Purdue takes first close-up photographs of West Nile virus

The Purdue team found the virus to be about two millionths of an inch wide -- small even in the minuscule realm of viruses.\n"It's small as viruses come, but that doesn't diminish in any way its ability to infect and kill cells," said Richard J. Kuhn, a professor of biological sciences in Purdue's School of Science.\nKuhn said his team's images show that the West Nile virus is different from irregularly shaped viruses such as influenza, HIV or measles. The surfaces of those viruses have proteins that project away in arm-like appendages they use to latch onto receptors on cells that they then hijack, infect and use to reproduce.\nBy contrast, the West Nile virus is spherical though slightly bumpy with surface proteins folded into an interlocking pattern resembling a herringbone jacket.\nUnderstanding the precise orientation of those proteins -- the Purdue team's next goal -- could speed the development of drugs to thwart its ability to infect cells in birds, humans, horses and other animals.\nThe West Nile virus' lack of projecting surface proteins, though, likely means it will be more difficult to pinpoint the precise mechanism it uses to infect cells, said John T. Roehrig, chief of the arbovirus diseases branch of the CDC's Division of Vector-Borne Infectious Diseases.\n"That's the part of the virus that's a really important target for trying to develop strategies to block the virus replication cycle. But knowing what it looks like really helps a lot," he said.\nTo obtain the images, the Purdue team froze West Nile viruses in liquid ethane to about minus 280 degrees Fahrenheit and aimed a stream of electrons at the frozen particles, one at a time.\nUsing a high-powered electron microscope, they made measurements of how the electrons bounced off the virus' atoms. That data was pieced together into the first detailed images of the virus.\nThe researchers deduced some of the virus's internal structure in part because of its strong resemblance to the structure of another mosquito-borne virus, the one that causes dengue fever.\nThe findings appeared in the Oct. 10 issue of the journal Science.\nScientists have mapped the relatively small genome of the West Nile virus, but that was just one step in understanding how it works.\nAmong other things, Roehrig said researchers are working on biochemical studies to determine how the virus actually replicates once it gets inside a cell.\nThe West Nile virus first appeared in the United States in New York City in 1999 and has since moved westward across the country and become a seasonal menace that is likely here to stay.\nIn areas of the nation where winters are cold, subfreezing readings halt mosquito activity, but in warmer areas the mosquitoes that spread the virus are active year-round.\nAs of Nov. 19, the Centers for Disease Control and Prevention reported 8,470 human cases this year, with 189 deaths attributed to the West Nile virus.\nA West Nile vaccine has been developed for horses, but none currently exists for humans.