Zika virus is not new. Last year, when I was asked if I knew of an expert on the disease in the UK, I searched for papers written by an author giving a UK address. I found 11 papers, six of which were written before I had started primary school in 1961. Yet in the past six months the virus has risen to the top of the infectious disease news headlines with very good reason.
It is now widely accepted that the infection is responsible for the epidemic of microcephaly (a devastating disability) seen in South America in babies of mothers infected during pregnancy. Furthermore, other serious neurological sequelae have been described in both children and adults, including Guillain-Barré syndrome, acute myelitis, and meningo-encephalitis.
The Zika virus is a member of the genus Flavivirus, which includes West Nile virus, dengue virus, and yellow fever virus. Like them, it is spread by mosquitoes, with both dengue and Zika being spread by mosquitoes of the genus Aedes—most effectively by A. aegypti but also A. albopictus. So far there is no proven therapy or an available vaccine. Recent experience with both dengue fever and chikungunya, both spread by Aedes mosquitoes, in the new world tells us that in the absence of an effective vaccine, controlling the epidemic spread of these viruses in low and middle income countries is extremely difficult. In addition to mosquito-borne transmission, Zika is also able to spread directly from person-to-person through sexual transmission.
On 18 May the European Office of the World Health Organization (WHO) issued a call to European Countries to prepare for the infection to spread to Europe. While there have been numerous reports of illness in travellers returning from infected countries, there have been no reports of mosquito-borne transmission in Europe to date. Nevertheless, the technical report accompanying the WHO alert points out that the mosquito species that are a vector for Zika are present in a number of countries.
Indeed, there have been reports of outbreaks of indigenous dengue and chikungunya in European countries. We recently produced maps of disease risk for dengue fever in Europe and most risk is focused on Mediterranean coast areas. Indeed, the largest outbreak of an Aedes transmitted disease (affecting some 217 people) occurred in north eastern Italy in 2007, one of the areas particularly highlighted in our study.
The risk of an outbreak of Zika in Europe is real, although such outbreaks are unlikely to lead to the disease becoming established, at least without further global warming. Nevertheless, it would be premature for people to start avoiding travel to southern Europe. An outbreak in Europe is not certain, and if one did occur its exact location would be impossible to predict in advance.
Europe benefits from the availability of good diagnostic virology laboratories and infectious disease surveillance that should be able to detect any outbreak at a relatively early stage. Nevertheless, if an outbreak did occur it would be likely to add further health and economic misery to parts of Europe already struggling to cope with the current migration crisis.
Paul Hunter is professor of health protection at the Norwich Medical School, University of East Anglia, and honorary consultant in medical microbiology at the Norfolk and Norwich University Hospital. His primary research interests focus on emerging infectious diseases, especially those driven by environmental factors, and he has worked in Europe, Asia, and Africa.
Competing interests: From October 2015 to March 2016 I was seconded to the World Health Organization, Geneva. Otherwise, no conflicts of interest.