H7N9 Bird Flu Transmits From Person to Person, Study Finds

The virus attaches itself to cells in the windpipe and lungs, infecting even cells lodged deep in the respiratory system

Contrary to previously published reports, the deadly H7N9 bird flu can spread from person to person and may be a serious threat to humans, Chinese health officials report.

The virus, which has killed one-third of the patients hospitalized with it, attaches itself to cells in the windpipe and lungs, infecting even cells lodged deep in the respiratory system, said researchers who analyzed the biological features of the virus.

This dual-target binding may make the virus better able to jump from birds to humans, according to their report, which was published July 3 in the journal Nature.

"The new virus has a unique binding property," said lead researcher Yuelong Shu, director of the Chinese National Influenza Center at the China CDC in Beijing.

There is no need for widespread alarm, however, another expert said. The same aspects of the H7N9 flu that make it so severe -- its location in the lower respiratory system, for example -- also make it harder to transmit from person to person.

Since this bird flu strain was identified in February, 132 cases, including 39 deaths, have been confirmed in China, according to the study. Most patients were elderly and at high risk of complications because of their age, and many had contact with poultry, according to previous reports.

Unlike H5N1 (another bird virus that appeared in 2003) and H1N1 flu viruses, the H7N9 binds to bird and human cells.

"Our study describes several important features of the novel avian H7N9 virus that has emerged in China," Shu said. "We strongly believe that it is a new pathogen posing high risks to humans."

Shu's team analyzed characteristics of the virus using cell and tissue samples, including some from three humans with H7N9.

"It is essential to characterize the biological features of the new virus so that appropriate public health measures could be planned to prepare if it becomes pandemic," Shu said.

Once infected, patients have unusually high levels of inflammatory and immune cells, referred to as a cytokine storm, which may contribute to symptom severity, he said.

The severity of H7N9 infection and its emerging resistance to antiviral drugs make treating it a challenge, Shu said. Also, its unpredictable evolution and adaptation and the lack of pre-existing immunity leave the human population at high risk, he said.

Dr. Marc Siegel, an associate professor of medicine at the NYU Langone Medical Center in New York City, said sustained transmission is what makes a virus a problem for humans.

"This is yet another virus with some potential to do humans harm, but not high on the list in terms of probabilities," he said.

"It's out there, meaning that scientists and epidemiologists have to keep careful track of it," he said. But at present, "there is no evidence that it spreads rapidly from human to human."

Still, Siegel supports developing a vaccine against H7N9 as a precaution. "But I wouldn't ramp up and start making a million doses," he said.

H7 flu viruses have never caused a human pandemic, Siegel said. "It's a bug we need to follow and scientists need to be concerned about it, but not the general public," he said.

A report in the June 23 issue of the journal The Lancet suggested that H7N9 has a lower death rate than H5N1, which killed about 60 percent of patients admitted to the hospital, but is deadlier than the 2009 H1N1 swine flu virus that killed 21 percent of patients who were hospitalized.

Source: CDC