An exploration of the protective effect of rodent species richness on the geographical expansion of Lassa fever in West Africa

Background: Lassa fever (LF) is one of the most devastating rodent-borne diseases in West Africa, causing thousands of deaths annually. The geographical expansion of LF is also a concern; cases were recently identified in Ghana and Benin. Previous ecological studies have suggested that high natural-host biodiversity reduces the likelihood of spillover transmission of rodent-borne diseases, by suppressing the activities of reservoir species. However, the association of biodiversity with the geographical expansion of LF has not been the subject of epidemiological studies. Methodology/Principal findings: We conducted a spatial analysis based on sociodemographic, geographical, and ecological data, and found that higher rodent species richness was significantly associated with a lower risk of LF emergence in West Africa from 2008 to 2017 (Odds Ratio = 0.852, 95% Credible Interval = 0.745–0.971). Conclusions/Significance: The results reinforce the importance of the ‘One Health’ approach by demonstrating that a high level of biodiversity could benefit human health. Author summary: Rodent diversity has been studied as a protective factor for rodent-borne diseases and rodent-related tick-borne diseases, such as hantavirus infection and Lyme diseases, in human population. The protective effect is called dilution effect and based on the ecological mechanism that the high diversity of rodent species could suppress the activities of reservoir rodents thereby reduce the likelihood of spillover transmission from rodents. However, the effect has been studied mostly for endemic diseases, and the effect on the geographical expansion of rodent-borne diseases has not been the subject of epidemiological studies. Considering that the dilution effect may also be applicable to the geographic expansion of rodent-borne infectious diseases in that a high rodent species diversity could decrease migration of infected rodents from the disease-endemic area, we examined the association between rodent species richness and the geographical expansion of Lassa fever (LF) in West African countries. Analyzing the regions without LF until 2007, the results showed that the region with lower number of rodent species showed higher risk of emerging LF cases from 2008 to 2017, implying the protective effect of higher rodent species richness on spatial expansion of LF. The results reinforce the importance of the ‘One Health’ approach by demonstrating that a high level of biodiversity could benefit human health.