West Nile virus -: An emerging transfusion-transmissible pathogen

Recently, some cases of transfusion-transmitted infections of West Nile virus (WNV) have been reported. As a member of the genus flavivirus, WNV may cause a febrile illness with meningoencephalitis. Since more than 95% of infections are asymptomatic, the virus can be transmitted by transfusion of blood from donors in the viremic phase. In Europe, infections in humans are very rare, but in North America the virus has spread through most states of USA and Canada. The epidemic started in New York in 1999, resulting in 149 clinically ill patients from 1999 to 2001 followed by a dramatic increase to more than 8,300 cases, including 182 deaths, in 2003. To our calculations, the risk for a donation to be contaminated with WNV in the USA ranged between 1: 1,000 and 1: 6,000 during summer and may be higher in certain regions. In the USA, PCR testing of approximately 6 million blood donations during June to December 2003 detected 818 viremic donors. In order to minimize the risk, German and Dutch guidelines require the rejection of donors returning from USA or Canada within the first 4 weeks after their return. From the medical point of view, this procedure seems appropriate to minimize the risk of transfusion-associated WNV infections with high efficiency and low expenditure.