The St. Jude team showed that the flu virus enzyme neuraminidase (NA) strips lung cells of their protective forest of molecules called sialic acid. The unprotected cells are then vulnerable to subsequent infection with Streptococcus pneumoniae bacteria. But treatment of the mice with the NA-inhibitor drug ostelamivir blocked the activity of flu virus NA and offered significant protection against pneumonia. The study's findings appear in the March 15 issue of the Journal of Infectious Diseases.
"We previously showed that when Streptococcus pneumoniae was given to mice seven days after they had been infected with flu virus, the mortality was extremely high," said Jonathan McCullers, MD, the lead author of the report. "Our current study using tissue in lab dishes, as well as live mice, showed that viral NA is the key to this deadly synergy between flu virus and pneumonia bacteria. The streptococcus bacteria also have NA," McCullers said, "but it is much less efficient than the viral enzyme in cutting away at the lung cell's sialic acid barrier."
The St. Jude finding is important because a combined infection with influenza and pneumonia is the sixth leading cause of all deaths worldwide, and is the top cause of death due to an infection, according to McCullers assistant member in the Department of Infectious Diseases at St. Jude. Moreover, the overall death rate associated with pneumonia and influenza increased by 59% between 1979 and 1994, according to a 1996 report in the Journal of the American Medical Association.
"The flu virus targets the sialic acid molecules on the lung cell membrane surface so it can get inside the lung cell and reproduce
Contact: Bonnie Cameron
St. Jude Children's Research Hospital