A brambling from Beijing, a wild bird from Korea and a duck from China’s Zhejiang province probably helped spawn the new flu variant that’s killed 11 people, a study in the New England Journal of Medicine found.
The birds were infected with avian flu strains that most resemble the H7N9 virus circulating in eastern China, according to an April 11 study by researchers at the Chinese Center for Disease Control and Prevention in Beijing and Fudan University in Shanghai.
At least 44 people have been sickened with H7N9 flu, which the authors said causes brain damage, muscles to break down and vital organs to fail in its most extreme form. Different mutations in samples taken from patients suggest the virus entered human populations at least twice, the study found.
“We are concerned by the sudden emergence of these infections and the potential threat to the human population,” Rongbao Gao and colleagues wrote. “An understanding of the source and mode of transmission of these infections, further surveillance, and appropriate counter measures are urgently required.”
The new strain, which hasn’t been detected in humans or animals before, raises “many urgent questions and global public health concerns,” Timothy Uyeki and Nancy Cox, flu scientists at the Centers for Disease Control and Prevention in Atlanta, said in an accompanying editorial in the journal.
There’s no evidence that the virus is spreading among people, though a previous avian flu outbreak caused by a related variant in the Netherlands showed limited human-to-human transmission is possible, the Chinese researchers said.
Beijing said today that a seven-year-old girl from the city whose parents sell live poultry was infected with H7N9, the first case to be reported in northern China.
Shanghai’s government reported two more cases and another death on its official microblog yesterday, taking the death toll in China’s financial hub to seven and the number of infections to 20. Other cases have been reported in the eastern provinces of Anhui, Zhejiang and Jiangsu, for a total of 43 infections and 11 fatalities.
In 2009, a novel swine flu virus, known as H1N1, touched off the first influenza pandemic in 41 years. The H5N1 bird flu strain, which killed at least 371 people over the past decade, hasn’t acquired the ability to spread easily among people.
“The 2009 H1N1 pandemic taught us many lessons, including that a pandemic virus can emerge from an animal reservoir in an unexpected location and be spread rapidly through air travel,” Uyeki and Cox wrote.
H7N9 infections are cause for concern because most patients observed so far have been severely ill, the World Health Organization said on its website, adding that both animal-to-human and human-to-human routes of transmission are being “actively investigated.”
It’s possible the severe cases that have been reported over the past five weeks represent a fraction of the total number of infections that have occurred, with some going undetected because they had mild or no symptoms, Uyeki and Cox said.
Detailed analysis of the genetic makeup of the H7N9 virus showed its six internal genes came from an avian H9N2 strain, resembling one collected from a brambling, a type of finch, isolated in Beijing last year, the Chinese researchers said.
The gene coding for a surface protein called hemagglutinin, which allows the virus to grip onto host cells, resembles an H7N3 virus collected from a duck in Zhejiang in 2011. The gene coding for neuraminidase, a protein on the surface of the virus that enables it to escape from infected cells, resembles an H7N9 virus isolated from a wild bird in Korea in 2011, they said.
The gene sequences indicate these viruses may be better adapted than other strains of bird flu to infecting mammals, Uyeki and Cox said. For example, a mutation in the hemagglutinin of H7N9 gene has been shown to aid its infiltration of the upper respiratory tract of mammals, and to increase transmissibility.
The coming weeks will reveal whether the disease pattern reflects a widespread outbreak in birds, whether an H7N9 pandemic is beginning, or something in between, Uyeki and Cox said.
“The key is intensified surveillance for H7N9 virus in humans and animals to help answer important questions,” they said. “We cannot rest our guard.”