Understanding the spread of African swine fever in Nepal: spatiotemporal analysis of early-phase outbreaks, March 2022–July 2024

Abstract

African swine fever (ASF) is a highly contagious disease of pigs that poses a significant threat to food security, economies, and livelihoods. In Nepal, where pig farming is an important livelihood of many vulnerable ethnic communities, ASF was first reported on 19 March 2022 and has since spread across the country. This study aimed to characterize the spatiotemporal patterns of ASF outbreaks in Nepal, identify high-risk clusters, and assess their associations with environmental factors to inform targeted ASF control and prevention. A retrospective analysis of confirmed ASF outbreaks reported from March 2022 to July 2024 was conducted. Temporal trends and seasonal patterns were analyzed, while spatial clustering was assessed using SaTScan. Associations between outbreaks and environmental variables (rainfall, temperature, dewpoint temperature, and relative humidity) were examined. A total of 43 outbreaks were reported across 21 of 77 districts in Nepal, including 42 in domestic pigs and one in wild boars. Most outbreaks (77%) were reported in 2022, with a peak during the summer months. Outbreaks were reported in all seven provinces, with Bagamati Province having the highest number of outbreaks (18/43). ASF outbreaks mostly occurred in small- and medium-scale holdings (36/42), while commercial farms were also affected. A significant cluster was identified in Sudurpaschim Province. Rainfall was significantly associated with outbreak occurrence (p = 0.0118). This study provides the first evidence on the spatiotemporal dynamics of ASF during the early phase of outbreaks in Nepal, supporting risk-based surveillance and targeted interventions to strengthen ASF prevention and control.

Keywords

African swine fever / Outbreak / Spatial analysis / Temporal patterns / Nepal

References

[1] AITC, 2024. Agriculture information and training centre. Agriculture Diary. [In Nepali] Cited 2024 July 4 https://aitc.gov.np/uploads/documents/agriculture-diary-2081-file-2081-03-2pdf-6568-329-1719146649.pdf

[2] Auchincloss AH, Gebreab SY, Mair C, Roux AVDA review of spatial methods in epidemiology, 2000–2010. Annual Review of Public Health, 2012, 33: 107-122.

[3] Bergmann H, Schulz K, Conraths FJ, Sauter-Louis CA review of environmental risk factors for African swine fever in European wild boar. Animals, 2021, 11(92692

[4] Boklund A, Cay B, Depner K, Földi Z, Guberti V, Masiulis M, Miteva A, More S, Olsevskis E, Šatrán P, Spiridon M, Stahl K, Thulke HH, Viltrop A, Wozniakowski G, Broglia A, Cortinas Abrahantes J, Dhollander S, Gogin A, Verdonck F, Amato L, Papanikolaou A, Gortázar CEpidemiological analyses of African swine fever in the European Union (November 2017 until November 2018). EFSA Journal, 2018, 16(11): 5494.

[5] Chailangkarn, T., Thaweerattanasinp, T., Wanitchang, A., Saenboonrueng, J., Kaewborisuth and C., Jongkaewwattana, A. 2025. Progress in the in vitro propagation of African swine fever virus and implications for vaccine development. Animal Diseases 5(1). https://doi.org/10.1186/s44149-025-00190-.

[6] Costard S, Mur L, Lubroth J, Sanchez-Vizcaino J, Pfeiffer DUEpidemiology of African swine fever virus. Virus Research, 2013, 1731):191-197.

[7] DLS, 2022. Livestock statistics of Nepal [In Nepali]. Department of Livestock Services. Cited 2024 July 4. https://dls.gov.np/downloadfiles/Livestock_Statistics_of_Nepal_2077_78_1659524236-1669717523.pdf

[8] European Food Safety Authority (EFSA)Ståhl K, Boklund A, Podgórski T, Vergne T, Abrahantes JC, Papanikolaou A, Zancanaro G, Mur LEpidemiological analysis of African swine fever in the European Union during 2022. EFSA Journal, 2023, 21(5e08016

[9] Funk, C., P. Peterson, M. Landsfeld, D. Pedreros, J. Verdin, J. Rowland, and G. Husak. 2015. The climate hazards infrared precipitation with stations—a new environmental record for monitoring extremes. Scientific Data, 2(1), 1–21. https://doi.org/10.1038/sdata.2015.66.

[10] Hersbach, H., B. Bel, P. Berrisford, S. Hirahara, A. Horányi, J. Muñoz-Sabater, and A. Simmons. 2020. The ERA5 global reanalysis. Quarterly Journal of the Royal Meteorological Society, 146(730), 1999–2049. https://doi.org/10.1002/qj.3803.

[11] Ito S, Bosch J, Jeong H, Aguilar-Vega C, Park J, Martínez-Avilés M, Sánchez-Vizcaíno JMSpatiotemporal epidemiology of the spread of African swine fever in wild boar and the role of environmental factors in South Korea. Viruses, 2022, 14122779

[12] Khanal P, Dhakal R, Khanal T, Pandey D, Devkota NR, Nielsen MOSustainable livestock production in Nepal: A focus on animal nutrition strategies. Agriculture, 2022, 125Article 679

[13] Kim Y, Nouvellet P, Rogoll L, Staubach C, Schulz K, Sauter-Louis C, Pfeiffer DU, Fournié GContrasting seasonality of African swine fever outbreaks and its drivers. Epidemics, 2023, 44100703

[14] Kulldorff M, Heffernan R, Hartman J, Assuncao R, Mostashari FA space-time permutation scan statistic for disease outbreak detection. PLoS Medicine, 2005, 23e59

[15] Kulldorff , M. (2018). SaTScan user guide for version 9.6. Boston, MA: Martin Kulldorff and Information ManagementServices Inc. Available at: https://www.satscan.org/. (Accessed: [25 August, 2024]).

[16] Martínez Avilés M, Montes F, Sacristán I, de la Torre A, Iglesias ISpatial and temporal analysis of African swine fever front-wave velocity in wild boar: Implications for surveillance and control strategies. Frontiers in Veterinary Science, 2024

[17] Microsoft Corporation., 2018. Microsoft Excel (Version 2019). https://www.microsoft.com/en-us/microsoft-365/excel

[18] Mighell E, Ward MPAfrican swine fever spread across Asia, 2018-2019. Transboundary and Emerging Diseases, 2021, 685): 2722-2732.

[19] MoALD., 2023. Statistical information on Nepalese agriculture 2078/2079, 2021/2022. Ministry of Agriculture and Livestock Development. https://moald.gov.np/wp-content/uploads/2023/08/Statistical-Information-on-Nepalese-Agriculture-2078-79-2021-22.pdf

[20] Nguyen-Thi, T., L. Pham-Thi-Ngoc, Q. Nguyen-Ngoc, S. Dang-Xuan, H. S. Lee, H. Nguyen-Viet, P. Padungtod, T. Nguyen-Thu, T. Nguyen-Thi, T. Tran-Cong, H. et al. 2021. An assessment of the economic impacts of the 2019 African Swine Fever outbreaks in Vietnam. Frontiers in Veterinary Science, 8, Article 686038. https://doi.org/10.3389/fvets.2021.686038

[21] NSO., 2023. National agriculture census 2078. National Statistics Office. [In Nepali]. https://agricensusnepal.gov.np/post/10_64fc38a5a62c8

[22] Nurmoja I, Mõtus K, Kristian M, Niine T, Schulz K, Depner K, Viltrop AEpidemiological analysis of the 2015–2017 African swine fever outbreaks in Estonia. Preventive Veterinary Medicine, 2020, 181104556

[23] Odoi A, Carter CN, Riley JW, Smith JL, Dwyer RMApplication of an automated surveillance-data-analysis system in a laboratory-based early-warning system for detection of an abortion outbreak in mares. American Journal of Veterinary Research, 2009, 70(2): 247-256.

[24] Olesen AS, Lohse L, Hansen MF, Boklund A, Halasa T, Belsham GJ, Rasmussen TB, Bøtner A, Bødker RInfection of pigs with African swine fever virus via ingestion of stable flies (Stomoxys calcitrans). Transboundary and Emerging Diseases, 2018, 65(5): 1152-1157.

[25] Pautienius A, Grigas J, Pileviciene S, Zagrabskaite R, Buitkuviene J, Pridotkas G, Stankevicius R, Streimikyte Z, Salomskas A, Zienius D, Stankevicius APrevalence and spatiotemporal distribution of African swine fever in Lithuania, 2014–2017. Virology Journal, 2018, 151177

[26] Pei X, Li M, Hu J, Zhang J, Jin ZAnalysis of spatiotemporal transmission characteristics of African swine fever (ASF) in mainland China. Mathematics, 2022

[27] Pfeiffer DU, Robinson TP, Stevenson M, Stevens KB, Rogers DJ, Clements ACASpatial analysis in epidemiology, 2008Oxford University Press14

[28] Posit Software, PBC, 2024. RStudio: Integrated development environment for R (Version 2024.04.2 Build 764). Posit Software, PBC. Retrieved from http://www.rstudio.com/

[29] QGIS Development Team., 2024. QGIS Geographic Information System (Version 3.38.0). Open Source Geospatial Foundation Project. Retrieved from http://qgis.org

[30] R Core Team., 2024. R: A language and environment for statistical computing (Version 4.4.1). R Foundation for Statistical Computing. Retrieved from https://www.R-project.org/

[31] Rogoll L, Güttner AK, Schulz K, Bergmann H, Staubach C, Conraths FJ, Sauter-Louis CSeasonal occurrence of African swine fever in wild boar and domestic pigs in EU member states. Viruses, 2023, 1591955

[32] Shao Q, Li R, Han Y, Han D, Qiu JTemporal and spatial evolution of the African swine fever epidemic in Vietnam. International Journal of Environmental Research and Public Health, 2022, 1913Article 8001

[33] Ward, M. P., and M. L. Farnsworth. 2009. An evaluation of the space-time permutation test for detecting disease clusters. ISVEE 12: Proceedings of the 12th Symposium of the International Society for Veterinary Epidemiology and Economics, Durban, South Africa, Theme 6: Epidemiological tools: Modeling, Epidemiological methods (pp. 25).

[34] World Organization for Animal Health (WOAH)., 2019. WOAH technical disease card: African swine fever. Retrieved February 16, 2024, from https://www.woah.org/app/uploads/2021/03/a-african-swine-fever-v2-0.pdf

[35] World Organization for Animal Health (WOAH)., 2024. Nepal - African swine fever virus - Follow up report 21. WAHIS. Retrieved June 25, 2024, from https://wahis.woah.org/#/in-review/4458?reportId=165508&fromPage=event-dashboard-url

Rights & permissions

The Author(s)