Yellow fever

Yellow fever is an acute viral disease.[3] In most cases, symptoms include fever, chills, loss of appetite, nausea, muscle pains particularly in the back, and headaches.[3] Symptoms typically improve within five days.[3] In some people within a day of improving, the fever comes back, abdominal pain occurs, and liver damage begins causing yellow skin.[3] If this occurs, the risk of bleeding and kidney problems is also increased.[3] The disease is caused by the yellow fever virus and is spread by the bite of an infected female mosquito.[3] It infects only humans, other primates, and several species of mosquitoes.[3] In cities, it is spread primarily by mosquitoes of the Aedes aegypti type.[3] The virus is an RNA virus of the genus Flavivirus.[4] The disease may be difficult to tell apart from other illnesses, especially in the early stages.[3] To confirm a suspected case, blood sample testing with polymerase chain reaction is required.[5] A safe and effective vaccine against yellow fever exists and some countries require vaccinations for travelers.[3] Other efforts to prevent infection include reducing the population of the transmitting mosquito.[3] In areas where yellow fever is common and vaccination is uncommon, early diagnosis of cases and immunization of large parts of the population is important to prevent outbreaks.[3] Once infected, management is symptomatic with no specific measures effective against the virus.[3] The second and more severe phase results in death in up to half of people without treatment.[3][6] Yellow fever causes 200,000 infections and 30,000 deaths every year,[3] with nearly 90% of these occurring in Africa.[5] Nearly a billion people live in an area of the world where the disease is common.[3] It is common in tropical areas of South America and Africa, but not in Asia.[3][7] Since the 1980s, the number of cases of yellow fever has been increasing.[3][8] This is believed to be due to fewer people being immune, more people living in cities, people moving frequently, and changing climate.[3] The disease originated in Africa, from where it spread to South America through the slave trade in the 17th century.[1] Since the 17th century, several major outbreaks of the disease have occurred in the Americas, Africa, and Europe.[1] In the 18th and 19th centuries, yellow fever was seen as one of the most dangerous infectious diseases.[1] In 1927 yellow fever virus became the first human virus to be isolated. wrote: