There's no conclusive evidence to show the current avian
influenza virus H5N1 can be spread among humans at present but the
evolution of the virus was unpredictable, according to a senior
official from the Chinese Center for Disease Control and
Prevention.
Suspected cases of human-to-human transmission in Indonesia have
set off international alarm bells. Six family members from a remote
farming village on Sumatra died after testing positive for the H5N1
virus -- the world's largest reported family cluster.
Shu Yuelong, director of the National Influenza Center under the
Chinese Center for Disease Control and Prevention, said suspected
cases of human-to-human transmission had also been reported in
Vietnam, Thailand and other countries.
However, there had been no conclusive evidence yet showing that
H5N1 had evolved into a human-to-human transmission virus, Shu was
quoted by China Population News as saying.
Both epidemiological and etiological evidence was needed to
determine whether a virus could be transmitted between humans, Shu
said.
The H5N1 virus had acquired the ability to infect and kill
mammals but the number of human infections was still small, Shu
said.
Research of the National Influenza Center showed the virus
extracted from Chinese bird flu patients was genetically different
from those in Vietnam, Thailand and Indonesia.
No trace of human influenza had been found in the gene of the
virus extracted from Chinese patients of bird flu, Shu added.
The H5N1 virus remained mainly a virus of birds but experts fear
it could change into a form easily transmitted from person to
person and sweep the world.
Most human cases can be traced to direct or indirect contact
with infected birds.
The virus has killed 130 people around the world since 2003
according to the World Health Organization (WHO). Some 200 million
birds have died or been culled.
So far China has recorded 19 human cases of bird flu with 12
deaths. More than 30 outbreaks of bird flu have been reported in
China since last October. The latest outbreak occurred in north
China's Shanxi Province, said sources with the Ministry of
Agriculture.
Liu Xiufan, a bird flu control expert, said the Chinese
government should review the strategies and effects of the bird flu
control efforts of the past two years and improve them to cope with
the situation which was still a serious threat.
"When, and to what extent, the current avian influenza virus
could evolve into a human pandemic is unpredictable,” said Liu. “We
should do our best to reduce the risk of a human pandemic breaking
out and make necessary preparations before such a situation becomes
reality."
Some changes in the H5N1 strain have occurred recently with and
increased virulence in ducks and the available vaccines were
ineffective in protecting poultry, said Liu.
The H5N1 strains isolated from 2004 to 2006 had increased their
ability to replicate in mammalian cell culture. The transmission
route of the virus was changing from fecal-oral to air bound, he
said. The virus had increased resistance to the environment
especially to temperature.
China faced an enormous challenge in eradicating the virus
because it had been circulating in poultry in China for some time.
He said in some Asian countries such as Japan, the Republic of
Korea and Malaysia outbreaks of bird flu in poultry did occur
several times in 2004 and 2005.
However, no human cases were reported because the outbreaks were
stamped out very quickly, Liu said.
Currently the chances of transmission of H5N1 from birds to
humans remained low as the species barrier exists, Liu explained.
However, the virus could adapt and might acquire the ability to
cross the species barrier to transmit infection to mammals and
humans through gene mutation, he added.
"Therefore the better avian flu in poultry is prevented and
controlled, the quantity and lifespan of the H5N1 virus is reduced,
thus lessening the risk that avian flu might evolve into a human
pandemic," Liu said.
(Xinhua News Agency June 22, 2006)