Yellow fever is a viral hemorrhagic disease spread between humans, as well as between certain other primates and humans, by the bite of yellow fever-infected mosquitoes. The virus is called simply Yellow fever virus and belongs to the virus family Flaviviridae.
There are three main types of the disease:
Sylvatic yellow fever (also known as “jungle yellow fever”) occurs when the disease is passed from monkeys infected by wild mosquitoes to humans.
Intermediate yellow fever—the most common type of outbreak in modern Africa—results when semi-domestic mosquitoes (which can infect both monkeys and humans) are present in an area where they commonly come into contact with humans.
Urban yellow fever occurs when the Aedes aegypti species of domestic mosquito transmits the virus between humans, without transmission via other primates.
Yellow fever is endemic in areas of Latin America and Africa, while imported cases have appeared throughout the world. Globally, the disease infects about 200,000 people per year, causing fever, chills, nausea, vomiting, muscle pain, and headache.
There is no cure for yellow fever. Treatment consists solely of attempts to make the patient more comfortable. While many patients recover after 3-4 days of such symptoms, approximately 15% enter a second phase of the illness after a remission. This second phase includes a return of high fever, as well as jaundice; abdominal pain and vomiting; bleeding from the mouth, nose, eyes, or stomach; and deteriorating kidney function. As many as half of the patients who experience the second phase may die. In all, yellow fever kills 30,000 people globally each year.
Yellow fever vaccination is typically performed only in areas where the disease is endemic. Vaccination is available for those traveling to regions where the virus is still widespread. The most recent statistics from the World Health Organization show immunization coverage of approximately 51% in 2007 in countries considered at risk for outbreaks. This is a vast increase from 1988, when the disease was at its modern peak with more than 5 million cases reported globally and immunization coverage of less than 5%. WHO cautions, however, that prevention of outbreaks in affected regions requires 60-80% coverage of an at-risk population.
Mass vaccination efforts continue in regions with a high incidence of the disease.