Friday, October 18, 2002

Testing for West Nile is a high-tech process



By Tim Bonfield
The Cincinnati Enquirer

How do the experts find out whether a tiny mosquito carries an even tinier killer, such as the West Nile virus?

It's a daylong, three-stage process that involves chill tables, microscopes, a Level 3 biohazard containment room, test tubes fitted with special filters, and a new tabletop analyzing machine called a Bio-Rad iCycler that cost the state about $45,000.

The process is fairly tough on the bugs involved.

In Ohio, which has experienced the nation's third-highest number of human cases and deaths from West Nile virus, a crew of seven people with the state's vector-borne disease unit were responsible for tracking the disease as it spread. They tested more than 145,000 mosquitoes this summer and more than 1,600 dead birds.

Human blood and spinal fluid samples were handled by a state lab near the Ohio State University Medical Center or by commercial labs. Horse testing was done by the Ohio Department of Agriculture.

The critical bug and bird work, however, occurred in three rooms at "The Warehouse," a nondescript, one-level building in an industrial park a few miles north of downtown Columbus.

The process starts with vials of dead mosquitoes sent from all over the state. Sitting at a chill table that keeps the surface as cold as zero degrees Celsius (32 degrees Fahrenheit), staffers sort the bugs by species, by hand, into "pools" of up to 50 mosquitoes each.

The sorted bugs then go across the hall to a Level 3 biohazard room, where the room air is constantly vented outside through special filters to keep infectious agents from affecting lab workers or spreading throughout the building. Here, the bugs are ground up and "digested" in a chemical solution. The resulting liquid is repeatedly filtered in specially fitted test tubes to extract viral genetic material called RNA from the rest of the bug.

The final part of the test takes place in a third room, at the Bio-Rad machine, which can analyze up to 94 samples at once. This device, about the size of a fax machine, applies precise levels of heat in repeating cycles to force the virus particles to multiply to measurable levels. About three hours later, the growth rates of each sample pop up as curving, color-coded tracks on a computer screen.

Positive samples appear as fast-rising curves that level off and stay high. Negative samples rise slowly, erratically or not at all.




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