Scientist Dr. Adrienne Meyers puts waste into a double-door autoclave to sterilize it with heat and pressure before the material leaves the Containment Level 4 laboratory of the Public Health Agency of Canada's National Microbiology Laboratory in Winnipeg, Manitoba. An international team of scientists at the laboratory is researching how the 1918 flu killed more than 50 million people around the world.

Washington ? A Frankenstein version of the “Spanish flu” virus, assembled from parts in the laboratory, has shed new light on how the microbe killed at least 50 million people worldwide in 1918 and 1919.

Experiments in monkeys reveal that the 1918 virus came with the pre-packaged capacity to limit the immune system’s ability to fight back in the first few days after infection. As the virus grows unchecked, the body attacks it with increasing quantities of highly toxic substances, which over time do as much harm to the host as to the invader. The result is often lethal damage to the lungs, where most influenza virus growth occurs.

The research provides further evidence that the 1918 virus had traits not found in other flu viruses, but that it was the body’s frantic effort to fight it that ultimately killed many of its victims.

“We know that the virus itself is different, and we know that the host response is different,” said Yoshihiro Kawaoka, a virologist at the University of Wisconsin, who headed the international research team working in Canada.

The flu was most lethal in young adults, the segment of the population that is usually most able to fight off severe infections. Many died a week or more after falling ill, with autopsies showing they had pneumonia caused by bacteria that had opportunistically infected their virus-damaged lungs.

There were many reports, however, of people dying more quickly, occasionally even within a day of first symptoms. They presumably succumbed to the viral infection alone.

While many of the victims of bacterial pneumonia would be saved today with antibiotics, which didn’t exist in 1918, there are still few treatments for the overwhelming viral pneumonia seen in Spanish flu. Consequently, understanding how it occurs on a molecular level is a high priority. That is especially true now, because the H5N1 “bird flu” strain of virus circulating in Southeast Asia has killed some of its 267 victims with viral pneumonias reminiscent of Spanish flu.

The new research, being published in the journal Nature, is possible because in 2005 American researchers successfully completed the laborious work of copying the 1918 virus’s genetic blueprint, or genome, using fragments of tissue from three victims of the pandemic.