The Absence of Yellow Fever in Asia: History, Hypotheses, Vector Dispersal, Possibility of YF in Asia, and Other Enigmas

Abstract

Since the recent epidemics of yellow fever in Angola and Brazil as well as the importation of cases to China in 2016, there has been an increased interest in the century-old enigma, absence of yellow fever in Asia. Although this topic has been repeatedly reviewed before, the history of human intervention has never been considered a critical factor. A two-stage literature search online for this review, however, yielded a rich history indispensable for the debate over this medical enigma. As we combat the pandemic of COVID-19 coronavirus worldwide today, we can learn invaluable lessons from the historical events in Asia. In this review, I explore the history first and then critically examine in depth major hypotheses proposed in light of accumulated data, global dispersal of the principal vector, patterns of YF transmission, persistence of urban transmission, and the possibility of YF in Asia. Through this process of re-examination of the current knowledge, the subjects for research that should be conducted are identified. This review also reveals the importance of holistic approach incorporating ecological and human factors for many unresolved subjects, such as the enigma of YF absence in Asia, vector competence, vector dispersal, spillback, viral persistence and transmission mechanisms.

Yellow fever in Asia–a risk analysis

“…This is in agreement with the current literature, which suggests that multiple societal, biological and environmental factors likely contribute to the absence of YF in Asia. 8 , 27 , 77 …”

“… 25 It has been suggested that YF had fewer historic opportunities for introduction into Asia, as Asian–African trade routes were primarily with East Africa, where YF incidence was lower. 26 , 27 However, as YF spread to both the Americas and Europe, it is unlikely that the opportunity for YF introduction into Asia never occurred. 25 Successful control of YF across Africa and the South America, through preventive vaccination campaigns or outbreak response vaccination, may have limited YF introduction into Asia during the 20th century.…”

Which Plagues are Coming Next?

“…As mentioned above, YF is endemic in mostly South American and Africa, with outbreaks consistently seen each year. Although not often heard about in North America and Asian countries, Yellow Fever was endemic hundreds of years ago in cities like New York, Philadelphia, Memphis, and New Orleans [19] and has the possibility to emerge in Asian countries [20,21]. Although Aedes mosquitoes are also native in parts of Asia, the absence of YF cases has long been a scientific enigma [21,22].…”

“…Although not often heard about in North America and Asian countries, Yellow Fever was endemic hundreds of years ago in cities like New York, Philadelphia, Memphis, and New Orleans [19] and has the possibility to emerge in Asian countries [20,21]. Although Aedes mosquitoes are also native in parts of Asia, the absence of YF cases has long been a scientific enigma [21,22]. Common theories to the lack of YF cases in Asia are: the east African mountain range provides a natural barrier for Asia [21], competition with Dengue virus limits YF transmission [23], and vector competency [20] among others.…”

“…Although Aedes mosquitoes are also native in parts of Asia, the absence of YF cases has long been a scientific enigma [21,22]. Common theories to the lack of YF cases in Asia are: the east African mountain range provides a natural barrier for Asia [21], competition with Dengue virus limits YF transmission [23], and vector competency [20] among others. However, in the recent years an increased number of imported YF cases into Asian countries have raised alarms to the potential introduction of YFV to the local environment [20].…”