A participatory expert-based risk assessment to inform zoonotic disease surveillance in Cameroon: the case of Ebola virus disease and Rift Valley fever

Background Viral haemorrhagic fevers (VHFs) are a group of zoonotic diseases caused by RNA viruses, including pathogens such as Ebola virus, Marburg virus, Lassa virus, and Rift Valley fever virus. Previous studies have identified Cameroon as a high-risk country, due to favourable ecoclimatic conditions and the presence of susceptible mammals and vectors that have been confirmed positive for viruses causing Rift Valley fever (RVF) and Ebola virus disease (EVD). Although evidence exists of RVF virus circulation in animals and serological reactivity to Ebola-related viruses among humans in Cameroon, the country has not officially documented epidemics of RVF or EVD. The objective of this study is to provide novel, context-refined knowledge of perceived risk factors and temporal patterns of RVF and EVD emergence in Cameroon, where epidemiological data on these two diseases are limited, with RVF explored through the livestock component and its early transmission dynamics in animal hosts, and zoonotic spillover to humans for EVD. Methods The present work proposes a risk assessment of RVF and EVD emergence through the development of a One Health integrated risk assessment tool for identifying perceived high-risk periods and key risk factors. A mixed, semi-quantitative approach involving expert semi-structured interviews, and a monthly calendar was used for data collection. Expert-based risk evaluation was then compared to risk factors derived from the scientific literature. Results For RVF, the wettest months seem to pose the highest risk, with increased inter-animal transmission during livestock transhumance. Key spatial determinants identified by experts included rainfall, host density, reservoirs, vectors, and livestock movements. For EVD spillover risk, human activities and behaviours, land cover, and host density were also perceived as critical. Convergences and divergences regarding expert-based and literature-based risk factors for RVF and EVD were observed, with variations concerning respectively livestock trade and socio-cultural practices linked to livelihood and forest-based subsistence. The distinction is likely attributable to the differing approaches of contextualization and generalization employed respectively by the two sources of weighting. Conclusions This study shows that, even in regions with no documented disease history, an integrated approach combining expert knowledge and literature-based evidence enables meaningful perceived risk assessment, generates novel and context-specific information, and supports the refinement of preventive strategies. The participatory visual tool introduced allows identification and quantification of putative zoonotic risk factors and their temporal dynamics, informing risk mapping, management, and communication.