This negative-stained transmission electron micrograph (TEM) image depicts the ultrastructural details of an influenza virus particle, or “virion” in a 1981 image released by the U.S. Centers for Disease Control (CDC), April 24, 2009. A deadly strain of flu never seen before has killed as many as 61 people in Mexico and has spread into the United States, where several people were reported ill. REUTERS/Cynthia Goldsmith/Centers for Disease Control/Handout (UNITED STATES HEALTH IMAGE OF THE DAY TOP PICTURE SCI TECH DISASTER) FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS
REUTERS/Ho