Abstract
This article discusses the peculiar conditions that favoured the unexpected introduction of Zika virus into the poorest northeastern region of Brazil in 2015, its speed of transmission to other Brazilian states, other Latin American countries and other regions, and the severity of related neurological disorders in newborns and adults. Contrasting with evidence that Zika had so far caused only mild cases in humans in the last six decades, the epidemiological scenario of this outbreak in Brazil indicates dramatic health effects: in 2015, an increase of 20-fold in notified cases of microcephaly and/or central nervous system (CNS) alterations suggestive of Zika congenital infection, followed by an exponential increase in 2016, with 2366 cumulative cases confirmed in the country by the end of December 2016. A significant increase in Guillain-Barré syndrome in adults has also been reported. Factors involved in viral dissemination, neural pathogenesis and routes of transmission in Brazil are examined, such as the role of social and environmental factors and the controversies involved in the hypothesis of antibody-dependent enhancement, to explain the incidence of congenital Zika syndrome in Brazil. Responses to the Zika outbreak and the development of new products are also discussed.
Highlights
The emergence of Zika virus (ZIKV) in Northeast Brazil in 2015, its unprecedented speed of transmission to other Brazilian states and other Latin American countries in nearly nine months and its global spread caught the scientific community, international organisations and policy makers by surprise, with 56 countries with reported outbreaks (WHO 2016) The exponential increase and extreme severity of ZIKV neurological disorders, congenital Zika syndrome in newborns and Guillain-Barré syndrome in adults, contrasting with evidence since its first isolation in humans in 1954 in a young girl in Eastern Nigeria (MacNamara 1954) of mild disease and non-life threatening symptoms, turned this new disease into one of the highest priorities of global public health concern
We present in this literature review the contributions from scientists from a broad range of disciplines, attempting to identify the biological, ecological and social processes involved in the peculiar conditions of Zika introduction, emergence and spread in Brazil
This study showed for the first time in Brazil that the ZIKV can cross the placental barrier and possibly cause cases of neurological disorders in newborns
Summary
Distribution of cumulative notified cases of Zika microcephaly and/or central nervous system (CNS) alterations as defined by the Surveillance Protocol. It is important to highlight, as indicated, that a sharp decline has been observed in the evolution of notified cases of microcephaly and/or alterations in CNS attributed to Zika in Brazil per month of notification and per regions from 2015 and 2016 (MS 2017c) This decline, sharp in the Northeastern region, might be seasonal, related to decreased mosquito infestation in winter/autumn and/or the result of postponed pregnancies caused by the increased awareness of women regarding Zika risks, which would lead, if confirmed, to a significant reduction in birth rates.
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