Spatio-temporal analysis of anthrax in livestock at zonal level in Ethiopia, 2008-2020

Ethiopia has not only one of the largest livestock populations in Africa, but also a substantial growing human population, increasing the risk of zoonotic disease transmission. Anthrax is a priority zoonosis in Ethiopia due to its risks to both human and animal health. Utilising 13 years of retrospective data (2008-2020) from 92 zones, this study investigated the spatio-temporal distribution of livestock anthrax cases in Ethiopia. High variability in annual incidence was observed, with the lowest number of cases (n=2357, 3.73%) in 2018 followed by the highest number of cases (n=8210, 12.98%) in 2019. Cattle contributed the majority of cases (n=36,104; 57.09%) with relatively even distribution across the other species (sheep, goats, camels, and equines). Kruskal-Wallis tests found that incidence of anthrax per 100,000 animals varied significantly by species, year, region and zone, with the largest effect size (0.20) observed between zones. Getis-Ord General G analysis found significant clustering of anthrax cases per 100,000 animals in multiple years for cattle (2013, 2018 and 2019), goats (2009, 2010 and 2012), and sheep (2013, 2015, 2016, and 2019). Getis-Ord Gi* hotspot analysis of data from these years identified zones contributing to these hotspot clusters, but none of the hotspots occurred in multiple species in the same location and year. Cattle hotspots were limited to zones in the Somali region and goat hotspots to neighbouring zones of the Amhara and Oromia regions. Sheep hotspots were not restricted in geographic distribution. Understanding these patterns is vital to coordinating anthrax control and prevention efforts in Ethiopia.