NEW YORK — The worrisome Zika virus apparently has been in Brazil at least a year longer than experts previously thought, according to new research.
Some experts have speculated the virus first came to the Americas sometime in 2014. But the new study — led by Brazilian researchers — concludes Zika landed in Brazil a year earlier.
The researchers coupled cutting-edge genetic sequencing of the virus with an analysis of human travel patterns.
They succeeded in piecing together "a very compelling story about both the route and the date of introduction of this virus into the Americas," said Dr. Ian Lipkin, a prominent infectious disease specialist at New York's Columbia University.
The sequence information also may help in future understanding of how the virus causes disease, Lipkin said. But it remains a mystery why the virus is increasingly linked to serious birth defects and other health problems, he added.
The study was published online Thursday by the journal Science.
Zika virus was first identified in Uganda in 1947. It is spread mainly by mosquitoes that bite infected people and then spread it to others. Most infected people suffer no symptoms. Others get only a mild, weeklong illness.
For decades, it was considered exotic and nonthreatening. The virus began to pop up in other parts of the world in the last decade, but it was not detected in the Americas until last year, when it was reported in Brazil.
The new research is based on blood and brain tissue samples taken last year from seven Brazilians.
The researchers found the virus specimens were similar to each other, and most closely related to Zika virus found in French Polynesia in 2013.
A good bet is the virus landed in June 2013 in the city of Recife, around the time of the 2013 Confederations Cup soccer tournament in Brazil, said one of the study's lead authors, Dr. Pedro Fernando da Costa Vasconcelos of Brazil's Health Ministry.