Lassa Fever – WHO facts sheet

Lassa fever was discovered in Nigeria in 1969 when two missionary nurses died after getting ill. The virus is named after the town in Nigeria where the first cases occurred. The disease is known to be prevalent in West Africa with a greatest risk of death. A total 733 cases were recorded in Nigeria between January and December and over 71 deaths – Nigeria Centre for Disease Control (NCDC) 2017.



Lassa fever is spread to humans through contact with household items contaminated with rodent droppings or infected urine of the multimammate rats (Mastomys natalensis). People become infected through inhaling aerosols in air contaminated with rodent excretions, swallowing the virus in food or contaminated utensils (or multimammate rats eaten as food), or through open wounds. Like Nigeria, Lassa fever virus is believed to be endemic (always present) in Benin, Guinea, Sierra Leone, Liberia. It has also been detected in the Ivory Coast, Ghana, Burkina Faso, Mali, Senegal, Gambia, and Central African Republic.


WHO Facts:

  • Lassa fever is an acute viral haemorrhagic illness of 2-21 days duration that occurs in West Africa.
  • The Lassa virus is transmitted to humans via contact with food or household items contaminated with rodent urine or faeces.
  • Person-to-person infections and laboratory transmission can also occur, particularly in hospitals lacking adequate infection prevention and control measures.
  • Lassa fever is known to be endemic in Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone, and Nigeria, but probably exists in other West African countries as well.
  • The overall case-fatality rate is 1%. Observed case-fatality rate among patients hospitalized with severe cases of Lassa fever is 15%.
  • Early supportive care with rehydration and symptomatic treatment improves survival.


What are the symptoms of Lassa Fever?

After an incubation period of 6 to 21 days, an acute illness with multiorgan involvement develops. Many infected by the deadly haemorrhagic virus do not develop symptoms. Nonspecific symptoms include fever, facial swelling, and muscle fatigue, as well as conjunctivitis and mucosal bleeding. The other symptoms arising from the affected organs are:

Gastrointestinal tract:

  • Nausea
  • Vomiting (bloody)
  • Diarrhea (bloody)
  • Stomach ache
  • Constipation
  • Dysphagia (difficulty swallowing)
  • Hepatitis

Cardiovascular system:

  • Pericarditis
  • Hypertension
  • Hypotension
  • Tachycardia (abnormally high heart rate)

Respiratory tract:

  • Cough
  • Chest pain
  • Dyspnoea
  • Pharyngitis
  • Pleuritis

Nervous system:

  • Encephalitis
  • Meningitis
  • Unilateral or bilateral hearing deficit
  • Seizures


How you can prevent Lassa fever?

Transmission of the Lassa virus can be prevented by avoiding contact with infected Mastomys rodents (The rat that causes Lassa fever) and infected human beings. Block all rat hideouts at home, cook foods thoroughly and cover all foods and water properly. If you suspect that rat has eaten any food, discard it immediately, keep your house and environment clean and store food items in rodent proof containers

Infected patients at hospitals should be isolated from unprotected persons until the disease has run its course. Health care providers should wear protective clothing, such as Masks, gloves, gowns, and Glasses.


Can Lassa Fever be treated?

There is currently no vaccine that protects against Lassa fever. Ribavirin, is an antiviral drug used in treatment of Hepatitis C has shown to be effective when administered early in the course of the illness, with success in people affected by Lassa fever.




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