Lassa virus is a type of virus that causes a disease known as Lassa fever. It is primarily found in West Africa and is transmitted to humans through contact with the urine or droppings of infected multimammate rats. The virus can also spread through direct contact with bodily fluids of infected individuals. Symptoms of Lassa fever can range from mild to severe and may include fever, weakness, and headaches. In some cases, the disease can lead to serious complications, such as bleeding and organ failure. Early diagnosis and treatment are crucial for improving outcomes in infected patients.