Endemic in West Africa, this hemorrhagic fever kills 5,000 to 6,000 people per year. The rodent, which carries Lassa fever, transmits it to humans via its excrement.
A virus rarely detected in France. A patient suffering from Lassa fever is hospitalized at the Bégin military hospital, in Saint-Mandé in Val-de-Marne, BFMTV learned this Thursday, May 2. This virus is rare in the Northern Hemisphere because it is endemic in West Africa, particularly in Nigeria, Guinea, Liberia and Sierra Leone.
“The virus circulates almost permanently, especially in Nigeria, the most affected country but also the most populated in Africa. In all, it is estimated that 160 to 180 million people are potentially at risk,” explains Sylvain Baize, head of the biology of emerging viral infections unit at the Institut Pasteur.
Isolated cases have also been reported in Ivory Coast and Burkina Faso, notes the U.S. Centers for Disease Control and Prevention. In Benin, two epidemics were recorded in 2014 and 2016.
5,000 to 6,000 deaths per year
This hemorrhagic fever infects between 100,000 and 300,000 people each year and causes between 5,000 and 6,000 deaths per year according to the Pasteur Institute. The virus takes its name from the town where it was first isolated in Nigeria in 1969 and which killed a nurse.
Lassa fever is the hemorrhagic fever most commonly found in northern countries: as of September 2019, more than twenty cases had been recorded since 1969.
The Source of this disease? A small rodent called the Natal rat that lives in West Africa. It transmits Lassa fever to humans via its feces.
“The virus can also be transmitted from human to human through direct contact with the blood, urine, excrement or other organic secretions of an infected person,” specifies the World Health Organization.
This human-to-human transmission has been reported in hospitals, particularly when hygienic conditions are not optimal.
80% of cases are asymptomatic
This disease is difficult to detect because, in 80% of cases, no symptoms occur. In the remaining 20% of cases, these symptoms, which appear gradually, are generally not specific: they are fevers, vomiting, nausea, abdominal pain, headaches, etc.
In 15% of cases, symptoms may worsen. Edema, pleurisy, oral, nasal or even vaginal hemorrhage then appear.
In 1% of cases, Lassal fever is fatal. And this, within 14 days following the appearance of symptoms. Note that pregnant women are particularly at risk.
The virus “frequently leads to the death of the mother and systematically to that of the fetus,” warns the Pasteur Institute.
After-effects sometimes appear in those who survive this fever: 25% become deaf. Only half regain their hearing after one to three months.
Only one treatment currently exists to treat Lassa fever: ribavirin, an anti-viral. However, it is only effective if it is administered very quickly after infection. However, as the symptoms are not very specific, when the diagnosis is made, it is often too late to administer it.
No vaccine has yet seen the light of day. However, clinical trials are underway. On April 28, the Pasteur Institute reported favorable results from the phase 1 clinical trial conducted internationally of a vaccine candidate.
