Zika virus hit earlier than thought in Brazil, Florida, genome tests reveal

Studies using gene sequencingequipment to trace the path of Zika through the Americas showthe virus arrived a year before the first case was detected inBrazil, and several months before it was first reported inFlorida.

The findings, published in three different papers in thejournal Nature, are drawn from nearly 200 Zika virus genomesequences collected from infected individuals and mosquitoesthat transmit the virus.

Collectively, they show the potential for newer, moreportable gene sequencing equipment to quickly trace the spreadof emerging infectious diseases, experts said.

In one study, a team led by Oliver Pybus of the Universityof Oxford found that Zika first arrived in Brazil at thebeginning of 2014, a full year prior to the first confirmedcases in May 2015.

• U.S. Zika pregnancies: 10% result in birth defects
• Brazil declares end to Zika emergency after fall in cases

Pybus' study focused on how the virus established an earlyfoothold in northeastern Brazil, from which it spread to otherareas. Northeast Brazil was the region with the most recordedcases of Zika and microcephaly, a birth defect caused by thevirus marked by small head and brain size.

Pybus said the region was "the nexus of the epidemic inBrazil" and played a key role in spreading the virus to otherbig Brazilian cities, such as Rio de Janeiro and Sao Paulo,before spreading across the Americas.

His team was part of a consortium of British and Brazilianscientists who traveled across Brazil in a minibus, analyzingsamples of the virus using Oxford Nanopore Technologies'pocket-sized MinION DNA sequencer. The portable device was usedin 2015 to track genetic changes in the Ebola virus as itevolved and spread in Guinea.

A companion study led by Pardis Sabetti and colleagues fromthe Broad Institute and Harvard University used data from 174genomes sequenced from patients and mosquito samples collectedin 11 different countries or territories.

The data allowed the team to follow the spread of the virusacross South and Central America, the Caribbean and into thesouthern United States.

Mosquito control key

They found that Zika had been circulating in Colombia,Honduras, Puerto Rico and other parts of the Caribbean from 4.5to 9 months before the first local infections were confirmed.

In another paper, Kristian Andersen of the Scripps ResearchInstitute in La Jolla, California, and colleagues focusedspecifically on Zika's introduction into Florida.

Andersen's team sequenced 39 Zika virus genomes frominfected patients and mosquitoes in and around Miami, Florida.

They discovered that Zika was introduced into local mosquitopopulations in Florida at least four times, most likely frominfected travelers from the Caribbean.

He believes the virus began circulating in Florida in thespring of 2016, months before the first reported case in July.

Andersen said these infections took hold in Florida mosquitopopulations because Florida is one of the rare places in theUnited States where Aedes aegypti mosquitoes which transmitZika are present year-round. The other such place in thecontinental United States is Brownsville, Texas, which also hadlocally transmitted Zika cases in 2016.

"In all likelihood, that means most of the United Statesprobably isn't at risk of Zika outbreaks," Andersen said in aconference call. It also means that mosquito control efforts cango a long way towards preventing outbreaks, he said.

Bronwyn MacInnis of the Broad Institute said the studiesreveal the power of using gene sequencing to trace emerginginfections, 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 arole in achieving this,"she said.