Lassa Fever

Learn more about the causes, treatments, symptoms, and other clinical features of the Lassa virus (a member of the arenavirus family of viruses).

What is Lassa Fever

Lassa fever is an acute viral hemorrhagic illness caused by the Lassa virus, a member of the arenavirus family of viruses. The reservoir of the Lassa virus is a rodent of the genus Mastomys known as a “multimammate rat”.

Lassa fever is endemic in Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone, Togo, and Nigeria, but it probably exists in other West African countries as well. The Lassa virus is transmitted to humans mainly through food or household items contaminated by infected rats’ urine and faeces.

According to WHO, about 80% of people infected will have no or mild symptoms. One in five people will develop a Severe disease.

Symptoms of Lassa Fever

• The incubation period ranges from 5-21 days.
• With 80% asymptomatic and mild symptoms presentation, the overall case fatality rate (CFR) is 1%.
• CFR can reach 15% or more among patients hospitalized with a severe presentation.
• The most common symptoms include:
• Gradual onset of fever, malaise, and general weakness;
• After a few days: headache, sore throat, muscle pain, chest pain, nausea, vomiting, diarrhea, cough, and abdominal pain.
• In severe cases, the patient may present with bleeding, neck/facial swelling, and shock.
• Sequelae: various degree of deafness has been shown to occur in 25% of survivors. Hearing returns after 1-3 months in only 50% of these patients.

Lassa Fever Diagnosis

• Symptoms are non-specific; clinical diagnosis may be difficult
• Differential diagnosis includes other viral hemorrhagic fevers, yellow fever, malaria, typhoid fever, shigellosis, and other viral and bacterial diseases.
• Patient history is essential and should include: exposure to rodents and/or area/village endemic for Lassa and/or contact with Lassa cases

Lassa Fever Laboratory Diagnosis

Definitive diagnosis requires testing:

• Reverse transcriptase polymerase chain reaction (RT-PCR) assay
• IgG and IgM antibodies enzyme-linked immunosorbent assay (ELISA)
• Antigen detection tests
• Virus isolation by cell culture
• Handling and processing specimens require suitably equipped laboratories under maximum biological containment conditions and staff collecting samples should be trained

Lassa Fever Treatment

• Intensive supportive care including monitoring fluid and electrolyte balance and renal function, careful rehydration
• Supportive drug therapy including painkillers, antiemetics for vomiting, anxiolytics for agitation, +/-antibiotics and/or antimalarial drugs

Lassa Fever Transmission

Reservoir Mastomys Rats

• The virus maintains itself in the Mastomys rat population
• The virus is present in the urine and feces of infected rats

Primary Human Infections

• 80 to 90 % of humans are infected through:
• Food or household items contaminated by infected rats’ urine and faeces
• Direct contact while handling Mastomys rats (food source)

Secondary Human Infections

• Secondary human-to-human transmission occurs through direct contact with the blood, secretions, organs or other body fluids of infected persons.

Lassa Fever In Pregnancy And Infants

• Particularly severe in pregnant women and their fetuses (fetal death rate greater than 85%)
• Increased maternal mortality in the third trimester (greater than 30%)
• A significant cause of pediatric hospitalizations in some areas of West Africa
• Infants (up to 2 years old) can present a ‘swollen baby syndrome and is associated with a high case fatality rate

Key Components For Lassa Fever Control

• Cases investigation
• Care for sick people
• Preventive measures in communities
• And healthcare settings

General Strategy To Control Lassa Outbreaks

• Conduct social and cultural assessments
• Engage with key influencers: women and /or youth associations, traditional healers, local authorities, and religious & opinion leaders
• Formal and informal communication
• Address community concerns
• Security, police
• Lodging, food
• Social and epidemiological mobile teams
• Finances, salaries
• Transport vehicles
• Triage in/out
• Barrier nursing
• Infection control
• Organize funerals
• Clinical trials
• Ethics committee
• Active case-finding
• Follow-up of contacts
• Specimens
• Laboratory testing
• Database analysis
• Search for the source

Community Engagement and Awareness

• Engage with communities to promote desired health practices and behaviors, including environmental hygiene and food consumption.
• Provide accurate and timely health advice and information on the disease.

How Can I Prevent Getting Infected With Lassa Fever?

• Wash your hands regularly
• Store food in containers with lids
• Keep your home clean and tidy to discourage rats from entering
• Keep a cat
• Cook all foods thoroughly

Reducing the Risk Of Rats-To-Human Transmission

• Prevention relies on promoting good community hygiene to discourage rodents from entering homes.
• Removing the source of attraction for rats
• Preventing rats from entering the house
• Avoid contact with infected rats and consumption of their raw meat.
• All animal products should be thoroughly cooked.

Reducing Human-To-Human Transmission

• Avoid contact with infected Lassa patients and deaths.
• Regular hand washing with soap and water.
• Encourage early treatment at Lassa Treatment Center.
• Hand-washing, using gloves and mask when caring for suspect Lassa patient at home, and seek for health advice

Source: World Health Organization, WHO

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