lowest in Senegal and highest in Nigeria, which has the second largest number of people living with HIV in Africa after South Africa. Nigeria's infection rate relative to the entire population, however, is much lower (3.7 percent) compared to South Africa's (17.3 percent). Ebola virus disease Ebola virus disease, first identified in 1976, typically occurs in outbreaks in tropical regions of Sub-Saharan Africa, including West Africa. From 1976 through 2013, the World Health Organization reported 1,716 confirmed cases. The largest outbreak to date is the ongoing 2014 West Africa Ebola virus outbreak, which is affecting Guinea, Sierra Leone, Liberia and Nigeria The outbreak began in Guinea in December 2013, but was not detected until March 2014, after which it spread to Liberia, Sierra Leone, and Nigeria. The outbreak is caused by the Zaire ebolavirus, known simply as the Ebola virus (EBOV). It is the most severe outbreak of Ebola in terms of the number of human cases and fatalities since the discovery of the virus in 1976. , the World Health Organization (WHO) reported a total of 2,240 suspected cases and 1,229 deaths (1,383 cases and 760 deaths being laboratory confirmed). On 8 August, it formally designated the outbreak as a public health emergency of international concern. This is a legal designation used only twice before (for the 2009 H1N1 (swine flu) pandemic and the 2014 resurgence of polio) and invokes legal measures on disease prevention, surveillance, control, and response, by 194 signatory countries. Various aid organisations and international bodies, including the Economic Community of West African States (ECOWAS), US Centers for Disease Control and Prevention (CDC), and the European Commission have donated funds and mobilised personnel to help counter the outbreak; charities including Médecins Sans Frontières, the Red Cross, and Samaritan's Purse are also working in the area. Famine Famine has been an occasional but serious problem in West Africa. In 1680s, famine extended across the entire Sahel, and in 1738 half the population of Timbuktu died of famine. Some colonial "pacification" efforts often caused severe famine. The introduction of cash crops such as cotton, and forcible measures to impel farmers to grow these crops, sometimes impoverished the peasantry in many areas, such as northern Nigeria, contributing to greater vulnerability to famine when severe drought struck in 1913. For the middle part of the 20th century, agriculturalists, economists and geographers did not consider Africa to be famine prone –