Between August 2015 and May 2016, Nigeria recorded 273 cases of, as well as 149 deaths from Lassa Fever. This outbreak was particularly significant both for its scope, with cases in 20 of Nigeria's 36 states, and for its greater-than-expected lethality. While Lassa infections commonly have mortality rates around 1%, and which climb to around 15% in extreme cases, the Nigerian outbreak saw a dearth rate over 50%, suggesting the emergence of a new, more lethal strain of the virus.
Many Nigerians have multiple and frequent points of exposure to and interaction with the rodent vectors which carry Lassa and other arenaviruses. Stores of grains and other foods may often be frequented by mice and rats, and, in some parts of the country, rodent meat is sold, eaten and makes up a significant portion of local diets. That the country is currently experiencing recession and significant tensions with regards to the nomadic cattle herders who produce much of the country's beef also contributes to pressures for other, more available sources of protein, increasing the risks of exposure to Lassa and similar zoonoses.