Yellow fever is a viral disease the spreads through the bites of mosquitos. Symptoms of infection include fever, headache, chills, fatigue, nausea, and vomiting. In severe cases, liver damage will develop leading to jaundice or yellowing of the skin (hence the name "yellow fever"). Individuals with severe cases will often also begin to vomit blood. If an individual survives the infection, then they are immune to future infections.
The yellow fever virus likely originated in Africa and spread to North and South America via the slave trade. The first documented case of yellow fever in the New World occurred in Barbados in 1647. In subsequent years, the West Indies gained a reputation as a dangerous region where outbreaks of yellow fever were common. Although yellow fever was most prevalent in regions with a tropical climate, the disease also spread further north to the United States; New York City reported an outbreak in 1668. During the 1793 epidemic in Philadelphia, approximately 5000 deaths were recorded between August and November. Since the population of the city was about 50,000 people at this time, this was one of the most severe outbreaks of disease in American history. Other American cities, notably New Orleans, continued to suffer serious outbreaks of yellow fever throughout the nineteenth century.
By the 1880s, physicians and scientists had come to suspect that yellow fever was being spread through mosquitos. Experiments began to test this hypothesis, and yellow fever was the first virus to be confirmed to be spread by mosquitos. This discovery led to public health efforts to control mosquito habitats and eventually to the development of a vaccine against the disease. In the present day, a safe and reliable vaccine is available and recommended for residents and visitors to certain regions where yellow fever is common. Yellow fever continues to cause thousands of deaths annually, primarily in Africa.