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It kills 5,000 every year… 10 things to know about Lassa Fever, Ebola’s ‘cousin’





An outbreak of Lassa fever has been reported in Lagos, with two deaths already recorded, including that of a 32-year-old pregnant woman

More than 100 people have been placed under surveillance, too.

To keep safe from this disease that has no established cure, here are a few things you need to know.


Lassa fever is as dangerous as Ebola and they both belong to a disease family called Viral Hemorrhagic Fevers (VHFs). VHFs in Nigeria include Lassa fever, Ebola, Dengue fever and Yellow fever.

The common feature of these diseases is that they are transmitted to human beings through animals or insects. Humans are not the natural reservoir of the viruses that cause diseases but are infected when they come into contact with infected animals or insects.  If a person is infected, the person can easily transmit the virus to another person.

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The outbreak of VHFs is sporadic and irregular. According to Nigeria Centre for Disease Control (NCDC), there is no cure or established drug treatment for these diseases.


Lassa fever is known as a zoonotic disease because it is transmitted to humans by animals. Arenavirus, which causes the disease, is mostly carried by rats. According to WHO, 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. Therefore, this disease is transmitted to humans via contact with food or household items contaminated with rodent urine or faeces.


The death of two missionary nurses led to the discovery of Lassa fever in 1969 in a town called Lassa in Borno State. It was named after the place where the first case was discovered. The disease has come to represent West Africa disease because it occurs mostly in this part of the world. 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.


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Lassa fever affects many people annually and kills many infected people. According to NCDC, it is responsible for an estimated 300,000 to 500,000 infections annually, with 5,000 deaths.

WHO says Lassa fever occurs in all age groups and both sexes. Persons at greatest risk are those living in rural areas where infected rats are usually found, especially in communities with poor sanitation or crowded living conditions. Health workers are at risk if caring for Lassa fever patients in the absence of proper barrier nursing and infection prevention and control practices.

Death usually occurs within 14 days of onset in fatal cases. The disease is especially severe late in pregnancy, with maternal death and/or fetal loss occurring in more than 80% of cases during the third trimester.


Lassa fever is an acute viral haemorrhagic illness that has an incubation period of six to 21 days. WHO says the onset of the disease, when it is symptomatic, is usually gradual, starting with fever, general weakness, and malaise. After a few days, headache, sore throat, muscle pain, chest pain, nausea, vomiting, diarrhoea, cough, and abdominal pain may follow. In severe cases, facial swelling, fluid in the lung cavity, bleeding from the mouth, nose, vagina or gastrointestinal tract and low blood pressure may develop. It also manifests in protein’s presence in the urine. In the later stages of the disease, it can cause shock, seizures, tremor, disorientation, and coma.


One may become infected with Lassa fever without knowing, as no symptoms occur. About 80% of people who become infected with Lassa virus have no symptoms. It is only one in five infections that result in severe disease that affects the liver, spleen, and kidneys of the infected patients. In severe cases, there is facial swelling, fluid in the lung cavity, bleeding from the mouth, nose, vagina, gastrointestinal tract and low blood pressure.

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Although the overall case-fatality rate of Lassa fever is 1% and observed case-fatality rate among patients hospitaliSed with severe cases is 15% but those who survive the disease often face other challenges. WHO notes that deafness occurs in 25% of patients who survive the Lassa fever but in half of these cases, hearing returns partially after one to three months. Lassa fever is also responsible for transient hair loss and gait disturbance during recovery.


It is often hard to tell if someone is suffering from Lassa fever because the symptoms can easily be mistaken for malaria or other fevers.  According to WHO, because the symptoms of Lassa fever are so varied and nonspecific, clinical diagnosis is often difficult, especially early in the course of the disease.

Lassa fever is difficult to distinguish from other viral haemorrhagic fevers such as Ebola virus disease as well as other diseases that cause fever, including malaria, shigellosis, typhoid fever and yellow fever. Definitive diagnosis of Lassa fever requires testing that is available only in reference laboratories.


There is currently no vaccine that protects against Lassa fever. WHO notes that the antiviral drug ribavirin seems to be an effective treatment for Lassa fever if given early on in the course of clinical illness. However, WHO points out that there is no evidence to support the role of ribavirin as a post-exposure prophylactic treatment for Lassa fever.


Personal hygiene and environmental cleanliness are the keys to preventing Lassa fever. The disease is transmitted by rats and as a matter of necessity; effort should be intensified 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. it is not possible to completely eliminate them from the environment. Finally, family members should always be careful to avoid contact with blood and body fluids while caring for sick persons.

Author profile

Chikezie can be reached at comeje@icirnigeria.org. Follow him on Twitter: @KezieOmeje

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