Ecological risk determinants potentiating wildlife anthrax occurrence, and bio-surveillance tools for control and prevention: A case study of Queen Elizabeth Conservation Area in Uganda

Abstract

Anthrax has long standing history at Uganda’s Queen Elizabeth National Park, where outbreaks have occurred consistently and periodically with significant wildlife mortalities. Bacillus anthracis, the causative agent, is a highly pathogenic, endospore forming, encapsulated, soil borne bacterium with diverse geographical global distribution. Herbivores are primary hosts. Humans are exposed through infected animal products. This study aimed to understand patterns of historical outbreaks, epidemiology, environmental risks, opportunities to improve control and prevention. Cases were enumerated through active carcass surveillance, and historical animal health record reviews from government archives. Historical outbreak patterns were assessed using descriptive statistics; epidemiological patterns, using two specific Hippopotamus amphibious models. Spatio-temporal clustering of cases, using permutation models of the spatial scan statistics; directionality in epidemic movements, using directional tests; patterns of epidemic propagation, using standard epidemic curves. B. anthracis Suitable Ecological Niche examined using Maxent Modeling. Gel electrophoresis PCR molecular methods and 57 formalin-fixed tissues and swabs, used for evaluating extend of the anthrax problem, efficacy of Bio-surveillance tools, sample preservatives and Protective Antigen Rapid Diagnostic Test against PCR as gold standard. Anthrax was confirmed from all outbreak years, spatial locations and species examined. Patterns showed unique spatial, species specific, seasonal variations, with human morbidity and mortality. Outbreaks were initiated during onset or end of first rains. Suitable niche favouring spore survival and distribution was a narrow-restricted corridor, defined by hot-dry climatic conditions with alkaline soils rich in potassium and calcium ions. Anthrax epidemiology in hippos was characterized by consistent highly significant spatio-temporal clustering of cases and directional epidemic movements, mixed point-source propagated epidemics. The RDT evaluated showed high specificity, moderate sensitivity. Sample preservation tools showed good efficacy. The study concludes that, at QEPA, anthrax is endemic, very prevalent, epidemics are driven by hippos with significant zoonotic potential but limited control exists. Pathogen strain/clonality, longitudinal predictive risk studies, targeted bio-surveillance are recommended