In 1950, there were 83 cities with populations exceeding one million; by 2007, this number had risen to 468.[26] The UN forecasts that today's urban population of 3.2 billion will rise to nearly 5 billion by 2030, when three out of five people will live in cities.[27] This increase will be most dramatic on the least-urbanized continents, Asia and Africa. Surveys and projections indicate that all urban growth over the next 25 years will be in developing countries.[28] One billion people, almost one-seventh of the world's population, now live in shanty towns.[29] In many poor countries overpopulated slums exhibit high rates of disease due to unsanitary conditions, malnutrition, and lack of basic health care.[30] By 2030, over 2 billion people in the world will be living in slums.[31] Over 90% of the urban population of Ethiopia, Malawi and Uganda, three of the world's most rural countries, already live in slums.