Bird Flu Genetic Analysis Reveals Easy Adaptation To Humans
April 15, 2013

Genetic Analysis Of H7N9 Bird Flu Strain Reveals Easy Adaptation To Humans

Lawrence LeBlond for - Your Universe Online

The new bird flu strain that has so far killed 11 people in China has been showing signs that it is quickly adapting to mammalian (particularly human) hosts, according to a new study led by Masato Tashiro of the Influenza Virus Research Center at the National Institute of Infectious Diseases (NIID) in Japan, along with Yoshiro Kawaoka of the University of Wisconsin-Madison (UWMadison) and the University of Tokyo.

Despite the growing fears that humans are readily being affected by this new strain, with at least 40 confirmed cases of sickness, the researchers maintain that it is still too early to predict potential for a global pandemic. The research was published April 11 in the journal Eurosurveillance.

The findings were drawn from genetic analysis of the new H7N9 virus strain. Samples of the strain had been deposited into an international database by Chinese researchers hoping to get a grip on the virus early. The research results are significant, as the first cases were seen less than three weeks ago — the first human cases were reported on March 31 by the US Centers for Disease Control and Prevention (CDC).

The research group examined the genetic sequences of H7N9 isolates from four human victims as well as samples from birds and environs of the Shanghai market where the birds were being sold.

Study coauthor Kawaoka, an avian influenza expert, said: "The human isolates, but not the avian and environmental ones, have a protein mutation that allows for efficient growth in human cells and that also allows them to grow at a temperature that corresponds to the upper respiratory tract of humans, which is lower than you find in birds."

When the research news broke four days ago, human cases were at 33 illnesses with nine deaths. Today´s figures confirm that cases are growing steadily, but still do not facilitate fears that a pandemic is in the making. Kawaoka said, however, that gaining access to the genetic information in the virus will help researchers understand how the virus is evolving and allowing for the development of a vaccine to prevent further infection.

Influenza depends on its ability to attach and take control of living cells in order to replicate and spread effectively. Avian bird flu rarely infects humans, but can pose a significant health risk if and when it does adapt.

"These viruses possess several characteristic features of mammalian influenza viruses, which likely contribute to their ability to infect humans and raise concerns regarding their pandemic potential," Kawaoka and his colleagues said in the report.

The majority of the viruses the researchers examined in the study — those that derived from both human and birds — have been found to display mutations in the surface protein hemagglutinin, which the virus uses to bind to host cells. Kawaoka explained that those mutations allowed the pathogen to easily adapt to infect human cells.

The researchers also found that the isolates from patients contained another mutation that allows the virus to easily replicate inside human cells. This same mutation lets the H7N9 thrive in the cooler temperatures of the upper respiratory system of humans.

Currently, the strain is spread among avian species, and humans who come into contact with affected birds run the risk of becoming infected as well. As it stands, the virus is not known to be transmissible between humans, but if the virus naturally evolves to adapt to human cells, it could make the leap from just bird-to-human transmission.

A study published last week in the New England Journal of Medicine (NEJM) also worked out the genetics of the avian H7N9 flu strain. In that analysis, researchers described three cases of the bird flu infection that were fatal, with human patients´ conditions deteriorating into severe pneumonia and Acute Respiratory Distress Syndrome (ARDS) relatively quickly. The three patients all had pre-existing medical conditions, and two had been in contact directly with poultry.

Paul Biedrzycki, director of disease control and environmental health for the Milwaukee Health Department, told JSOnline's Karen Herzog that the new bird flu strain appears to have a mortality rate of 20 to 30 percent.

Biedrzycki, who acknowledged that he receives regular reports from federal officials, said it was not known exactly how many cases and/or deaths had been directly linked to H7N9, but did say that health officials believe “we may have an outbreak in Shanghai.”

Chinese public health officials have also not confirmed which avian species is responsible for the spread of the virus, according to Biedrzycki. But researchers are studying a host of birds, including quail and pigeons, which are high on the suspect list.

Kawaoka, speaking to JSOnline in an earlier interview, said the new H7N9 strain is more worrisome than the previous H5N1 strain that he and his colleagues studied previously. Because the strain has not caused severe symptoms in avian species, infection of H7N9 is not as easily detected as H5N1 was, he added.

It´s possible that many birds are carrying this new strain, and humans may not realize they have it if their symptoms are not severe, noted Kawaoka.

"This virus does not have features like highly pathogenic H5N1 viruses," he added. "Unless people show severe infections, such viruses would not be looked at carefully."

Kawaoka´s research on identifying the genetic changes that could potentially allow the H5N1 virus to become a human-to-human spread virus was halted over a year ago when concerns arose that such knowledge could be dangerous if it were to fall into the wrong hands, like those of bioterrorists.

But he maintained that finding those mutations that allow the virus to jump to humans, researchers would be better prepared to assess the likelihood of a new virus becoming dangerous. And it would also allow for the more rapid development of drugs and vaccines to fight it.

The moratorium on the research was lifted this past January, allowing for the research to resume.