Rapid Risk Assessment - Zika virus epidemic in the Americas: potential association with microcephaly and Guillain-Barré syndrome (Fourth update, 09 March 2016)

Abstract

This update assesses the risks associated with the Zika virus epidemic currently affecting countries in the Americas. It assesses the association between Zika virus infection and congenital central nervous system malformations, including microcephaly, as well as the association between Zika virus infection and Guillain–Barré syndrome.

Main conclusions and options for response

Considering the continued spread of Zika virus in the Americas and Caribbean, the strong evidence of an association between Zika virus infection during pregnancy and congenital central nervous system malformations, the association between Zika virus infection and Guillain–Barré syndrome, and the risk of establishment of local vector-borne transmission in Europe during the 2016 summer season, EU/EEA Member States are recommended to consider a range of mitigation measures.

The following uncertainties have been taken into consideration in developing the proposed options for response:

• At present, there is a lack of evidence at which stage of the pregnancy the foetus is most vulnerable to Zika virus infection. Therefore the entire duration of pregnancy should be considered at risk.

• The presence of infectious Zika virus in semen has been detected up to three weeks after onset of disease; the longest interval reported between the onset of symptoms in a male and the subsequent onset of the disease thought to be due to sexual transmission in a female partner is 19 days.

• The role of asymptomatic males in the sexual transmission to women is unknown.

• The roles of different mosquito species as potential vectors of Zika virus should be clarified. If current assumptions prove inaccurate or incorrect, vector control strategies have to be adapted and revised.