In a study of nonhuman primates infected with the influenza virus that killed 50 million people in 1918, an international team of scientists has found a critical clue to how the virus killed so quickly and efficiently.
Writing this week (Jan. 18, 2007) in the journal Nature, a team led by University of Wisconsin-Madison virologist Yoshihiro Kawaoka reveals how the 1918 virus – modern history’s most savage influenza strain – unleashes an immune response that destroys the lungs in a matter of days, leading to death.
The finding is important because it provides insight into how the virus that swept the world in the closing days of World War I was so efficiently deadly, claiming many of its victims people in the prime of life. The work suggests that it may be possible in future outbreaks of highly pathogenic flu to stem the tide of death through early intervention.
The study “proves the 1918 virus was indeed different from all of the other flu viruses we know of,” says Kawaoka, a professor in the UW-Madison School of Veterinary Medicine and at the University of Tokyo.
The new study, conducted at the Public Health Agency of Canada’s National Microbiology Laboratory in Winnipeg, Manitoba, utilized the 1918 flu virus, which has been reconstructed by researchers using genes obtained from the tissues of victims of the great pandemic in a reverse genetics process that enables scientists to make fully functioning viruses.
By infecting monkeys with the virus, the team was able to show that the 1918 virus prompted a deadly respiratory infection that echoed historical accounts of how the disease claimed its victims. Importantly, the new work shows that infection with the virus prompted an immune response that seems to derail the body’s typical reaction to viral infection and instead unleashes an attack by the immune system on the lungs. As immune cells attack the respiratory system, the lungs fill with fluid and victims, in essence, drown.
The same excessive immune reaction is characteristic of the deadly complications of H5N1 avian influenza, the strain of bird flu present in Asia and which has claimed nearly 150 human lives but has not yet shown a capacity to spread easily among people. “What we see with the 1918 virus in infected monkeys is also what we see with H5N1 viruses,” Kawaoka says, suggesting that the ability to modulate immune response may be a shared feature of the most virulent influenza viruses.