Lassa Fever is caused by the Lassa virus belonging to the Arenaviridae family. It is a zoonosis – an animal disease that can spread to humans – transmitted by rats belonging to the Mastomys genus. A person may acquire the virus if they come into contact with the urine and feces of an infected rat. Human to human transmission occurs when a person comes into contact with body fluids such as the blood, urine, and saliva of an infected person. Sexual transmission of the Lassa virus has also been reported. In addition, the virus can spread through unhygienic healthcare settings via improperly sterilized medical instruments, infected blood products, and lack of infection control gear such as masks, gloves, and gowns.
Lassa Fever is present in west Africa. Travellers staying in crowded living areas with poor sanitation conditions are at increased risk. Patients who require medical care in substandard medical facilities and healthcare practitioners working in unhygienic conditions are also at greater risk.
In the majority of cases, the infection is asymptomatic – persons do not exhibit symptoms. Those with symptoms get ill 1 to 3 weeks after contact, starting with flu-like symptoms including fever and general weakness. The illness progresses with a headache, sore throat, cough, muscle, abdominal and chest pain, nausea, vomiting, and diarrhea. More severe symptoms, occurring in 15% to 20% of patients, include facial swelling, uncontrolled bleeding from the mouth, nose, vagina, and gastrointestinal tract. During the later stages, a patient may have convulsions, tremors, disorientation, partial or complete deafness, and may end up in a coma. Lassa Fever can be fatal. Treatment includes supportive care of the symptoms and taking the antiviral drug Ribavirin.
There is no preventive medication or vaccine against Lassa Fever.
Lassa virus images, life cycle, and distribution maps: Infection Landscapes
Information last updated: April 28, 2021.