(ENS) HANOI -- Newly published research suggests a common source for several of the highly pathogenic bird flu viruses circulating in East Asia. The viruses have claimed the lives of 46 people and hundreds of millions of birds since December 2003 when the most recent outbreaks were first reported in Vietnam and Thailand.
The paper by Doan C. Nguyen and 20 others published in the current issue of the "Journal of Virology" is based on the study of poultry in live bird markets in Hanoi during 2001.
"Since 1997, outbreaks of highly pathogenic H5N1 and circulation of H9N2 viruses among domestic poultry in Asia have posed a threat to public health," Nguyen and his team wrote.
The research team collected samples of five virus subtypes -- H5N1, H9N2, H4N6, H5N2, and H9N3 -- from 189 birds and 18 environmental samples.
The scientists found that certain genes of the H5N1 viruses "shared high amino acid identities with genes of other H5N1 viruses isolated in Asia" during 2001, "but they were genetically distinct from those of H5N1 viruses isolated from poultry and humans in Vietnam during the early 2004 outbreaks."
"These results establish that HP [highly pathogenic] H5N1 viruses with properties similar to viruses isolated in Hong Kong and mainland China circulated in Vietnam as early as 2001, suggest a common source for H5N1 viruses circulating in these Asian countries, and provide a framework to better understand the recent widespread emergence of HP H5N1 viruses in Asia," Nguyen and his colleagues wrote.
The World Health Organization and national health officials around the world are concerned that the virus may mutate to a form that can spread easily from human to human.
Meanwhile, the Vietnamese Ministry of Health March 11 confirmed an additional 10 cases of human infection with H5N1 avian influenza.
The report is an official notification to the World Health Organization (WHO) of some recent cases, whose infection was detected in March, combined with retrospective notification of older cases, some of which date back to late January.
Of these newly reported cases, three people have died of the disease.
This report brings the total number of laboratory confirmed cases in Vietnam, detected since mid-December 2004, to 24. Of these, 13 have been fatal.
This notification of cases follows new reporting procedures established within the Ministry of Health in collaboration with WHO staff in Hanoi. Health officials say the new arrangements will eliminate ambiguous diagnoses, misidentification of patients, and double counting.
WHO said it will issue details showing dates of onset, outcome, and province for all 24 cases as soon as the information comes in from Vietnam's Ministry of Health.
Full information on new cases, including those that may be closely related in time and place, is critical to ongoing assessment of the pandemic risk posed by the H5N1 virus, WHO said in a statement Friday
"Rapid field investigation of each new case is essential to ensure timely detection of clusters of cases occurring in family members or health care workers. Such cases can provide the first signal that the virus is altering its behaviour in human populations and thus alert authorities to the need to intervene quickly," the World Health Organization said.
The first human cases of H5N1 infection, linked to poultry outbreaks in parts of Asia that have been ongoing since December 2003, were reported in January 2004 in Vietnam and Thailand. Since then, a total of 69 cases have been reported, of which 46 were fatal.
Human cases have occurred in three phases, said the international agency. From January through March 2004 there were 35 cases, and 24 deaths.
From August through October 2004, nine cases were reported, of which eight were fatal.
And in the present phase, from December 2004 to date, there have been 25 cases, with 14 deaths. This total includes a single case in Cambodia, which was fatal, in addition to those in Vietnam.
One health care worker in Thailand is breathing a sigh of relief on learning that she escaped infection. A nurse suspected as having bird flu has tested negative for the disease, Vietnamese health officials announced Sunday. Test results provided by the Center for Tropical Diseases in Hanoi showed the nurse was free of H5N1, the deadly strain of avian influenza, said Vietnam's Central Institution of Sanitation and Epidemiology.
The nurse, who worked in a hospital in the Red River Delta province of Thai Binh, was previously thought to be infected and was hospitalized for treatment.
Another male nurse, infected with bird flu four days ago after having had direct contact with infected patients, has shown signs of improvement, doctors said.
The institution is now carrying out an extensive search on how the virus gets circulated in the province of Thai Binh, where a number of people were found to be affected by the disease.
In an attempt to halt the spread of these viruses among poultry, duck flocks in the Mekong Delta will be vaccinated against bird flu in April, according to the Animal Health Department under the Ministry of Agriculture and Rural Development.
The recent inoculation of chicken in the northern province of Ha Tay has shown "encouraging" results, the department announced.
Animal health officials plans to continue using bird flu vaccines made in China and the Netherlands for this inoculation.
The decision to vaccinate birds is a change in the country's official control policy, health officials say. The last government report on control measures issued on February 28, specified the following measures: control of arthropods; control of wildlife reservoirs; quarantine; movement control inside the country; stamping-out policy; and screening.
Chief veterinary officers from 28 countries meeting in Ho Chi Minh City February 23 to 25, declared, "with the success of vaccination in preventing and controlling the disease in the past year in several countries and regions, the meeting agreed that vaccines can be a strong weapon in the fight against the disease in poultry, and the possibility of vaccinating ducks should be explored."
But the veterinary officers called for further study "on the conditions in which vaccines can be delivered with minimum risk to human health."
To date, only China and Indonesia officially allow avian influenza vaccination. Thailand indicated in December 2004 that its health officials are planning field vaccination trials.
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