H1N1 swine flu virus. Coloured transmission electron micrograph (TEM) of swine influenza (flu) virus particles (virions) from the April 2009 outbreak, which originated in Mexico City, Mexico. Swine flu is a respiratory disease of pigs caused by type A influenza viruses. This H1N1 strain also contains genetic material from bird and human influenza viruses and is able to spread from human to human. These characteristics give the virus potential to cause a pandemic. Symptoms are similar to those of regular human flu and include fever, cough, sore throat, body aches, headache, chills and fatigue. It can be fatal.
Credit: CDC/SCIENCE PHOTO LIBRARY