Abstract
Lassa virus (LASV) is endemic in parts of West Africa where it causes Lassa fever (LF), a viral hemorrhagic fever with frequent fatal outcomes. The diverse LASV strains are grouped into six major lineages based on the geographical location of the isolated strains. In this study, we have focused on the lineage II strains from southern Nigeria. We determined the viral sequences from positive cases of LF reported at tertiary hospitals in Ebonyi and Enugu between 2012 and 2016. Reverse transcription-polymerase chain reaction (RT-PCR) showed that 29 out of 123 suspected cases were positive for the virus among which 11 viral gene sequences were determined. Phylogenetic analysis of the complete coding sequences of the four viral proteins revealed that lineage II strains are broadly divided into two genetic clades that diverged from a common ancestor 195 years ago. One clade, consisting of strains from Ebonyi and Enugu, was more conserved than the other from Irrua, although the four viral proteins were evolving at similar rates in both clades. These results suggested that the viruses of these clades have been distinctively evolving in geographically separate parts of southern Nigeria. Furthermore, the epidemiological data of the 2014 outbreak highlighted the role of human-to-human transmission in this outbreak, which was supported by phylogenetic analysis showing that 13 of the 16 sequences clustered together. These results provide new insights into the evolution of LASV in southern Nigeria and have important implications for vaccine development, diagnostic assay design, and LF outbreak management.
Highlights
Lassa virus (LASV) is the causative agent of Lassa fever (LF), a viral hemorrhagic fever with manifestations that range from asymptomatic to an acute, severe form associated with significant mortality [1, 2]
Lassa fever (LF) is a viral hemorrhagic fever caused by Lassa virus (LASV)
These results provide additional information on the evolution of LASV in southern Nigeria and LF outbreak management
Summary
Lassa virus (LASV) is the causative agent of Lassa fever (LF), a viral hemorrhagic fever with manifestations that range from asymptomatic to an acute, severe form associated with significant mortality (up to 50% in hospitalized patients) [1, 2]. The initial manifestations are usually those of a generalized flu-like symptoms which renders clinical diagnosis difficult owing to several possible differential diagnoses [3,4,5]. LF is associated with significant maternal morbidity during pregnancy, with a range of clinical features that include vaginal bleeding, threatened abortion, puerperal infection, intrauterine fetal death, premature labor, and eventual mortality, all of which depend on the stage of the pregnancy [6]. Human-to-human transmission is one of the routes of transmission, especially in hospital settings, and this has been estimated to be responsible for 20% of LASV transmissions a recent study demonstrated human to human transmission in 3% of 169 LASV sequences that were analyzed [12,13,14,15,16]
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