Worrying bird flu mutations

Oct 7 2007

According to researchers in the United States even thought the H5N1 bird flu virus has not transformed into a pandemic strain, it has nevertheless slowly evolved into a pathogen better equipped to infect humans.

Dr. Yoshihiro Kawaoka of the University of Wisconsin-Madison says they have identified a specific change that could make bird flu grow in the upper respiratory tract of humans and that is a worry.

Dr. Kawaoka and an international team of scientists conducted a study on the virus and say samples of the virus recently taken from birds in Africa and Europe all carry the mutation and these viruses now circulating in those areas are the ones closest to becoming a human virus.

The new study also involved two different viruses isolated from a single patient -- one from the lungs, the other from the upper respiratory system.

Dr. Kawaoka says the virus from the upper respiratory system showed a single amino acid change in one of the key proteins for amplification of influenza virus genes.

The virologist says while he does not intend to spread alarm it is important the scientific community understands what is happening.

The H5N1 avian flu virus is in the main a disease of birds and has been circling the globe since it reappeared in 2003.

Since then it has infected 329 people in 12 countries, killing 201 of them, but it is almost always contracted by handling infected birds or poultry.

It is rarely passed from one person to another, but should it mutate and acquire that ability it could cause a pandemic.

It is in the nature of all flu viruses to constantly evolve and mutate and scientists believe it is only a matter of time before the H5N1 changes from one that infects birds easily into one that infects humans easily.

Dr. Kawaoka who is an internationally recognized authority on influenza, says birds usually have a body temperature of 41°C (106 °F), and humans are 37°C (98.6 °F) and the human nose and throat, where flu viruses usually enter, is usually around 33°C (91.4 °F).

However the particular mutation seen in the study does allows H5N1 to live well in the cooler temperatures of the human upper respiratory tract and is closer to to human-like flu says Dr. Kawaoka, potentially setting the stage for a flu pandemic.

The study is reported in the Public Library of Science journal PLoS Pathogens.