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A word about the H7N9 influenza

Posted on by Laurie Garrett

Ten months ago, this new form of bird flu, which appears to represent a recombination of four forms of influenza that have circulated in China for a few years, surfaced in people in Shanghai. By March, the virus seemed to be in widespread circulation across a densely populated swath of Eastern China, surrounding Shanghai and Jiangsu. At the time I wrote a piece for Foreign Policy asking, “Are we watching a pandemic being born?”

Chinese authorities responded to the outbreak with obvious frustration, as the human cases – in some instances spreading between people – had no obvious source. After two months of hard sleuthing, amid a mounting human death toll, Chinese researchers determined that people were getting H7N9 from live poultry, sold in animal markets all over the region. Shutting down those markets stopped the H7N9 outbreak, with human cases slowing to isolated, sporadic ones by late May. Despite the clear evidence that live animal markets were a crucial piece of the puzzle, and calls from Hong Kong scientists for permanent closure of the poultry vending points, Chinese authorities were stumped. After more than six months of research scientists found some animal market workers last spring had mild, unreported ailments due to their exposures to H7N9. The epidemiology pointed to the animal markets, but the birds were not ailing or dying, and no single species seemed to be clearly linked to any human case. Meanwhile, H7N9 seemed significantly more virulent in humans than any other flu, save H5N1 avian influenza that has been in circulation since the mid-1990s. About one third of H7N9 patients have died from the infection.

(Courtesy Reuters/Jason Lee)

With seasonal warming, H7N9 disappeared, and health authorities around the world crossed their finders, hoping they’d seen the last of the virus. But H7N9 resurfaced in October, on the other side of China: Guangdong province and, from there, Hong Kong. As was the case ten months ago, authorities cannot find clear connections between infected birds and humans, there is some evidence of human-to-human transmission, and closure of live animal markets seems advisable. China’s neighbors are now getting nervous, and recently, the U.S. Centers for Disease Control and Prevention issued a level two travel advisory for China. (Shanghai health authorities announced that from January 31 to April 1, 2014, all its animal markets will be shut down. We were left to wonder why they are waiting until late January, given H7N9 is already in circulation; why the closure isn’t extending across a broader Chinese geography; and where people will find chickens, ducks, geese, and pigeons to eat. It is not common practice in China to sell poultry that is butchered, wrapped in cellophane, and sold from refrigerated supermarket cases, as is the case in the West. If Chinese people can manage to find poultry to eat during a live market shutdown, why not now make the transition to safer market sales of bird meat?)

Recent surveys find distribution of influenza across China is a mosaic of the older H5N1 virus, H7N9, and several other bird flus, creating real headaches for the country’s surveillance team. Finding flu in a bird doesn’t mean it’s the right flu. In October, researchers reported the H7N9 virus has an unusual dual capacity, genetically, to infect mammalian respiratory tract cells while retaining avian infection capacity. This week, researchers from the Mount Sinai School of Medicine in New York revealed that genetic studies of H7N9 show more disturbing facets of the virus. It is completely resistant to the primary anti-flu drug Tamiflu (oseltimivir) and its chemical kin, and partially resistant to the only other class of anti-influenza drugs. Despite having the capacity to withstand anti-viral treatment, H7N9 remains virulent and transmissible. One set of mutations imparting resistance has not forced a predicted diminution in other powers of the virus.

We will be watching H7N9 closely as winter unfolds in Asia.