A fresh wave of H5N1 is responsible for the death of a teenager in Egypt and thousands of chickens in India. Specialists fear the virus is mutating and that the vaccine against it is no longer effective.
REUTERS - The re-emergence of birdflu in in Asia and Egypt has prompted experts to ask tough questions: are poultry vaccines effective against a virus that is constantly mutating, and are governments doing enough to stop it spreading?
The virus turned up last week in a farm equipped with modern biosecurity measures in Hong Kong, killing over 100 chickens and leading to the culling of some 80,000 birds there, in nearby farms and a wholesale market.
Now Guan Yi, an expert on the H5N1 virus at the University of Hong Kong, has warned that poultry farms in some parts of the world were using vaccines that didn't provide full protection against the H5N1 and can't keep up with its mutations.
"That vaccine (used in Hong Kong) was made to fight an American strain of the H5N2, and it is very distant from the Guangdong strain of the H5N1 virus here," he said.
"When there were no outbreaks, we just assumed it was protective. Now that there is an outbreak (in the Hong Kong farm), we assume it is useless," he said in an interview.
While the use of human vaccines is overseen by the World Health Organisation, supervision over the use of veterinary vaccines is far more lax.
"For human vaccines we have recommendations by the WHO. For veterinary vaccines there is no such thing at this oment,"
said Albert Osterhaus, a leading virologist at the Erasmus Medical Center in Rotterdam.
"There is a quality issue and there have been lower quality vaccines seen in the past.
Since late November, the virus has infected two children in Indonesia, killing one of them. It also killed a 16-year-old girl in Egypt this week and made a young man in Cambodia ill after he ate chicken that later tested positive for the virus.
Alarm is also building in India, where hundreds of thousands of chickens are being culled in West Bengal, Assam and neighbouring Meghalaya following outbreaks of H5N1.
Vaccine no longer effective
"The virus is definitely mutating," Guan said, warning that in some areas authorities were using batches of vaccine that
were no longer effective.
Guan said the poultry vaccine China currently uses is based on a H5N1 virus strain from 1996/1997, while Hong Kong uses a vaccine based on a 1995 strain of the H5N2 virus.
"But we are going into 2009 now. Could these vaccines still be effective?" he asked.
Since 1997, when H5N1 was first identified in people in Hong Kong, scientists have discovered 10 clades, or branches, of the H5N1, which shows the speed and extent at which it is mutating.
The strain that is circulating in Indonesia, for example, is very different from the H5N1 strain that has been making the rounds in Europe, the Middle East and Africa, which experts say was brought to those parts by migratory birds after picking up the virus in China's Qinghai Lake.
"The poultry vacines do work if they are used correctly, but there are speculations that the strains that are being represented in the vaccine do not match well enough with the circulating virus," Osterhaus said.
"There is a theoretical possibility the strain being used in the vaccine is too far away from the circulating strain."
While the H5N1 virus remains largely a disease among birds, it has infected 391 people in 15 countries since 2003, killing
246 of them. Experts fear it could trigger a pandemic killing millions if it could transmit more easily among people.
Doctors and bird flu experts are monitoring about 100 villagers in Guwahati city in Assam after they came down with fever and respiratory infections, symptoms of the H5N1 bird flu virus in humans, but the cases have yet to be confirmed.
Lo Wing-lok, an infectious disease expert in Hong Kong, says governments have also to be alert to the smuggling of chickens across borders, especially when poor vaccines may be "masking" the disease in poultry, but not preventing its spread.
"Governments must know when the high-smuggling seasons are and stop such activities," Lo said.
Date created : 2008-12-16