Between August 2015 and 24 January 2016, 172 suspected and confirmed Lassa fever cases have been reported in Nigeria with 83 suspected and confirmed deaths (CFR 48%), according to Nigerian health officials.

Image/ C. S. Goldsmith, P. Rollin, M. Bowen This transmission electron micrograph (TEM) depicted numbers of Lassa virus virions adjacent to some cell debris.  The virus, a member of the virus family Arenaviridae, is a single-stranded RNA virus, and is zoonotic, or animal-borne that can be transmitted to humans. The illness, which occurs in West Africa, was discovered in 1969 when two missionary nurses died in Nigeria, West Africa.In areas of Africa where the disease is endemic (that is, constantly present), 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. Lassa fever is also associated with occasional epidemics, during which the case-fatality rate can reach 50%. There are a number of ways in which the virus may be transmitted, or spread, to humans. The Mastomys rodents shed the virus in urine and droppings. Therefore, the virus can be transmitted through direct contact with these materials, through touching objects or eating food contaminated with these materials, or through cuts or sores. Because Mastomys rodents often live in and around homes and scavenge on human food remains or poorly stored food, transmission of this sort is common. Contact with the virus also may occur when a person inhales tiny particles in the air contaminated with rodent excretions. This is called aerosol or airborne transmission. Finally, because Mastomys rodents are sometimes consumed as a food source, infection may occur via direct contact when they are caught and prepared for food.
C. S. Goldsmith, P. Rollin, M. Bowen

The 4 most affected states are Bauchi, Edo, Oyo and Taraba, which account for 54% of the confirmed cases (n=54) and 52% of the reported deaths (n=34). The remaining 15 States have reported less than 5 confirmed cases.

To date, 4 health care workers were laboratory-confirmed for Lassa fever; of these 4 cases, 2 passed away. It is important to note that these cases are not considered as cases of hospital-acquired infection as no confirmed or suspected cases were reported in the 4 different health facilities where these health care workers were employed.

Nigeria’s neighbor to the west, Benin, has reported a confirmed Lassa fever case in the health zone of Tchaourou.

Lassa fever is endemic in Nigeria and causes outbreaks almost every year in different parts of the country, with yearly peaks observed between December and February. The disease is an acute viral hemorrhagic illness caused by Lassa virus, a member of the arenavirus family of viruses.

It is transmitted to humans from contacts with food or household items contaminated with rodent excreta. The disease is endemic in the rodent population in parts of West Africa. Person-to-person infections and laboratory transmission can also occur, particularly in the hospital environment in the absence of adequate infection control measures. Diagnosis and prompt treatment are essential.

Benin reported an outbreak of Lassa fever in 2014 and it was declared over in early 2015.