Date Published: April 4, 2017
Publisher: Public Library of Science
Author(s): Chau Minh Bui, Lauren Gardner, Raina MacIntyre, Sahotra Sarkar, Gui-Quan Sun.
Zoonotic avian influenza poses a major risk to China, and other parts of the world. H5N1 has remained endemic in China and globally for nearly two decades, and in 2013, a novel zoonotic influenza A subtype H7N9 emerged in China. This study aimed to improve upon our current understanding of the spreading mechanisms of H7N9 and H5N1 by generating spatial risk profiles for each of the two virus subtypes across mainland China.
In this study, we (i) developed a refined data set of H5N1 and H7N9 locations with consideration of animal/animal environment case data, as well as spatial accuracy and precision; (ii) used this data set along with environmental variables to build species distribution models (SDMs) for each virus subtype in high resolution spatial units of 1km2 cells using Maxent; (iii) developed a risk modelling framework which integrated the results from the SDMs with human and chicken population variables, which was done to quantify the risk of zoonotic transmission; and (iv) identified areas at high risk of H5N1 and H7N9 transmission. We produced high performing SDMs (6 of 8 models with AUC > 0.9) for both H5N1 and H7N9. In all our SDMs, H7N9 consistently showed higher AUC results compared to H5N1, suggesting H7N9 suitability could be better explained by environmental variables. For both subtypes, high risk areas were primarily located in south-eastern China, with H5N1 distributions found to be more diffuse and extending more inland compared to H7N9.
We provide projections of our risk models to public health policy makers so that specific high risk areas can be targeted for control measures. We recommend comparing H5N1 and H7N9 prevalence rates and survivability in the natural environment to better understand the role of animal and environmental transmission in human infections.
A zoonotic avian influenza virus (AIV) of subtype H5N1 emerged in humans in Hong Kong in 1997. The virus has since spread across Asia, Africa and Europe, and has infected over 854 humans and caused over 450 deaths . In 2013 a new subtype H7N9 emerged in humans in China and the human case count by December 2016 was over 795, with over 314 deaths . Differences in the epidemiology of H7N9 and H5N1 have previously been described: human H5N1 cases report higher severity of disease  and higher levels of contact with sick or dead birds ; H7N9 is asymptomatic in birds  and found at lower prevalence rates in poultry ; and the spatial distribution of H5N1 within a comparable time frame is considerably greater than that of H7N9 . This study aimed to improve upon our current understanding of the spreading mechanisms behind H7N9 and H5N1, provide a geographic risk profile for each of the two virus subtypes across all of mainland China, and highlight the regions at greatest risk of experiencing AIV transmission.
In this study, we (i) developed a refined data set of H5N1 and H7N9 locations with consideration of animal/animal environment case data as well as spatial accuracy and precision of coordinates; (ii) used this data set along with environmental variables in Maxent to build SDMs for each subtype in high resolution spatial units of 1km2 cells; (iii) developed a risk analysis framework, which integrated Maxent models with human and chicken population density to estimate the geographic risk of zoonotic transmission of H5N1 and H7N9; and (iv) identified areas of China at high risk of H5N1 and H7N9 transmission differentiated into two groups, those that have and have not yet reported cases.
H5N1 and H7N9 subtypes have persisted in animal hosts and continue to cause human infections since their emergence in China. Additionally, novel zoonotic AIVs (such as H10N8 and H5N6) have also emerged in mainland China, and human infections from these subtypes have so far been restricted to China. Furthermore, surveillance of poultry reveals there are many new reassortant AIVs being discovered [83,84]. Hence, zoonotic avian influenza poses a major risk to China.