Prevalence and Incidence of Lassa Virus Infection in Southern Mali

In West Africa, as many as 300,000 people are infected annually with Lassa virus (LASV), resulting in approximately 5,000 deaths. Most commonly, human infection comes from contact with infected rodent hosts (Mastomys natalensis), or ingestion or inhalation of virus-laden particles. Person-to-person transmission is also well documented and can cause outbreaks, especially in nosocomial settings. Infection in pregnancy, especially the third trimester, is particularly severe, with maternal mortality rates estimated at 20% and fetal mortality rates nearing 100%. A survey of rodents captured in the village of Soromba (rural commune of Sibirila, district of Bougouni, Mali) found that 25% of M. natalensis had evidence of LASV infection. A 2015 study of LASV infection in the human populations of this region showed seroprevalence of 33.2% and annual incidence rate of 6.3% in 2016. The purpose of this serosurvey study is to determine the prevalence and incidence of human exposure to LASV in the administrative districts of Bougouni, Yanfolila, and Kolondieba in southern Mali. The study involves 2 separate sub-studies. Study 1 is a cross-sectional serosurvey of residents of the general population selected from a census. The study will follow up to 500 participants at each of 4 study sites (Fakola, Bamba, Filamana, and Guelelinkoro). Participants will be asked to give blood samples at baseline and annually for up to 3 years. Study 2 is a clinic-based serosurvey conducted at local health centers following up to 500 participants per year at each of the 4 study sites (Fakola, Bamba, Filamana, and Guelelinkoro). Patients who report with febrile illness suggestive of Lassa fever will be asked to give blood and nasal swab samples, then return for follow-up visits 5 and 21 days later for clinical consultation and additional blood and swab collection. All participants will be provided with free medical treatment according to local standard of care as needed for the duration of the study. They will be followed passively between study visits and instructed to report to their local health center if they have a fever. Study visits will be conducted through a common end date, up to 3 years. Blood and nasal swab samples will be used to identify history of or current LASV infection and for exploratory studies into the biochemistry and pathophysiology of LASV infection. Elucidating the prevalence of LASV infection in the populations of southern Mali may help Malian authorities improve surveillance, and additional research may help develop diagnostics and treatment.