Seasonal Changes in Vegetation and Land Use in Lassa-Fever-Prone Areas (Kenema and Kailahun Districts) in Eastern Sierra Leone

Abstract

Lassa Fever is endemic to the eastern region of Sierra Leone. It is a haemorrhagic disease that is often transmitted from rats to humans and then human to humans. Ecological disturbances such as changes in land use involving conversion of natural ecosystems to agriculture, mining or for urban expansion are reported to bring humans into close contact with animals such as the Mastomys rat that carries the Lassa Fever virus thereby posing health problems.The nature and extent of such ecological disturbances or land use changes within areas known to be endemic to Lassa Fever are not clearly understood from a research context in Sierra Leone. This study was therefore undertaken to identify the pattern of changes in land use and cropping practices and their potential to bring humans into close interactions with the Mastomys rat that is the host for the Lassa Fever virus. Four communities were chosen for the study, two rural (Lalehun and Majihun) and two urban (Lambayama section in Kenema City and Largo Square section in Segbwema Town). Different vegetation and land use/cropping practices were identified and observations were made on the pattern of changes at different times in the cropping year. There were four common vegetation and cropping practices found in all communities: upland rice intercropping, old fallow, young fallow, and swamp rice cultivation. The study revealed the variations in land use patterns and cropping practices between urban and rural settlements. Agro-forestry practices such as perennial cash crops cacao and rubber plantations were more common in rural communities. The study also revealed that while fallow vegetation persisted in rural areas there had been expansion of settlements into old fallow vegetation indicating a greater threat to the persistence of natural ecosystem in urban than in rural settlements. These disturbances resulted in habitat fragmentation and increased the likelihood of contact between humans and animal species (e.g. Mastomys * Corresponding author.A. Kamara et al. 451 rat) associated with various habitats.

A Unified Framework for the Infection Dynamics of Zoonotic Spillover and Spread

“…The task is not free of challenges, especially for emerging diseases [ 18 ]. This is further complicated by abiotic factors such as land use change [ 4 ] and social difference demonstrating how risks are not generalisable [ 19 ]. Here, we start proposing some measures for the risk of zoonotic spillover and their link with drivers of transmission.…”

“…a broad set of pathogen life histories and periodicity of infection prevalence), and anthropogenic activities ( e.g. land-use and behavioural changes affecting direct and indirect interactions with reservoir hosts) [ 4 ]. Particularly challenging are zoonoses with stuttering transmission, as separating the contribution of animal-to-human from human-to-human transmission is extremely difficult.…”

Understanding the cryptic nature of Lassa fever in West Africa

“…Like many endemic tropical diseases, LASV spillover dynamics emerge from complex interactions between multiple human and environmental factors [59]. In rodents such factors may include seasonal population and viral transmission dynamics [39, 41,42] and behaviour such as consumption of food in people's homes [40], and in people may include variation in rodent consumption [62], land use practices [59,64] and age and genderr elated exposure risk [20,59]. This complexity presents challenges for risk forecasting and planning interventions, since local social-ecological system dynamics may vary across tropical West Africa.…”

“…Rainfall is associated with LF risk [66], which may relate to the link between rainfall and M. natalensis recruitment and population density [39]. In Sierra Leone there is evidence that dry season land use practices, such as soil perturbation, burning of fields to prepare for planting, wetland cultivation and rodent pest management, may bring people into closer contact with rodents [59,64,65]. Human-reservoir contact rates may also vary due to seasonal movement of rodents into homes and gardens to seek stored food, but the evidence of seasonal differences in M. natalensis abundance between villages and fields is inconclusive [40,42].…”

Climate Change and the Neglected Tropical Diseases

“…Several other environmental factors including pH, water flow and presence of algae are also important drivers of egg, larval, pupal and adult stage survival, larval feeding behaviour, larval-adult development time, gonotrophic cycle rate and population abundance (e.g. Araújo et al, 2012;Gouagna et al, 2012;Kamara et al, 2015).…”