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  • Rana Abdelhalim and Sophie Gregoire-Mitha

Lassa Fever Outbreak!

In 2018, Nigeria faced the largest recent outbreak of Lassa fever.

What is Lassa Fever?

Lassa fever is an acute, viral hemorrhagic illness with a duration 2 to 21 days. 1 in 5 infections result in severe disease in which the virus affects many organs, such as the kidneys, spleen, and liver. This disease occurs every year in West Africa. This illness is a zoonotic disease as the virus is transmitted from rodents to humans through contact with food or household items contaminated with rodent urine or feces. It can also be transmitted from person to person and by laboratory transmission, especially in hospitals with inadequate infection prevention and without sufficient control measures.

Dangers and Symptoms:

The overall case-fatality rate, the proportion of deaths within the designated cases, of this illness is only 1%. The case-fatality rate of people with severe cases of Lassa fever is 15%. The case-fatality rates are quite low, likely because when it is confirmed that a person has the disease, they are promptly isolated, there is good infection prevention and control practices, and rigorous contact tracing can stop outbreaks. The issues lie in the detection of the disease. Since the clinical course of the disease is so variable, detection of the disease in affected patients is difficult. It can also be difficult to detect because about 80% of people who have Lassa virus have no symptoms. Persons infected with Lassa fever, first experience a fever and weakness. Next, they have a sore throat, muscle pain, chest pain, nausea, and abdominal pain. In severe cases, bleeding in mouth and nose, facial swelling, and fluid in lung cavity is possible. Other symptoms include seizures, coma, and temporary and permanent deafness.


The Lassa virus outbreak in Nigeria in 2018 was a record worst. By just March of 2018, 376 cases were confirmed, which is three times more than it was at that point in 2017. Health officials were not sure if the outbreak was caused by the same strain of the virus in the past or a new strain. That question was answered quickly, mid-outbreak and it confirmed that the virus in 2018 was caused by the same strain as past years. That question was answered quickly possibly due to portable DNA sequencers which allow scientists to read the genetic information of viruses emerging without large laboratory infrastructure. These sequencers can also be used to determine if the virus is being transmitted among people or from different rodents to different people. This can be determined by seeing if the viral DNA from several people is similar or distinct. This technology has helped researchers and health professionals gain control over the outbreak and fin the source of the problem.


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