History of yellow fever

The evolutionary origins of yellow fever are most likely African. Phylogenetic analyses indicate that the virus originated from East or Central Africa, with transmission between primates and humans, and spread from there to West Africa. The virus as well as the vector Aedes aegypti, a mosquito species, were probably brought to the western hemisphere and the Americas by slave trade ships from Africa after the first European exploration in 1492. However, some researchers have argued that yellow fever might have existed in the Americas during the pre-Columbian period as mosquitoes of the genus Haemagogus, which is indigenous to the Americas, have been known to carry the disease.

The first outbreaks of disease that were probably yellow fever occurred in the Windward Islands of the Caribbean, on Barbados in 1647 and Guadeloupe in 1648. Barbados had undergone an ecological transformation with the introduction of sugar cultivation by the Dutch. Plentiful forests present in the 1640s were completely gone by the 1660s. By the early 18th century, the same transformation related to sugar cultivation had occurred on the larger islands of Jamaica, Hispaniola, and Cuba. Spanish colonists recorded an outbreak in 1648 on the Yucatán Peninsula of Mexico that may have been yellow fever. The illness was called xekik (black vomit) by the Maya.

At least 25 major outbreaks followed in North America, such as in 1793 in Philadelphia, where several thousand people died, more than nine percent of the total population. The American government, including President George Washington, had to flee the city, which was the capital of the United States at the time. In 1878, about 20,000 people died in an epidemic which struck the towns of the Mississippi River Valley and its tributaries. The last major outbreak in the US occurred in 1905 in New Orleans. Major outbreaks also occurred in Europe in the 19th century in Atlantic ports following the arrival of sailing vessels from the Caribbean, most often from Havana. Outbreaks occurred in Barcelona, Spain, in 1803, 1821, and 1870. In the 1870 outbreak, 1,235 fatalities were recorded of an estimated 12,000 cases. Smaller outbreaks occurred in Saint-Nazaire in France, Swansea in Wales, and in other European port cities, following the arrival of vessels carrying the mosquito vector.

The first mention of the disease by the name "yellow fever" occurred in 1744. Many famous people, mostly during the 18th through the 20th centuries, contracted and then recovered from, or died of, yellow fever.

The yellow fever epidemic of 1793 struck during the summer in Philadelphia, Pennsylvania, where the highest fatalities in the United States were recorded. The disease probably was brought by refugees and mosquitoes on ships from Saint-Domingue. It rapidly spread in the port city, in the crowded blocks along the Delaware River. About 5,000 people died, ten percent of the population of 50,000. The city was then the national capital, and the national government left the city, including President George Washington. Philadelphia, Baltimore, and New York suffered repeated epidemics in the 18th and 19th centuries, as did other cities along the East and Gulf Coasts.

At the time, the known solution to recovery was found to be long and tedious as it was expected that patients needed to consume bitters and country air away from the metropolitan area in order to recover. Yet the average citizen typically sought medical help from the Pennsylvania Hospital. Year after year starting in 1793, yellow fever returned to major cities along the east coast including Philadelphia leaving investigators stagnant in regard to progress made in the search for the cause of yellow fever. Yellow fever's prevalence during this era killed over 10,000 people starting in 1793 where nearly 5,000 people died, striking again in 1797 tallying about 1,500 people, and again the next year in 1798 killing 3,645 people.

With the spread of yellow fever in 1793, physicians of the time used the increased number of patients to increase the knowledge in disease as the spread of yellow fever, helping differentiate between other prevalent diseases during the period as cholera and typhus were current epidemics of the time as well. As doctors and people of interest investigated the cause of yellow fever, two main hypotheses derived from the confusing data they collected. The first was that the disease is contagious, as the disease is spread through the contact of people, as ships from the already infected Caribbean Islands had spread to major cities. The second hypothesis was that the disease derived from local sources; doctors proposed that contact with these sources caused the sickness rather than contact with people with the disease, as yellow fever seemed to be prevalent in major cities and less effective in rural areas.

The majority of the British soldiers sent to Haiti in the 1790s died of disease, chiefly yellow fever. There has been considerable debate over whether the number of deaths caused by disease was exaggerated.