Lassa fever: transmission, symptoms and treatment
Lassa fever is an acute viral haemorrhagic illness caused by Lassa virus, a member of the arenavirus family, and occurs in West Africa. Humans are usually infected through food or household items contaminated with the urine or faeces of infected rodents. About 80% of infections are mild or without symptoms, but severe cases can be fatal.
Where Lassa fever occurs
The disease was discovered in 1969 in Nigeria and is named after the town where the first cases occurred. Lassa fever is known to be endemic in Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone and Nigeria, and probably exists in other West African countries. Estimates widely cited by Institut Pasteur put the burden at 100,000 to 300,000 infections and about 5,000 deaths per year in West Africa.
How Lassa virus is transmitted
The natural reservoir is a rodent that sheds the virus in urine and droppings. People become infected through contact with contaminated food or household items. Person-to-person transmission occurs through direct contact with blood, secretions, urine, faeces or other body fluids of an infected person, and has occurred in health-care settings. Sexual transmission has been reported.
Symptoms and course
The incubation period ranges from 2 to 21 days. Fever, general weakness and malaise are usually the first symptoms in people who become ill. Lassa fever is hard to distinguish from malaria, shigellosis, typhoid fever, yellow fever and other VHFs such as Ebola. Disease is more severe in pregnant women, with frequent maternal death and very often fetal loss. In survivors, fever usually resolves about ten days after onset, but fatigue, malaise and dizziness can continue for weeks. Hearing loss is a recognised complication.
| Incubation period | 2–21 days |
|---|---|
| Mild or asymptomatic infections | About 80% |
| Observed case fatality in hospitalised severe cases | 15% |
| Licensed vaccine | None |
Diagnosis and treatment
Confirmation requires laboratory testing, typically RT-PCR. The antiviral ribavirin is used and is considered effective when given early in the course of clinical illness. There is no evidence supporting ribavirin as post-exposure prophylaxis.
Lassa fever is occasionally exported by travellers. Although malaria and typhoid are far more common, Lassa fever should be considered in febrile patients returning from West Africa, especially after stays in rural areas or contact with hospitals in endemic countries.
Prevention
- Store grain and other food in rodent-proof containers.
- Keep homes clean and discourage rodents from entering.
- Health workers should apply standard infection-control precautions with every patient and additional barrier precautions for suspected Lassa fever.
Medical note: this page summarises public-health sources for general information. It is not medical advice. If you develop fever after travel to an affected area or after contact with a patient or with animal blood or ticks, contact a doctor or your local health authority by phone before attending in person, and mention the exposure.
Frequently asked questions
How do people catch Lassa fever?
Mostly through food or household items contaminated with urine or faeces of infected rodents, and less often through direct contact with blood or body fluids of an infected person.
Is Lassa fever always severe?
No. About 80% of infections are mild or without symptoms. Among hospitalised patients with severe disease, observed case fatality is about 15%.
Is there a Lassa fever vaccine?
No licensed vaccine against Lassa fever is available.
How is Lassa fever treated?
With supportive care and the antiviral ribavirin, which works best when started early in the illness.
Which countries have Lassa fever?
It is known to be endemic in Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone and Nigeria, and probably in other West African countries.