Distribution
Yellow fever occurs in West, Central, and East Africa, as well as in South America from Panama to northern Argentina. Its vector, the yellow fever mosquito (Aedes aegypti), once occurred in Europe and was responsible for serious yellow fever outbreaks. After disappearing following World War II, its reappearance and wide spread remain possible, similar to the Asian tiger mosquito (Aedes albopictus), which has re-emerged in Europe in recent years.
Host Species
In forest environments, the virus circulates among non-human primates, while in populated areas it spreads among humans. Every unvaccinated person in an endemic zone is at risk. In recent years, several unvaccinated European and North American tourists have died after visiting affected areas. In certain tropical regions, yellow fever mosquito (Aedes aegypti) is a common and widespread mosquito species, representing a significant infection risk and the potential for large-scale outbreaks.
Transmission and Vectors
Yellow fever is transmitted exclusively through the bite of an infected, virus-carrying mosquito. The most well-known vectors are the yellow fever mosquito (Aedes aegypti) and the Asian tiger mosquito (Aedes albopictus). An infected female mosquito can pass the virus on to the next generation via its eggs. A person without immunity to yellow fever who is bitten by an infected mosquito can themselves become infectious. High levels of the virus are present in the blood from the day before symptoms appear, and typically for the next four days, during which time the person can infect additional blood-feeding mosquitoes.
Symptoms
In African non-human primates, infection is either asymptomatic or causes only mild illness, and it mainly comes to attention when humans become infected. In contrast, the virus is lethal to South American non-human primates, and outbreaks there are often detected because the rainforest falls silent following the death of howler monkeys.
In humans, symptoms appear suddenly, 3–5 days after infection, and can range from mild to fatal. Clinical cases typically present with sudden fever, severe headache, and joint and muscle pain. Jaundice may develop by the third day, and in severe cases spontaneous bleeding, kidney failure, delirium, coma, and death can occur. The case fatality rate in clinical yellow fever can reach up to 80%. Recovery is prolonged and often accompanied by serious complications.
Treatment and Prevention
The YF 17D vaccine provides safe, effective, and low-cost protection against yellow fever and has been used successfully for more than fifty years. Immunity develops ten days after vaccination and lasts for life. The infection can be confirmed by serological testing to detect specific antibodies one week after infection. Once the disease develops, supportive care is the only treatment option. The use of aspirin and other blood-thinning medications is strictly prohibited.