Lassa fever
Lasting effects in survivors

Lassa fever is caused by infection with a virus through consuming or encountering contaminated food or domestic items by infected rodent waste. Lassa fever is most prevalent in West Africa. An estimated 100 000 to 500 000 infections are reported yearly, with 20% becoming ill. Lassa fever frequently causes hearing loss, even in those who only show mild illness.

The Lassa virus is one of several viruses that are likely to cause future epidemics and may spread beyond its current territory.



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What causes Lassa fever

Lassa fever is a zoonotic disease that humans contract from infected rodents. Lassa virus belongs to the Arenaviridae family, commonly linked with rodent transmitted viruses.

The virus is mainly transmitted through ingestion and exposure to rodent excretions such as urine and faeces or through the consumption of under-cooked rodent meat.

The most common reservoir or the host of the virus is Mastomys natalensis or the common African rat. The virus does not affect the rats themselves. Lassa virus can spread between humans by exposure to infected bodily fluids such as blood, urine, and feces.

Image: the common African rat, a vector for Lassa virus.

Where is Lassa fever found

Lassa fever is endemic to West Africa including Sierra Leone, Guinea, Liberia, and Nigeria. However, the West African countries such as Mali, Benin, Togo, Cote d’Ivoire, Burkina Faso, and Ghana have also reported cases of the disease. The first case of Lassa fever was reported in 1969 when two missionary nurses died of a mysterious illness named after the city of Lassa in Nigeria.

Risk factors include poverty, malnutrition, deforestation, lack of sanitation, and urbanization.

Image: Geographical distribution of Lassa fever

What are the symptoms of Lassa fever

The incubation period for the virus can range from 6 to 21 days. The symptoms of Lassa fever can range from asymptomatic to acute febrile ilness with gradual signs of fever, malaise, headache, and chest pain. Over 70% of the patients also experience headaches, sore throat, muscle pain, chest pain, nausea, vomiting, diarrhea, cough, and abdominal pain.

In severe cases patients may experience facial swelling, fluid in the lung cavity, bleeding from the mouth, nose, vagina, or gastrointestinal tract, and low blood pressure. Later stages of the disease involve shock, seizures, tremor, disorientation, and coma where death generally occurs within 14 days of onset in fatal cases.

The most common complication of Lassa fever is deafness. Various degrees of deafness occur in approximately one-third of infections, and in many cases hearing loss is permanent. Further complications of the disease include spontaneous abortion and fatal mortality among pregnant women. Infants can develop swollen baby syndrome which causes generalized edema, abdominal distention, and bleeding. Many of the babies who are affected die.

About 15–20% of hospitalized cases result in death. Overall case fatality is projected to be 1%, but mortality rates can climb up to 50% during an outbreak.

How can Lassa fever be prevented

Currently, there is no vaccine for the prevention of Lassa fever. Community hygiene is promoted to prevent animal-to-human transmission of the virus. This includes measures to discourage rodents from entering the homes. These effective measures include using rodent-proof food containers, proper disposal of garbage, maintaining clean houses, and keeping cats as pets.

In healthcare settings, patients suspected of Lassa fever should be isolated.

How is Lassa fever diagnosed

Due to its resemblance to other viral haemorrhagic fevers such as Ebola virus disease and other diseases that cause fever, clinical diagnosis is often difficult. On the other hand, 80% of the infections do not show any symptoms. Lassa fever frequently has non-specific symptoms, further complicating diagnosis.

The diagnosis of Lassa fever is centered on clinical suspicion, patient history, and physical examination which later is confirmed using various laboratory testing methods. The infection can be confirmed using Polymerase chain reaction (PCR) tests, such as the ones made available by the WoIDM. Lassa fever can also be diagnosed by an ELISA test which detects antibodies to the virus with 88% sensitivity and 90% specificity.

Other laboratory finding are lymphocytopenia (low white blood cell count), thrombocytopenia (low platelets) and elevated aspartate transaminase levels.

Early diagnosis and fast treatment reduces the severity of the disease and prevents disabilities and death.

How is Lassa fever treated

Supportive treatment is used for Lassa fever, consisting of keeping the patient hydrated and managing symptoms.

Ribavirin, an antiviral drug, can be used as treatment but with weak evidence. Treatment is most effective when it is started early in the course of the disease.


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