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Yellow fever is an acute viral haemorrhagic disease transmitted by infected mosquitoes. The "yellow" in the name refers to the jaundice that affects some patients. Up to 50% of severely affected persons without treatment will die from yellow fever. There are an estimated 200 000 cases of yellow fever, causing 30 000 deaths, worldwide each year, with 90% occurring in Africa. The virus is endemic in tropical areas of Africa and Latin America, with a combined population of over 900 million people. The number of yellow fever cases has increased over the past two decades due to declining population immunity to infection, deforestation, urbanization, population movements and climate change. There is no specific treatment for yellow fever. Treatment is symptomatic, aimed at reducing the symptoms for the comfort of the patient. Vaccination is the most important preventive measure against yellow fever. The vaccine is safe, affordable and highly effective, and a single dose of yellow fever vaccine is sufficient to confer sustained immunity and life-long protection against yellow fever disease and a booster dose of yellow fever vaccine is not needed. The vaccine provides effective immunity within 30 days for 99% of persons vaccinated.

WHO response WHO is the Secretariat for the International Coordinating Group for Yellow Fever Vaccine Provision (ICG). The ICG maintains an emergency stockpile of yellow fever vaccines to ensure rapid response to outbreaks in high risk countries. The Yellow Fever Initiative is a preventive control strategy of vaccination led by WHO and supported by UNICEF and National Governments, with a particular focus on most high endemic countries in Africa where the disease is most prominent. The Initiative recommends including yellow fever vaccines in routine infant immunizations (starting at age 9 months), implementing mass vaccination campaigns in high-risk areas for people in all age groups aged 9 months and older, and maintaining surveillance and outbreak response capacity. Between 2007 and 2012, 12 countries have completed preventive yellow fever vaccination campaigns: Benin, Burkina Faso, Cameroon, Central African Republic, Côte d’Ivoire, Ghana, Guinea, Liberia, Mali, Senegal, Sierra Leone and Togo. The Yellow Fever Initiative is financially supported by the GAVI Alliance, the European Community Humanitarian Office (ECHO), the Central Emergency Response Fund (CERF), the Ministries of Health, and the country-level partners.

Yellow fever

Yellow fever (YF) is a viral haemorrhagic fever transmitted by infected mosquitoes. Yellow fever can be recognized from historic texts stretching back 400 years. Infection causes a wide spectrum of disease, from mild symptoms to severe illness and death. The "yellow" in the name is explained by the jaundice that affects some patients, causing yellow eyes and yellow skin. There are three types of transmission cycle: sylvatic, intermediate and urban. All three cycles exist in Africa, but in South America, only sylvatic and urban yellow fever occur.

Sylvatic (or jungle) yellow fever occurs in tropical rainforests where monkeys, infected by sylvatic mosquitoes, pass the virus onto other mosquitoes that feed on them; these mosquitoes, in turn bite and infect humans entering the forest. This produces sporadic cases, the majority of which are often young men working in the forest e.g. logging. The intermediate cycle of yellow fever transmission occurs in humid or semi-humid savannahs of Africa, and can produce small-scale epidemics in rural villages. Semi-domestic mosquitoes infect both monkey and human hosts and increased contact between man and infected mosquito leads to disease. This is the most common type of outbreak seen in recent decades in Africa. Urban yellow fever results in large explosive epidemics when travellers from rural areas introduce the virus into areas with high human population density. Domestic mosquitoes, most notably Aedes aegypti, carry the virus from person to person. These outbreaks tend to spread outwards from one source to cover a wide area. Yellow fever can be prevented by vaccination. In order to protect people living in areas at high risk of yellow fever transmission, WHO's dual strategy for prevention of yellow fever epidemics relies on preventive mass immunization campaigns followed by infant routine immunization. Yellow fever causes epidemics that can affect 20% of the population. When epidemics occur in unvaccinated populations, case-fatality rates may exceed 50%. No treatment beyond supportive care exists. For more information

Paul I. Howell, MPH; Prof. Frank Hadley Collins/Centers for Disease Control and...Paul I. Howell, MPH; Prof. Frank Hadley Collins/Centers for Disease Control and Prevention (CDC) (Image Number: 9534)An infectious disease, yellow fever infects humans, all species of monkeys, and certain other small mammals. The virus is transmitted from animals to humans and among humans by several species of mosquitoes. Yellow fever is one of the great epidemic diseases of the tropical world, and in earlier centuries it was one of the great plagues of the New World. At one time the tropical and subtropical regions of

Yellow fever is diagnosed clinically, with laboratory confirmatory testing available.

Yellow fever is diagnosed clinically, with laboratory confirmatory testing available.

Fever Headache Muscle pain Backache Chills Loss of appetite Nausea and/or vomiting

High fever Abdominal pain Bleeding from the gums, nose, eyes, and/or stomach Vomit that appears black due to blood content Low blood pressure Liver failure, which may lead to jaundice Kidney failure Confusion Seizure Coma

SymptomsYellow fever symptoms appear within a week after a person is bitten by an infected mosquito. Typically, acute phase symptoms will persist for 3 to 4 days, and then disappear. A small percentage of people progress into the toxic phase. The toxic phase symptoms begin within 24 hours of the end of the acute phase. Recovery from yellow fever provides lifetime immunity from the disease.

The death toll from a yellow fever epidemic in Philadelphia hits 100 on this day in 1793. By the time it ended, 5,000 people were dead. Yellow fever, or American plague as it was known at the time, is a viral disease that begins with fever and muscle pain. Next, victims often become jaundiced (hence, the term "yellow" fever), as their liver and kidneys cease to function normally. Some of the afflicted then suffer even worse symptoms. Famous early American Cotton Mather described it as "turning yellow then vomiting and bleeding every way." Internal bleeding in the digestive tract causes bloody vomit. Many victims become delirious before dying. The virus, like malaria, is carried and transferred by mosquitoes. The first yellow fever outbreaks in the United States occurred in late 1690s. Nearly 100 years later, in the late summer of 1793, refugees from a yellow fever epidemic in the Caribbean fled to Philadelphia. Within weeks, people throughout the city were experiencing symptoms. By the middle of October, 100 people were dying from the virus every day. Caring for the victims so strained public services that the local city government collapsed. Philadelphia was also the seat of the United States government at the time, but federal authorities simply evacuated the city in face of the raging epidemic. Eventually, a cold front eliminated Philadelphia's mosquito population and the death toll fell to 20 per day by October 26. Today, a vaccine prevents yellow fever in much of the world, though 20,000 people still die every year from the disease.

Western Africa has long been regarded as the home of yellow fever, although the first recorded outbreaks of the disease were in central and coastal South America after the Spanish conquest in the 16th century. For the next 300 years, yellow fever, given various names such as Yellow Jack and “the saffron scourge,” was one of the great plagues of the New World. The tropical and subtropical regions of the Americas were subjected to devastating epidemics, and serious outbreaks occurred as far north as Philadelphia, New York, and Boston but also as far away from the endemic centres as Spain, France, England, and Italy.

Between the College's advisory on August 25 and the death of Dr. Hutchinson from yellow fever on September 7, panic spread throughout the city; more people fled. Between August 1 and September 7, 456 people died in the city. On September 8, 42 deaths were reported.[18] An estimated 20,000 people left the city through September, including national leaders.[9] The daily death to

l remained above 30 until October 26. The worst 7-day period was between October 7 and 13, when 711 deaths were reported.[18]

During the Yellow Fever Epidemic of 1793 in Philadelphia, Pennsylvania, 5000 or more people were listed in the official register of deaths between August 1 and November 9. The vast majority of them died of yellow fever, making the epidemic in the city of 50,000 people one of the most severe in United States' history. By the end of September, 20,000 people had fled the city. The mortality rate peaked in October, before frost finally killed the mosquitoes and brought an end to the epidemic in November. Doctors tried a variety of treatments, but knew neither the origin of the fever nor that it was transmitted by mosquitoes (which was not verified until the late nineteenth century).