The Food and Drug Administration has approved the first West Nile virus (WNV) blood test to screen donors of blood, organs, cells, and tissues. The test, called the Procleix WNV Assay, detects viral ribonucleic acid.

So far, 30 people who probably acquired WNV from a blood transfusion have been identified. Nine of them died. Using the test to check blood supplies for WNV, blood banks across the nation have found about 1,600 infected donations.

Carried by mosquitoes, WNV is the leading cause of arboviral encephalitis in the United States, according to the Centers for Disease Control and Prevention (CDC). The CDC reports that WNV caused more disease in 2005 than in 2004, with nearly one-third of human cases occurring in California.