Systematic review and meta-analysis of the epidemiology of Lassa virus in humans, rodents and other mammals in sub-Saharan Africa

Abstract

Accurate data on the Lassa virus (LASV) human case fatality rate (CFR) and the prevalence of LASV in humans, rodents and other mammals are needed for better planning of actions that will ultimately reduce the burden of LASV infection in sub-Saharan Africa. In this systematic review with meta-analysis, we searched PubMed, Scopus, Africa Journal Online, and African Index Medicus from 1969 to 2020 to obtain studies that reported enough data to calculate LASV infection CFR or prevalence. Study selection, data extraction, and risk of bias assessment were conducted independently. We extracted all measures of current, recent, and past infections with LASV. Prevalence and CFR estimates were pooled using a random-effect meta-analysis. Factors associated with CFR, prevalence, and sources of between-study heterogeneity were determined using subgroup and metaregression analyses. This review was registered with PROSPERO, CRD42020166465. We initially identified 1,399 records and finally retained 109 reports that contributed to 291 prevalence records from 25 countries. The overall CFR was 29.7% (22.3-37.5) in humans. Pooled prevalence of LASV infection was 8.7% (95% confidence interval: 6.8-10.8) in humans, 3.2% (1.9-4.6) in rodents, and 0.7% (0.0-2.3) in other mammals. Subgroup and metaregression analyses revealed a substantial statistical heterogeneity explained by higher prevalence in tissue organs, in case-control, in hospital outbreak, and surveys, in retrospective studies, in urban and hospital setting, in hospitalized patients, and in West African countries. This study suggests that LASV infections is an important cause of death in humans and that LASV are common in humans, rodents and other mammals in sub-Saharan Africa. These estimates highlight disparities between sub-regions, and population risk profiles. Western Africa, and specific key populations were identified as having higher LASV CFR and prevalence, hence, deserving more attention for cost-effective preventive interventions.

Fig 1. Flow-chart describing study selection process.

Fig 2. Human case fatality rate due to Lassa virus in sub-Saharan Africa.

Fig 3. Prevalence of Lassa virus infections in humans in sub-Saharan Africa.

Fig 4. Prevalence of Lassa virus infections in rodents in sub-Saharan Africa.

*Negative rodents include Gerbilliscus species, Lemniscomys species, Praomys daltoni, Praomys species, Rattus rattus, Uranomys ruddi, Nannomys minutoides/mattheyi, Myomys daltoni, Praomys rostratus, Lemniscomys striatus, Praomys cf. rostratus, Crocodura species, Lophuromys sikapusi, Tatera cf. guinea, Gerbilliscus kempi, Praomys jacksoni, Mus setulosus, and Mus minutoides. #Negative rodents include Gerbilliscus kempi, Mus setulosus, Praomys jacksoni, Lemniscomys bellieri/zebra, Uranomys ruddi, Crocidura buettikoferi, Gerbilliscus guineae, Lophuromys sikapusi, and Mus mattheyi.

Fig 5. Prevalence of Lassa virus infections in other mammals in sub-Saharan Africa.

Fig 6. Lassa virus case fatality rate in humans and Lassa virus prevalence in humans, rodents, and other mammals in sub-Saharan Africa, 1970–2020.

LASV: Lassa virus prevalence; Past contacts denote articles with unspecified antibodies or IgG positive subjects. Recent contacts denote articles with IgM or IgM and IgG positive subjects. Current contacts denote studies with antigen, RNA, virus positives or subjects with an increase in antibody titer between acute and convalescent samples. Current, recent and past contacts are indicated by shades of red, blue and green respectively. Lines 1, 2, 3, 4 and 5 indicate the LASV case fatality rate in humans, the prevalence of LASV in humans, Mastomys natalensis, non-Mastomys natalensis rodents and other mammals respectively.