In 1999, more than 100 countries were considered malarious and more than 300 million acute episodes of the disease occurred. While malaria is epidemic and increasingly difficult to treat in many areas throughout the world, lack of compliance with preventative measures is the primary reason for malaria in travelers. The majority of U.S. and Canadian travelers who acquire malaria do not develop symptoms until after returning home. Travelers should always consider malaria if they develop a fever after returning home from a malarious area. Prompt diagnosis and treatment is critical.
Yellow fever occurs in tropical areas only in certain regions of South America and Africa.
Urban yellow fever is transmitted by an Aedes aegypti mosquito from one infected person to another. Aedes aegypti smosquitoes bite primarily during daylight hours - especially during the early morning and late afternoon. Since the 1980's yellow fever has re-emerged across Africa and South America with the largest number of cases being reported in Nigeria. In Africa, both urban and jungle transmission cycles occur. In 1992, yellow fever reappeared in Kenya after a 50-year absence and in 1995 Gabon reported its first case ever.