Lassa fever: From causes to symptoms and treatment; everything you need to know

The United Kingdom recently confirmed three cases of Lassa fever in individuals who had a travel history to West Africa. However, according to UK officials, this life-threatening zoonotic, acute viral illness risk remains low for general public.

“The UK Health Security Agency (UKHSA) continues to follow up and closely monitor individuals identified as contacts of 3 recently confirmed cases of Lassa fever. No further cases have been identified to date. NHS Trusts have performed risk assessments on individuals and patients who have worked or stayed in the same ward areas as the Lassa patients. Individuals have been given advice on monitoring and testing. The majority of individuals will complete monitoring by early March. The risk to the general public remains very low,” The UK Health Security Agency (UKHSA) noted in its February 11, 2022 statement.

Though the risk remains low, it is important to be wary of the infection, that is endemic in West Africa. As per World Health Organization’s statistics registered on February 14, 2022, in Nigeria, from January 3-30, 2022, 211 laboratory confirmed Lassa fever cases including 40 deaths (case fatality ratio: 19 per cent) have been cumulatively reported in 14 of the 36 Nigerian states and the Federal Capital Territory across the country.

WHO notes that the annual peak of Lassa fever cases is typically observed during the dry season (December–April). Thus, the number of infections is expected to rise further until the end of the dry season.

Here’s all you need to know

What causes Lassa fever?

Lassa fever is a hemorrhagic illness caused by Lassa virus, a single-stranded RNA virus that belongs to the Arenaviridae family. Lassa fever was first recognised in Lassa, Nigeria in 1969. “There are approximately 3,00,000 cases and 5,000 deaths annually,” said Dr Manish Wadhwani, consultant intensivist, Masina Hospital.

WHO mentions that the animal reservoir, or host, of Lassa virus is a rodent of the genus Mastomys, commonly known as the “multimammate rat.” Mastomys rats infected with Lassa virus do not become ill, but they can shed the virus in their urine and faeces.


Lassa fever is associated with broad spectrum of clinical manifestations. The incubation period is 1-3 weeks. “Individuals with Lassa fever are not believed to be contagious prior to the onset of symptoms. Most infected individuals have mild symptoms (approximately 80 per cent) like low grade fever, malaise and headache and may not seek medical help,” said Dr Wadhwani.

More serious signs and symptoms, in approximately 20 per cent of individuals, can be pharyngitis, cough, nausea, vomiting, diarrhea, muscle pain, chest pain, back pain, and abdominal pain. “In severe cases, facial swelling, respiratory failure, fits, coma, bleeding (from the mouth, nose, vagina, or gastrointestinal tract), and drop in BP may develop. This can progress to multi-system involvement due to shock causing vital organ failure one after another. The most common complication of Lassa fever is hearing loss, which occurs in up to one-third of patients and may develop in the setting of mild or severe illness. Hearing may improve after 1-3 months in approximately 50 per cent of cases,” stated Dr Wadhwani.

It is important to seek treatment (Source: Getty Images/Thinkstock)

As per the expert, approximately one per cent of Lassa virus infections result in death, among hospitalised patients with fatality rates ranging from 15 to 30 per cent.


Treatment of Lassa fever consists of an antiviral drug Ribavirin. “Ribavirin has been reported to be most effective when given within the first six days after onset of fever. Apart from ribavirin, treatment includes supportive care like maintaining blood pressure with adequate fluids, and maintaining oxygen levels with external oxygen support,” said Dr Wadhwani.

According to WHO, there is currently no vaccine that protects against Lassa fever.


WHO recommends 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. Since 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.

On travel exposure, WHO states that 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.

Dr Wadhwani added, “Patients with signs and symptoms of infection should be considered contagious, even if the clinical manifestations are mild.”

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