MELBOURNE, Australia — Genetic variations in the deadly bird flu virus circulating in China increase the potential for a pandemic strain to emerge, researchers in Shanghai said.
Three new variants of the avian influenza type-A H7N9 virus have been found this winter, spurred by transmission in poultry and the incorporation of genetic material from another strain called H9N2, scientists at the Shanghai Public Health Clinical Center and Institutes of Biomedical Sciences said. The new strains may be behind a surge of infections in Guangdong, the southern province bordering Hong Kong.
So far, 178 people are known to have been infected with H7N9 this year, 19 more than in 2013, according to a list of confirmed cases kept by Internet message board FluTrackers. Each case increases the risk of the virus becoming better suited to humans, rather than birds, giving it the ability to spread easily from person to person. Zhejiang and Guangdong provinces and the Shanghai metropolitan area have been the worst affected regions, the scientists wrote in a paper published in Eurosurveillance Thursday.
“The rapidly increasing number of cases of A(H7N9) virus infection in these three regions may raise concerns as to whether there is an association between circulation of the new A(H7N9) reassortment strains identified and accelerated transmission of A(H7N9) virus in humans,” the scientists said. “It is of the utmost importance to monitor the risk of a potential pandemic initiated by various influenza virus strains.”
Even though H7N9 hasn’t mutated to become as contagious as seasonal flu, strains that emerge in China are of special interest to researchers. The 1957-58 Asian Flu and 1968-69 Hong Kong Flu pandemics were first identified in the world’s most populous nation, and an earlier bird flu strain known as H5N1 is thought to have come from the southern province of Guangdong in 1996. Years later, a new seasonal flu was found in neighboring Fujian and triggered explosive epidemics worldwide.
H7N9 has infected about 350 people, killing more than 70, mostly in mainland China, according to FluTrackers.
The new reassortments generated by H7N9 and H9N2 strains may produce variants that are more adaptive and have an increased ability to cause disease in humans, according to the Eurosurveillance report.
“Our findings suggest there is a possible risk that a pandemic could develop,” the authors said.
So far, there is no evidence of sustained human-to-human transmission, the World Health Organization in Geneva said in a Feb. 11 statement.
“Each new strain could be one that is better genetically equipped to transmit from person to person,” Ian Mackay, an associate professor of clinical virology at the University of Queensland in Brisbane, said in an email Friday. “Without contemporary sequence analysis, such a strain could emerge from among the ‘noise’ of human infection by less efficient strains, to begin spreading rapidly and with pandemic potential.”
It’s impossible to predict whether such a virus with the ability to spread worldwide would remain so deadly, killing about one in five people known to have been sickened with it.
Thursday’s research was based on a study of 72 genetic sequences of a flu gene called PB1 analyzed from samples collected in 11 Chinese provinces and cities since March 2013.
The authors didn’t show why changes in the PB1 gene might be related to increased pandemic risk, said Masato Tashiro, a director at Japan’s National Institute of Infectious Diseases in Tokyo, who reviewed the Eurosurveillance report. Other genes may contribute to the risk, he said.
Still, the research is “interesting and important,” Tashiro said Friday in an email.
“The H7N9 virus has undergone many gene reassortments with different domestic H9N2 viruses in poultry in different areas in China,” he said, adding that it’s not clear when the genetic reassortments occurred.
The increase in human cases during the Northern Hemisphere winter may reflect a wider spread of the H7N9 virus in poultry. The virus can circulate widely in chickens, ducks and geese without causing the mass die-offs characteristic of the H5N1 bird flu virus. Its stealth has made it difficult to track and contain a germ that’s typically more active during the colder winter months, scientists said.
The initial wave of H7N9 cases last year occurred late in the Northern winter and was limited to a smaller geographic region compared with the second wave, which began in October and was being fanned by a surge in poultry production timed for lunar New Year feasts that began at the end of January. These factors may facilitate greater genetic diversity of the circulating H7N9 strains, the University of Queensland’s Mackay said.
“We do see minor genetic differences” in H7N9 samples, said Ian Barr, deputy director of the WHO’s Collaborating Center for Reference and Research on Influenza in Melbourne. “We’re still in the dark a little about the significance of any minor clades” or genetic variants.
“The epidemiological data doesn’t support the premise that we have got either increased transmissibility or increased pathogenicity with this current outbreak versus the one in early 2013,” Barr said in a telephone interview today.
Sequencing studies involving genes other than PB1 are needed to get a better understanding of how the H7N9 strain is evolving, Mackay said.
“We have yet to see similar examination of the rest of the H7N9 genome in such detail,” he said. “That is urgently needed to tell the experts what today’s H7N9 is potentially capable of.”