacts of these three individuals have been sampled and monitored for influenza and influenza like illness. To date, it does not appear that these viruses have been able to transmit from human to human. The source of all three infections is currently unknown.
Initial fears were that a new highly pathogenic avian influenza (HPAI) strain of H7 was the culprit. However, recent information from the CDC indicates that these viruses lack the polybasic cleavage site that defines a highly pathogenic strain. Additionally, the virus seems to be a reassortant with internal genes that are very similar to H9N2 viruses.
This marks the second time that a virus containing genes from an H9N2 via reassortment has caused deaths in humans. The HPAI H5 virus isolated in the Hong Kong outbreak of 1997 also contained internal gene segments that matched H9N2 viruses.
My own personal research has focused on the threat that H9N2 viruses could pose to the human population. Our research has focused on reassortant viruses of the H9 subtype, and we have found that H9 viruses can gain infectivity, pathogenicity, and aerosol transmissiblity in ferrets and swine via reassortment, especially in regards to the 2009 pandemic H1N1.
The results we have gathered from lab and the recent outbreak once again highlight the potential dangers of H9N2 influenza viruses to humans. The viruses can infect humans, readily reassort with other viruses, and twice now have created viruses with significant effects in a human host.