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Item Lassa Fever in post-Ebola Sierra Leone. Sociodemographics and case fatality rates of in-hospital patients admitted at the Kenema Government Hospital Lassa Fever Ward between 2016-2018(Springer Science and Business Media LLC, 2019-11-06) Kangbai, Jia BaingaBackground Lassa fever (LF) is a zoonotic acute viral illness mainly found in West Africa. The disease is endemic in some parts of West Africa including Sierra Leone, Liberia, Guinea and Nigeria; while other neighboring countries at high risk of its outbreak since the animal vectors are distributed throughout the region.Methods This is a retrospective mixed cohort study that analysed the treatment history containing the sociodemographic and clinical characteristics of 52 laboratory-confirmed LF cases that were admitted to the Kenema Government Hospital Lassa Fever Ward (KGHLFW) during 2016 to 2018; i.e. during the post Ebola outbreak in Sierra Leone. The LF patients whose treatment history we analysed came from either within or outside Kenema district were the KGHLFW is located.Results Majority (59.6%, n = 31/52) of the LF cases recorded during the period under review were adults; females (65.4%, n = 34/52). 2016 recorded more (40.4%, n = 21/52) LF cases; 2017 (28.8%, n = 15/52) and 2018(30.8%, n = 16/52).Conclusions We highlighted the significance of LF preventive and control measures that can target its seasonal epidemics. These measures could include strategies that can reduce human contact with the rodent vector as well as raise sensitization and awareness about LF among local residents especially those residing along the LF belt in eastern Sierra Leone.Item Endotheliopathy and Platelet Dysfunction as Hallmarks of Fatal Lassa Fever(Centers for Disease Control and Prevention, 2020-09-29) Horton, Lucy E.L assa fever (LF) is an acute viral hemorrhagic fever endemic to West Africa, where ≈300,000-500,000 cases/year occur and mortality rates are high (1).Humans primarily are infected from exposure to excreta from the rodent host, Natal multimammate mouse (Mastomys natalensis).Pregnant women especially are susceptible to severe disease; infection during pregnancy usually leads to spontaneous abortion (2).The high rates illness and death, lack of vaccines or approved treatments, and potential to cause a public health emergency led to the US Centers for Disease Control and Prevention to classify LF as a category A bioterrorism agent (https://emergency.cdc.gov/agent/agentlist-category.asp) and the World Health Organization to classify LF as a priority disease (https://www.who.int/dg/priorities).Early clinical manifestations and symptoms of LF often are nonspecific and easily confused with other diseases prevalent in the endemic region, such as malaria and typhoid fever.Consequently, patients often are not admitted for LF treatment until symptoms are severe and they have failed other therapies.Bleeding at mucous membranes and edema generally are seen in the most severe cases (3,4), but bleeding diathesis reportedly was common during a recent outbreak in Nigeria (4).Overt hemorrhage is rare, mostly limited to the mucosal surfaces, and not severe enough to cause shock.Pathologic changes seen on autopsy lack major cell and tissue injury but include signs of pleural effusion, pulmonary edema, ascites, and gastrointestinal mucosa bleeding (5,6), all indications of systemic vascular leakage.Severely ill LF patients often have mild to moderate thrombocytopenia, but rarely have platelet counts <100,000/μL (7).Thrombocytopenia is a common feature of hemorrhagic fevers and vascular permeability disorders (8), but the decrease in platelet counts in acute LF is not low enough to cause spontaneous hemorrhage.LF could be characterized as a disease of enhanced vascular permeability but the underlying Endotheliopathy and Platelet Dysfunction as Hallmarks of Fatal Lassa FeverItem Ecological correlates and predictors of Lassa fever incidence in Ondo State, Nigeria 2017–2021: an emerging urban trend(Nature Portfolio, 2023-11-27) Cadmus, SimeonLassa fever (LF) is prevalent in many West African countries, including Nigeria. Efforts to combat LF have primarily focused on rural areas where interactions between rodents and humans are common. However, recent studies indicate a shift in its occurrence from rural to urban areas. We analysed secondary data of reported LF outbreaks from 2017 to 2021 in Ondo State, Nigeria to identify the distribution pattern, ecological variations, and other determinants of disease spread from the ward level using nearest neighbour statistics and regression analysis. Data utilised include LF incidence, ecological variables involving population, nighttime light intensity, vegetation, temperature, market presence, road length, and building area coverage. ArcGIS Pro 3.0 software was employed for spatial analysis. Results revealed spatio-temporal clustering of LF incidents between 2017 and 2021, with an increasing trend followed by a decline in 2021. All wards in Owo Local Government Area were identified as LF hotspots. The ecological variables exhibited significant correlations with the number of LF cases in the wards, except for maximum temperature. Notably, these variables varied significantly between wards with confirmed LF and those without. Therefore, it is important to prioritise strategies for mitigating LF outbreaks in urban areas of Nigeria and other LF-endemic countries.Item Current sampling and sequencing biases of Lassa mammarenavirus limit inference from phylogeography and molecular epidemiology in Lassa fever endemic regions(Public Library of Science, 2023-11-08) Arruda, Liã BárbaraLassa fever (LF) is a potentially lethal viral haemorrhagic infection of humans caused by Lassa mammarenavirus (LASV). It is an important endemic zoonotic disease in West Africa with growing evidence for increasing frequency and sizes of outbreaks. Phylogeographic and molecular epidemiology methods have projected expansion of the Lassa fever endemic zone in the context of future global change. The Natal multimammate mouse (Mastomys natalensis) is the predominant LASV reservoir, with few studies investigating the role of other animal species. To explore host sequencing biases, all LASV nucleotide sequences and associated metadata available on GenBank (n = 2,298) were retrieved. Most data originated from Nigeria (54%), Guinea (20%) and Sierra Leone (14%). Data from non-human hosts (n = 703) were limited and only 69 sequences encompassed complete genes. We found a strong positive correlation between the number of confirmed human cases and sequences at the country level (r = 0.93 (95% Confidence Interval = 0.71-0.98), p < 0.001) but no correlation exists between confirmed cases and the number of available rodent sequences (r = -0.019 (95% C.I. -0.71-0.69), p = 0.96). Spatial modelling of sequencing effort highlighted current biases in locations of available sequences, with increased sequencing effort observed in Southern Guinea and Southern Nigeria. Phylogenetic analyses showed geographic clustering of LASV lineages, suggestive of isolated events of human-to-rodent transmission and the emergence of currently circulating strains of LASV from the year 1498 in Nigeria. Overall, the current study highlights significant geographic limitations in LASV surveillance, particularly, in non-human hosts. Further investigation of the non-human reservoir of LASV, alongside expanded surveillance, are required for precise characterisation of the emergence and dispersal of LASV. Accurate surveillance of LASV circulation in non-human hosts is vital to guide early detection and initiation of public health interventions for future Lassa fever outbreaks.Item Identifying risk factors for Lassa fever infection in Sierra Leone, 2019-2021(2024-04-12) Sama, Daniel JumaBackground Lassa fever (LF) virus (LASV) is endemic in Sierra Leone and poses a significant public health threat to the region; however, no risk factors for LASV infection have been reported in Sierra Leone. The objective of this study was to identify the risk factors for LASV infection in an endemic community in Sierra Leone. Methods We conducted a case-control study by enrolling 37 laboratory-confirmed LF cases identified through the national LF surveillance system in Sierra Leone, and 140 controls resided within a one-kilometre radius of the case household. We performed conditional multiple logistic regression analysis to identify the risk factors for LASV infection. Results Of the 37 cases enrolled, 23 died (62% case fatality rate). Cases were younger than controls (19.5 years vs 28.9 years, p<0.05) and more frequently female (64.8% vs. 52.8%). Compared to the controls, LF cases had contact with rodents (rats or mice) in their households more frequently in the preceding three weeks (83.8% vs.47.8%). Households with a cat reported a lower presence of rodents (73% vs 38%, p<0.01) and contributed to a lower rate of LF (48.6% vs 55.7%) although not statistically significant (p=0.56). The presence of rodents in the households (Matched Adjusted Odds Ratio \[mAOR\]: 11.1), and younger age (mAOR: 0.99) were independently associated with LASV infection. Conclusion Rodent access to households is likely a key risk factor for LASV infection in rural Sierra Leone and potentially in other countries within the West African region. Controlling rodent access to households might help reduce household-level LASV infection in Sierra Leone.Item Drivers of Lassa fever in an endemic area of southwestern Nigeria (2017–2021): An epidemiological study(Public Library of Science, 2025-06-25) Cadmus, SimeonBACKGROUND: Reporting two million human Lassa fever (LF) cases with around 10,000 associated annual mortality, the West African sub-region is endemic for Lassa fever virus (LASV). The true incidence of LF is difficult to determine because most LASV-infected individuals show no differentiating clinical signs and symptoms. We investigated the distribution of cases, post-hospitalization survival patterns, and evaluated factors contributing to infection and clinical course of the disease during an outbreak of LF in Ondo State, Nigeria, from 2017 to 2021. METHODS: We extracted LF data from the Integrated Disease Surveillance and Response weekly report of the Nigerian Centre for Disease Control for 2017-2021. Kaplan-Meier estimate was used to describe the probability of survival among the LF cases. Also, a univariable binary logistic regression was used to explore factors associated with mortality among the study participants. Key informant was interviewed and environmental assessments were also done. RESULTS: LASV infection was confirmed in 1,115 (24.5%) of 4,551 cases with clinical signs suggestive of LF (age 35.24 ± 20.77) and case fatality rate of 25.5%. Hospitalized patients who did not recover within 17 days had less than 50% chance of survival. Age is a strong predictor of survival; hospitalized patients >40 years were significantly more likely than younger ones to experience mortality (Odds ratio:2.46; 95% CI = 1.67-3.62; p < 0.01). Similarly, male patients were significantly less likely than the females to survive beyond 10 days of hospitalization. Open sun drying of food items and congested urban residential settings with history of frequent rat sightings are possible factors for the increase of LF cases in the study area. CONCLUSION: Current case definition in Ondo State identified close to 25% of laboratory confirmed LASV infection. Human activities during the dry season (October-March) are associated with increased LF cases. We propose a One Health disease surveillance approach that synchronizes farming activities with educational campaigns as a mitigation strategy against LASV infection and mortality in Nigeria.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.