Lassa fever case in Val-de-Marne: what is this endemic virus from West Africa?

A patient suffering from Lassa fever is hospitalized in Saint-Mandé, at the Bégen military hospital, in Val-de-Marne. The patient is doing well, but an epidemiological investigation is underway to identify high-risk contact cases. Here’s what you need to know about this acute viral hemorrhagic fever ravaging West Africa.

It is endemic in several countries, notably Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone and Nigeria, where it caused twenty deaths in one week in mid-April.

This virus, identified in 1960 in Lassa, Nigeria, is a zoonosis, meaning it is transmitted from animals to humans. It can be transmitted in two ways: either through contact with food or household items contaminated with the excrement and urine of a rodent of the genus Mastomys, commonly called the “multiple rodent”, that lives near homes, or from person to person, through direct contact with the organic secretions of an infected person .

80% of infected patients are asymptomatic

The virus infects between 100,000 and 300,000 people and causes between 5,000 and 6,000 deaths per year, according to the Pasteur Institute. According to the World Health Organization (WHO), the mortality rate for this pathology is 1%. In a hospital setting, the proportion of patients with severe forms can reach 15%.

About 80% of people infected with Lassa virus have no symptoms, but one in five infections results in “serious damage to multiple organs such as the liver, spleen and kidneys.”

Vomiting, headache, stomach pain…

The incubation period varies from 2 to 21 days. If the disease is symptomatic, Lassa fever manifests itself as fever, general weakness, then headache, throat irritation, nausea, vomiting, diarrhea, cough and even pain in the chest, muscles and abdomen. In severe cases, symptoms worsen with swelling or even hemorrhagic signs.

The disease is extremely serious for pregnant women, especially in late pregnancy. According to WHO, maternal and/or fetal death occurs in more than 80% of cases observed in the third trimester. Patients who survive may continue to have serious sequelae, such as deafness.

There is no vaccine against Lassa fever. In terms of treatment, one molecule is effective, but only if it is administered immediately after infection: ribavirin. However, at the first stage of the disease, diagnosis is often difficult. Lassa fever particularly resembles other viral hemorrhagic fevers such as Ebola.