Zika puzzle in Brazil: peculiar conditions of viral introduction and dissemination - A Review

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.

Fig. 1. : spatial distribution of notified cases of microcephaly and/or central nervous system (CNS) alterations. Cumulative cases up to epidemiological week 21. Brazil 2016. Source: MS (2016a). Data from States and Municipalities updated up to May 28, 2016.

Fig. 2. : municipalities with reported and confirmed cumulative cases of congenital Zika syndrome, in percentage of municipalities. Epidemiological week 50. Brazil, December 17, 2016. Source of data: Ministry of Health of Brazil, Epidemiological Report for epidemiological week 50/2016. Data from State and Municipalities Health Departments and Federal District (data updated up to 17/12/2016).

Fig. 3. : evolution of notified cases of microcephaly and/or alterations in central nervous system (CNS) attributed to Zika per month of notification and regions. Brasil, 2015 and 2016. Source: MS (2017c). Data provided by Health Departments of States and Municipalities up to 17/12/2016.