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.
Figure
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.
References
- 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
- Kraemer, MUG, Sinka, ME, Duda, KA et al. The global distribution of the arbovirus vectors Aedes aegypti and Ae. albopictus. eLife. 2015; 4: e08347
- 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
- Weaver, SC and Lecuit, M. Chikungunya virus and the global spread of a mosquito-borne disease. N Engl J Med. 2015; 372: 1231–1239
- 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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