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Scientists at University of Oxford and the Evandro Chagas Institute in Brazil have reported on the sequencing of seven Zika virus (ZIKV) genomes from the recent South American outbreak, including one fatal adult case and one newborn with microcephaly. This data offers new information on how and when the virus might have entered the Americas and the researchers hope will begin to shed some light on transmission and pathogenicity factors. 

The investigators found that ZIKV in the Americas arose from a single introduction, estimated to have occurred between May and December 2013, more than 12 months prior to the first detection of ZIKV in Brazil.

The findings from this study were published recently in Science through an article entitled “Zika virus in the Americas: Early epidemiological and genetic findings.”

This estimated date of origin coincides with increased rates of air passengers to Brazil from ZIKV-endemic areas as well as with reported outbreaks in the Pacific Islands. Interestingly, one hypothesis put forth by the researchers involves virus introduction during the Confederations Cup soccer tournament, which involved French Polynesian participation from Tahiti.

“We looked at broad-scale patterns of human movement and focused on air passengers who travelled to Brazil from countries that had reported Zika since 2012, explained co-author Oliver Pybus, Ph.D., a biologist in Oxford University's Department of Zoology. “From late 2012 onwards, there was a 50% rise in the number of passengers travelling to Brazil from countries with Zika.”

“Although the American outbreak virus is most closely related to a strain from French Polynesia, it's also possible that Zika was introduced separately to the Americas and French Polynesia from South East Asia,” Dr. Pybus added. “To better understand Zika transmission history, we need more information about the epidemiology and genetic diversity of Zika viruses in South East Asia.”

Municipality-level analysis indicates that reports of suspected microcephaly in Brazil best correlate with ZIKV incidence around week 17 of pregnancy (or week 14 for severe microcephaly)—although the researchers stress that this does not demonstrate causation. Work is ongoing to establish whether or not ZIKV is a true causal factor for microcephaly and other conditions.

“This is the first study into the Zika outbreak in Brazil using genomic data, and it gives us a good baseline for future research,” remarked led study author Nuno Faria, Ph.D., research lecturer at University of Oxford and the Evandro Chagas Institute. “We tried to address some of the hypotheses being put forward – for example, analyzing the correlation between Zika and microcephaly. We found some spatial and temporal correlation consistent with this hypothesis, but to test the link conclusively we must wait for case-control epidemiological studies to be completed.”

“There is a lot of work still to be done in terms of tracking and predicting the spread of Zika in Brazil,” Dr. Faria continued. “We will have a much better picture of the virus later this year.”

Márcio Nunes, Ph.D., head of the Evandro Chagas Institute and co-senior study author added that “our genome sequencing efforts have provided a clearer picture of the Zika virus in Brazil. However, more genomic data are urgently needed to understand the origin, spatial spread, and evolution of the virus in the Americas and in Brazil.”

In the past several months, Brazil has experienced an unprecedented epidemic of ZIKV, with around 30,000 cases reported thus far.

“At present, 22 out 27 Brazilian states and Federal District have reported autochthonous cases of Zika virus, which means that upwards of 80% of the population is at risk of infection,” stated co-senior study author Pedro Vasconcelos, M.D., Ph.D., research scientists at the Evandro Chagas Institute. “The Brazilian Ministry of Health has estimated that between 0.5 million and 1.5 million people were infected by Zika during 2015. Approximately 4,000 suspected cases of microcephaly were reported, with 500 being linked to Zika virus.”

The researchers are committed to continuing their efforts to understand all they can about this disease and hope that this initial data will provide a baseline for future studies of the evolution and molecular epidemiology of ZIKV within emerging virus areas.

“Zika represents a serious threat to the country,” Dr. Vasconcelos concluded.  “Accordingly, actions to prevent or minimize its occurrence need to be implemented as quickly as possible in Brazil and other Latin American and Caribbean countries where the virus is endemic.”

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