1793 Philadelphia yellow fever epidemic immune to the fever. Many of the slaves in Charleston in 1742 could have gained immunity before having been transported from Africa, by having been exposed to yellow fever in a mild case. People who survived one attack gained immunity. A total of 240 blacks died, in proportion to their population at the same rate as whites. Given the limited resources and knowledge of the times, the city's response was credible. The medical community did not know the natural history of yellow fever, a viral infection spread by the "Aedes aegypti" mosquito. Efforts to clean the city did not defeat
History of yellow fever The entire Mississippi River Valley from St. Louis south was affected, and tens of thousands fled the stricken cities of New Orleans, Vicksburg, and Memphis. An estimated 120,000 cases of yellow fever resulted in some 20,000 deaths. Memphis suffered several epidemics during the 1870s, culminating in the 1878 epidemic (called the Saffron Scourge of 1878), with more than 5,000 fatalities in the city. Some contemporary accounts said that commercial interests had prevented the rapid reporting of the outbreak of the epidemic, increasing the total number of deaths. People still did not understand how the disease developed or was transmitted, and