%0 Journal Article %T 2009 Swine-Origin Influenza A (H1N1) Resembles Previous Influenza Isolates %A Carl Kingsford %A Niranjan Nagarajan %A Steven L. Salzberg %J PLOS ONE %D 2009 %I Public Library of Science (PLoS) %R 10.1371/journal.pone.0006402 %X Background In April 2009, novel swine-origin influenza viruses (S-OIV) were identified in patients from Mexico and the United States. The viruses were genetically characterized as a novel influenza A (H1N1) strain originating in swine, and within a very short time the S-OIV strain spread across the globe via human-to-human contact. Methodology We conducted a comprehensive computational search of all available sequences of the surface proteins of H1N1 swine influenza isolates and found that a similar strain to S-OIV appeared in Thailand in 2000. The earlier isolates caused infections in pigs but only one sequenced human case, A/Thailand/271/2005 (H1N1). Significance Differences between the Thai cases and S-OIV may help shed light on the ability of the current outbreak strain to spread rapidly among humans. %U http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0006402