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Lassa Fever: Symptoms, Transmission, Treatment & Prevention | WHO Fact Sheet

Lassa fever is an acute viral haemorrhagic illness caused by the Lassa virus, first identified in Nigeria in 1969. It is endemic in several West African countries and poses a significant public health challenge due to its potential for severe illness and healthcare-associated outbreaks.

Key Facts at a Glance

• Cause: Lassa virus, a member of the Arenaviridae family.
• Endemic Regions: Benin, Ghana, Guinea, Liberia, Mali, Nigeria, and Sierra Leone. Likely present in other West African nations.
• Primary Transmission: Contact with food or household items contaminated with urine or faeces of infected Mastomys rats (multimammate rats).
• Human-to-Human Transmission: Occurs via direct contact with bodily fluids of an infected person, particularly in healthcare settings without adequate infection control.
• Case Fatality Rate (CFR): Approximately 1% overall, but CFR can exceed 15% among hospitalized severe cases.
• Survival Improvement: Early, intensive supportive care—including rehydration and symptom management—significantly improves survival chances.

Transmission: From Rodents to Humans

Humans primarily contract Lassa virus through zoonotic transmission from rodents.

• Rodent Reservoir: The primary host is the Mastomys rat, common in West Africa. Infected rats shed the virus in their urine and faeces.
• Common Routes: Infection occurs via inhalation or ingestion of contaminated materials, or direct contact with broken skin.
• Secondary Human Transmission: Spreads through direct contact with blood, urine, faeces, or other secretions of an infected person. This is a major risk in healthcare settings with poor infection prevention and control (IPC).
• Other Notes: The virus can persist in semen for months after recovery, but sexual transmission is not conclusively documented. Airborne spread between humans is not supported by evidence.

Symptoms and Clinical Course

The incubation period ranges from 2 to 21 days.

Early Symptoms (Often Gradual Onset):

• Fever
• General weakness and malaise
• Headache
• Sore throat
• Muscle and chest pain

Progression to Severe Disease (in ~20% of cases):

• Nausea, vomiting, diarrhoea, abdominal pain
• Cough
• Facial swelling
• Fluid in the lung cavity
• Bleeding from mouth, nose, vagina, or gastrointestinal tract
• Hypotension (low blood pressure)
• Shock, seizures, tremor, disorientation, coma

Death, if it occurs, typically happens within 14 days of symptom onset.

High-Risk Groups:

• Pregnant Women: Lassa fever is particularly devastating in the third trimester, with fetal mortality >80% and maternal mortality >30%.
• Healthcare Workers: At high risk if appropriate IPC measures are not followed.

Long-Term Effects (Sequelae):

• Sensorineural Hearing Loss: Occurs in up to 25% of survivors, often permanent.
• Other possible sequelae include transient hair loss, visual impairment, joint pain, and neurological or psychological disorders.

Diagnosis

Clinical diagnosis is difficult as early symptoms mimic malaria, typhoid, and other haemorrhagic fevers. Confirmatory tests must be conducted in high-containment laboratories:

• Reverse transcriptase polymerase chain reaction (RT-PCR)
• Antibody enzyme-linked immunosorbent assay (ELISA)
• Antigen detection tests
• Virus isolation by cell culture

Treatment and Management

• Supportive Care: The cornerstone of treatment. Includes rehydration, pain relief, and management of specific organ dysfunction.
• Antiviral Therapy: The drug ribavirin has been used, but its efficacy remains uncertain. Patients should be enrolled in clinical trials when possible to evaluate ribavirin or other investigational therapeutics.
• No Licensed Vaccine: Several candidate vaccines are in development but none are currently available for public use.

Prevention and Control

1. Community-Level Prevention (Rodent Control):

• Store grain and food in rodent-proof containers.
• Dispose of garbage far from living areas.
• Maintain clean households and practice safe food preparation.
• Keep cats as they may deter rodents.

2. Healthcare Setting Prevention:

• Standard IPC Precautions: Strict hand hygiene, use of personal protective equipment (PPE), safe injection practices.
• Additional Contact Precautions: For suspected/confirmed cases, implement extra measures to prevent contact with bodily fluids and contaminated surfaces.
• Early Recognition and Isolation: Suspected cases should be isolated and referred to designated treatment centers immediately.

3. For Travellers and Health Workers:

• Travellers returning from endemic areas with fever should be assessed for Lassa fever, especially if they had potential exposures.
• Healthcare workers suspecting a case should contact local/national experts immediately for advice and diagnostic arrangements.

WHO Response

The World Health Organization (WHO) supports endemic countries through:

• Strengthening surveillance, laboratory capacity, and clinical management.
• Promoting infection prevention and control in healthcare facilities.
• Facilitating research and development for diagnostics, therapeutics, and vaccines under the R&D Blueprint.
• Coordinating international expertise and community engagement efforts.

https://www.who.int/news-room/fact-sheets/detail/lassa-fever