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Research Article
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A Geospatial Perspective Toward the Role of Wild Bird Migrations and Global Poultry Trade in the Spread of Highly Pathogenic Avian Influenza H5N1
Mehak Jindal, Haley Stone, Samsung Lim, C. Raina MacIntyre
First published: 25 March 2025
https://doi.org/10.1029/2024GH001296 Sections
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Abstract
This study presents the interplay between wild bird migrations and global poultry trade in the unprecedented spread of highly pathogenic avian influenza, particularly the H5N1 clade 2.3.4.4b strain, across the world and diverse ecosystems from 2020 to 2023. We theorized the role of migratory birds in spreading pathogens as various wild bird species traverse major flyways between the northern and southern hemispheres. Simultaneously, we analyzed the global poultry trade data to assess its role in H5N1's anthropogenic spread, highlighting how human economic activities intersect with natural avian behaviors in disease dynamics. Lastly, we conducted spatial hotspot analysis to identify areas of significant clustering of H5N1 outbreak points over different bird families from 2003 to 2023. This approach provides a strong framework for identifying specific regions at higher risk for H5N1 outbreaks and upon which to further evaluate these patterns with targeted intervention studies and research into what is driving these patterns. Our findings indicate that both the poultry sector and wild bird migrations significantly contribute to global H5N1 transmission, which helps better understanding of H5N1 transmission mechanisms when combined with ecological, epidemiological, and socio-economic perspectives. The results are intended to inform policy-making and strategic planning in wildlife conservation and the poultry trade to improve public health and animal welfare globally. Key Points
- We investigated the role of wild bird migration in the inter-continental spread of avian influenza on a global scale
- We analyzed the global poultry trade data to highlight how human economic activities intersect with disease dynamics
- Our findings indicate that both the poultry sector and wild bird migrations significantly contribute to avian influenza transmission
The unprecedented scale and simultaneous infection of avian influenza across multiple species raise concerns about the potential threats to human health, especially in the upcoming years, if not months. The looming increase in bird migrations to the south adds a layer of complexity and urgency to the situation. As we navigate this evolving landscape, it becomes imperative to closely monitor and comprehend the altered dynamics of the virus to implement effective strategies for mitigating the risks associated with human infections. In this study, we tracked the movement of some wild birds according to their seasonal migration along with the incidence of avian influenza. While the spread patterns revealed that the avian influenza had started in Asian countries, it is not clear how it spread from Asia to Europe because, with the birds we analyzed, it was unable to find a flyway from Asia to Europe. However, every spread after the first incidence of avian influenza in Europe can be correlated with the seasonal migration of birds from one country to the other. Europe to Greenland to North America to South America can be established with different wild birds along with the spread from Europe to Africa.
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4 Results
4.1 Wild Bird Migration Routes, Poultry Trade and H5N1 Incidence
To understand the global shift of avian influenza from Asia to Europe, The Americas, and Africa, we examined wild bird migration patterns. It aims to elucidate the role of migration in the disease's intercontinental transmission. Initially, species such as waterfowl (e.g., Anseriformes, including ducks, geese, and swans) and Charadriiformes (such as waders, gulls, and auks) were considered primary vectors. However, data from WHO, upon categorization by bird families (Figure 1), revealed that Pelecaniformes (e.g., cormorants and pelicans) and Accipitriformes (notably the Eurasian buzzard, peregrine falcon, hawks, and vultures), also play significant roles in AIV spread. This highlights an expanding host range, indicating the need for broader surveillance across avian taxa.
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5 Discussion
The findings presented in this study shed light on the role of wild bird migration in the significant inter-continental spread of the H5N1 strain affecting wild birds, mammals, and domestic birds at a wide scale. These results hold significant implications for the potential mutation of the virus in human beings. By examining the migration routes of the wild birds along with the incidence of H5N1 especially clade 2.3.4.4b from 2020 to 2023, we were able to uncover the transmission of the virus from Europe to the American continent and parallelly from Europe to the African continent. In light of these results, several important points emerge for consideration.
In January 2020, AIV was predominantly observed in Asian countries, notably China and India. China, a key player in the poultry industry, exports poultry to several countries including Japan, Mongolia, Hong Kong, Cambodia, and Malaysia. Similarly, India engages in poultry exports to Maldives, Malaysia, Bhutan, Bahrain, Mauritania, and Comoros. The potential dissemination of AIV to Malaysia, Vietnam, and surrounding islands is speculated to be linked to the import of poultry from other Asian countries. As the northward migration of birds occurred in February and March 2020, AIV subsequently spread to Europe, with Denmark being an early affected country, and continued to propagate in neighboring nations.
In December 2020, during the southward migration of birds, a few cases of AIV began to emerge in Africa, specifically in the Mali region. This timeline highlights the dynamic nature of AIV spread, intricately connected with bird migration patterns and international poultry trade.
In March 2021, the northward migration facilitated the spread of AIV to several northern European countries, including Germany, the Netherlands, the UK, Hungary, Denmark, Poland, and Slovakia. By the end of 2021, the virus had become widespread across European nations. Notably, during the southward migration in late July, AIV extended its reach to Africa, affecting regions such as Mali and Nigeria.
The occurrence of AIV in South Africa from March to June 2021 appears to be unrelated to bird migration, given that this period corresponds to the northern hemisphere's breeding season when birds typically remain in the north. Instead, the introduction of AIV to South Africa is associated with the importation of poultry from Denmark, Ireland, and Spain.
Throughout the latter half of 2021, cases continued to proliferate in Europe, Africa, and Asia. In October, a single dead bird was discovered in Iceland, signaling the presence of the virus in that region. Subsequently, in December, a dead owl was found on the eastern coast of Canada, indicating the initiation of AIV spread to the Americas.
Between February and July 2022, a substantial spread of AIV occurred from the east coast to the west coast of the US and extended into Canada. In October, AIV cases began to emerge in Panama and Mexico, aligning with the southward migration period. By the beginning of November, the virus had extended its reach to Peru, manifesting along the entire coast. The mid-November to December timeframe witnessed the further spread of AIV to Chile, encompassing the entire coastal region. These temporal and geographical patterns underscore the dynamic nature of AIV dissemination, influenced by migratory patterns and regional factors.
In January and February 2023, the westward spread of AIV to the coastal regions of South Africa, particularly in Chile, is notable, and the infections in this region appear to primarily affect wild mammals, possibly seals. By late February, a sporadic increase in AIV cases in Argentina was predominantly observed in domestic poultry. However, as the situation progressed, cases in Uruguay and Brazil during May were noted to predominantly involve wild birds and mammals. These observations highlight the diverse patterns of AIV spread, with variations in affected species and modes of transmission in different geographic regions.
Analysis from 2005 to 2023 indicated a cyclic occurrence of the H5N1 every 5 years. However, a noteworthy deviation from this established pattern has become apparent in the latest outbreak since 2020. The ecological dynamics of the virus seem to have undergone a significant shift, manifesting in an unprecedented surge in cases compared to previous outbreaks. What distinguishes this event is the simultaneous and extensive infection of poultry, birds, and mammals during the same season—a phenomenon not witnessed in prior instances.
Overall hotspot analysis confirms that the rate of H5N1 infection has been declining in the Asian countries as shown by the consistent coldspots in these regions across all bird families, while the hotspots have now shifted to the UK and USA regions.
The unprecedented scale and simultaneous infection across multiple species raise concerns about the potential threats to human health, especially in the upcoming years, if not months. The looming increase in bird migrations to the south adds a layer of complexity and urgency to the situation. As we navigate this evolving landscape, it becomes imperative to closely monitor and comprehend the altered dynamics of the virus to implement effective strategies for mitigating the risks associated with human infections.
6 Concluding Remarks
In this study, we tracked the movement of some wild birds according to their seasonal migration along with the incidence of H5N1. While the spread patterns revealed that the AIV had started in Asian countries, it is not clear how it spread from Asia to Europe because, with the birds we analyzed, it was unable to find a flyway from Asia to Europe. However, every spread after the first incidence of AIV in Europe can be correlated with the seasonal migration of birds from one country to the other. Europe to Greenland to North America to South America can be established with different wild birds along with the spread from Europe to Africa.
By tracking the migratory pathways of wild birds during their migration periods and correlating them with incidences of AIV outbreaks, this study has provided some insights into the patterns of AIV spread. However, there are several avenues for further research and enhancement of the existing framework.
First, the inclusion of detailed spatial data on poultry farm locations and poultry networks will enable a more comprehensive understanding of the interactions between wild birds and domestic poultry in the transmission of AIV. By analyzing the proximity of migratory bird habitats to poultry farms and tracing potential transmission pathways, we can better elucidate the mechanisms driving AIV transmission dynamics.
Furthermore, the potential for mapping out African avian outbreaks in greater detail presents an important opportunity for addressing the gaps in AIV surveillance in the region. Given the scarcity and delay in reporting AIV outbreaks in many African countries, leveraging geospatial analysis to identify high-risk areas and predict outbreak hotspots can significantly enhance early detection and response efforts.
Moreover, incorporating advanced geospatial modeling techniques, such as spatial clustering analysis and predictive modeling, can further refine our understanding of the spatial-temporal patterns of AIV transmission. By integrating diverse data sets, including environmental factors, land use patterns, and human population density, we can develop more accurate predictive models to anticipate future outbreaks and inform targeted intervention strategies. Overall, by leveraging geospatial technologies and interdisciplinary approaches, we can enhance surveillance, prediction, and control efforts to mitigate the impact of AIV on both animal and human health.
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https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024GH001296