Zika Virus Circulated Long Before Detection, Scientists Say

(CN) – The Zika virus circulated through the Americas well before the first infections were detected, according to a new study published Wednesday.

The findings, published in the journal Nature, come from an analysis of 174 Zika genomes – the complete blueprint of inheritable traits – sequenced from mosquito and patient samples collected in 11 affected nations and territories.

In several regions, the mosquito-borne virus circulated for months before local cases were identified. The analysis suggests that Zika was in Brazil by February 2014, a year before the nation’s first confirmed infections were reported. The study also found that Zika appeared in Colombia, Puerto Rico, Honduras and elsewhere in the Caribbean about 4 1/2 to 9 months before local cases were detected.

The results were delayed due to challenges in sequencing Zika, particularly from patient samples. The difficulties stem from the virus typically being present at very low levels in patients, and that the virus also disappears quickly.

As a result, very few Zika genomes were generated prior to the study, which left researchers with little basis for understanding how the virus is evolving and spreading.

“Genomics allowed us to reconstruct how the virus traveled and changed across the epidemic – which also means that genomics could have helped detect it much earlier,” said co-senior author Bronwyn MacInnis, associate director of malaria and viral genomics in the Broad Institute, a nonprofit research organization that partners with MIT and Harvard.

“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.”

The team developed new analytical and laboratory methods for capturing substantial Zika genomic data and applied them to samples collected in partnership with international collaborators, which helped generate 110 new genomes for the study. The researchers combined those genomes with an additional 64 available in GenBank, a publicly-accessible genetic sequence database maintained by the National Center for Biotechnology Information.

“We knew it was important to understand the viral populations driving the epidemic, which motivated us to tackle the challenges of sequencing Zika,” said study co-first author Hayden Metsky, a graduate student in the Sabeti lab at Harvard. “Because the data we generated capture the geographic diversity of the virus across the Americas, they provide an opportunity to trace how and when the virus spread.”

In a companion study also published Wednesday in Nature, researchers shed light on how Zika entered and circulated in Florida in 2016 – something that may happen again this year.

According to the team, the Zika outbreak in Florida resulted from at least four separate introductions that each started local chains of transmission. Three of the strains came from the Caribbean islands, while one spread through Central America. It was common for multiple strains to circulate in a single area.

Florida is particularly at risk for future Zika outbreaks due to its large population of Aedes aegypti mosquitoes that transmit the virus, its climate and Miami-area residents who frequently travel to nations where the virus is present.

The researchers believe a similar transmission pattern is likely to emerge this year.

A Zika infection can cause fevers, rashes, headaches and joint and muscle pain, though more severe symptoms have also been reported. The virus has also been linked to birth defects in some babies born to infected mothers including microcephaly, which leads to underdeveloped heads and brain damage.

 

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