Viral and immunological characteristics of Zika virus and its impact on pregnancy

Zika virus (ZIKV) is a newly emerging flavivirus primarily transmitted by Aedes mosquitoes, but also via sexual contact, maternal-fetal transmission, and bloodborne routes. Congenital Zika syndrome (CZS) is a spectrum of severe birth defects including microcephaly, cortical malformations in the brain, ocular defects and growth restrictions that are caused by infection during pregnancy. The severity of the outcomes depends on what point the infection occurs in pregnancy, the immunological status of mother and relative viral load — with first-trimester infections considered the most dangerous.

Endogenous immune pathogen defense mechanisms, namely basic innate, interferon mediated pathways as well as adaptive B and T cell directed responses are required for host suppression of infection; however cross reactivity with pathogenic strains of flavivirus may contribute to antibody dependent enhancement (ADE). The structure, neurotropism and multiple routes of transmission of ZIKV present challenges to public health.

Prevention efforts focus on vector control, safe sex practices, maternal care and the development of a vaccine. Understanding both viral biology as well as its interplay with the immune system is key to preventing congenital sequelae and for optimal management of maternal-fetal outcomes.