Chickens and ducks didn’t get sick from a new strain of bird flu that emerged in Asia in 2013, but they gave it to people and many died. Infected birds were culled, live-bird markets temporarily closed and farms quarantined to prevent its spread, but the virus probably still lurks. The new avian-flu variant killed more than 130 people in China. Since peaking in January 2014, human infections have diminished, easing concern that the germ could touch off a global contagion if it mutated into a more infectious form.
Over 400 cases of H7N9 avian flu were recorded by the FluTrackers infectious disease message board between February 2013 and April 2014. Almost a third occurred in an initial wave from February to May 2013, mostly in eastern China. A second wave in winter sickened 301 people, including four from Hong Kong. Some patients spent months in the hospital after catching the germ, which can cause suffocation and organ failure. H7N9 isn’t nearly as infectious as the H1N1 swine flu strain that set off the 2009 influenza pandemic, the first in 41 years, but it appears to be a lot more deadly. Precisely how people get infected isn’t known, but poultry are implicated because most people are affected after exposure to fowl or to environments that might be contaminated with bird flu virus, like markets. There’s no evidence of sustained human-to-human spread. Dozens of farm workers have antibodies against H7N9, suggesting many were infected without getting sick.
H7N9 is a novel virus that evolved from several avian flu strains. People have no natural immunity to it and there’s no vaccine. The germ is adept at invading both bird and human cells but it hasn’t acquired the mutations needed to spread easily through coughing and sneezing. That risk increases with more human cases. The virus does have the ability to incorporate a mutation that causes resistance to Tamiflu, the world’s best-selling flu treatment, and reduced sensitivity to a related drug called Relenza.
H7N9 is hard to stop because it spreads among poultry without causing the mass die-offs characteristic of previous bird-flu outbreaks. That makes the tradeoff between economics and health especially tricky. Public health officials want live-bird markets closed and affected flocks slaughtered in affected regions, which disrupts the poultry trade and hinders the local economy. That tussle has implications beyond China, a country with a history of spawning viruses that go global and not always getting a jump on them. The 1957-58 Asian Flu and 1968-69 Hong Kong Flu pandemics were first identified in the world’s most populous nation. Both pandemic viruses contained genes from bird flu strains.
The Reference Shelf
- Read frequently asked questions on H7N9 from the Food and Agriculture Organization of the United Nations (FAO), Centers for Disease Control and Prevention (CDC), and the World Organization for Animal Health (OIE).
- The U.S. CDC answers the question: Is H7N9 flu something to worry about?
- Zhang Zhongqiu, director general of the veterinary bureau in China’s Ministry of Agriculture, explains what’s being done to control H7N9.
- WHO gives an overview of the emergence and characteristics of H7N9 and the late Edwin D. Kilbourne chronicles the three flu pandemics of the 20th century.