**2. Global public health impact**

encephalitis [ADEM]), and YEL-AVD (yellow-fever associated viscerotropic disease, which

Although YF has undoubtedly been endemic in tropical Africa for thousands of years, it was only after the arrival of the European migrants in the New World at the end of the fifteenth century that this scourge emerged in the form of devastating epidemics. The term 'vomito‐ negro' was used in those days to describe clinical aspects of this pathological condition, be‐ cause death was frequently preceded by black vomit or by partially digested blood. Other terms used to designate yellow fever included 'Yellow Jack' and 'Safran scourge,' with refer‐

Griffin Hughes was the first to use the term "yellow fever" to describe the disease in his book in 1750 [6]. At different stages of human development, YF has caused untold hardship and indescribable misery among different populations in the Americas, Europe, and Africa. Hundreds of thousands of people have been affected by the disease throughout ages among which tens of thousands have died. YF brought economic disaster in its wake, constituting a

YF is known for bringing on a characteristic yellow tinge to the eyes and skin, and for the terrible "black vomit" caused by bleeding into the stomach [8,9]. It was one of the most feared lethal diseases before the development of effective vaccine. Today the disease still af‐ fects as many as 200,000 persons annually in the tropical regions of Africa and South Ameri‐ ca, and poses a significant hazard to unvaccinated travellers to these areas [10]. Recent increases in the density and distribution of the urban mosquito vector, *Ae. aegypti*, as well as the rise in air travel has increased the risk of introduction and spread of yellow fever to

In East Africa, yellow fever remains as a disease of increasing epidemic risk. The most recent yellow fever outbreak in the region was reported by the WHO in the late 2010 and included the first human cases reported in Uganda in almost 50 years [11]. Prior to this, outbreaks oc‐ curred in Sudan (2003 and 2005) and were the first reports of yellow fever from that country in approximately 50 years. These events were preceded by the first outbreak ever reported in Kenya (1992–1993), which were the first reported human cases in East Africa for close to

Over the last 20 years the number of yellow fever epidemics has risen and more countries are reporting cases. Mosquito numbers and habitats are increasing. Nevertheless, in both Af‐ rica and the Americas, there is a large susceptible, unvaccinated population. Changes in the world's environment, such as deforestation and urbanization, have increased contact with the mosquito/virus. Widespread international travel plays an important role in spreading the disease. The priorities are vaccination of exposed populations, improved surveillance and epidemic preparedness [12]. During the 20th century yellow fever has reemerged as a cause of human suffering. The recent epidemics are clearly indicating the vulnerability and potentiality of the YF as a global public health threat in the changing environment. In this

usually involves multi-organ failure including liver, renal and circulatory failure) [4].

ence to the jaundice observed in many patients [5].

North and Central America, the Caribbean and Asia [10].

context, the present chapter becomes more significant and pertains.

stumbling block to development too [7].

25 years [11].

208 Encephalitis

The virus is endemic in tropical areas of Africa and Latin America, with a combined popula‐ tion of over 900 million people [13]. During the past decade, official reports of YF incidence (50-120 cases a year from South America and 200–1200 cases a year from Africa) probably underestimate the true number of cases. Many cases of jaundice and fever (a surveillance definition of yellow fever) are not assessed, unexplained deaths go unreported, symptoms suggest alternative diagnoses, and, in some countries, surveillance systems for yellow fever are not in place [14]. The case-fatality rate ranges from 20% to 50% and is partly dependent on case recognition and testing practices [15,16]. The continued presence and epidemic po‐ tential of yellow fever virus make it a global health threat. The growth of international travel to endemic areas annually has increased the number of travelers potentially exposed to the virus and consequently it has increased the risk of introduction into other new areas where competent vectors are present [10].
