Lassa virus persistence in body fluids after recovery from acute Lassa fever: a 2-year interim analysis of a prospective longitudinal cohort study

Background: There is anecdotal evidence for Lassa virus persistence in body fluids. We investigated various body fluids after recovery from acute Lassa fever and describe the dynamics of Lassa virus RNA load in seminal fluid. The primary objective of this study was to quantitatively describe virus persistence and clearance and assess the infectivity of seminal fluid. Methodology: In this prospective, longitudinal, cohort study, we collected plasma, urine, saliva, lacrimal, vaginal and seminal fluids from Lassa fever survivors at Irrua Specialist Teaching Hospital in Edo State, Nigeria. Inclusion criteria for participants were RT-PCR-confirmed Lassa fever diagnosis and age 18 years and above. Samples were taken at discharge from hospital (month 0) and at months 0·5, 1, 3, 6, 9, 12, 18, and 24 after discharge. Lassa virus RNA was detected using real-time RT-PCR. Infectivity was tested in cell culture and immunosuppressed mice. We used a linear mixed-effect model to analyse the dynamics of virus persistence in seminal fluid over time. Results: Between Jan 31, 2018, and Dec 11, 2019, 165 participants were enrolled in the study, of whom 159 were eligible for analysis (49 women and 110 men). Low amounts of Lassa virus RNA were detected at month 0 in plasma (45%, n=49/110), urine (34%, 37/110), saliva (5%, 5/110), lacrimal fluid (9%, 10/110), and vaginal fluid (21%, n=7/33 female participants). Virus RNA was cleared from these body fluids by month 3. However, 35 (80%) of 44 male participants had viral RNA in seminal fluid at month 0 with a median cycle threshold of 26·5. Lassa virus RNA remained detectable up to month 12 in seminal fluid. Biostatistical modelling estimated a clearance rate of 1·19 log₁₀ viral RNA copies per month and predicted that 50% of male survivors remain Lassa virus RNA-positive in seminal fluid for 83 days after hospital discharge, and 10% remain positive in seminal fluid for 193 days after discharge. Viral RNA persistence in seminal fluid for 3 months or more was associated with higher viraemia (p=0·006), more severe disease (p=0·0075), and longer hospitalisation during the acute phase of Lassa fever (p=0·0014). Infectious virus was isolated from 48 (52%) of 93 virus RNA-positive seminal fluid samples collected between month 0 and 12. Conclusion: Lassa virus RNA is shed in various body fluids after recovery from acute disease. The persistence of infectious virus in seminal fluid implies a risk of sexual transmission of Lassa fever.