The Zika Virus Epidemic in Brazil: From Discovery to Future Implications

Abstract

The first confirmed case of Zika virus infection in the Americas was reported in Northeast Brazil in May 2015, although phylogenetic studies indicate virus introduction as early as 2013. Zika rapidly spread across Brazil and to more than 50 other countries and territories on the American continent. The Aedesaegypti mosquito is thought to be the principal vector responsible for the widespread transmission of the virus. However, sexual transmission has also been reported. The explosively emerging epidemic has had diverse impacts on population health, coinciding with cases of Guillain-Barré Syndrome and an unexpected epidemic of newborns with microcephaly and other neurological impairments. This led to Brazil declaring a national public health emergency in November 2015, followed by a similar decision by the World Health Organization three months later. While dengue virus serotypes took several decades to spread across Brazil, the Zika virus epidemic diffused within months, extending beyond the area of permanent dengue transmission, which is bound by a climatic barrier in the south and low population density areas in the north. This rapid spread was probably due to a combination of factors, including a massive susceptible population, climatic conditions conducive for the mosquito vector, alternative non-vector transmission, and a highly mobile population. The epidemic has since subsided, but many unanswered questions remain. In this article, we provide an overview of the discovery of Zika virus in Brazil, including its emergence and spread, epidemiological surveillance, vector and non-vector transmission routes, clinical complications, and socio-economic impacts. We discuss gaps in the knowledge and the challenges ahead to anticipate, prevent, and control emerging and re-emerging epidemics of arboviruses in Brazil and worldwide.

Keywords: Congenital Zika Syndrome; Zika virus; epidemiology; microcephaly; socio-economic impact; surveillance; vector control.

Figure 1

Spatial diffusion of Zika virus (ZIKV) in Brazil from 2014 to 2016 according to case reports and epidemiologic data produced by the Federal Ministry of Health and state secretaries of health [7]. The current permanent dengue transmission area is shown in grey [8].

Figure 2

Spatial diffusion of microcephaly in Brazil, June 2015 to March 2016. Data obtained from the public health events registry (RESP) information system, provided to the authors by the Brazilian Ministry of Health.

Figure 3

Notified Zika cases for the main regions of Brazil (North, Northeast, Southeast, South, and Central-West) per epidemiological week in 2016. Data obtained from the national notifiable disease information system (SINAN).

Figure 4

Notified microcephaly cases for the main regions of Brazil (North, Northeast, Southeast, South, and Central-West) per epidemiological week from January 2015 to April 2016. Data obtained from the RESP information system.

Figure 5

Summary of known epidemiological features of ZIKV. Unresolved questions are highlighted in blue. R₀ is the basic reproduction number (the expected number of secondary cases produced by a single infection in a completely susceptible population).