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
1793 Philadelphia yellow fever epidemic was also advocated by Dr. Edward Stevens, who in mid-September claimed it had cured Alexander Hamilton, Secretary of the Treasury, of the fever. Rush searched the medical literature for other approaches. Benjamin Franklin had given him letters sent by Dr. John Mitchell, related to treating patients during a 1741 yellow fever outbreak in Virginia. (Franklin never published the letters.) Mitchell noted that the stomach and intestines filled with blood and that these organs had to be emptied at all costs. "On this account," Mitchell argued, "an ill-timed scrupulousness about the weakness of the body is of bad consequences in these