Sunday, February 19, 2017

Guangdong CDC: Two H7N9 `Variants' Isolated From Human Cases

Credit NIAID


Throughout its relatively short (4 year) reign, we've watched H7N9's evolution closely for signs that it might be evolving into a more dangerous pathogen.  During that time we've seen its genetic diversity grow rapidly through continual reassortment with other avian viruses (particularly H9N2), antigenic drift, and its passage through a variety of host species.
A process dubbed `genetic tuning’ by the authors of a paper that appeared in Eurosurveillance back in 2014 (see Genetic Tuning Of Avian H7N9 During Interspecies Transmission).

With this diversity we've also seen some subtle (sometimes regional) changes in H7N9's behavior, something which was the topic of last December's  MMWR: Assessing The 4th Epidemic Wave Of H7N9 In China, where researchers warned of `the continued geographic spread, identification of novel reassortant viruses, and pandemic potential of the virus' - stating that `using the Influenza Risk Assessment Tool (10), CDC found that A(H7N9) virus has the highest potential pandemic risk of any novel influenza A viruses that have been assessed.' 
But the two constants with H7N9 until now have been its low pathogenicity in birds and its lack of sustained transmission in humans.
Today we've a brief announcement from Guangdong's CDC that two virus samples collected from human hosts last month suggest one of those constants may be changing; its pathogenicity in birds.

While the ultimate significance and impact of this discovery remains unclear, this is another sign that the H7N9 virus continues to evolve in unexpected ways.  First the (translated) announcement, then I'll be back with a bit more.

H7N9 virus mutant was found in human cases from China

Release Date: 2017-02-19 Views: Contributed by: Information Department of Publicity: Office Font: Big Middle Small

In January 2017, Guangdong Provincial Center for Disease Control and Disease on the two cases of human infection H7N9 cases were isolated virus gene sequencing analysis, found in the two strains of hemagglutinin link peptide position of the gene insertion mutation occurred, the test results Has been confirmed by the National Center for Viral Disease National Influenza Center.

I center experts to judge and communicate with the relevant experts in the agricultural sector that H7N9 virus in the hemagglutinin link peptide position of the gene insertion mutation, suggesting that the virus mutation to the highly pathogenic virus against birds; the second is based on the virus Sequence analysis results have not yet appeared in the mutant virus that has increased resistance to human infectivity, virulence and interpersonal communication.

Two cases of disease before the incidence of bird exposure history, and in the exposure of poultry birds have occurred in the phenomenon of death. At present, a case has been cured, another case is still in treatment. All the 105 cases of close contact after two weeks of medical observation, were not fever, cough and other symptoms.

H7N9 virus is a influenza virus, one of its main features is prone to gene reassignment and mutation. Some mutations may lead to the virus on the human appeal, virulence and interpersonal communication ability enhancement, so the virus variation has been widely concerned about the domestic and foreign.

It is understood that the agricultural sector laboratory also from Guangdong, four poultry specimens found similar to the variation of the virus. China's health care system will work together with the agricultural sector, the common source of the virus, the scope of the impact of in-depth study, and continue to strengthen the monitoring of H7N9 virus, in time to find any possible variation.

The results have been communicated to the World Health Organization.

China Center for Disease Control and Prevention
Although capable of causing serious (even fatal) illness in humans, H7N9 has - at least until now - been strictly an LPAI (Low Pathogenic Avian Influenza) virus in birds. As such, it has been very difficult to identify and contain in domesticated or wild bird populations.
A change to an HPAI virus might make identification in poultry flocks easier  (potentially a good thing) - but could also serve as an evolutionary `bridge' to other changes; changes that might negatively  impact how it behaves in mammalian hosts. 
Admittedly, I've employed a lot of `weasel words' here, since we simply don't know where this new fork in H7N9's evolutionary road will lead. The fact that it has been detected in both humans and poultry in Guangdong Province, however, suggests it isn't just some `spontaneous' dead end mutation. 
But until we learn more we won't know how biologically `fit' these variants really are. 

Interestingly, on Friday Science Magazine ran a story (see Bird flu strain taking a toll on humans) with an interview with renown virologist Dr. Guan Yi from the University of Hong Kong, which seems to have telegraphed this discovery. 
"It is too late to contain the virus in poultry," Guan says. He predicts that the virus will continue to spread in China's farms, possibly evolving into a strain that would be pathogenic for poultry. Authorities have culled more than 175,000 birds this winter to stamp out local outbreaks of H7N9 and other avian flu strains. Further spread of H7N9 "will naturally increase human infection cases," Guan says. 
While today's announcement doesn't necessarily move H7N9 closer to becoming a pandemic strain, it is a reminder how labile and unpredictable influenza viruses can be. 

Stay tuned.