H7N7: More danger from bird flu

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Not only do H7N9 viruses pose a significant risk, H7N7 also pose a massive risk

The spread of bird flu in China is of increasing concern to researchers worldwide. Since March, more than 130 people have been infected with the "novel H7N9 influenza A virus", 44 patients have died as a result of the infection, Chinese researchers, together with British and American colleagues in the journal "Nature", describe the course to date Epidemic. The research team led by Huachen Zhu and Yi Guan from the University of Hong Kong has recently investigated the genesis of the H7N9 virus and found a connection to the H7N7 virus.

Now the scientists fear that the avian influenza viruses of the genus H7N7 could possibly be dangerous for humans. "Although there is no evidence to date that the H7N7 strain can infect humans," the latest studies have found that "the H7 avian viruses constantly mix and increasingly exchange genetic material," report Guan and colleagues. The process is known in the professional world as "reassortment" and harbors the risk that the H7N7 viruses could also develop into human-pathogenic viruses in the future.

Avian influenza viruses exchange genetic material
Regarding the development of the H7N9 virus in China, the researchers said that the virus "is a reassortment of H7, N9 and H9N2 avian influenza viruses." This carries some amino acids with which it can dock to the receptors of mammals. The scientists were able to show that "H7 viruses generally passed from domestic ducks to chicken populations" and then a reassortment with viruses of the genus H9N2 followed, which gave rise to the H7N9 viruses. They also discovered an H7N7 line not previously linked to this. The H7N7 viruses have been detected in chickens and have also been shown to be infectious in mammals in further experiments, write Guan and colleagues. The discovery suggests that "H7 viruses pose a threat that goes well beyond the current outbreak," the researchers explain. The international team of researchers concluded that the high prevalence of H7 viruses in poultry could lead to the generation of highly pathogenic variants, with an ongoing risk that the viruses would acquire human-to-human transferability.

H7N7 bird flu viruses a hitherto unknown danger?
"H7 is out there in China and not just in the form of H7N9," said co-author Richard Webby, influenza specialist at the St. Jude Children's Research Hospital in Memphis (Tennessee). The discovered H7N7 strain has so far not infected humans, but in laboratory tests, the researchers found that the viruses can infect ferrets, "which suggests that transmission to humans is also possible," said Yi Guan. In the experiments, all ferrets had developed severe pneumonia. With the current H7N9 infections in China, severe pneumonia was one of the most common symptoms of bird flu. Guan and colleagues conclude that if the H7N7 virus continues to spread in the chicken population, transmission to humans is to be expected in the medium term. Yi Guan therefore advocated better monitoring of the Chinese bird population.

Poultry markets as breeding grounds for new bird flu variants
The research team led by Yi Guan had taken throat and intestinal smears from 1,341 birds (including chickens, ducks, geese, pigeons, partridges and quail) in poultry markets around Shanghai. 1,006 water and faecal samples from bird markets were also analyzed. "Over ten percent of the samples tested were positive for an influenza virus, including 15 percent for an H7 virus," the researchers write. David Morens, influenza specialist at the US National Institutes of Health in Bethesda, Maryland, said, “The evolutionary path followed by the viruses suggests that more surveillance and better hygiene practices in poultry markets are critical to risk monitoring for human health. "(fp)

Also read about bird flu:
Bird flu virus H7N9 in the stool
Disturbing experiments with avian flu viruses

Photo credit: schemmi / pixelio.de

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