H7N9 cases pause; new report details reassortants

No new H7N9 infections were reported out of China today, but the flow of new information about the virus continued, with a genetic analysis hinting that reassortants could be one factor fueling the second wave of infections, especially in southern provinces such as Guangdong.

The apparent pause in disease activity follows a flurry of infections noted yesterday, including two imported cases reported from Hong Kong and Malaysia and seven new infections from the mainland.

The World Health Organization (WHO) said today that an assessment it conducted on Feb 11 has not changed the public health risk regarding H7N9 since its last risk assessment on Jan 21. In that assessment the WHO said sporadic infections, primarily in people who have contact with poultry and their environments, are likely to continue, but so far the virus doesn't appear to transmit easily among humans.

The number of H7N9 cases reported in the second wave stands at 211, compared with 136 reported last spring. For both waves the total is 347, according to a running tally kept by FluTrackers, an infectious disease message board. The unofficial death count is 72.

Details emerge about Malaysian case

Hong Kong's Centre for Health Protection (CHP) today revealed a few new details about the case-patient detected in Malaysia, the first to be identified outside of China. It said the 67-year-old woman from Guangdong province had symptoms and sought care on Jan 30 before departing for Malaysia with 16 family members on Feb 3.

While in Malaysia her condition worsened, and on Feb 7 she was hospitalized. She is receiving treatment in the intensive care unit of a private hospital, and her specimens tested positive for H7N9 on Feb 11.

Fourteen of the woman's traveling companions flew to Hong Kong on Feb 8 on their way back to Shenzhen in Guangdong province. Hong Kong health officials boarded the plane to assess the 14 travelers, all who denied having symptoms or contact with birds over the past 10 days. Three of the people had a mild fever.

The group had arranged to travel by private cars back to Shenzhen, where local authorities will follow up, the CHP said.

Gene study raises concerns about H7N9 reassortants

In other developments, a research team from China that analyzed H7N9 genetic sequences submitted by China last year and in January identified three reassortants of H7N9 with local H9N2 strains in poultry, which they say could be playing a role in the reemergence of the disease. The group reported its findings today in Eurosurveillance.

After the virus first emerged last spring, experts found that the H7N9 virus is a triple reassortant, all from avian sources, that contains the internal genes from the H9N2 strain.

The team looked at 72 gene sequences of H7N9 viruses collected from 11 Chinese provinces and cities that were deposited in the Global Initiative on Sharing Avian Influenza Data (GISAID) database from March 2013 to January 2014. They also included the most recent isolates from Hong Kong.

They conducted a phylogenetic analysis and DNA mutation analysis of the PB1 gene, finding four lineages and three new reassortants.

The findings suggest that continuous H7N9 transmission in Chinese poultry has led to increased diversity and reassortment of H7N9 with local H9N2 strains, the group wrote, adding that the new reassortment strains, such as those found in a Guangdong/Hong Kong transmission cluster, could be triggering the reemergence of infections.

Also, they said the reassortants may produce avian influenza strains that are more adapted to and pathogenic in humans, highlighting the importance of continuous monitoring.

Researchers pointed out that areas in which new reassortant strains are being found—Shanghai, plus Zhejiang and Guangdong provinces—have been among the hardest hit in China so far this year.

Though the case-fatality rate in January was lower than the first wave last spring, the quickly growing case totals in those regions raise concerns that there might be a link between circulation of the new reassortants and the accelerated transmission of H7N9 in humans, the group wrote.

Expert weighs in on new findings

Ian Mackay, PhD, a virologist from Australia, told CIDRAP News that the detailed analysis focuses on the PB1 segments of H7N9, mostly collected from 2013 strains. He said the concerning, but not unexpected, take-home message is that even in just one of H7N9's eight segments, the researchers found consistent genetic changes.

Mackay is with the Australian Infectious Diseases Research Centre at the University of Queensland, and he authors the Virology Down Under blog.

"The intermixing of early H7N9 with other flu viruses is continuing to create subtle variants thanks to the high influenza virus burden and diversity to be found among poultry in China," he said.

Since the number of human H7N9 cases this year has already topped last year's total, there's a need to extend the analysis to isolates from this year and to explore other genome segments, Mackay said.

However, he said flu databases are noticeably lacking H7N9 sequence data from 2014. "Such data are essential for experts worldwide to keep track of the virus, seeking changes that may hint at changes to the way it spreads or the efficient of that spread among humans."

See also:

Feb 13 WHO risk assessment

Feb 13 CHP statement

Feb 13 Eurosurveill report

FluTrackers H7N9 human case list

Virology Down Under blog

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