Abstract
BackgroundDeveloping disease risk maps for priority endemic and episodic diseases is becoming increasingly important for more effective disease management, particularly in resource limited countries. For endemic and easily diagnosed diseases such as anthrax, using historical data to identify hotspots and start to define ecological risk factors of its occurrence is a plausible approach. Using 666 livestock anthrax events reported in Kenya over 60 years (1957–2017), we determined the temporal and spatial patterns of the disease as a step towards identifying and characterizing anthrax hotspots in the region.MethodsData were initially aggregated by administrative unit and later analyzed by agro-ecological zones (AEZ) to reveal anthrax spatio-temporal trends and patterns. Variations in the occurrence of anthrax events were estimated by fitting Poisson generalized linear mixed-effects models to the data with AEZs and calendar months as fixed effects and sub-counties as random effects.ResultsThe country reported approximately 10 anthrax events annually, with the number increasing to as many as 50 annually by the year 2005. Spatial classification of the events in eight counties that reported the highest numbers revealed spatial clustering in certain administrative sub-counties, with 12% of the sub-counties responsible for over 30% of anthrax events, whereas 36% did not report any anthrax disease over the 60-year period. When segregated by AEZs, there was significantly greater risk of anthrax disease occurring in agro-alpine, high, and medium potential AEZs when compared to the agriculturally low potential arid and semi-arid AEZs of the country (p < 0.05). Interestingly, cattle were > 10 times more likely to be infected by B. anthracis than sheep, goats, or camels. There was lower risk of anthrax events in August (P = 0.034) and December (P = 0.061), months that follow long and short rain periods, respectively.ConclusionTaken together, these findings suggest existence of certain geographic, ecological, and demographic risk factors that promote B. anthracis persistence and trasmission in the disease hotspots.
Highlights
Developing disease risk maps for priority endemic and episodic diseases is becoming increasingly important for more effective disease management, in resource limited countries
Anthrax is an acute, often fatal disease of animals caused by a soil-borne Bacillus anthracis (B. anthracis) that exists in two forms; the vegetative toxin-producing form, and the dormant spore form that persists in soil for long periods [1, 2]
The World Health Organization (WHO) estimates that > 90% of human B. anthracis infections globally are attributed to contact with or consumption of livestock and their products and approximately 5% attributed to contact with wildlife [12]
Summary
Developing disease risk maps for priority endemic and episodic diseases is becoming increasingly important for more effective disease management, in resource limited countries. For endemic and diagnosed diseases such as anthrax, using historical data to identify hotspots and start to define ecological risk factors of its occurrence is a plausible approach. The disease is endemic in Africa and Asia where domestic and wild herbivores are infected by ingesting or inhaling spores during feeding and in watering points, whereas humans are infected through contact with infected animal carcasses or their products [2,3,4,5,6]. Whereas anthrax has a worldwide distribution, incidence has declined in most developed countries due to livestock vaccination programs and other sanitary measures. The global incidence of anthrax varies with time and location, triggered by a combination of geographic and ecological factors that support B. anthracis persistence, and the changing animal and human demographics that enhance exposure to the pathogen [9,10,11]. The World Health Organization (WHO) estimates that > 90% of human B. anthracis infections globally are attributed to contact with or consumption of livestock and their products and approximately 5% attributed to contact with wildlife [12]
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