Researchers report the results of the first ever genome-wide association study (GWAS) of a biosafety level 4 (BSL-4) virus. The team found two key human genetic factors that could help explain why some people develop severe Lassa fever, and a set of LARGE1 variants linked to a reduced chance of getting Lassa fever. The work could lay the foundation for better treatments for Lassa fever and other similar diseases. The scientists are already working on a similar genetics study of Ebola susceptibility.