Question 1

How is Lassa fever transmitted?

Accepted Answer

The primary route is contact with the multimammate rat (Mastomys natalensis) — specifically its urine, faeces, or saliva — or by handling and consuming infected rats. Human-to-human transmission occurs through direct contact with blood, urine, faeces, vomit, or other bodily fluids of an infected person. Lassa fever is NOT airborne; casual contact poses minimal risk. Healthcare workers are at risk without adequate PPE. Sexual transmission is documented during convalescence, as the virus persists in semen for up to three months.

Question 2

Is Lassa fever contagious between people?

Accepted Answer

Lassa fever can spread person-to-person, but is far less contagious than diseases like measles or COVID-19. Transmission requires direct contact with the blood, urine, faeces, vomit, or other bodily fluids of an infected person — casual contact, sharing air, or coughing do not spread the virus. Healthcare workers who treat Lassa patients without adequate PPE are at significant risk. Sexual transmission is documented during convalescence because the virus persists in semen for up to three months. Large household clusters are uncommon; most secondary cases occur in healthcare settings without strict infection control. This is in contrast to Ebola, which has caused much larger nosocomial clusters.

Question 3

Which countries report the most Lassa fever cases?

Accepted Answer

Nigeria has the highest reported burden, with thousands of cases annually tracked by the Nigeria Centre for Disease Control (NCDC). Sierra Leone, Liberia, and Guinea are also highly endemic. Sporadic cases have occurred in Mali, Ivory Coast, and Benin. International importation has been recorded in Europe and North America among returning travellers. The WHO regularly issues Disease Outbreak News alerts for Nigeria, with peak transmission typically between January and April.

Question 4

How can Lassa fever be prevented?

Accepted Answer

Prevention focuses on reducing contact with the multimammate rat (Mastomys natalensis), the primary animal reservoir. Key measures recommended by the WHO and CDC include: (1) Store food in rodent-proof containers and dispose of garbage away from the home. (2) Keep homes clean and seal entry points to discourage rats. (3) Avoid contact with rodents, their nests, urine, or faeces. (4) Healthcare workers must use appropriate personal protective equipment (PPE) — gloves, gowns, masks — when caring for suspected or confirmed Lassa fever patients, and follow strict infection control protocols. (5) Community education in endemic areas (Nigeria, Sierra Leone, Liberia, Guinea) on the risks of handling or consuming rats. There is currently no approved vaccine for Lassa fever, though multiple candidates are in clinical development under CEPI funding.

Question 5

What is the mortality rate of Lassa fever?

Accepted Answer

The overall case fatality rate (CFR) is approximately 1%, reflecting the high proportion of mild or asymptomatic cases. In hospitalised patients — who represent the severe end of the spectrum — the CFR rises to 15-25%. Lassa fever accounts for an estimated 5,000 deaths per year across West Africa. Pregnant women in the third trimester face especially high risk: foetal mortality approaches 80%, and maternal mortality is also significantly elevated.

Question 6

What are the symptoms of Lassa fever?

Accepted Answer

Symptoms begin 6-21 days after exposure. Mild cases present with fever, general weakness, headache, sore throat, and mild gastrointestinal symptoms. Severe cases (about 20% of infections) include high fever, chest pain, vomiting, diarrhoea, facial swelling, and haemorrhagic manifestations (bleeding from gums, nose, or eyes). A key late complication is sensorineural hearing loss, occurring in 25-30% of patients — including those who recover from acute illness — and is often permanent.

Question 7

Is there a treatment for Lassa fever?

Accepted Answer

Ribavirin, an antiviral drug, is effective when given early — ideally within 6 days of fever onset. Early supportive care (IV fluids, electrolyte correction, treating secondary infections) also significantly improves outcomes. Convalescent plasma has been explored but its efficacy is not firmly established. There is currently no WHO-approved vaccine for Lassa fever, though multiple vaccine candidates are in clinical development.

Question 8

How is Lassa fever different from Ebola?

Accepted Answer

Both are African viral haemorrhagic fevers, but they differ significantly. Lassa is caused by an arenavirus, Ebola by a filovirus. Lassa is endemic and causes tens of thousands of cases annually; Ebola causes sporadic large outbreaks. Lassa's overall CFR (~1%) is much lower than Ebola's (25-90%), though hospitalised Lassa patients face higher mortality (~15-25%). Lassa does not spread person-to-person as easily as Ebola. Both require similar PPE for healthcare workers.

Question 9

What is Lassa fever?

Accepted Answer

Lassa fever is an acute viral haemorrhagic illness caused by Lassa mammarenavirus (Arenaviridae family). It is endemic in West Africa — primarily Nigeria, Sierra Leone, Liberia, and Guinea — and was first identified in 1969 in Lassa, Nigeria. The disease is a zoonosis: its primary reservoir is the multimammate rat (Mastomys natalensis). Approximately 80% of infections are mild or asymptomatic; the remaining 20% can progress to severe disease involving haemorrhagic manifestations and multi-organ failure.

Fiebre de Lassa

Strains

Transmission

Symptoms

Mild to moderate (majority of cases)

Severe disease (~20% of symptomatic cases)

Key clinical differentiators

Treatment

Vaccine status

Endemic regions

Frequently asked questions

Sources