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Permanent URI for this collectionhttps://dspace.njala.edu.sl/handle/20.500.144402/169
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Item Land use gradients drive spatial variation in Lassa fever host communities in the Eastern Province of Sierra Leone(Wiley, 2025-11-21) Simons, DavidThe natal multimammate mouse (Mastomys natalensis) is the primary reservoir host of Mammarenavirus lassaense (LASV), a zoonotic pathogen causing Lassa fever and endemic to West Africa. The occurrence and abundance of this species is regulated by the human environment and biotic interactions with other small-mammal species, but these ecological drivers remain poorly understood in the regions where Lassa fever outbreaks are observed. We developed a Bayesian multi-species occupancy model incorporating incomplete detection to assess habitat use from data obtained as part of a multi-year small-mammal trapping study (43,226 trap nights across four village sites in Sierra Leone, 2020-2023). We investigated the effects of land use gradients and small-mammal community dynamics on the spatial distribution of M. natalensis. Mastomys natalensis occupancy increased along a gradient from forest to agriculture to village habitats but was reduced in the peri-urban site compared to rural settings. Invasive rodent species influenced this pattern, with Mus musculus presence associated with reduced M. natalensis occupancy in the peri-urban site. We did not observe a similar effect when considering the co-occurrence of invasive Rattus rattus with M. natalensis in rural settings. These findings suggest that land use and species interactions drive spatial heterogeneity in M. natalensis populations, potentially explaining reduced Lassa fever incidence in urban areas. The results highlight the importance of considering community dynamics when predicting the risk of outbreaks of endemic zoonoses and the need to widen the context of studies of LASV transmission beyond the primary reservoir host species. To better assess public health risk and improve allocation of limited resources, we recommend more precise characterisation of small-mammal communities in LASV endemic regions, particularly in areas undergoing rapid land use change which may alter community-level small-mammal biodiversity.Item Contact networks of small mammals highlight potential transmission foci of Lassa mammarenavirus(African Field Epidemiology Network, 2025-08-10) Simons, DavidIntroduction Lassa fever, caused by Mammarenavirus lassaense (LASV), is an endemic zoonosis in several West African countries. Human infections primarily arise from rodent-to-human transmission, with Mastomys natalensis, a synanthropic species, serving as the principal reservoir. In Sierra Leone, small-mammal communities vary across land use gradients, potentially shaping LASV transmission risk in human populations. However, the extent to which anthropogenic environments facilitate small-mammal interactions conducive to viral transmission remains poorly understood. Methods We conducted small-mammal sampling over 43,266 trap nights, detecting 684 rodents and shrews in the LASV-endemic Eastern Province of Sierra Leone. To assess potential for within- and between-species transmission, we constructed space-sharing networks based on co-trapping within species-specific radii informed by home range estimates. These networks approximated shared space use rather than direct interaction, allowing comparison of potential encounter patterns across habitats. Results Small-mammal communities in agricultural settings had greater species richness and were more connected than those in villages and forests, although overall space-sharing rates did not differ substantially. Network topology varied by land use, with greater modularity in village networks. Notably, space sharing among M. natalensis individuals was more frequent in agricultural settings than in villages, suggesting that land use may modulate opportunities for intra-specific viral transmission. LASV seroprevalence across the small-mammal community was 5.7%, with antibodies detected in nine species. We found no major differences in seroprevalence by land use or network complexity. Conclusion These findings underscore the importance of cross-habitat surveillance to understand host ecology and LASV transmission. Accounting for species-specific space use and habitat-dependent interaction structures is crucial for identifying key hosts and spillover settings.Item Contact Networks of Small Mammals Highlight Potential Transmission Foci of Mammarenavirus lassaense(American Society of Tropical Medicine and Hygiene, 2026-04-28) Simons, DavidLassa fever (LASV; Mammarenavirus lassaense) is an endemic zoonosis in West Africa. Human infections arise from rodent-to-human transmission, primarily from the synanthropic reservoir Mastomys natalensis (M. natalensis). In Sierra Leone, small-mammal communities vary across land-use gradients, shaping LASV transmission risk. How anthropogenic environments facilitate the rodent-rodent interactions remains poorly understood. Small mammals were sampled over 43,266 trap nights in Sierra Leone's LASV-endemic Eastern Province, detecting 684 rodents and shrews. To assess potential transmission, space-sharing networks were constructed from co-trapping events within species-specific home range radii. Shared space use was approximated in these networks, enabling the comparison of encounter patterns across habitats. Network topology varied significantly by land use. Village networks were the most connected (highest average degree), whereas agricultural communities supported the most species (higher rarefied richness) and were the most fragmented (higher modularity). Notably, the probability of intraspecific space sharing among M. natalensis was highest in agricultural settings, suggesting that land use modulates key intraspecific transmission pathways. Lassa fever seroprevalence was 5.7% community-wide, with antibodies detected in nine species. No statistically significant association was found between overall seroprevalence and land use or aggregate network structure (mean degree). However, predictive modeling for M. natalensis indicated that a higher individual degree is associated with seropositivity, suggesting complex, scale-dependent relationships. These findings reveal that simple ecological drivers do not fully explain LASV exposure, highlighting the importance of species-specific behaviors (i.e., M. natalensis clustering in agriculture) and the multihost serological landscape in assessing transmission risk.