Drs. Hong Zhang and Ling Chen of Zunyi Medical College, China, compared the gene segments to other influenza virus sequences in GenBank. Six gene segments probably came from swine viruses circulating between 1999 and 2001 in the US, and two segments possibly originated from swine viruses circulating in Europe between 1985 and 1998. Where, when and how they recombined and formed the current reassortment H1N1 viruses are "important questions," according to the authors, who note:
The [future] prevention and control of the worldwide spread of pandemic inﬂuenza will need improved animal and human surveillance, early detection and differentiation of causative viruses.A July NEJM article on the history of this swine flu virus provides additional information, and concludes similarly, highlighting the:
critical need for deeper understanding of zoonotic viruses, including in vivo studies of pathogenesis in animals, field epidemiologic studies, and surveillance in animal populations, along with the development of computational models.