**7. Recent emergence and resurgence of YF**

**5. The paradoxical absence of yellow fever from Asian countries**

Asia [26].

212 Encephalitis

**Between 1668 and 1870 nearly 15 epidemics**

**epidemic in 1793**

**between 1668 and 1867 30**

**6. History of human YF outbreaks**

1648 and occurred in the Yucatan, Mexico and Guadeloupe [27].

**1668** United States America New York and

**1795 outbreak** West Indies European troops

**Year Countries Name of City Cases Deaths**

**1793** United States America NA NA NA

**1793 outbreak** United States America Philadelphia NA 4000 United States America New Orleans NA 7849 United States America Charleston NA 682 persons United States America Mississippi Valley NA 13,000 people

**1905** United States America New Orleans 4000 423 **1647** Barbados NA 6000 **1802** Haiti NA NA 29000

YF has never been reported from Asia, but, should it be accidentally imported, the potential for outbreaks, as the appropriate mosquito vector is present over there [21]. The lack of YFV in Asia is not clearly understood, although a number of hypotheses have been put forward [24]. The mosquito vector *Ae. aegypti* is prevalent in Asia and Pacific countries and has been important in the rapid emergence of dengue as a major public health problem in the twenti‐ eth century [25]. Laboratory studies indicate that Asian strains of *Ae. aegypti* can transmit YFV but are less competent than strains from the Americas. Demographic factors, including the remote location of sylvatic YF transmission and the cross-protective immunity provided by prior exposure to dengue and other flaviviruses, likely play a role in the lack of YF in

At the beginning of the 20th century, a large number of yellow fever epidemics were record‐ ed in both African and American cities, and these occurred against a background of annual cases. Table 1 and 2 lists an overview on the historical outbreaks in both tropical Africa and America by year and countries. Yellow fever epidemics are re-emerging in Africa and Amer‐ ica, and the occurrence of repeated rural outbreaks increases the risk for major urban epi‐ demics. The first disease outbreak that can reliably be regarded as YF was documented in

Philadelphia

United States America Philadelphia NA 3500

stationed there

United States America New York NA In 1798, 1 500 people died

NA NA

NA 3 1,000 people died

In the 18th and 19th centuries, YF was a huge public health problem until mosquito control measures and production of an effective vaccine brought the epidemics under control in the 20th century. Yet as we enter the 21st century this virus is once again a significant public health problem [15,26,28] and is classified as a reemerging disease. Urban YF has not been reported from the Americas since 1954, but jungle yellow fever transmitted by Haemagogus vectors increasingly affects forest dwellers in Bolivia, Brazil, Columbia, Ecuador, and Peru, and periodically causes small outbreaks [15, 29,30]. The reinvasion of South America by *Ae. aegypti* after relaxation of the eradication programme in the 1970s, and presence of *Ae. aegyp‐ ti* in cities near areas in which sylvatic yellow fever is endemic, poses a threat of urbanisa‐ tion of yellow-fever transmission [25,29]. Following several decades of relative calmness, YF reappeared in Africa in the 1980s, endangering populations not only in the so-called endem‐ ic countries but in the rest of the world too [31]. The resurgence of YF is also closely connect‐ ed with changes in the modern world and with the interaction of various economic, climatic, social and political factors [32].
