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As CDC director Frieden indicated in his piece this morning on CNN, with the Chinese Lunar New Years celebration in full swing, there is growing concern over the spread of the avian H7N9 virus among people in Eastern China. While no one can predict when – or even if – this virus will achieve efficient transmission between humans, it is currently considered the the virus to watch right now.
Today the World Health Organization has updated their background & summary document on the H7N9 virus, reflecting the knowledge gained over the past 10 months and 270+ plus human cases, along with the publication this week of an updated FAQs on human infection caused by the avian influenza A(H7N9) virus.
As this new summary document runs 5 pages, I’ll just excerpt some highlights. Follow the link below to access the PDF file.
Background and summary of human infection with avian influenza A(H7N9) virus – as of 31 January 2014
The influenza A(H7N9) virus is one subgroup among the larger group of H7 viruses, which normally circulate among birds.
Human infections with other subgroups of H7 influenza viruses (H7N2, H7N3, and H7N7) have previously been reported in Australia, Canada, Italy, Mexico, the Netherlands, the United Kingdom and the United States of America. Most of these infections occurred in association with poultry outbreaks. The infections mainly resulted in conjunctivitis and mild upper respiratory symptoms, with the exception of one death, which occurred in the Netherlands.
Since the first notification at the end of March 2013, China has been reporting to WHO cases of human infection with H7N9 virus. This is the first time infection with this virus has been found in humans.
Epidemiology
The laboratory-confirmed cases have been reported from 13 provinces/municipalities in eastern mainland China, Hong Kong, Special Administrative Region, China, and the Taipei Centers for Disease Control (Taipei CDC). Most cases are presumed to have contracted the infection directly from infected animals or their environment, particularly as a result of visiting live animal markets. Only a few small clusters with possible human-to-human transmission have occurred among family members, but there has been no evidence of sustained human-to-human transmission to date.
As of 28 January 2014, the case fatality rate of all confirmed cases is 22%, but many cases are still hospitalized. Of all cases, 67% were male. The median age of reported cases is 58 years and that of fatal cases is 66 years.Cases occurred in a first wave (n=133) from February through May 2013. Reports of human infection decreased during the summer, with only two cases reported; they have increased since October, demonstrating a second wave, likely in conjunction with cooler temperatures.
For the latest information on cases and outcomes, see:
Virology
Thus far the H7N9 viruses detected in China are homologues. The HA gene is most similar to that of A(H7N3) viruses detected in ducks in Eastern China. The NA gene is most similar to N9 NA genes from viruses circulating recently in domestic ducks in China and Korea. The six internal genes are derived from influenza A(H9N2) viruses circulating in poultry in eastern Asia. Sequence analyses have shown that the genes of the H7N9 viruses from China are of avian origin, but with signs of adaptation to mammalian species. The adaptation includes increased ability to bind to mammalian cell receptors, and to grow at temperatures close to the normal body temperature of mammals, which is lower than that of birds. Antigenically, the H7N9 viruses are different from seasonal influenza viruses infecting humans, but closely related to A/Anhui/1/2013 (H7N9), the recommended virus for H7N9 vaccine development.Human-Animal Interface
The source of infection is assumed to be infected poultry or contaminated environments. Many of the human cases have reported visiting markets where live poultry were sold. This virus has been detected in both poultry and in markets that patients reported visiting. However, because this virus does not appear to cause clinical signs in infected poultry, clear links between infections in poultry and human cases have been difficult to establish.
