About 80% of people who become infected with the Lassa virus never have symptoms, reports the WHO. That's what makes it so difficult to detect the virus. The virus is a zoonotic illness that is transmitted to people via contact with food or household items contaminated with rat urine or feces. But it can also be spread from person to person via infected blood or fluids.
For those who have symptoms, they are usually mild and include a low fever and overall weakness. Those who have more serious symptoms may experience bleeding in their eyes, gums and nose, as well as vomiting, respiratory distress, facial swelling, deafness and severe pain. Only about 1% of Lassa virus infections result in death.