Zika circumnavigates the globe to go for gold

At the time of writing, the press is full of speculation that the Olympic Games should be avoided because of the risk of exposure to Zika virus. How did this possibility come to dominate the headlines? Zika was first isolated in 1947 in the Zika forest of Uganda [1] and added to a long list of similar flaviviruses that are spread by mosquitoes, cause transient febrile illness, but have limited morbidity and no serious complications. This perspective was initially supported when Zika spread east to the Micronesian island of Yap in 2007 and then further east to French Polynesia in October 2013, and even further east to Easter Island in 2015, causing epidemics of maculopapular rash, headache, muscle and joint pains, and conjunctivitis [2,3]. However, in French Polynesia, cases with Guillain‐Barré syndrome were reported at the time, and a retrospective study recently reported a significant association with microcephaly, with an estimated risk of 1% for a woman infected in the first trimester [3,4]. In 2015, cases of Zika were reported from South America as the virus continued its eastward progress around the globe. Coincident with this, cases of microcephalywere reported from Brazil [5]. Microcephaly has multiple causes, including virus infections, particularly cytomegalovirus (CMV), toxins, genetics, and malnutrition. The possibility that Zika was not the only cause of the increasing number of reported cases was discussed because many of the women in Brazil who delivered affected babies came from the poorer sections of society where malnutrition and exposure to chemical toxins could provide alternative etiologies [6]. Nevertheless, the public response that greeted the pictures of babies with obvious microcephaly led the WHO to declare a public health emergency of international concern in February 2016. As one member of WHO put it: Zika was assumed to be guilty until proven innocent [6]. Several case‐ control studies are underway in Brazil and Colombia to define the incidence of microcephaly, the incidence of Zika, the correlation between the two, and the contribution Zika makes to the overall incidence of disease. While waiting for the results of these studies, a group from the Centers for Disease Control and Prevention assessed Zika against the 6 relevant criteria set out by Shepard to assess causality [7]. They accepted that Zika met 4 of the criteria (proven exposure during pregnancy, specific clinical syndrome, concordance of rare syndrome with rare exposure, and plausible biology) but not two others (high‐quality epidemiological studies and animal teratogenicity). The public discussion in temperate zones focussed on the perceived risks of women of childbearing age travelling to foreign parts to be exposed to Zika, without considering the far greater risks they take unknowingly on a daily basis from endemic CMV infection that damages the intellectual potential of more babies than does Down syndrome and is the commonest cause of sensorineural hearing loss [8,9]. This illustrates how the “shock of the new” can trump evidence‐ based assessments of risk. In fact, concerns about Zika may bring CMV out from the shadows to reveal its true effects on the population [10]. Public discussion then morphed into concern about the safety of athletes visiting Rio in August 2016 and even into calls for the Olympic Games to be cancelled for fear of spreading Zika to other parts of the world. Setting aside the fact that Zika has already circumnavigated the globe without help from the games, how might countries mitigate the theoretical risk of importation? Countries are at risk of importing Zika through athletes or spectators returning home while incubating the infection. If they are then bitten by mosquitoes in their home country, infected insects could transmit to other citizens and establish the infection in previously uninfected areas. To achieve this, countries would have to have resident mosquitoes that are competent to transmit Zika, that is, Aedes aegypti or Aedes albopictus. The United Kingdom is free of such pests, although other parts of Europe and the rest of the world are not so fortunate. The example of Chikungunya (an alphavirus) being transmitted in Rev. Med. Virol. 2016; 26: 307–308. Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/rmv.1901 Reviews in Medical Virology