Release date: 2015-03-18
No one knows whether H7N9 avian flu, which has caused more than 560 infections and 204 deaths in China, has the potential to evolve to be easily spread among people. A far-reaching genomic survey to date on H7N9 in poultry provides a more detailed picture of the evolution and spread of this virus.
H7N9 was first discovered in Shanghai and surrounding areas at the end of March 2013, and the cases in April of that year began to soar. The initial epidemic was quickly controlled after determining that the live poultry market was the main route of disease transmission to humans. Although people hope that the virus can gradually disappear, this expectation eventually shattered. In the winter of that year, H7N9 returned again, causing a second wave of large-scale human infections to the south. There were no new cases in the summer of 2014, confirming its seasonal pattern. At the end of last year, the infection rose again, and this third wave of infection is still continuing.
In a paper published this week in Nature, an international research team led by Chinese scientists described how to cross the border from eastern China from October 2013 to July 2014. Poultry swabs were obtained from the live poultry market in 15 cities to track the virus. The study examined the average of 7 urban live poultry markets and 3% of the H7N9 virus.
The team sequenced the genomes of 438 strains and found that as the virus spread south, it evolved into three major branches with multiple sub-branches.
Yi Guan, a virologist at the State Key Laboratory of Newly Infectious Diseases, and Huachen Zhu of Shenzhen Third People's Hospital are co-authors of the paper.
This diversification is anticipating, and tracking it can help identify the major trade routes and markets that drive the spread of the virus. Guan Wei said: "The extent of the spread of the virus in the flock is not very clear. Our paper confirms that the virus is differentiated into some local pedigrees. The eastern part of China is still the reservoir and 'distribution center' of this virus. ."
Guan Wei pointed out that as influenza viruses evolve and diversify in birds, some genetic changes can alter their infectivity, virulence, or ability to spread between people. Human infections also provide opportunities for viruses to better adapt to their hosts.
Genetic monitoring is therefore extremely important for tracking mutations and for testing whether influenza strains are capable of spreading in mammals such as ferrets and other animal models. From the outbreak of the epidemic, some mutations carried by H7N9 made it easier to spread from birds to humans than H5N1 avian influenza. Since its appearance in 2003, H5N1 has caused 784 infections and 429 deaths in 16 countries.
Lack of monitoring
The current wave of H7N9 infections may have a different pattern of transmission than the second wave of infections tracked by the research team. Prior to this latest research update, only eight genomic sequences from birds were collected in the GenBank library in 2014, with only 258 sequences in 2013. Marius Gilbert, an avian flu epidemiologist and ecologist at the Free University of Brussels, says this is not enough to map out the geographic map of the virus over time.
The Nature News team analyzed the number of sequencing genomes for all avian influenza subtypes presented to GenBank over the past 15 years. The results show that global genetic testing is still very unfavorable and not fast enough. Most viruses are sequenced after months or years of collection.
Guan Wei agrees that timely monitoring is very important. But monitoring and virus testing are costly and time consuming – especially when it comes to separating and sequencing viruses. This means that it is difficult to routinely monitor influenza viruses in fauna, usually only in response to an outbreak. For H7N9, sequencing viruses require the right to use Biosafety Level 3 laboratories. In view of these complex factors, Guan Wei believes that the number of H7N9 sequences stored in GenBank has not been too small.
Coupled with the time lag, public agencies and researchers conducting sequencing of influenza strains sometimes only make the data public when they publish their papers. The authors of the new study have sent the sequence to GenBank, which has previously shared this data with the World Health Organization (WHO) and other agencies.
Spread risk
The threat of H7N9 is unlikely to disappear quickly. The virus is now circulating in poultry throughout China, and it is likely that people will continue to experience sporadic infections. The researchers warned, "Like the previous H5N1 and H9N2 flu viruses, it seems that it is only a matter of time before poultry flows through cross-border trade to spread the virus outside of China."
Guan Yu and his co-authors said that given that H7N9 can infect humans, it should be considered "a major candidate for the emergence of a pandemic virus." Guan Wei pointed out that given the sheer volume of influenza viruses, it is necessary to control disease and vaccines. Development is the main goal, and H7N9 should be at the top of the list.
There are quite a few potential threats at the moment. Last month, WHO warned that the current diversity and geographical distribution of new animal flu viruses is “unprecedented†– new hodgepods of new viruses have emerged around the world, including H10N8, H5N2, H5N3, H5N6 and H5N8. There is evidence that different subtypes are currently exchanging genes more easily and rapidly to form new strains. Guan Wei said that it is “almost impossible†to assess whether these increased diversity represent a greater threat to emerging pandemic viruses.
Source: Biopass
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