Prevalence and Incidence of Lassa Virus Infection in Southern Mali

Background: The disease Lassa fever mostly affects people in Western Africa. It is very similar to other diseases that cause fever, like malaria and yellow fever. People get Lassa fever from mice infected with Lassa virus. It can also be spread from body fluids of people with the disease. Researchers want to learn more about this virus in Mali so they can develop better tools to diagnose and prevent it. Objective: To find out how many people in certain areas of southern Mali have ever had Lassa fever and count how many people get the disease every year. Eligibility: People ages 6 months to 99 years who live in certain areas of Mali Design: Women who are could become pregnant will have a urine pregnancy test at each visit. Participants will be asked questions about their age, if they have ever had a fever, and if they have ever seen mice in or around their home. This will take about 20 minutes. Participants will give a blood sample using a needle in a vein in the arm. Young children will give it by pricking a finger or heel with a needle. Patients with a fever illness will have a medical history and physical exam. They will give blood and nasal swabs 3 times over 21 days. Participants may be asked to come back 1 time each year for up to 3 more years to take another sample of blood and answer more questions.