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Now, two deadly strains of virus

http://www.100md.com   2006-3-24 xinhuanet
     BEIJING, March 24 -- The fight against avian flu is like an "endless hurdle race," once you cross one, there is another.

    That is the challenge facing the world, Julie Hall, co-ordinator of communicable disease surveillance and response in the Beijing office of the World Health Organization (WHO), said yesterday.

    During the Consultation on Social Determinants of Health in the Western Pacific Region, WHO officials told their audience that the disease is still dangerous, the virus is mutating quickly, and the prospects for man-to-man transmission, though not detected till now, remain highly likely.

    And all that mankind can do to cross all the hurdles is by being on a constant alert and readily sharing information among countries and international organizations, she said.

    So far, the virus has killed 103 people in Asia and the Middle East since 2003, including 10 in China.

    Moreover, as Hall reported, the WHO confirmed that new genetic changes of the bird flu virus have recently been reported by scientists in the United States.

    An analysis of H5N1 influenza samples in Southeast Asia showed that the two strains that had caused human infections belong to two different, distinct genetic subgroups.

    Researchers from the US Centres for Disease Control and Prevention reported their findings on Monday at the International Conference on Emerging Infectious Diseases, according to the American Society for Microbiology.

    "As the virus continues its geographic expansion, it is also undergoing genetic diversity expansion," said Rebecca Garten, a researcher who took part in the study.

    "Back in 2003, we had only one genetically-distinct population of H5N1 with the potential to cause a human pandemic; now, we have two."

    Garten and her colleagues conducted a phylogenetic analysis of over 300 H5N1 virus samples taken from both avian and human sources from 2003 through the summer of 2005.

    Not all H5N1 viruses are genetically the same. Over the years, researchers have identified different groups called genotypes. The majority of the viruses, including all the human cases, belonged to genotype Z.

    The WHO has classified genotype Z into subgroups called clades, Julie Hall said.

    In 2003 and 2004, clade 1 viruses were primarily responsible for outbreaks, including all infections among people, in Viet Nam, Cambodia and Thailand. But in 2005, a second strain of H5N1 began causing infections among humans in Indonesia and China.

    "We see now that the predominant cases are caused by clade 2, which, we believe are now spreading through Europe and Africa,?she said.

    Clade 1 and clade 2 viruses may share the same ancestor but are different and can be likened to cousins, Garten said.

    Garten's thoughts were echoed by Hall, who said the two viruses were very closely related and they came from the same source a few years ago.

    Constant changes

    What this means, says Garten, is that the pool of H5N1 candidates with the potential to cause a human influenza pandemic is becoming more genetically diverse.

    "Change is the only constant. Only time will tell whether the virus evolves or mutates in such a way that it can be transmitted from human to human efficiently,?said Garten.

    "We do not know which of these clades, or either of these clades, will cause a pandemic. But it is certainly important we have a library or factual vaccine developed, based on clade 1 and clade 2,?Julie Hall noted.

    So, it is also important for scientists to continue to collect samples of viruses, testing them and developing vaccines based on them, she said.

    In terms of developing pandemic vaccines, she said that scientists can not currently develop a vaccine that will definitely fight against the virus that might cause a pandemic.

    Scientists are producing vaccines based on clade 1 and 2 now. This is an ongoing process, she said.

    "So every time we see new different strains of viruses in particular areas, we have to develop something that can be added to that base vaccine,?she noted.

     Migrant birds

    Although no new human infection cases have been reported in China (and the one suspect case in Shanghai is still to be confirmed, officials said), the return of the warm weather will inevitably give another round of bird migration.

    Millions of wild birds, which may carry the virus, will fly back to their habitats, including the wetland around Northwest China's Qinghai Lake, where a major outbreak of the epidemic was reported in spring 2004.

    Although the virus doesn't generally like hot weather, it may start to spread along with the travelling birds, Hall said. "The important thing is that we now know when the birds come and we know the routines they will take, so we can be better prepared.?

    WHO is urging governments of all nations to do a better job this year in monitoring birds, and especially in sampling the ill-looking ones, she said.

    As an indication of the impact she and her colleagues have made, the municipal government of Beijing issued an open letter to all residents on March 14, calling them to be on high alert. In a couple of days, flyers printed with the open letter were seen in many of the residential neighbourhoods.

    Owners of pigeons, especially, were told that they were not expected to set free their pets in the coming weeks. Because any local birds?mixing with the migrating birds would add new complications to the disease control effort.

    At the same time, at Huairou Reservoir in the northeast suburbs of Beijing, a satellite surveillance system worth 500,000 yuan (US$63,000) has been installed, to monitor the activities of birds flying back from the southern regions.

    It is quite difficult for people to control the migrant birds, or give vaccines to them, experts said. What can be done now, as the public health and agricultural experts agreed at the meeting, is to build a better system of surveillance and do whatever possible to isolate ill birds from human beings and poultry.

    "Migrant birds certainly play a role in transmitting the virus, but it is only one part of the picture,?said Shigeru Omi, regional director of WHO Western Pacific. "The movement of chickens also causes the spread of the virus.?Both factors deserve great attention, he pointed out.

     Surveillence

    Omi also urged China to improve surveillance of wild birds and animals. None of China's 15 cases of human infection of bird flu (10 deaths) occurred in areas where authorities had reported outbreaks in the poultry industry, he noted.

    At the moment, the Chinese disease control system, as Hall of WHO Beijing office noted, is depending heavily on people showing up to hospitals. And as is often the case, those who have the money have the access to the hospitals.

    But poverty makes many people, especially those in rural and distant areas, reluctant to go to hospitals even if they don't feel well. So it is very important that the surveillance system is moved from the healthcare centres to communities and villages, she said.

     Pets at risk

    Other than wild birds, Hall noted, cats, tigers and many other animals have the same degree of infectious risks as human beings. "We do know there have been animals, such as tigers and cats in Thailand, that have been infected by the virus,?she said.

    And with laboratory conditions, scientists can make the virus spread among one cat to the next, although "this is not what we have seen in the wild,?she added.

    So far, like humans, animals can only get infected through direct contact with sick chickens or sick birds. "We believe that the present situation with cats and tigers are similar to the situation within humans,?she said.

    No evidence has been found where the virus is transmitted among cats and other pets, from cats to humans, or human to human transmission. This, according to experts at the Beijing conference, is a good piece of news for most pet owners, at least for the time being.

    Chinese Tamiflu

    At the same time, industry sources say generics of Tamiflu, the only effective drug against bird flu, is expected to be produced in Shanghai by early May.

    Guided by the document of "Special Process for Drug Approval,?the State Food and Drug Administration recently approved bioequivalence studies of oseltamivia (generics of Tamiflu) on human beings, Xinhua News Agency reported.

    "Actually, we have started the clinical trial in Shanghai, which will take around one month.?said an official of Shanghai Sunve Pharmaceutical Co Ltd, who declined to be named.

    "We know globally there is a shortage of this drug. It would be nice if there was a good partnership between China and Roche because China has a large production capacity,?Hall of WHO Beijing office said.

    She said WHO was looking forward to the day when China could produce a version of this drug and hopefully its accessibility to the people would be increased.

    (Source: China Daily)

    Editor: Yao Runping

 
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