Yellow fever seems to play a role in single, sudden breakouts of the disease. Three epidemiologically different infectious cycles occur, in which the virus is transmitted from mosquitoes to humans or other primates. In the "urban cycle", only the yellow fever mosquito "A. aegypti" is involved. It is well adapted to urban areas, and can also transmit other diseases, including Zika fever, dengue fever, and chikungunya. The urban cycle is responsible for the major outbreaks of yellow fever that occur in Africa. Except for an outbreak in Bolivia in 1999, this urban cycle no longer exists in South America. Besides the urban
Yellow fever blood, hence the Spanish name for yellow fever, "vómito negro" ("black vomit"). There may also be kidney failure, hiccups, and delirium. The toxic phase is fatal in about 20% to 50% of cases, making the overall fatality rate for the disease about 3.0 to 7.5%. However, the fatality rate of those with the toxic phase of the disease may exceed 50%. Surviving the infection provides lifelong immunity, and normally no permanent organ damage results. Yellow fever is caused by the yellow fever virus, a 40– to 50--wide enveloped RNA virus, the type species and namesake of the family "Flaviviridae". It