It was first described in the 1950s, however the virus causing the disease was not identified until 1969, when
it’s discovered in two missionary hospitals in the Lassa town of Borno State, the virus is a single-stranded
RNA. Most of the people infected (about 80%) usually are not symptomatic. In severe cases, it can result in
Lassa fever is mainly found in Sierra Leone, Liberia, Guinea, and Nigeria and is spread by rats. Other
neighbouring countries are also at risk because the type of rat that spreads the virus is also found
throughout the West African region.
Because the clinical course of the disease is so variable, detection of the disease in affected patients has
been difficult. However, when presence of the disease is confirmed in a community, prompt isolation of
affected patients, good infection protection and control practices and rigorous contact tracing can stop
It is, ‘zoonotic,’ or animal-borne. Lassa fever is endemic in parts of west Africa which include the following
Humans usually become infected with Lassa virus from exposure to urine or faeces of infected Mastomys
rats. Lassa virus may also be spread between humans through direct contact with the blood, urine, faeces, or
other bodily secretions of a person infected with Lassa fever. There is no epidemiological evidence supporting
airborne spread between humans. Person-to-person transmission occurs in both community and health-care
settings, where the virus may be spread by contaminated medical equipment, such as re-used needles. Sexual
transmission of Lassa virus has been reported.
Lassa fever occurs in all age groups and both sexes. Persons at greatest risk are those living in rural areas
where Mastomys are usually found, especially in communities with poor sanitation or crowded living conditions.
Health workers are at risk if caring for Lassa fever patients in the absence of proper barrier nursing and
infection control practices.
The number of people who experience Lassa fever each year in west Africa is estimated to be between
100,000 and 300,000, with around 5,000 people dying from the virus.
SIGNS AND SYMPTOMS
The signs and symptoms of Lassa fever commonly happen 1-3 weeks after a person has come into contact with
the virus. For most of those with a Lassa fever virus infection; around 80%, symptoms are mild and under-
diagnosed. Mild symptoms include:
Around 20% of infected people; however, the disease might progress to more serious symptoms which include:
Bleeding from the infected person’s eyes, gums, or nose and other parts of the body.
Pain in the back, chest and abdomen.
Facial swelling and shock.
Neurological issues such as tremors, hearing loss and encephalitis.An infected person may die
of their initial symptoms because of multi-organ failure.The most common complication of Lassa fever is
deafness. Different degrees of deafness happen in around one-third of those who become infected.
Between 15-20% of people who are hospitalized for Lassa fever die from the illness. Only 1% of all Lassa
virus infections; however, result in the person’s death. The death rates for women in the third trimester of
pregnancy are exceptionally high.
The symptoms of Lassa fever are varied and non-specific, clinical diagnosis is often difficult, especially early
in the course of the disease.
Definitive diagnosis requires testing that is available only in specialized 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:
antibody enzyme-linked immunosorbent assay (ELISA)
antigen detection tests
reverse transcriptase polymerase chain reaction (RT-PCR) assay
virus isolation by cell culture.
‘Ribavirin,’ is an antiviral drug that has been used with success in people affected by Lassa fever in its early
Supportive care that consists of maintenance of:
2. Blood pressure.
3. Treatment of complicating infections.
4. Appropriate fluid and electrolyte balance.
Prevention of Lassa fever relies on promoting good “community hygiene” to discourage rodents from entering
homes. Effective measures include storing grain and other foodstuffs in rodent-proof containers, disposing
of garbage far from the home, maintaining clean households and keeping cats. Because Mastomys are so
abundant in endemic areas, it is not possible to completely eliminate them from the environment. Family
members should always be careful to avoid contact with blood and body fluids while caring for sick persons.
In health-care settings, staff should always apply standard infection prevention and control precautions when
caring for patients, regardless of their presumed diagnosis. These include basic hand hygiene, respiratory
hygiene, use of personal protective equipment (to block splashes or other contact with infected materials),
safe injection practices and safe burial practices.
Health workers caring for patients with suspected or confirmed Lassa fever should apply extra infection
control measures to prevent contact with the patient’s blood and body fluids and contaminated surfaces or
materials such as clothing and bedding. When in close contact (within 1 metre) of patients with Lassa fever,
health-care workers should wear face protection (a face shield or a medical mask and goggles), a clean, non-
sterile long-sleeved gown, and gloves (sterile gloves for some procedures).
Laboratory workers are also at risk. Samples taken from humans and animals for investigation of Lassa virus
infection should be handled by trained staff and processed in suitably equipped laboratories.
On rare occasions, travellers from areas where Lassa fever is endemic export the disease to other countries.
Although malaria, typhoid fever, and many other tropical infections are much more common, the diagnosis of
Lassa fever should be considered in febrile patients returning from West Africa, especially if they have had
exposures in rural areas or hospitals in countries where Lassa fever is known to be endemic. Health-care
workers seeing a patient suspected to have Lassa fever should immediately contact local and national experts
for advice and to arrange for laboratory testing.