Editorial Commentary: Variant Influenza A(H3N2) Virus: Looking Through a Glass, Darkly

Abstract

First detected in July 2011 [1], the influenza A(H3N2) variant virus (H3N2v), a swine-like progeny virus from the 2009 pandemic H1N1 virus, has caused considerable public health alarm. Most children <10 years of age are thought to be susceptible [2], and evidence of limited H3N2v person-to-person transmission has been reported [1]. Soon after its discovery, public health officials became quite concerned regarding this novel viral threat. In November 2011, the World Health Organization released a virus construct A/Minnesota/11/2010 for vaccine development. In August 2012, the US Centers for Disease Control and Prevention released special H3N2v diagnostic and agricultural fair guidance. In this issue of Clinical Infectious Diseases, Jhung et al [3] summarize the largest human H3N2v outbreak to date (306 cases in 10 states), clearly associating it with pig exposure at agricultural fairs. The authors’ case identification methods and exposure assessments were sound and a number of their findings were quite remarkable: Among the infected persons, 82% were ≤11 years of age, 95% had recent swine exposure, the estimated incubation period was 2.9 days after pig exposure, 16 patients were hospitalized (1 patient died), and 15 likely acquired H3N2v from another human. Although agricultural fairs have been previously shown to be a risk factor for swine influenza virus (SIV) infections in humans [4–8], never before have the epidemiological data been so strong and geographically widespread. The legion of authors in this paper demonstrates the huge interagency effort that was required to gain such a comprehensive view. The authors are to be commended for this important work. However, it seems rather tragic that after the 2009 H1N1 pandemic and this large outbreak, we still do not have a clear view of the dynamic ecology of SIV-like viruses that are freely circulating between swine and human populations. Instead we must often wait for humans to serve as sentinels through their infection with such novel viruses. Although novel SIV viruses are reportable when detected in humans or in pigs, there is sparse testing of healthy pigs for novel SIV; when influenza testing does occur, swine farmers’ participation in the US Department of Agriculture’s influenza surveillance programs is for the most part voluntary. Why should the swine industry pay for SIV surveillance and virus characterization among pigs, when pigs often carry influenza A viruses without clinical signs [8] and the viruses are not transmitted to humans via meat products? Unless a novel virus emerges to cause significant morbidity in pigs, and that virus is characterized, the novel virus is not likely to be discovered and reported by veterinary professionals. Lack of SIV ecologic data is also due in part to concerns that research findings might cause economic damage to the pork industries. Why should pork farmers permit researchers to study SIV transmission in their farms when such research could lead to discoveries that would hamper the sale of a farmer’s pigs or require expensive renovations to swine barns? Hence, although we clearly see that novel SIV human infections can be numerous and widespread and that these crossspecies influenza A virus jumps can occur at agriculture fairs or among individuals occupationally exposed to pigs [9–11], we still do not yet know how to effectively mitigate this risk. It seems to these authors that what we must do is engage in multidisciplinary research to prospectively study the large commercial and small hobby farms that Received 12 September 2013; accepted 15 September 2013; electronically published 24 September 2013. Correspondence: Gregory C. Gray, MD, MPH, FIDSA, Department of Environmental and Global Health, College of Public Health and Health Professions, University of Florida, Box 100188, Gainesville, FL 32610 (gcgray@phhp.ufl.edu). Clinical Infectious Diseases 2013;57(12):1713–4 © The Author 2013. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals. permissions@oup.com. DOI: 10.1093/cid/cit650