Researchers, using needles thinner than human hair, have injected mosquitoes with an aJtered virus that blocked the insects' ability to transmit dengue fever, a major killer i&the tropics, "We don't know how practical this is," said Ken Olson, a researcher at the Oregon State University, US, "But we have shown it is feasible to molecularly alter a mosquito so that the dengue virus cannot reproduce," Olson, lead author of the study, said the researchers altereq a virus called Sindbis so that it made a particular sequence of RNA that blocked the replilation of dengue virus.