Tired of Hollywood's formulaic holiday fare? Check out a movie showing this week on Science's Web site --a mystery thriller with a cast of two. The 87-second clip shows a malaria parasite entering a human liver cell, apparently jostling its way right through, then exiting as if nothing had happened. Researchers say the strange behavior adds another twist to the parasite's already complex life cycle.
Most researchers thought that after entering the bloodstream via a mosquito bite, the parasite, then in a life cycle stage called a sporozoite, quickly traveled to the liver to infect a single cell. The fact that these needle-shaped sporozoites may travel through as many as four other liver cells before settling down in one comes as a surprise.
The movie was shot in 1989 by a New York University (NYU) team, but it was never published; most researchers didn't quite know what to make of the findings, and some thought the behavior displayed in the short movie might be an artifact. But when cell biologist Ana Rodríguez came to the same NYU department last year, she took a closer look. Together with her colleague Maria Mota, Rodríguez designed a series of experiments to find out what was happening. For instance, when they added mosquito saliva containing sporozoites to cultured mouse liver cells, 10% to 30% of the cells showed signs of punched membranes, the team reports in the 5 January issue of Science. Such wounds don't occur during an ordinary infection, in which the parasite induces the liver cell to encapsulate it.
"I think it's a very elegant demonstration of a new phase in the parasite's life cycle," says Stephen Hoffman, a malaria researcher at the Naval Medical Research Center in Silver Spring, Maryland. Rodríguez speculates that the parasites like to shop around to find a "good" liver cell to infect. Or maybe passing through multiple liver cells somehow activates the parasite, preparing it for the real thing. Rodríguez's first priority now is to find out why parasites show this behavior and how they do it. Watch for the sequel.