Thursday, January 28, 2016

Anticipating the international spread of Zika virus from Brazil

In May, 2015, locally acquired cases of Zika virus—an arbovirus found in Africa and Asia-Pacific and transmitted via Aedes mosquitoes—were confirmed in Brazil. The presence of Aedes mosquitoes across Latin America, coupled with suitable climatic conditions, have triggered a Zika virus epidemic in Brazil, currently estimated at 440 000–1 300 000 cases.1 Viraemic travellers have now introduced Zika virus into at least 13 additional countries, where susceptible Aedes mosquitoes have become infected and perpetuated local transmission cycles. In Brazil, a precipitous surge in infants born with microcephaly and the detection of Zika virus RNA in the amniotic fluid of affected newborns has been reported.1 We sought to identify high-risk international pathways for the dispersion of Zika virus and global geographies conducive to autochthonous transmission.
We created a global Zika virus spread model by adapting a seasonal model for dengue that integrates global ecological niche data for Aedes aegypti and albopictus and worldwide temperature profiles.2, 3 In Brazil, we identified airports within 50 km of areas conducive to year-round Zika virus transmission. We mapped the final destinations of international travellers departing from these airports from September, 2014, to August, 2015, using worldwide flight itinerary data from the International Air Transport Association. We used LandScan, a gridded global population dataset, to estimate numbers of people living in geographies at risk for autochthonous Zika virus transmission.
9·9 million travellers departed from the aforementioned Brazilian airports for international destinations, with 65% to the Americas (figure), 27% to Europe, and 5% to Asia. Traveller volumes were greatest to the USA (2 767 337), Argentina (1 314 694), Chile (614 687), Italy (419 955), Portugal (411 407), and France (404 525). China and Angola received the highest volume of travellers in Asia (84 332) and Africa (82 838), respectively. Argentina, Italy, and the USA have more than 60% of their populations residing in areas conducive to seasonal Zika virus transmission, whereas Mexico, Colombia, and the USA have an estimated 30·5, 23·2, and 22·7 million people, respectively, living in areas conducive to year-round transmission.
Thumbnail image of Figure. Opens large image


Final destinations of travellers departing Brazil by potential for autochthonous Zika transmission
In parallel to the recent experience with chikungunya,4 Zika virus has the potential to rapidly spread across Latin America and the Caribbean. With no vaccine or antiviral therapy available, possible interventions include: personal protection (ie, repellent use) and daytime avoidance of mosquito bites (especially pregnant women until more is known about the association between Zika virus infection and microcephaly); daytime avoidance of mosquito bites among Zika virus-infected individuals to disrupt human to mosquito to human transmission cycles (80% of infected individuals are asymptomatic and the remainder have clinical syndromes overlapping with dengue and chikungunya);5 and community-level mosquito surveillance and control measures. The summer Olympic Games in Brazil in August, 2016, heighten the need for awareness of this emerging virus.
KK is the founder of BlueDot, a social benefit corporation that models global infectious disease threats. MIC, MG, and AW have received employment income from BlueDot. IIB has consulted to BlueDot. We acknowledge support from the Canadian Institutes of Health Research, National Institute of Health, R01 LM010812 , the Wellcome Trust ( #095066 ), the Bill & Melinda Gates Foundation ( OPP1119467, OPP1106023, and OPP1093011 ), and the RAPIDD program of the Science & Technology Directorate, Department of Homeland Security, and the Fogarty International Center, National Institutes of Health.


  1. European Centre for Disease Prevention and Control. Rapid risk assessment: Zika virus epidemic in the Americas: potential association with microcephaly and Guillain-Barré syndrome. 10 December 2015. ECDC, Stockholm; 2015
  2. Kraemer, MUG, Sinka, ME, Duda, KA et al. The global distribution of the arbovirus vectors Aedes aegypti and Ae. albopictus. eLife. 2015; 4: e08347
  3. Brady, OJ, Golding, N, Pigott, DM et al. Global temperature constraints on Aedes aegypti and Ae. albopictus persistence and competence for dengue virus transmission. Parasit Vectors. 2014; 7: 338
  4. Weaver, SC and Lecuit, M. Chikungunya virus and the global spread of a mosquito-borne disease. N Engl J Med. 2015; 372: 1231–1239
  5. Duffy, MR, Chen, T-H, Hancock, WT et al. Zika virus outbreak on Yap Island, Federated States of Micronesia. N Engl J Med. 2009; 360: 2536–2543

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