Parasite can't survive without its tail.

The parasite that causes African sleeping sickness can't survive in the mammalian bloodstream without its tail, scientists report. The finding could lead to novel ways to fight this disease.

Trypanosoma brucei has a two-part life cycle in which it inhabits the tsetse fly and then a mammal. Although the parasite takes on slightly different forms in these two hosts, both forms have along, whiplike tail called a flagellum.

While investigating how T. brucei's flagellum operates, microbiologist Keith Gull of the University of Oxford in England and his colleagues made an exhaustive catalog of the structure's 380 proteins. Then, to determine the proteins' functions, the researchers selectively prevented the parasite from making each one.

Disabling any flagellum protein in the T. brucei form that inhabits the tsetse fiyprevented the protozoan from moving around in lab dishes but had little effect on its hardiness or reproductive success. However, when the researchers performed the same experiment on the form that inhabits mammals, they found that the parasite couldn't divide effectively. Rather than splitting, it formed abnormally large cells with multiple nuclei and then rapidly died.

Developing drugs that have a similar effect on T. brucei's flagellum proteins could eventually be a strategy for attacking the parasite in people, Gull's team suggests in the March 9 Nature.--C.B.