Wednesday, October 05, 2005

Bird Flu (3): Source of 1918 Pandemic Reconstructed

...And guess what? It was a strain of bird flu. The Financial Times has the scoop:
The virus responsible for the 1918 Spanish flu pandemic, which killed an estimated 50m people worldwide, has been reconstructed by genetic engineering in a high-security US laboratory.

Preliminary studies show that it is an avian flu virus that mutated to spread quickly between people just as many experts fear will happen soon with the current H5N1 strain of bird flu in Asia. Details of the project are published today in the journals Science and Nature. The US National Institutes of Health approved the research, despite its apparent risk, because it will help scientists find new treatments for the most dangerous types of flu.

The Centres for Disease Control laboratory in Atlanta made a live virus with the full genetic sequence of Spanish flu, using an engineering technique called “reverse genetics” developed at Mount Sinai Hospital in New York.

“We felt we had to recreate the virus and run these experiments to understand the biological properties that made the 1918 virus so exceptionally deadly,” said Terrence Tumpey, head of the CDC team. “We wanted to identify the specific genes responsible for its virulence, with the hope of designing antivirals or other interventions that would work against virulent influenza viruses.”

The key genetic data for the experiment came from the Armed Forces Institute of Pathology in Washington DC. Over the past eight years scientists there have pieced together the entire Spanish flu genome, from viral fragments isolated from preserved lung samples of patients who died in 1918 and from a female victim whose body was fortuitously frozen in Alaskan permafrost.

Many of the flu viruses circulating today were descendants of the H1N1 strain that swept the world in 1918 so the population still had some protective immunity against it, said Jeffery Taubenberger, leader of the AFIP team. “It is unlikely that a1918-like virus wouldbe able to cause a pandemic today.”

The research suggests that Spanish flu arose in a different way to the viruses that caused the other two 20th century pandemics. In 1957 and 1968 an existing human virus underwent genetic mixing with a bird virus to produce a new “reassorted” strain in one step.

In 1918, however, an entirely avian virus gradually adapted to function in humans through a sequence of mutations. Although the analysis is incomplete, about four to six mutations seemed to have taken place in each of the eight viral genes, Dr Taubenberger said.

Ominously, the H5N1 strain currently circulating in Asia is undergoing similar humanising mutations though it has not accumulated as many changes as Spanish flu.

■ Health officials in Jakarta and Hong Kong on Wednesday said tests had shown H5N1 virus in apparently healthy chickens in Indonesia. Until now it had been thought that chickens quickly sickened and died when infected with H5N1. The presence of infected but symptomless chickens could complicate the fight against bird flu.