Lassa Fever

What is Lassa Fever?

Lassa fever is a serious viral infection that lasts 1-4 weeks. About 80 percent of the cases are mild or with no symptoms at all. However, the other 20 percent may suffer severe failure of multiple organs. The disease is more severe in pregnancy, and maternal death is common. The overall death rate is about 1 percent, but in severe cases, it can be 15 percent. Lassa fever is associated with epidemics, during which up to 50 percent of the patients might die.

It is estimated that 100,000 to 300,000 people in west Africa are infected each year with approximately 5,000 deaths. 

How do you get Lassa Fever?

Wild rodents in western Africa are the source of this virus, and people become infected through direct contact with contaminated rat droppings or urine, or contact with objects or eating food contaminated with rat droppings and urine. People may also inhale tiny particles of air contaminated with rodent excretions (airborne transmission). 

Lassa fever may also spread from person to person through contact with infected blood, tissues, secretions, or excretions.  This kind of transmission is common in health care settings where it can also be spread by contaminated medical equipment.

Susceptibility and Resistance

Susceptibility is general. The length of duration of immunity after surviving an infection is unknown.

Incubation Period

The incubation period for Lassa Fever is 6-21 days.

What are the Symptoms?

The symptoms include a gradual onset of fatigue, fever, headache, sore throat, cough, nausea, vomiting, diarrhoea, muscle aches and chest pain. The fever is intermittent and often spikes to high levels. In severe cases, complications can include loss of blood pressure, haemorrhaging, seizures, and brain inflammation due to different organs being affected.

Preventative Measures

Avoiding contact with rodents that carry the disease is the best form of prevention. Protecting food sources and keeping a clean environment discourages rodents from entering homes. In the hospital setting, preventive precautions include wearing protective clothing, such as masks, gloves, gowns and goggles, and using infection control measures.


Early treatment (within the first 6 days of illness) with the anti-viral drug, Ribavirin, is the most effective therapy available.


Where Does It Commonly Occur?

Lassa fever can be found in Nigeria, Guinea, Liberia, and Sierra Leone. It may be present in other countries in west Africa.