West Nile Virus Lineage 2 from Blood Donor, Greece

To the Editor: West Nile virus (WNV) is a mosquito-borne fl avivirus that primarily causes an asymptomatic or mild disease in humans; however, in <1% of infected persons, it causes neurologic disease. The virus has received increased attention since 2002 when it was established that WNV is transmissible by blood transfusion and organ transplantation (1). A major WNV outbreak occurred in 2010 in Greece; most cases occurred in the northern part of the country (2). Of the 197 WNV neuroinvasive cases reported, 33 were fatal (3). Many nonneuroinvasive cases were observed (4). A lineage 2 WNV (Nea Santa-Greece-2010 strain) was detected in Culex pipiens mosquitoes collected at 2 locations where WNV cases had been reported (5). Although this strain shows high genetic identity to a Hungarian WNV strain isolated from birds in 2004, it has the amino acid substitution H 249 P in nonstructural protein 3 (NS3) (6). This mutation has been associated with increased virulence in WNV lineage 1 strains (7). Clinical WNV disease in humans had not been previously documented in Greece, and surveillance of blood donors in 2006 and 2007 did not show any WNV-positive result (8). On August 11, 2010, shortly after confi rmation of the outbreak of WNV infections in humans in Greece, an action plan for the protection of blood safety was initiated. All donors were asked to report any fever-like illness up to 15 days after donation. Individual donation nucleic acid testing (NAT) of all blood donors living in the WNV-The WNV-positive blood donor was a 40-year-old immunocompetent woman, a resident of a village in northern Greece. The village is located between 2 lakes, and the area is one of Europe's major wetlands. The 2 locations where the WNV-positive mosquitoes were collected are near each other (online Appendix Figure, wwwnc.cdc.gov/EID/article/18/4/11-0771-FA1.htm). The woman was working in an open-air fi sh market and reported numerous mosquito bites. At the time of blood donation, she was asymptomatic; 2 days later she had myalgia, arthralgia, and severe retro-orbital pain, lasting 2–3 days each. A second blood sample taken on August 26 was also NAT positive. An index ≈1.5 for IgM and ≈1.1 for IgG was considered positive. No antibodies were detected in the initial and second serum samples; however, a third sample taken on September 20 was positive for WNV IgM and IgG (indices 4.7 and 3.8, respectively). Nested reverse transcription PCRs with the initial blood sample …