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 The findings, published in three different papers in the journal
Nature, are drawn from nearly 200 Zika virus genome sequences
collected from infected individuals and mosquitoes that transmit the
virus.
Collectively, they show the potential for newer, more portable gene
sequencing equipment to quickly trace the spread of emerging
infectious diseases, experts said.
In one study, a team led by Oliver Pybus of the University of Oxford
found that Zika first arrived in Brazil at the beginning of 2014, a
full year prior to the first confirmed cases in May 2015.
Pybus' study focused on how the virus established an early foothold
in northeastern Brazil, from which it spread to other areas.
Northeast Brazil was the region with the most recorded cases of Zika
and microcephaly, a birth defect caused by the virus marked by small
head and brain size.
Pybus said the region was "the nexus of the epidemic in Brazil" and
played a key role in spreading the virus to other big Brazilian
cities, such as Rio de Janeiro and São Paulo, before spreading
across the Americas.
His team was part of a consortium of British and Brazilian
scientists who traveled across Brazil in a minibus, analyzing
samples of the virus using Oxford Nanopore Technologies'
pocket-sized MinION DNA sequencer. The portable device was used in
2015 to track genetic changes in the Ebola virus as it evolved and
spread in Guinea.
A companion study led by Pardis Sabetti and colleagues from the
Broad Institute and Harvard University used data from 174 genomes
sequenced from patients and mosquito samples collected in 11
different countries or territories.
The data allowed the team to follow the spread of the virus across
South and Central America, the Caribbean and into the southern
United States.
They found that Zika had been circulating in Colombia, Honduras,
Puerto Rico and other parts of the Caribbean from 4.5 to 9 months
before the first local infections were confirmed.
In another paper, Kristian Andersen of the Scripps Research
Institute in La Jolla, California, and colleagues focused
specifically on Zika's introduction into Florida.
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Andersen's team sequenced 39 Zika virus genomes from infected
patients and mosquitoes in and around Miami, Florida. They
discovered that Zika was introduced into local mosquito populations
in Florida at least four times, most likely from infected travelers
from the Caribbean.
He believes the virus began circulating in Florida in the spring of
2016, months before the first reported case in July.
Andersen said these infections took hold in Florida mosquito
populations because Florida is one of the rare places in the United
States where Aedes aegypti mosquitoes - which transmit Zika - are
present year-round. The other such place in the continental United
States is Brownsville, Texas, which also had locally transmitted
Zika cases in 2016.
"In all likelihood, that means most of the United States probably
isn't at risk of Zika outbreaks," Andersen said in a conference
call. It also means that mosquito control efforts can go a long way
towards preventing outbreaks, he said.
Bronwyn MacInnis of the Broad Institute said the studies reveal the
power of using gene sequencing to trace emerging infections, and
could have helped detect the virus much earlier.
“We were way behind the curve on Zika. We need to be well ahead of
the next emerging viral threat, and genomics can have a role in
achieving this,” she said.
(Reporting by Julie Steenhuysen; Editing by Bernard Orr)
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