Lassa fever is an animal-borne, or zoonotic, acute viral illness.

This disease was discovered in 1969 and was named after the town in Nigeria where the first cases occurred.

Lassa fever is endemic in parts of West Africa consisting of Sierra Leone, Liberia, Guinea and Nigeria. Neighboring countries also are in danger, as the animal vector for Lassa virus, the “multimammate rat” (Mastomys natalensis) is distributed throughout the region.

What is the Current situation of Lassa fever?

The Nigeria Center for Disease Control declared an outbreak of Lassa fever in Nigeria due to an increase in the number of cases reported across the country since the beginning of the year. Cases have been identified in several states.

Brief history of Lassa fever

Lassa fever was first reported in Lassa community in Borno State, Nigeria, when two missionary nurses died from an unusual febrile illness. Since then cases and outbreaks continue to be reported in Nigeria and the diseases is increasingly recognized to be endemic in many parts of West Africa, including Nigeria, Benin, Ghana, Mali and the Mano River region (Sierra Leone, Liberia and Guinea), with the disease probably existing in other West African countries as well. Estimated 300,000-500,000 cases and 5,000 related deaths occur annually in West Africa.

How is Lassa fever transmitted?

 Lassa fever is transmitted to man by infected multi-mammate rats, the mastomys natalensis species complex which is the reservoir host. Humans end up been  infected from direct contact with the urine and faeces of the rat which contains the virus, through touching soiled objects, eating contaminated food, or exposure to open cuts or sores. Secondary transmission from person to person can occur following exposure to the virus in the blood, tissue, urine, faeces or other bodily secretions of an infected individual. Hospital-acquired (nosocomial) transmission from person to person are not uncommon, and importantly can occur if appropriate Personal Protective Equipment (PPE) is not worn when managing suspected cases.

What are the Signs and Symptoms of Lassa fever?

The Signs and symptoms of Lassa fever commonly occur 1-3 weeks after the patient comes into contact with the virus. For the bulk of Lassa fever virus infections (approximately 80%), symptoms are mild and are undiagnosed. Mild signs and symptoms include slight fever, general malaise and weakness, and headache.  Twenty percent (20%) of infected individuals, however, disease may progress to more serious symptoms including hemorrhaging (in gums, eyes, or nose, as examples), respiratory distress, repeated vomiting, and facial swelling, pain in the chest, back, and abdomen, and shock. Neurological issues have additionally been described, including hearing loss, tremors, and encephalitis. Death might also occur within two weeks after symptom onset due to multi-organ failure.

Approximately (15%-20%) of patients hospitalized for Lassa fever die from the illness. However, just only (1%) of all Lassa virus infections result in death. The death rates for women within the third trimester of pregnancy are particularly high. Spontaneous abortion is a serious complication of infection with an estimated 95% mortality in fetuses of infected pregnant mothers.

Since the sign and symptoms of Lassa fever are so varied and nonspecific, clinical diagnosis is often difficult. It is also associated with occasional epidemics, during which the case-fatality rate can reach 50% in hospitalized patients.

Diagnosis/Testing of Lassa fever

A high index of suspicion aids diagnosis, especially in endemic areas like Nigeria, or in patients returning from other endemic areas in West Africa. Diagnosis is based on clinical features (guided by case definitions above) and laboratory confirmation. Laboratory diagnosis is by viral amplification from blood samples using Reverse-Transcription Polymerase Chain Reaction (RT-PCR).


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

How can I Prevent Lassa fever?

Lassa fever can be prevented with the following precautions

By averting contact with Mastomys rodents, especially within the geographic regions in which outbreaks occur.

By putting food away in rodent-proof boxes or containers and keeping the house clean help to discourage rodents from entering homes. Using these rodents as a food source isn’t recommended.

Trapping in and around homes can help reduce rodent populations; however, the extensive and wide distribution of Mastomys in Africa makes complete control of this rodent reservoir impractical.

When caring for person or patient with Lassa fever, further transmission of the disease through an individual to another person contact or nosocomial routes are often avoided by taking preventive precautions against contact with patient secretions (referred to as VHF isolation precautions or barrier nursing methods). Such preventive precautions include wearing protective clothing, like masks, gloves, gowns, and goggles; using infection control measures, like complete equipment sterilization; and isolating infected patients from contact with unprotected persons until the disease has run its course.

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.

Reviewed on 10/4/2020