ECDC Confirms Locally-Acquired Zika Cases in France

Zika virus was previously only found in regions of Asia, the Pacific Islands, South America, and Africa. Incidents elsewhere were all attributed to travelers, rather than the native mosquito population. In the United States, all Zika cases have been linked to travel outside the United States.

The European Centre for Disease Prevention and Control (ECDC) has now confirmed 3 locally-acquired cases of Zika virus in Hyères, a town in the south of France, occurred in August 2019.

The third individual who became infected had no travel history to Zika-endemic countries, and resides near the location where the first 2 cases were identified. The impacted individuals were likely part of the same transmission cycle, as they developed symptoms around the same time.

Zika virus is typically transmitted by the Aedes aegypti, which is not found in France. Instead, authorities believe the likely culprit was the Aedes albopictus.

Aedes albopictus is native to tropical and subtropical areas of Southeast Asia, but in recent years has spread. Aedes albopictus has been widely established through southern Europe, where it was previously linked to the transmission of dengue, and now the ECDC considers the mosquito a competent vector for Zika virus.

ECDC’s epidemiological assessment found that the probability of ongoing vector-borne local transmission in southern Europe is unlikely. Further, there is no evidence of a more extensive cluster of Zika cases. This led to the conclusion that risk of spread outside the area is low. Travelers to the area of southern France are not considered likely to bring the virus back to their localities and ECDC did not advise limiting travel to the area.

ECDC also wrote in their initial statement on the first locally acquired case that “as temperatures are progressively decreasing during autumn, the environmental conditions are currently not favorable for sustained transmission. The current risk posed to the population, including pregnant women and their unborn children, is very low.” Given seasonal changes, the likelihood of acquiring mosquito bites altogether continues to decrease.

In response to the 3 cases, French health authorities are conducting epidemiological surveillance to identify other possible instances of Zika transmission. Health care providers in the French town and surrounding area, particularly midwives and gynecologists, were alerted and provided with instructions for the management of pregnant patients that live in or visited the affected area between July and September 2019. ECDC also launched a communication campaign to inform the public about protective measures against mosquitos and destruction of larval sites.

The third case reinforces the established likelihood that the Hyères city cases were Europe’s first locally-acquired Zika transmissions.. While the risk of an outbreak appears very low, experts from ECDC indicated they would continue monitoring the situation and the cases may present a landmark change in future expectations around where Zika virus can and can not occur.