Live Animal Markets in Minnesota: A Potential Source for Emergence of Novel Influenza A Viruses and Interspecies Transmission

August 5, 2015 — 

Live animal markets have been implicated in transmission of influenza A viruses (IAVs) from animals to people. We sought to characterize IAVs at two live animal markets in Minnesota to assess potential routes of occupational exposure and risk for interspecies transmission.

METHODS:
We implemented surveillance for IAVs among employees, swine, and environment (air and surfaces) during a 12-week period (October 2012-January 2013) at two markets epidemiologically associated with persons with swine-origin IAV (variant) infections. Real-time reverse transcription polymerase chain reaction (rRT-PCR), viral culture, and whole genome sequencing were performed on respiratory and environmental specimens, and serology on sera from employees at beginning and end of surveillance.

RESULTS:
Nasal swabs from 11 (65%) of 17 employees tested positive for IAVs by rRT-PCR; seven employees tested positive on multiple occasions and one employee reported influenza-like illness. Eleven (73%) of 15 employees had baseline hemagglutination-inhibition antibody titers ≥40 to swine-origin IAVs, but only one demonstrated a 4-fold titer increase to both swine-origin, and pandemic A/Mexico/4108/2009 IAVs. IAVs were isolated from swine (72/84), air (30/45) and pen railings (5/21). Whole genome sequencing of 122 IAVs isolated from swine and environmental specimens revealed multiple strains and subtype codetections. Multiple gene segment exchanges among and within subtypes were observed, resulting in new genetic constellations and reassortant viruses. Genetic sequence similarities of 99%-100% among IAVs of one market customer and swine indicated interspecies transmission.

CONCLUSIONS:
At markets where swine and persons are in close contact, swine-origin IAVs are prevalent and potentially provide conditions for novel IAV emergence.

Choi MJ, Torremorell M, Bender JB, Smith K, Boxrud D, Ertl JR, Yang M, Suwannakarn K, Her D, Nguyen J, Uyeki TM, Levine M, Lindstrom S, Katz JM, Jhung M, Vetter S, Wong KK, Sreevatsan S, Lynfield R; Live Animal Markets in Minnesota: a Potential Source for Emergence of Novel Influenza A Viruses and Interspecies Transmission; Clin Infect Dis. 2015 Jul 29. pii: civ618. [Epub ahead of print]