More than 10 years ago, Jerome Vanderberg of New York University captured on film a sporozoitea stage in the life cycle of the malaria-causing Plasmodium parasiteblasting through a human liver cell like a speeding bullet. It was not textbook behavior. Most researchers assumed that, post-mosquito-bite, Plasmodium sporozoites targeted single cells almost immediately, tricking the cells into cloaking them within vacuoles, as do most other parasites, and setting up shop. (From there, the sporozoites normally produce tens of thousands of merozoites, which go on to infect red blood cells.) But in Vanderberg's movie, the sporozoite shot right through the liver cell, merely punching holes in its membrane. Scientists didn't know what to make of it, and some assumed it was an artifact: perhaps the parasite swam beneath the cell, not through it. So the clip was filed away and never published.
Until now, that is. Cell biologist Ana Rodrguez joined the NYU department last year and dusted off the old footage. She and colleague Maria Mota devised a series of experiments to determine whether seeing was believing for the fleeting parasite. They developed means for testing when cells had been wounded and repaired, and applied it to cultured mouse liver cells exposed to Plasmodium yoelii sporozoitesand to liver cells from living animals infected with malaria. Their results, published in today's issue of Science, showed that 10 to 30 percent of the cells had been punctured. In addition, many had spilled their contents. The team further demonstrated that the parasites hadn't formed vacuoles inside affected cells and that their passage didn't lead to infection. Only after several quick invasions did the sporozoites settle down inside one cell. Next Rodrguez hopes to find out why the parasites seem to shop around for a host cell.