Yellow fever in Asia. Since the 1980s, the number of cases of yellow fever has been increasing. This is believed to be due to fewer people being immune, more people living in cities, people moving frequently, and changing climate increasing the habitat for mosquitoes. The disease originated in Africa, from where it spread to South America through the slave trade in the 17th century. Since the 17th century, several major outbreaks of the disease have occurred in the Americas, Africa, and Europe. In the 18th and 19th centuries, yellow fever was seen as one of the most dangerous infectious diseases. In 1927
1793 Philadelphia yellow fever epidemic atmosphere that might last 50 years and make deadly epidemics almost certain. Yellow fever epidemics became seen as a national crisis. When in 1855 a French doctor published an 813-page history of yellow fever in Philadelphia, covering outbreaks from 1699 to 1854, he devoted only a few pages to the 1793 epidemic. General 20th-century US histories, such as the 10-volume "Great Epochs in American History," published in 1912, used short excerpts from Carey's account. The first history of the epidemic to draw on more primary sources was J. H. Powell's "Bring Out Your Dead" (1949), but he did not use