Updated: Mar 29

Lassa fever, also known as Lassa hemorrhagic fever (LHF), is a type of viral hemorrhagic fever caused by the Lassa virus. It is an acute and often fatal viral disease, with fever, occurring mainly in West Africa. The Lassa virus is a member of the Arenaviridae virus family.

Lassa fever was first described in the 1950s, and the viral particle was identified in 1969 from three missionary nurses who died in the town of Lassa, in Borno State, Nigeria, after caring for an infected obstetrical patient. The virus is named after the town in Nigeria where the first cases occurred. It is the most commonly "exported" hemorrhagic fever.

Outbreak Distribution Map

Lassa fever virus is believed to be endemic (always present) in West Africa such as Nigeria, Benin, Guinea, Sierra Leone and Liberia. It has also been detected in the Ivory Coast, Ghana, Burkina Faso, Mali, Senegal, Gambia, and Central African Republic.

There are about 300,000 to 500,000 cases which result in 5,000 deaths each year worldwide. Deaths are especially common in children. Case fatality is 1% in general, although severe cases have a case fatality of 15%.

Signs and Symptoms

Many of those infected by the virus do not develop symptoms early.

After an incubation period of six to 21 days, an acute illness with multi-organ involvement develops. Nonspecific symptoms include fever, facial swelling, and muscle fatigue, as well as conjunctivitis and mucosal bleeding. The other symptoms arising from the affected organs are:

Gastrointestinal tract

  • Nausea

  • Vomiting (bloody)

  • Diarrhoea (bloody)

  • Stomach ache

  • Constipation

  • Dysphagia (difficulty swallowing)

  • Hepatitis

Cardiovascular system

  • Pericarditis

  • Hypertension

  • Hypotension

  • Tachycardia (abnormally high heart rate)

Respiratory tract

  • Cough

  • Chest pain

  • Dyspnoea

  • Pharyngitis

  • Pleuritis

Nervous system

  • Encephalitis

  • Meningitis

  • Unilateral or bilateral hearing deficit

  • Seizures

Clinically, Lassa fever infections are difficult to distinguish from other viral hemorrhagic fevers such as Ebola and Marburg, and from more common febrile illnesses such as malaria, shigellosis, typhoid fever, and yellow fever.

Note: As soon as you suspect Lassa fever, or you have persistent fever not responding to the normal/common treatment for malaria and typhoid, report to the nearest Health facility.


Lassa fever virus is an Arenavirus that is mainly a zoonosis (a disease spread to humans from animals). It is transmitted from animals, specifically it spreads to humans from a rodent known as a natal multimammate mouse (Mastomys natalensis). This is probably the most common mouse in equatorial Africa, ubiquitous in human households and eaten as a delicacy in some areas. It is also called the natal multimammate rat or African rat.

In these rodents, infection is in a persistent asymptomatic state. The virus is transmitted to humans by contact with food or household items contaminated with rodent’s urine or faeces (majorly through rodents having access to grain stores in residences). If rat eat your grain or other food the virus could transfer to the food.

Infection in humans can also occur by exposure to animal excrement through the respiratory or gastrointestinal tracts. Inhalation of tiny particles of infectious material (aerosol) is believed to be the most significant means of exposure.

It is possible to acquire the infection through broken skin or mucous membranes that are directly exposed to infectious material.

Transmission from person to person has also been established, presenting a disease risk for healthcare workers, particularly in hospitals lacking adequate infection prevention and control measures. It can be contracted through direct contact with infected human blood excretions and secretions, including through sexual contact. No evidence of airborne transmission person-to-person is seen. Transmission through breast milk has also been observed.


Because the symptoms of Lassa fever are so varied and non-specific, clinical diagnosis is often difficult, especially early in the course of the disease. Lassa fever is difficult to distinguish from other viral haemorrhagic fevers such as Ebola virus disease as well as other diseases that cause fever, including malaria, shigellosis, typhoid fever and yellow fever.

Definitive diagnosis requires testing that is available only in reference laboratories. Laboratory specimens may be hazardous and must be handled with extreme care. Lassa virus infections can only be diagnosed definitively in the laboratory using the following tests:

  • reverse transcriptase polymerase chain reaction (RT-PCR) assay

  • antibody enzyme-linked immunosorbent assay (ELISA)

  • antigen detection tests

  • virus isolation by cell culture.


All persons suspected of Lassa fever infection should be admitted to isolation facilities and their body fluids and excreta properly disposed of.

Ribavirin, an antiviral drug, has been used with success in Lassa fever patients. It has been shown to be most effective when given early in the course of the illness. Patients should also receive supportive care consisting of maintenance of appropriate fluid and electrolyte balance, oxygenation and blood pressure, as well as treatment of any other complicating infections.

What are Complications for Lassa Fever?

The risk of death once infected is about one percent and frequently occurs within two weeks of the onset of symptoms. Among those who survive about a quarter have deafness which improves over time in about half.

When is Lassa Fever no Longer Contagious?

It is not clear when infected humans are contagious or for how long, but the virus is cleared from the blood during recovery about three weeks after onset of symptoms.

The virus is still present in the urine for between three and nine weeks after infection and in semen for three months.

What is the Prognosis of Lassa Fever?

Early supportive care with rehydration and symptomatic treatment improves survival.

About 15–20% of hospitalized Lassa fever patients will die from the illness. The overall mortality rate is estimated to be 1%, but during epidemics, mortality can climb as high as 50%. The mortality rate is greater than 80% when it occurs in pregnant women during their third trimester; foetal death also occurs in nearly all those cases. Abortion decreases the risk of death to the mother. Some survivors experience lasting effects of the disease and can include partial or complete deafness.

Because of treatment with ribavirin, fatality rates are continuing to decline.

How to Prevent Lassa Fever

Prevention requires isolating those who are infected and decreasing contact with the rats. There is currently no vaccine that protects against Lassa fever.

  1. Store grain and other foodstuffs in rodent-proof containers.

  2. Dispose of garbage far from the home.

  3. Maintain clean households.

  4. Prevent and avoid rodents living in your homes and surroundings by trapping in and around your homes to reduce rodent populations and blocking all rat hideouts.

  5. You may want to keep cats.

  6. Cook all foods thoroughly.

  7. If you suspect that rat has eaten any food, discard it.

  8. Using rats as a food source should be discouraged.

When caring for infected persons, careful measures should be observed so as to avoid person-to-person contact. Measures such as:

  1. Wearing protective clothing, such as masks, gloves, gowns, and goggles.

  2. Using infection control measures, such as complete equipment sterilization.

  3. Isolating infected patients from contact with unprotected persons until the disease has run its course.

Further, educating people in high-risk areas about ways to decrease rodent populations in their homes will aid in the control and prevention of Lassa fever. Other challenges include developing more rapid diagnostic tests and increasing the availability of the only known drug treatment, ribavirin. Research is presently under way to develop a vaccine for Lassa fever.

....making effort to "STAY WELL"


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The contents herein are for informational purposes only, therefore, should not be used as an alternative to seeking independent medical advice, and we cannot take responsibility for an individual’s decision to use them as such. Always seek the advice of your physician or other qualified health care provider with any questions you may have regarding a medical condition.