Did the 2009 pandemic influenza virus originate in humans?

Replication, Pathogenesis and Transmission of Pandemic (H1N1) 2009 Virus in Non-Immune Pigs

(2010) Sharon M. Brookes et al.   PLoS One

Replication of avian, human and swine influenza viruses in porcine respiratory explants and association with sialic acid distribution

(2010) Sjouke GM Van Poucke et al.   Virology Journal

Pathogenesis and transmission of the novel swine-origin influenza virus A/H1N1 after experimental infection of pigs

(2009) E. Lange et al.   JOURNAL OF GENERAL VIROLOGY

Genetic and Pathobiologic Characterization of Pandemic H1N1 2009 Influenza Viruses from a Naturally Infected Swine Herd

(2009) H. M. Weingartl et al.   JOURNAL OF VIROLOGY

Experimental Infection of Pigs with the Human 1918 Pandemic Influenza Virus

(2009) H. M. Weingartl et al.   JOURNAL OF VIROLOGY

Origins and evolutionary genomics of the 2009 swine-origin H1N1 influenza A epidemic

(2009) Gavin J. D. Smith et al.   NATURE

Antigenic and Genetic Characteristics of Swine-Origin 2009 A(H1N1) Influenza Viruses Circulating in Humans

(2009) R. J. Garten et al.   SCIENCE

Characterization of an influenza A virus isolated from pigs during an outbreak of respiratory disease in swine and people during a county fair in the United States

(2009) Amy L. Vincent et al.   VETERINARY MICROBIOLOGY

Panorama phylogenetic diversity and distribution of type A influenza viruses based on their six internal gene sequences

(2009) Ji-Ming Chen et al.   Virology Journal