Lassa Fever

Lassa fever is an acute viral haemorrhagic illness caused by the Lassa virus, a member of the Arenavirus family. It is endemic in Nigeria and several other West African countries. The virus is transmitted to humans primarily through contact with the urine or faeces of infected multimammate rats (Mastomys natalensis), which are common household pests in Nigeria. Person-to-person transmission also occurs through contact with bodily fluids of infected individuals. Nigeria reports thousands of suspected Lassa fever cases each year, with Edo, Ondo, Ebonyi, Bauchi, Borno, and Plateau states among the highest-burden areas. While approximately 80% of infections cause mild or no symptoms, severe disease can be fatal — Lassa fever accounts for significant healthcare worker deaths in affected areas.

About 80% of Lassa fever infections produce mild or no symptoms. When symptoms occur, they appear 6–21 days after exposure: Mild symptoms: • Fever • General weakness and malaise • Headache Moderate-to-severe symptoms (occur in approximately 20% of infections): • Fever with chills • Severe headache • Sore throat and difficulty swallowing • Muscle aches and chest pain • Nausea, vomiting, and diarrhoea • Cough • Abdominal pain • Swelling of the face Severe haemorrhagic manifestations (in a minority): • Bleeding from the gums, nose, vagina, or gastrointestinal tract • Bleeding into the skin (petechiae, ecchymoses) • Encephalitis: confusion, tremors, seizures • Deafness: hearing loss occurs in approximately 25% of survivors and may be permanent • Shock and organ failure

Lassa fever is caused by the Lassa virus. Primary transmission — rodent to human: • Contact with urine, faeces, blood, or saliva of infected Mastomys natalensis rats (multimammate rats) • Handling or eating infected rodents • Eating food or using utensils contaminated by rat excreta • Inhaling dust contaminated with rat urine (aerosolisation during sweeping) Secondary transmission — human to human: • Direct contact with blood, urine, faeces, vomit, or other bodily fluids of a sick person • Nosocomial (hospital) transmission: healthcare workers are at high risk if infection control precautions are inadequate • Sexual transmission has been documented Lassa virus is NOT spread through casual contact, respiratory droplets (coughs, sneezes), or insect bites.

• Living in or travelling to Lassa-endemic states of Nigeria (Edo, Ondo, Ebonyi, Bauchi, Borno, Plateau) • Living in homes with poor rodent control, food storage, or sanitation • Handling or eating rodents • Healthcare workers caring for Lassa fever patients without adequate PPE • Close contact with a confirmed Lassa fever case • Pregnancy: severe disease and maternal mortality are markedly higher in the third trimester

• Hearing loss: occurs in approximately 25% of survivors; can be permanent and severe • Neurological complications: confusion, tremors, seizures, meningitis • Liver damage • Spontaneous abortion: very high rates in infected pregnant women; the fetus rarely survives infection • Multi-organ failure in severe disease • Death: overall case fatality rate is approximately 1% of all infections; among hospitalised patients with severe disease, 15–20% • Healthcare worker deaths: healthcare-associated Lassa fever is a significant occupational risk in endemic areas

Rodent control: • Store food in sealed, rodent-proof containers • Dispose of garbage properly and keep homes clean • Seal holes and gaps in walls and floors where rats can enter • Avoid sleeping on the ground without a protective mat or bed • Do not handle or eat rodents • Wet-sweep or mop floors rather than dry-sweep (reduces dust and rat urine aerosolisation) Personal hygiene: • Wash hands frequently with soap and water • Avoid contact with blood or bodily fluids of sick individuals Healthcare settings: • Healthcare workers caring for suspected Lassa fever cases should immediately apply standard, contact, and droplet precautions (gloves, gown, mask, eye protection) • Follow NCDC infection prevention and control guidelines Treatment: • Ribavirin (antiviral medication) is most effective when started early in the course of illness; early presentation is critical • Report suspected cases immediately to the NCDC and State Ministry of Health