Susan Young Rojahn

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Bird Flu: On the Move and Hard to Track

The H7N9 virus is deadly to humans but does not present symptoms in birds, which makes it more difficult to control.

  • April 25, 2013

A 53-year-old Taiwanese man has contracted the H7N9 influenza virus, most likely while on a business trip to China, reported the New York Times on Wednesday. This is the first time the virus has been reported outside of China, where that country’s Health and Family Planning Commission says the new strain has infected more than 100 people, 23 fatally, according to CNN.

On Thursday, a study in the medical journal the Lancet provided the first scientific confirmation that the virus is transmitted from birds to humans. The researchers used genetic analysis to test swabs from poultry in live markets in China. They found the virus in pigeons and chickens, but did not find it in any ducks or quail (Chinese officials have reported finding the virus in ducks, according to CNN). The researchers compared the genes and genomes of viruses taken from birds to viruses found in four H7N9 patients and concluded that each human case arose from a bird-to-human transmission.

The study also characterizes the symptoms and outcomes of the four patients; the patients had high fevers, lower respiratory-tract infections and difficulty breathing followed by respiratory failure within three to 14 days. Two of the patients described in the study died.

Co-lead author Kwok-Yung Yuen of the University of Hong Kong told the Lancet that all evidence suggests the virus is transmitted from birds to humans and not between humans. “Controlling [the epidemic in humans] will therefore depend on controlling the epidemic in poultry,” he said.

However, a study published on Wednesday in the New England Journal of Medicine raises the possibility that human-to-human transmission of the virus occurred within two different families after “close prolonged, unprotected contact with a symptomatic patient.”

Birds do not show signs of infection from H7N9, making it hard to track and control its movement in and between flocks, said the World Health Organization at a press conference in China on Wednesday. To minimize the chance that the virus could evolve the ability to pass between humans, the authors of the Lancet article suggest “aggressive intervention[s],” including temporary closure of live bird markets, improved biosecurity, and possibly vaccination programs in poultry. These measures, they say, “seem necessary to halt evolution of the virus into a pandemic agent.”

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