West Nile virus, a mosquito-borne flavivirus, first appeared in the U.S. in 1999, infecting birds and horses, and then shortly thereafter human cases appeared. According to the Centers for Disease Control and Prevention, there were 62 reported human cases in 1999; 4,156 in 2002; 4,269 in 2006; 720 in 2009; and 5,674 in 2012.
At first, WNV was thought to be transmitted to humans only through infected mosquitoes, but in 2002 it was determined that transfusion transmission had caused WNV infection in at least 21 people. Because 80 percent of people infected with WNV are asymptomatic, the only way to detect infected blood donors is to screen a sample of their blood using tests based on nucleic acid amplification technology. NAT tests have been under development since 2003 and were used initially under IND (investigational new drug) testing. In December 2005, FDA approved the first NAT test to screen for WNV in donors of blood, organs, cells and tissue as well as non-heart-beating donors. In 2006, a total of 340 prospective blood donors tested positive when screened for WNV. A total of 145 prospective blood donors tested positive when screened for WNV in 2009, as reported to AABB's surveillance program.
AABB works closely with the FDA and CDC to continually assess the latest scientific information and develop appropriate tools and policies to further reduce the risk of WNV transmission through blood transfusions.
AABB encourages blood centers and testing laboratories to report suspected reactive and presumed viremic donations (PVDs) to the West Nile Virus Biovigilance Network promptly.