Fournié, G

Pfeiffer, D U

English

RVC Research Online

Commentwww.thelancet.com   Published online October 31, 2013   http://dx.doi.org/10.1016/S0140-6736(13)62109-1 1Can closure of live poultry markets halt the spread of H7N9?After isolation of avian infl uenza A H7N9 virus from live poultry markets (LPMs), and reports that several people who were infected with the virus had visited such markets a few days before disease onset, LPMs were suspected to be a main source of human exposure to H7N9 in China.1 After LPM closure was enforced in several Chinese cities, the incidence of H7N9 human cases rapidly reduced.2 In The Lancet, Hongjie Yu and colleagues3 quantify the risk of human infections before and after LPM closure in the Chinese cities of Nanjing, Shanghai, Hangzhou, and Huzhou. The investigators used information about laboratory-confi rmed cases of avian infl uenza A H7N9 virus infection reported in the four cities by June 7, 2013, to fi t a statistical model to assess the daily probability of infection for each susceptible individual before and after LPM closure. They report that closure of LPMs reduced the mean daily number of infections by 99% (95% credibility interval 93–100%) in Shanghai, 99% (92–100%) in Hangzhou, 97% (68–100%) in Huzhou, and 97% (81–100%) in Nanjing.3 They conclude that LPM closure should be sustained in areas with high risk of disease spread, and implemented in any urban areas where avian infl uenza A H7N9 virus appears in the future.LPMs are known to be a high-risk environment for pathogen transmission between birds and for zoonotic transfer to people. If birds spend a suffi  cient amount of time in LPMs to become infected and transmit the virus to other susceptible birds, sustained virus circulation in LPMs can occur.4 LPMs can then become a permanent source of infection for poultry fl ocks and for people who are in close contact with infected poultry and contaminated fomites. LPM closure would therefore be expected to stop human infections caused by a zoonotic pathogen transmitted within markets.Although LPM closure seems to have had an important eff ect on incidence of avian infl uenza A H7N9 virus infection in people, the underlying epidemiological and socioeconomic system is complex. LPM closure might not have been the most important cause of a reduction in incidence. Indeed, soon after LPM closures in Nanjing, Shanghai, Hangzhou, and Huzhou, human infections were also interrupted in other cities where this measure was not implemented.3 An example of the complex chain of interacting socioeconomic and epidemiological factors is that reports that poultry is a source of avian infl uenza A H7N9 virus triggered a drop in demand for poultry meat and consequently in poultry prices.5 Some producers were even forced to destroy their fl ocks because poultry rearing became cost prohibitive,6 which probably reduced the absolute number of poultry substantially in aff ected areas and reduced viral circulation, irrespective of LPM closure.Strong consumer reactions to zoonotic health hazards are not uncommon. Fears of avian infl uenza A H5N1 virus led to reduced consumption of poultry products in Asia in early 2004.7 However, these reductions were temporary: consumers’ anxiety decreased rapidly after the fi rst wave of the outbreak.8 Consumption of poultry products resumed within a few months, sometimes exceeding levels recorded before the outbreak,7 even though the virus had become endemic and human cases were reported regularly.Reduced consumer demand could have increased the compliance of poultry production stakeholders with LPM closures in China, because informal alternative ways to sell poultry were unavailable. Avian infl uenza A H7N9 virus is probably still circulating in Chinese poultry fl ocks, as suggested by new human cases reported in August, 2013.9 If poultry consumption resumes, the seasonal increase in poultry production and trading activities that usually occurs in the months preceding Chinese New Year could amplify virus circulation, resulting in a surge in human cases. If this increase occurs and consumer reactions are not as strong as during the spring of 2013, Published OnlineOctober 31, 2013http://dx.doi.org/10.1016/S0140-6736(13)62109-1See Online/Articleshttp://dx.doi.org/10.1016/S0140-6736(13)61904-2Yang Bo/ColorChinaPhoto/Associated PressComment2 www.thelancet.com   Published online October 31, 2013   http://dx.doi.org/10.1016/S0140-6736(13)62109-1the apparent eff ect of LPM closure—whether mediated directly through reductions in human exposure or indirectly through other eff ects—might not be repeated. Informal marketing channels could develop, providing an opportunity for stakeholders to minimise economic losses resulting from reduced market access.Although China has the resources to prevent develop-ment of informal trading activities, other nearby countries do not. In other countries where avian infl uenza A H5N1 virus is endemic, compliance to LPM closure is low10,11 and smuggling of poultry is common.12,13 However, the risk of introduction of avian infl uenza A H7N9 virus in these countries—with which China shares close epidemiological links, as indicated by the continuing spread of H5N1 variants in the region—is high. Live poultry trade creates networks of contacts between poultry and human popu-lations, thereby aff ect ing zoonotic disease dynamics. If LPM closure cannot be eff ectively enforced, unintended changes in the structure of networks could be triggered, possibly increasing the potential for disease spread, and probably resulting in reduced ability to do targeted surveillance and other risk management activities. Therefore, before such an intervention is implemented, its feasibility and the likelihood of unintended adverse results should be carefully assessed.Although LPM closure in specifi c circumstances can eff ectively interrupt human exposure to avian infl uenza A H7N9 virus, if applied alone this measure is unlikely to eliminate the zoonotic threat. Because disease incidence in people is low at present, the focus should move beyond detection of human cases and emergency response towards prevention at the infection source.14 A multisectoral approach would be needed fi rst to identify and then target the inter-related social, economic, cultural, biological, and environmental drivers underlying disease emergence and spread. These drivers are often ignored during attempts to deal with human and animal health risks, but the motivation behind adoption of some trading practices and factors aff ecting purchasing behaviour of consumers needs to be considered. By contrast with LPM closure, a multisectoral approach leading to restructuring rather than destabilisation of the LPM system would be more likely to result in a sustainable reduction in the risk of disease spread while also protecting livelihoods and food security.*Guillaume Fournié, Dirk U Pfeiff erVeterinary Epidemiology, Economics and Public Health Group, Production and Population Health Department, Royal Veterinary College, Hatfi eld AL9 7TA, UKgfournie@rvc.ac.ukWe declare that we have no confl icts of interest.1 Chen Y, Liang W, Yang S, et al. Human infections with the emerging avian infl uenza A H7N9 virus from wet market poultry: clinical analysis and characterisation of viral genome. Lancet 2013; 381: 1916–25. 2 Murhekar M, Arima Y, Horby P, et al. Avian infl uenza A(H7N9) and the closure of live bird markets. Western Pac Surveill Response J 2013; 4: 4–7.3 Yu H, Wu JT, Cowling BJ, et al. Eff ect of closure of live poultry markets on poultry-to-person transmission of avian infl uenza A H7N9 virus: an ecological study. Lancet 2013; published online Oct 31. http://dx.doi.org/10.1016/S0140-6736(13)61754-7.  4 Fournié G, Guitian FJ, Mangtani P, Ghani AC. Impact of the implementation of rest days in live bird markets on the dynamics of H5N1 highly pathogenic avian infl uenza. J R Soc Interface 2011; 8: 1079–89. 5 Reuters. China poultry sector losses exceed $1·6 billion on bird fl u scare. April 16, 2013. http://www.reuters.com/article/2013/04/16/us-china-birdfl u-poultry-idUSBRE93F06Z20130416 (accessed Sept 24, 2013). 6 ProMED-mail. Avian infl uenza (43): (China) zoonotic LPAI H7N9, animal update. April 22, 2013. http://www.promedmail.org/direct.php?id= 20130422.1664423 (accessed Sept 24, 2013). 7 Taha FA. How highly pathogenic avian infl uenza (H5N1) has aff ected world poultry-meat trade. A report from the Economic Research Service, USDA. 2007. http://www.ers.usda.gov/publications/ldpm-livestock,-dairy,-and-poultry-outlook/ldpm-15902.aspx (accessed Sept 24, 2013). 8 Figuie M, Fournier T. Avian infl uenza in Vietnam: chicken-hearted consumers? Risk Anal 2008; 28: 441–51. 9 ProMED-mail. Avian infl uenza, human (104): China (GD), H7N9 poultry worker. Aug 11, 2013. http://www.promedmail.org/direct.php?id=20130811.1875467 (accessed Sept 24, 2013). 10 Fournié G, Guitian J, Desvaux S, et al. Interventions for avian infl uenza A (H5N1) risk management in live bird market networks. Proc Natl Acad Sci USA 2013; 110: 9177–82. 11 Naysmith S. Observations from a live bird market in Indonesia following a contained outbreak of avian infl uenza A (H5N1). Ecohealth 2013; published online July 10. DOI:10.1007/s10393-013-0858-y. 12 Yupiana Y, de Vlas SJ, Adnan NM, Richardus JH. Risk factors of poultry outbreaks and human cases of H5N1 avian infl uenza virus infection in West Java province, Indonesia. Int J Infect Dis 2010; 14: e800–05. 13 Biswas PK, Christensen JP, Ahmed SS, et al. Risk for infection with highly pathogenic avian infl uenza virus (H5N1) in backyard chickens, Bangladesh. Emerg Infect Dis 2009; 15: 1931–36. 14 Chatham House. Shifting from emergency response to prevention of pandemic disease threats at source. Meeting report. April, 2010. http://www.chathamhouse.org/publications/papers/view/109284 (accessed Sept 24, 2013).

Can closure of live poultry markets halt the spread of H7N9?

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Can closure of live poultry markets halt the spread of H7N9?

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