Throughout history, yellow fever has been a devastating viral hemorrhagic infection. It is a flavivirus whose symptoms range from none to hemorrhagic fever. In the past, the incidence of yellow fever was controlled by vaccination along with mosquito control; however, the incidence is on the rise in poorer countries, such as tropical Africa and Central and South America. The rare occurrence in the United States has been related to international travel. Worldwide, an estimated 200,000 cases are diagnosed annually.
Yellow fever is a virus transmitted by Aedes aegypti mosquitoes worldwide, by Haemagogus mosquitoes in South America, and by Aedes africanus mosquitoes in Africa. The mosquitoes bite monkeys, which act as hosts for the virus, and then the mosquitoes bite humans, transmitting the disease via saliva. The virus can also be transmitted directly by mosquitoes to humans, especially in urban areas. People who work in or near mosquito-infested areas are at increased risk for contracting yellow fever. A successfully treated bout of yellow fever confers lasting immunity.
The yellow fever vaccine has been in use for several decades and confers immunity for approximately 10 years. It should be obtained by people traveling to or living in areas where yellow fever has been reported, such as parts of South America and Africa. Some countries require proof of vaccination. The vaccine should also be given to laboratory personnel who are exposed to the yellow fever virus. Four groups of persons who should not take the vaccine include infants under age 6 months, pregnant women, persons who are allergic to eggs, and persons who are immune suppressed.
Complications of yellow fever include coagulopathy and bleeding problems, liver failure and, possibly, renal failure. Secondary infections may lead to respiratory failure. Delirium and coma may occur. Yellow fever is fatal in 15% to more than 50% of patients, primarily in those who progress to the toxic phase.