a. pereda , c. perfumo , and d. r. perez contributed to the concept and design of the study ; a. rimondi , m. angel , j. ye , t. sutton , m. dibrbora , v. olivera , and m. i. craig analyzed and interpreted the virological and molecular data ; j. cappuccio , m. quiroga , and m. machuca performed necropsies , analyzed , and interpreted the histopathological data ; a ferrero provided technical support ; a. pereda , c. perfumo , and d. r. perez revised and approved the final version of the manuscript .
phylogenetic tree of hemagglutinin 
 ( 1a ) , na ( 1b ) , and mp ( 1c ) genes .
unrooted trees were generated by 
 the neighborjoining method in 11 the paup * program .
viruses characterized in this study are 
 highlighted in bold , and swine influenza clusters are identified in 
 colored boxes .
h1n1pdm corresponds to h1n1 2009 pandemic virus , 
 ch1n1a to classical swine h1n1 , rh1n1b to triple reassortant swine 
 h1n1 , h1n2c to triple reassortant swine h1n2 , huh1d to humanlike 
 swine h1 , hun1 or hun2 to humanlike swine n1 and n2 , 
 respectively , and swn1 to swine n1 .
 
 please cite this paper as : pereda et  al . 
 ( 2011 ) evidence of reassortment of pandemic h1n1 influenza virus in swine in argentina : are we facing the expansion of potential epicenters of influenza emergence ? 
 influenza and other respiratory viruses 5(6 ) , 409412.in this report , we describe the occurrence of two novel swine influenza viruses ( sivs ) in pigs in argentina . 
 these viruses are the result of two independent reassortment events between the h1n1 pandemic influenza virus ( h1n1pdm ) and humanlike sivs , showing the constant evolution of influenza viruses at the human  swine interface and the potential health risk of h1n1pdm as it appears to be maintained in the swine population . 
 it must be noted that because of the lack of information regarding the circulation of sivs in south america , we can not discard the possibility that ancestors of the h1n1pdm or other sivs have been present in this part of the world . 
 more importantly , these findings suggest an everexpanding geographic range of potential epicenters of influenza emergence with public health risks . 
Addendum
Supporting information