Tests Identify the First Human Case of Avian Influenza in Japan
By LAWRENCE K. ALTMAN
Published: December 23, 2004
Tests performed in Japan have identified that country's first human case of avian influenza and four other cases that are almost certainly the same ailment, a World Health Organization official said yesterday.
The organization, a United Nations agency, has said it is deeply concerned about the possibility of the virus, A(H5N1) , mutating into a lethal new virus and causing an epidemic that, at worst, could rapidly sweep the world.
But in these cases, which resulted from an outbreak among chickens in February, none of the people developed symptoms of the respiratory disease, said the health organization official, Dr. Klaus St?
The blood tests were performed only in recent weeks, Dr. St?said, because the lab procedures to identify human avian influenza cases can be very complicated, particularly among people with few or no symptoms.
All five people are believed to have become infected from contact with chickens and none transmitted the virus, known as A(H5N1) avian influenza, to another person, said Dr. St? who is the health organization's top influenza specialist.
Bird flu is highly lethal, having killed 32 of the 44 people previously confirmed to have caught it this year, all in Thailand and Vietnam.
But the tests from Japan confirm reports that the virus can also cause infection that produces mild symptoms or none. Such findings have come from tests of farmers and health workers exposed to the A(H5N1) virus in an outbreak in Hong Kong in 1997, and a different type of avian influenza in the Netherlands in 2003.
''So it is no surprise that it has happened in Japan,'' Dr. St?said by telephone from Geneva.
''Very few people would believe that there haven't been hundreds, even thousands, of transmissions of avian influenza virus that led to a considerable number of mild infections,'' he added.
The confirmed and suspected infections in Japan were found among blood samples taken last spring from 58 people who helped dispose of the dead chickens. The tests detect proteins known as antibodies that develop to fight off infection.
Health officials suspect that the infected people did not take proper precautions, like wearing masks, when they came in contact with the birds or contaminated areas.
Scientists at the National Institute of Infectious Diseases in Tokyo had to adapt laboratory tests developed elsewhere to detect antibodies to A(H5N1) virus in humans. The more sophisticated tests are needed because the level of antibodies of the virus that humans form is much lower than the level formed in response to the regular human influenza, Dr. St?said.
Because the tests involve live viruses, they must be conducted in a laboratory with tight biological security, he said. Scientists also must confirm the findings by using tests validated by other laboratories.
But because the 58 people whose blood was tested were a tiny fraction of workers exposed to the A(H5N1) virus, they did not represent a scientifically valid random sample, Dr. St?said, and firm conclusions about the frequency of symptomless infections cannot be drawn. More information may come from tests to be done on 1,200 blood samples obtained in Korea and hundreds more in China, Thailand and Vietnam.
Scientists need to learn how many people develop asymptomatic infection to understand the risk that avian and human flu viruses will swap genes and create a lethal virus, Dr. St?said. They want better information to learn, among other things, how long people who became infected were exposed to infected animals.