An outbreak of suspected Lassa fever in at least 10 states in Nigeria since November has resulted in up to 40 fatalities, according to Nigerian health officials.  Health Minister Isaac Adewole said during a news conference yesterday, “The total number (of suspected cases) reported is 86 and 40 deaths, with a mortality rate of 43.2 percent.”

Nigeria/Alvaro1984 18
Nigeria/Alvaro1984 18

Adewole noted that 22 of the 40 cases have been laboratory confirmed and the remainder of the tests are pending.

Bauchi State reported the first case in Nov. 2015 and since then, nine other states, both in the north and the south have been affected.

According to the US Centers for Disease Control and Prevention (CDC), Lassa fever is an acute viral illness that occurs in West Africa. The virus, a member of the virus family Arenaviridae, is a single-stranded RNA virus and is zoonotic, or animal-borne.

Related: Lassa fever: 20 percent of cases could be due to human-to-human transmission, Cambridge study

Lassa fever is a significant cause of morbidity and mortality. While Lassa fever is mild or has no observable symptoms in about 80% of people infected with the virus, the remaining 20% have a severe multisystem disease.

The animal host of Lassa virus is a rodent known as the “multimammate rat” of the genus Mastomys. Humans get infected with Lassa through aerosol or direct contact with excreta from the rodent. Laboratory infections do occur primarily through contaminated needles.

The symptoms of Lassa fever typically occur 1-3 weeks after the patient comes into contact with the virus. These include fever, retrosternal pain (pain behind the chest wall), sore throat, back pain, cough, abdominal pain, vomiting, diarrhea, conjunctivitis, facial swelling, proteinuria (protein in the urine), and mucosal bleeding. Neurological problems have also been described, including hearing loss, tremors, and encephalitis.

Related: Lassa fever virus has ‘very ancient roots’, traced back a millennium to what is now Nigeria