In early April 2009, authorities from the Mexican public health observed a high number of influenza-like illnesses in their territory, and informed about this outbreak to the regional office of the World Health Organization (WHO). In mid April, the Centers for Disease Control from USA identified the new virus in two cases from California. The new virus spread rapidly throughout the world, and as a consequence the WHO authorities declared the "Pandemic (H1N1) 2009" on June 11, 2009 [3] . It is thought that the new 2009 H1N1 pandemic virus (from here, 2009 H1N1pdm) has emerged through at least four reassortment and transmission events among swine, avian and human H1N1 lineages, probably in Asia and North America [4] . Particularly, the HA segment of 2009 H1N1pdm was originated from American swine lineage, whereas the NA segment derived from the European swine lineage [5, 6] . It is believed that the ancestors of this pandemic strain remained undetected for approximately one decade due to lack of a *Address correspondence to this author at the Rio de la Plata y Lagerenza, CP 1120 Asunción, Paraguay; Tel: +595 21 424 520; Fax: +595 21 480 185; E-mail: emilioespinola@hotmail.com surveillance system in pigs, the historical "mixing vessel" for new influenza viruses. Furthermore, the closest ancestors of the new pandemic strains emerged probably in January 2009 [4] .