Low to moderate risk of locally transmitted cases of Zika in parts of Europe

ECDC has updated its rapid risk assessment on the Zika epidemic that continues to evolve in the Americas and the Caribbean.

The risk assessment synthesises the main scientific developments from the past month, considers the main risks for the EU and its citizens and sets out a range of options for EU/EEA Member States' consideration.

The 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 geographic expansion of the outbreak, mean that the epidemic remains of public health importance.

The evolution of the Zika epidemic in the Americas demands close monitoring as it has a direct impact on the risk of importation and possible occurrence of local transmission in the European Union.

Mosquito-borne transmission risk

Mosquito-borne transmission of Zika virus infection in the EU is only considered possible in areas where mosquitoes capable of carrying and transmitting the virus are present. The transmission depends on several factors related to the mosquito, the virus and the environment, notably:

• The introduction of the virus by a viraemic traveller during the summer season where Aedes albopictus is established can be expected. Aedes albopictus is established around the Mediterranean basin (see ECDC mosquito maps)
• Those areas with Aedes albopictus will have increasingly suitable conditions during the spring (April to June), and by analogy with other mosquito-borne disease transmission, the conditions will remain favourable in those areas during the summer and autumn.

Given the low vector competence of the studied European populations of Aedes albopictus, the likelihood of local vector-borne transmission in the EU is considered to be low to moderate.

In addition, Madeira is of particular concern because of the presence of Aedes aegypti, the primary vector for Zika virus, and the probability of transmission of vector-borne pathogens is considered high during the summer months.

Sexual transmission of Zika virus

There have been confirmed cases of sexual transmission of Zika virus infection from symptomatic male partners throughout 2016, and one instance of transmission from an asymptomatic male.

Scientific studies have shown that the Zika virus can be present in semen up to 62 days after the first symptoms. However, of known cases of sexual transmission, the longest time between the onset of symptoms and transmission is 19 days.

Therefore, to reduce the risk of Zika transmission, males who have been in areas with active transmission should be advised to use a condom for at least one month after returning and use a condom with a pregnant partner until the end of the pregnancy.

Updated country categorisation

ECDC has modified how countries and territories currently experiencing local Zika virus transmission are categorised.

As of week 17, 2016, ECDC extended the period for classifying whether a country or territory has active local transmission from two to three months. This change reflects that Zika virus outbreaks usually last more than two months. In addition, ECDC added a 'countries and territories with past vector-borne transmission' category for countries having experienced transmission since 2007 up to three months ago.