Lassa virus (LASV) is the causative agent of Lassa fever (LF), an often-fatal hemorrhagic disease. LF is endemic in Nigeria, Sierra Leone and other West African countries. Diagnosis of LASV infection is challenged by the genetic diversity of the virus, which is greatest in Nigeria. The ReLASV Pan-Lassa Antigen Rapid Test (Pan-Lassa RDT) is a point-of-care, in vitro diagnostic test that utilizes a mixture of polyclonal antibodies raised against recombinant nucleoproteins of representative strains from the three most prevalent LASV lineages (II, III and IV). We compared the performance of the Pan-LASV RDT to available quantitative PCR (qPCR) assays during the 2018 LF outbreak in Nigeria. For patients with acute LF (RDT positive, IgG/IgM negative) during initial screening, RDT performance was 83.3% sensitivity and 92.8% specificity when compared to composite results of two qPCR assays. 100% of samples that gave Ct values below 22 on both qPCR assays were positive on the Pan-Lassa RDT. There were significantly elevated case fatality rates and elevated liver transaminase levels in subjects whose samples were RDT positive compared to RDT negative.
Antibodies, Viral/metabolism , Diagnostic Tests, Routine/methods , Lassa Fever/diagnosis , Lassa virus/isolation & purification , RNA, Viral/genetics , Adult , Antigens, Viral/immunology , Disease Outbreaks , Female , Humans , Lassa virus/genetics , Lassa virus/immunology , Male , Middle Aged , Nigeria , Point-of-Care Systems , Sensitivity and Specificity , Sequence Analysis, RNA , Young Adult
During 2018, an unusual increase in Lassa fever cases occurred in Nigeria, raising concern among national and international public health agencies. We analyzed 220 Lassa virus genomes from infected patients, including 129 from the 2017-2018 transmission season, to understand the viral populations underpinning the increase. A total of 14 initial genomes from 2018 samples were generated at Redeemer's University in Nigeria, and the findings were shared with the Nigerian Center for Disease Control in real time. We found that the increase in cases was not attributable to a particular Lassa virus strain or sustained by human-to-human transmission. Instead, the data were consistent with ongoing cross-species transmission from local rodent populations. Phylogenetic analysis also revealed extensive viral diversity that was structured according to geography, with major rivers appearing to act as barriers to migration of the rodent reservoir.
Genome, Viral , Lassa Fever/virology , Lassa virus/genetics , RNA, Viral/analysis , Adolescent , Adult , Animals , Bayes Theorem , Disease Reservoirs , Female , Genetic Variation , Humans , Lassa Fever/epidemiology , Lassa Fever/transmission , Male , Markov Chains , Middle Aged , Nigeria/epidemiology , Phylogeny , Phylogeography , Rodentia , Sequence Analysis, RNA , Zoonoses/transmission
