A Sporadic and Lethal Lassa Fever Case in Forest Guinea, 2019

Abstract

Lassa fever is a rodent-borne disease caused by Lassa virus (LASV). It causes fever, dizziness, vertigo, fatigue, coughing, diarrhea, internal bleeding and facial edema. The disease has been known in Guinea since 1960 but only anectodical acute cases have been reported to date. In January 2019, a 35-year-old man, a wood merchant from Kissidougou, Forest Guinea, presented himself at several health centers with persistent fever, frequent vomiting and joint pain. He was repeatedly treated for severe malaria, and died three weeks later in Mamou regional hospital. Differential diagnosis identified LASV as the cause of death. No secondary cases were reported. The complete LASV genome was obtained using next-generation sequencing. Phylogenetic analysis showed that this strain, namely the Kissidougou strain, belongs to the clade IV circulating in Guinea and Sierra Leone, and is thought to have emerged some 150 years ago. Due to the similarity of symptoms with malaria, Lassa fever is still a disease that is difficult to recognize and that may remain undiagnosed in health centers in Guinea.

Keywords: Guinea; Kissidougou; Lassa fever; Lassa genome; phylogeny.

Figure 1

Map of Guinea showing the towns of interest, Kissidougou where the patient lived and Mamou where he died. Faranah, Macenta and Nzérékoré are the towns where Lassa virus sequences obtained from humans have been documented. The pink stars represent the locations of Lassa fever cases described in Henderson et al. 1972 [17], Bausch et al. 2001 [12] and this study.

Figure 2

Time-calibrated phylogeny of the Lassa virus strains, gathering 41 sequences belonging to lineages IV and V (i.e., represented by “South Mali/North CIV”) and showing the new one from Kissidougou (in pink). The trees show the complete glycoprotein precursor and nucleoprotein in a linked model (A), and the complete polymerase (B). The trees were inferred by using the Bayesian Markov chain Monte Carlo method, with GTR + gamma model, strict clock, constant population size and partitioning into codon positions 1, 2, 3. Posterior probabilities are coded as follows: 0.7, green dots; 0.80 to < 0.85, purple-blue dots; > 0.97, red dots. Geographical origins are noted on the right of each tree, and scale axis represents the time in years.