Scientists have found that a strain of the H5N1 bird flu virus circulating in Thailand is resistant to the flu drug amantadine, and they called for rigorous study of H5N1 strains to better treat human victims.
While the WHO has long recommended that Tamiflu be used as the first line of defense against H5N1, it said last May that a "dual therapy" combining amantadine and Tamiflu may be considered in case of an outbreak.
Yong Poovorawan, a medical professor at Chulalongkorn University in Bangkok, said an H5N1 strain in the central part of Thailand had become resistant to amantadine, casting more doubt over its use to fight the disease .
"It would be very dangerous if we don´t know the sensitivity or resistance of the strain to amantadine and we use amantadine (to treat people infected with this strain of H5N1)," Yong said.
He urged more rigorous surveillance and study.
"If you follow any new strain you will know the genetic changes, you analyze its molecular structure, make experiments to see which drug it is sensitive to and find out which is the best antiviral for any given strain," he said.
"It´s like a jigsaw, we have to find the pieces and see the big picture."
Yong and his researchers came to the latest conclusion after studying the molecular structure of the strain, which has been circulating in Thailand, Cambodia and Vietnam since 2004.
"We need to conduct in vitro experiments," he said, referring to experiments in a laboratory or other controlled settings.
However, he could not say how effective a dual Tamiflu-amantadine therapy may be as Thailand has not tried administering such a treatment.
Their findings were published in the March issue of the journal Emerging Infectious Diseases.
There are two H5N1 strains circulating in Thailand, one in the northeast and the other in the central part of the country.
Yong identified the strain in the northeast province of Nakhon Phanom as the Fujian-like strain, which an international group of virologists said in October may start another wave of H5N1 outbreaks in poultry in Southeast Asia and Eurasia.
The Fujian-like strain was first isolated in China´s southern Fujian province in 2005.
"The Nakhon Phanom strain is the same as the Fujian-like strain...which is also in (the Chinese provinces of) Anhui and Zhejiang, and Laos," Yong said.
"From the molecular structure, we would say it is sensitive to Tamiflu and amantadine."
Although H5N1 mostly affects birds, the big concern is that it could mutate into a disease that easily passes between people, triggering a global pandemic.
The emergence of various strains of H5N1 is a matter of deep concern because each one may respond differently to different antiviral drugs and vaccines.
"If there are too many strains and they are very different, we will not know the efficacy of the vaccines," Yong said.