Vector-borne transmission and evolution of Zika virus

Abstract

Zika virus (ZIKV), discovered in the Zika Forest of Uganda in 1947, is a mosquito-borne flavivirus related to yellow fever, dengue and West Nile viruses. From its discovery until 2007, only sporadic ZIKV cases were reported, with mild clinical manifestations in patients. Therefore, little attention was given to this virus before epidemics in the South Pacific and the Americas that began in 2013. Despite a growing number of ZIKV studies in the past three years, many aspects of the virus remain poorly characterized, particularly the spectrum of species involved in its transmission cycles. Here, we review the mosquito and vertebrate host species potentially involved in ZIKV vector-borne transmission worldwide. We also provide an evidence-supported analysis regarding the possibility of ZIKV spillback from an urban cycle to a zoonotic cycle outside Africa, and we review hypotheses regarding recent emergence and evolution of ZIKV. Finally, we identify critical remaining gaps in the current knowledge of ZIKV vector-borne transmission.

Fig. 1 |. Emergence and evolution of Zika virus vector-borne transmission.

Zika virus was first detected in Uganda in 1947. Seroprevalence data suggests the virus was present in Africa and Asia starting from the 1950s and spread to the Pacific and the Americas from 2013 onwards. There are three recognized lineages of Zika virus (African lineage, green; Asian lineage, blue and American lineage, purple), characterized by key pre-epidemic and post-epidemic mutations, shown on the phylogeny.

Fig. 2 |. Zika virus vector-borne transmission.

a, Horizontal transmission of ZIKV occurs in two distinct cycles: a sylvatic cycle in which the virus circulates between animal vertebrate hosts (i.e., probably nonhuman primates) and zoophilic mosquitoes, and an urban cycle in which the virus is transmitted to humans by highly anthropophilic mosquitoes (such as Ae. aegypti). b, Vector-borne transmission of ZIKV occurs via three main patterns: horizontal transmission between vertebrates and vectors, vertical transmission from and infected mosquito female to its progeny, and venereal transmission from an infected female to a mosquito male and vice versa.

Fig. 3 |. Distribution of vector species naturally infected with Zika virus.

The colour code used for countries and territories represents the Zika virus lineages that have been epidemiologically associated with human infections in those regions.

Fig. 4 |. Distribution of host orders reported as susceptible to Zika virus in natural conditions.

The colour code used for countries and territories represents the Zika virus lineages that have been epidemiologically associated with human infections in those regions (serological assays have been the tests used to assess ZIKV exposure and susceptibility in 87.1% of animals sampled in the field).