Scientists Examine New Bird Flu's Potential to Spread

They looked at transmission between humans and mammals in lab

WEDNESDAY, July 10, 2013 (HealthDay News) -- The new strain of H7N9 bird flu virus has traits that potentially could spark a worldwide flu outbreak, according to a new laboratory study involving virus that was found in humans, then given to animals.

Since it first appeared in China in March 2013, the virus has sickened more than 130 people and killed at least 40 of them, according to the U.S. Centers for Disease Control and Prevention. Many who were infected had contact with poultry. "No evidence of sustained person-to-person spread of the H7N9 virus was found," according to the CDC website.

Authors of the new study are concerned about what could happen if the virus became widespread.

"H7N9 viruses have several features typically associated with human influenza viruses and therefore possess pandemic potential and need to be monitored closely," team leader Yoshihiro Kawaoka, of the University of Wisconsin, Madison, and the University of Tokyo, said in a University of Wisconsin news release.

In this study, an international team analyzed samples of the H7N9 virus from patients and found that it could infect and reproduce in several species of mammals -- including ferrets and monkeys -- and can be transmitted between ferrets.

These findings suggest that the virus has the potential to become a worldwide threat to human health, according to the study, which was published July 10 in the journal Nature.

The ability of the H7N9 virus to infect and replicate in human cells may be due to just a few amino acid changes in the genetic sequence of the virus, the researchers said.

"These two features are necessary, although not sufficient, to cause a pandemic," said Kawaoka, one of the world's leading experts on bird flu. The virus depends on host cells, which it hijacks to make new virus particles and sustain the chain of infection.

In monkeys, the H7N9 virus infected cells in both the upper and lower respiratory tract. In contrast, standard human flu viruses are usually restricted to the upper airway of nonhuman primates infected with them.

"If H7N9 viruses acquire the ability to transmit efficiently from person to person, a worldwide outbreak is almost certain since humans lack protective immune responses to these types of viruses," Kawaoka said.

An expert not involved with the study discussed H7N9's potential to cause a dangerous flu outbreak.

"Fortunately, the epidemic in China was short-lived," said Dr. Bruce Hirsch, of the division of infectious diseases at North Shore University Hospital in Manhasset, N.Y. "Authorities closed some open-air live poultry markets as a precaution. While this virus has the potential to be a major health threat, no one knows if the series of necessary accidents and coincidences at the root of any pandemic will occur."

"The H7N9 strain is completely new in humans," Hirsch said. "People have no immunity and we are vulnerable. As of July 4, 2013, the World Health Organization has reported 133 known cases from which 43 persons have died. This mortality rate of 32 percent is high and indicates that the virus has the potential to cause severe illness."

The new study, he said, "shows how this bird flu virus can attach to human receptors and cause severe illness. The commonly used antivirals, such as Tamiflu, have only modest activity against the virus. They show that the virus can spread between experimental animals. This strain fulfills the conditions to be a 'big one.'"

Both vigilance and further research are needed, said Dr. Adolfo Garcia-Sastre, co-director of the Emerging Pathogens Institute at the Icahn School of Medicine at Mt. Sinai Medical Center in New York City.

"This study ... highlights the need for continuous surveillance for this virus to prevent as much as possible its re-emergence," Garcia-Sastre said. "Up until now, this virus has not been able to transmit efficiently in humans, but we cannot completely exclude that it might acquire this ability by mutation or reassortment. Thus, further research on the biology of the virus and on antiviral and vaccine development is needed."

More information

The U.S. Centers for Disease Control and Prevention has more about the H7N9 virus.

Robert Preidt

Robert Preidt

Updated on July 10, 2013

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