Overview of Zika virus (ZIKV) infection in regards to the Brazilian epidemic

Abstract

Zika virus (ZIKV), a mosquito-borne flavivirus, belongs to the Flaviviridae family, genus Flavivirus. ZIKV was initially isolated in 1947 from a sentinel monkey in the Zika forest, Uganda. Little clinical importance was attributed to ZIKV, once only few symptomatic cases were reported in some African and Southeast Asiatic countries. This situation changed in 2007, when a large outbreak was registered on the Yap Island, Micronesia, caused by the Asian ZIKV lineage. Between 2013 and 2014, ZIKV spread explosively and caused many outbreaks in different islands of the Southern Pacific Ocean and in 2015 autochthonous transmission was reported in Brazil. Currently, Brazil is the country with the highest number of ZIKV-positive cases in Latin America. Moreover, for the first time after the discovery of ZIKV, the Brazilian scientists are studying the possibility for the virus to cause severe congenital infection related to microcephaly and serious birth defects due to the time-spatial coincidence of the alarming increase of newborns with microcephaly and the Brazilian ZIKV epidemic. The present review summarizes recent information for ZIKV epidemiology, clinical picture, transmission, diagnosis and the consequences of this emerging virus in Brazil.

Figure 1. World epidemiology of ZIKV infection. A, Global expansion of the Asian lineage. After the characterization and isolation of ZIKV in Uganda, until 2007 only few human cases were reported in some African and Southeast Asiatic countries. The first significant ZIKV outbreak was registered in Yap Island, Micronesia, geographically situated close to Indonesia, where ZIKV is endemic (arrow). Between 2013 and 2014, ZIKV was rapidly spread to many of the islands of the Southern Pacific Ocean, causing the largest outbreak in French Polynesia. In 2015, the first autochthonous cases were detected in Brazil. B, Epidemiology of ZIKV infection in Central and South America. Currently, Brazil is the most affected country in South America followed by Colombia (maps adapted from the Pan-American World Health Organization, PAHO, Zika-epidemiological update).

Figure 2. Transmission of ZIKV in its African sylvatic and urban cycles. In nature, it is thought that ZIKV infection is transmitted among non human primates with the help of different forest-dwelling mosquitoes, principally of the Aedes genus. It is unknown how the urban transmission occurs. Probably during heavy rainfalls, the sylvatic mosquito population can grow up progressively and disseminate the virus to nearby villages, and from there to larger urban centers, thus the urban cycle may occur with human-to-human transmission (A). Another possible route for human-to-human ZIKV infection is the direct human invasion of the forest habitats, where the infection can be transmitted to human hosts from forest dwelling mosquitoes (B).