This book brought together internationally recognized scientists with complementary expertise to compare and contrast the emergence of chikungunya virus (CHIKV) and Zika virus (ZIKV). Although belonging to two different genera, Alphavirus and Flavivirus, they share common transmission components, namely, human hosts and Aedes mosquito vectors (Higgs and Vanlandingham, Chapter 2). Both evolved in Africa (Mawlouth, Chapter 4) and until recently, were mainly restricted to and endemic in Africa and Asia. With the unanticipated and large epidemics in the Americas, it was realized that there was a need for specific diagnostics and, ultimately, vaccines. For vaccine development, in particular there was a need for better-characterized nonhuman primate models and also small animal models. Chapter 10 by Morrison describes the development of animal models, while Chapter 11 by Metz and Pijlman describes the multiple vaccines that are now at some stage of development. Chapter 9 by Zannoli et al. describes the current status of diagnostic platforms that have been critical to identify infected people and also to differentiate between infections with viruses, especially dengue, which can present as similar symptoms.
Although diseases caused by chikungunya and Zika virus infections have been recognized for many years, until recently they had attracted little interest by the scientific community and were essentially unknown to the general public. As described by Sam in Chapter 5, although chikungunya had historically been responsible for large outbreaks in Asia, an introduction from Africa into Indian Island Ocean Islands, firstly Comoros and then LaReunion were prequels to an unprecedented range expansion that culminated in the introduction into the Americas (Vasconcelos et al., Chapter 7). As described in Chapter 8 by Huang, a key contributing factor to these new outbreaks was a single-point mutation in the E2 gene that increased viral infectivity for the Asian tiger mosquito Aedes albopictus. When introduced by a traveler into Italy, the mutant virus was able to efficiently infect local Ae albopictus populations and cause a local outbreak. Although travel-related cases were identified in many countries, in Europe, only Italy and France reported autochthonous cases (Zannoli et al., Chapter 6).
At an international conference in Malaysia in 2013, many of the international experts who have authored chapters for this book, met to discuss their data, research priorities, and options for control. At the end of this conference, one of the coeditors of this book, Ann Powers, commented to me that she had just been assigned to help investigate a suspect chikungunya/Zika outbreak on the Island of Yap. It soon became apparent that this outbreak was not due to Zika virus but due to chikungunya virus. This emergence involved rapid dispersal of infected travelers to areas where competent Aedes vectors were present, principally Ae. aegypti and Ae. albopictus.
Although the chikungunya epidemic attracted considerable attention, because of the scale and more importantly, hitherto-unreported or rare severe diseases symptoms, ZIKV demanded much greater responses. In particular, the development of debilitating or fatal microcephaly in infants infected in utero highlighted our lack of understanding of this virus. Chapter 3 by Scott Halstead not only describes human disease caused by the viruses, but also very importantly presents historical evidence to show that outbreaks of chikungunya virus had previously occurred in the Americas but had been misdiagnosed as dengue fever.
In the final chapter, Tom Monath reviews the emergence of these old world diseases and speculates on potential future of these and related mosquito-borne viruses.