Geographic Distribution and Genetic Characterization of Lassa Virus in Sub-Saharan Mali

Abstract

Background

Lassa fever is an acute viral illness characterized by multi-organ failure and hemorrhagic manifestations. Lassa fever is most frequently diagnosed in Nigeria, Sierra Leone, Liberia, and Guinea, although sporadic cases have been recorded in other West African countries, including Mali. The etiological agent of Lassa fever is Lassa virus (LASV), an Arenavirus which is maintained in nature and frequently transmitted to humans by Mastomys natalensis. The purpose of this study was to better define the geographic distribution of LASV-infected rodents in sub-Saharan Mali.

Methodologies/Principal Findings

Small mammals were live-trapped at various locations across Mali for the purpose of identifying potential zoonotic pathogens. Serological and molecular assays were employed and determined LASV infected rodents were exclusively found in the southern Mali near the border of Côte d'Ivoire. Overall, 19.4% of Mastomys natalensis sampled in this region had evidence of LASV infection, with prevalence rates for individual villages ranging from 0 to 52%. Full-length genomic sequences were determined using high throughput sequencing methodologies for LASV isolates generated from tissue samples of rodents collected in four villages and confirmed the phylogenetic clustering of Malian LASV with strain AV.

Conclusions/Significance

The risk of human infections with LASV is greatest in villages in southern Mali. Lassa fever should be considered in the differential diagnosis for febrile individuals and appropriate diagnostic techniques need to be established to determine the incidence of infection and disease in these regions.

Author Summary

Lassa fever is an acute infection associated with hemorrhagic manifestations and multi-organ failure in West Africa. The etiological agent of Lassa fever is Lassa virus (LASV), a rodent-borne arenavirus, which is maintained in nature and transmitted to humans by the multimammate rat, Mastomys natalensis. Despite the ubiquitous nature of the rodent reservoir, LASV-infected animals are most commonly documented in Nigeria, Sierra Leone, Guinea and Liberia. These four countries represent the historic endemic region for Lassa fever, although there is increasing evidence of sporadic cases occurring in other West African nations including Mali. To better define the geographic distribution of LASV-infected rodents in Mali, we tested samples from small animals collected at 27 sites across the country. Although M. natalensis was the predominant rodent species in the majority of villages, evidence of LASV infection was exclusively found in southern Mali, where overall nearly 20% of rodents were positive. The full genomic sequence was determined for five isolates and confirmed LASV in Mali is closely related to strain AV. We conclude that there is a risk of human exposure to LASV in villages in southern Mali and Lassa fever should be considered in the differential diagnosis for acutely ill, febrile patients.