Prediction and prevention of urban arbovirus epidemics: A challenge for the global virology community

Abstract

The recent emergence and rapid spread of Zika virus in tropical regions of the Western Hemisphere took arbovirologists and public health officials by surprise, and the earlier transfers of West Nile and chikungunya viruses from the Old to the New World were also unexpected. These pandemics underscore the increasing threat of zoonotic arboviruses, especially those that are capable of entering into human-amplified, urban transmission cycles transmitted by Aedes (Stegomyia) aegypti and sometimes other Aedes (Stegomyia) spp. mosquitoes. This review serves as an introduction to a World Health Organization-sponsored conference to be held on June 18-19, 2018 in Geneva, titled "From obscurity to urban epidemics: what are the next urban arboviruses?" It is intended to set the stage and fuel discussions of future urban arbovirus threats, how we can predict these risks from known and unknown viruses, and what factors may change these risks over time.

Fig. 1.

The most common mechanism of human infection by most arboviruses is direct spillover from enzootic transmission cycles (involving various wildlife as amplification hosts). This occurs when enzootic vectors, or bridge vectors that bite both wild animals and humans, transmit. An example is West Nile virus, which emerged in the Americas after its introduction into New York in 1999, and which uses birds as amplification hosts and Culex spp. mosquitoes as vectors (Roehrig, 2013).

Fig. 2.

Some arboviruses undergo secondary amplification in domesticated animals with spillover to humans, resulting in increased exposure and disease. Examples include epizootic strains of Venezuelan equine encephalitis virus, which amplify in equids as during the last major epizootic/epidemic in Venezuela and Colombia in 1995 (Weaver et al., 1996); another is Japanese encephalitis virus, which amplifies in swine and causes endemic disease in the Asian topics and summer epidemics in temperate climates (Pearce et al., 2018); and another is Rift Valley fever virus, which amplifies in ruminants, with several epizootics/epidemics since 2000 (Kenawy et al., 2018).

Fig. 3.

The most important human arboviral pathogens undergo human-amplified, typically urban transmission cycles, which evolve from primate-amplified, ancestral enzootic cycles (see Fig. 1). These include dengue, yellow fever, chikungunya and Zika viruses (Wilder-Smith et al., 2016). Direct human-human transmission (arrow at top) has only been documented for Zika virus (Aliota et al., 2017).