Paper on how swine flu might spread to birds retracted for error

Emerging Infectious Diseases, a CDC journal, is retracting a 2010 paper about swine flu by a group of Minnesota researchers who acknowledged misinterpreting their results.

The study, a letter titled “Triple Reassortant Swine Influenza A (H3N2) Virus in Waterfowl,” claimed to shed new light on how flu viruses might jump between species:

In 1998, a new lineage of triple reassortant influenza A (H3N2) virus (TR-H3N2) with genes from humans (hemmaglutinin [HA], neuraminidase [NA], and polymerase basic 1 [PB1]), swine (matrix [M], nonstructural [NS], and nucleoprotein [NP]), and birds (polymerase acidic [PA] and PB2) emerged in the U.S. swine population. Subsequently, similar viruses were isolated from turkeys (1,2), minks, and humans in the United States and Canada (3,4). In 2007, our national influenza surveillance resulted in isolation of 4 swine-like TR-H3N2 viruses from migratory waterfowl (3 from mallards [Anas platyrrhynchos] and 1 from a northern pintail [Anas acuta] of 266 birds sampled) in north-central South Dakota. We report on the characterization of these TR-H3N2 viruses and hypothesize about their potential for interspecies transmission.

…

The mode of transmission of swine-origin virus to waterfowl is not clear. In previously published cases, where swine influenza viruses have been identified in turkeys, the flocks were in close proximity to swine herds (2). Similarly, we identified a swine herd in north-central South Dakota where all 4 waterfowl were sampled. Respiratory secretions from the pigs possibly could have spread to birds through aerosols or droplets. It is also likely that swine and waterfowl shared common water sources, which contained feces from influenza-infected waterfowl or respiratory secretions from influenza-infected swine. This mode of influenza virus transmission from birds to pigs has been documented (6–9). Indeed, a waterborne source for transmission is most likely because influenza A virus can persist in water for several months depending on environmental factors such as pH, temperature, and salinity (10). Finally, because the swine herd in this area was housed outdoors in open pens, direct interaction with waterfowl was possible.

In late 2008, serum samples were collected from this swine herd. Hemagglutination inhibition test (1) showed that 10 of 19 samples reacted with all 4 waterfowl isolates; titers ranged from 10 to >640. Although low titers may have occurred because pigs were exposed to heterologous cross-reactive viruses, the high titers in most animals with positive serum samples suggest exposure to an influenza (H3N2) virus similar to that recovered from the waterfowl. Our data emphasize the need to investigate the possible role of waterfowl in the maintenance and transmission of influenza A viruses to humans and to lower mammalian species.

But according to the retraction notice:

To the Editor: We would like to retract the letter entitled “Triple Reassortant Swine Influenza A (H3N2) Virus in Waterfowl,” which was published the April 2010 issue of Emerging Infectious Diseases (1). The nucleoprotein gene sequences from the viruses reported in that letter are very closely related to those from the earliest detected triple reassortant swine influenza viruses [CY095676 A/sw/Texas/4199–2/1998(H3N2)]. Although these viruses could have acquired a swine-origin segment, the branch lengths are quite short for 9 years of evolution. Therefore, we have withdrawn these 4 isolates from GenBank and subsequently retract this letter.

The paper has been cited twice, according to Thomson Scientific’s Web of Knowledge.

We’ve tried to reach the corresponding author, Sagar Goyal, and the journal, but haven’t heard anything.