"By blocking the virus NA we protect the sialic acid molecules covering the lung cells," says McCullers. "That leaves the pneumonia bacteria stranded outside the cells and gives the immune system time to destroy them before they can cause respiratory disease."
In the study, one group of mice received prophylactic (protective) doses of oseltamivir for five days, beginning four hours before being infected with flu virus. Another group got oseltamivir for five days starting 48 hours after being infected with flu.
Mice that received delayed treatment lost weight and had greatly increased levels of virus in their lungs by the time they received oseltamivir. However, these mice still had significant protection against subsequent infection by streptococcus bacteria compared to control mice that received no treatment.
"The key to significantly reducing the rate of death in these mice was not reducing virus levels or maintaining weight," McCullers explains. "What was important was blocking the virus NA enzyme with oseltamivir and preserving the protective sialic acid molecules."
The St. Jude team also studied the effect of oseltamivir on bacterial pneumonia using live mice infected with genetically modified streptococcus. These modified bacteria were engineered to carry on a light-producing chemical reaction--the same chemical reaction used by fireflies. The light, too faint for humans to see, passed through the skin of the mice and was picked up by a special camera.
In mice given flu virus and then the "glowing" streptococcus but no oseltamivir, the camera captured images of extensive bacterial infections throughout the thorax--the part of the body containing the lungs. In mice that also received oseltamivir as a delayed treatment after infection with flu virus, the light emitted from the lungs was l
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Contact: Bonnie Cameron
bonnie.cameron@stjude.org
901-495-4815
St. Jude Children's Research Hospital
7-Mar-2003