Challenges in testing for West Nile virus. (Infectious Diseases).

Blood transfusions and organ transplants appear to have infected some people with the West Nile virus, a sometimes lethal germ that can cause fevers, encephalitis, and even polio symptoms (SN: 9/28/02, p. 293). In response, the Food and Drug Administration is trying to figure out how blood banks can detect signs of West Nile infection in donors and, eventually, test donated blood for the virus itself.

Blood carrying a significant risk of infection will be culled from blood banks, vowed Jesse Goodman, deputy director of the FDA in Rockville, Md., on Sept. 19. However, he noted, no adequate means now exists to screen blood for the virus.

Developing one won't be easy, either. For one thing, blood concentrations of the virus tend to be very low. Although a lab could assay blood for antibodies to the virus, Goodman noted that these may not show up in a person's blood until a few days after the virus begins circulating. Blood donated by that person in that period could therefore contain virus but no telltale antibodies.

Moreover, observes Lyle Petersen of the Centers for Disease Control and Prevention in Fort Collins, Colo., the antibodies can linger in blood for a year or more--well beyond the week or so that infectious viruses would be present. Several hundred thousand U.S. residents probably will get West Nile infections this year, Petersen says, and most will carry antibodies, but they'll remain "perfectly safe blood donors." In fact, Petersen argues, antibody carriers "may be the safest donors" since most will be virus-free and temporarily immune to reinfection.

Goodman asserts that blood-testing agencies need an assay "for nucleic acid--the virus itself." Though one such test exists, Petersen notes that it doesn't establish whether the virus is alive and infective.--J.R.