One Traveler May Have Brought Zika to the Americas in 2013

[Guest Nicole]

The Zika virus now spreading widely throughout the hemisphere probably arrived in the Americas in a single traveler in the second half of 2013 — almost a year earlier than previous estimates — according to a new study of the virus’s genome led by Brazilian and British researchers.

Experts were divided in their opinions of the new study, published Thursday in the journal Science. Some praised the work, while others said it was too limited to draw such a specific conclusion.

By counting mutations in the viral genomes in different blood samples over time, the scientists created a “molecular clock” that estimates how fast the virus mutated.

The researchers then compared new samples with earlier ones from Asia, where the Zika virus had circulated for decades, and from the South Pacific, where it began circulating in 2007. The team calculated that the Zika virus arrived in the Americas between May and December 2013.

They also concluded that it probably — but not necessarily — arrived in Brazil first.

The virus was not positively identified in Brazil until May 2015. But by then it had clearly been circulating in the country’s northeast for many months, because cities there were experiencing large outbreaks of a mysterious disease causing rash, fever and bloodshot eyes.

(The virus did not become headline news around the world untilDecember, when health officials in Brazil, alarmed over a surge in infants born with tiny heads, warned women not to become pregnant. The World Health Organization declared a global health emergency on Feb. 1.)

The new study relies on just 23 viral genomes. They include samples of Zika virus obtained in Thailand, French Polynesia and the Cook Islands and 20 in the Americas, including nine from Brazil and the rest from Colombia, Martinique, Haiti, Guatemala, Suriname and Puerto Rico.

The Haitian virus was noted as being particularly unusual, because it was collected in December 2014 — more than a year before the virus’s presence in Haiti was confirmed by the W.H.O. this past January.

The gene sequences from the Americas were all closely related, and most resembled one collected in French Polynesia in November 2013.

Two earlier studies have suggested that the virus reached Brazil either with the influx of athletes and tourists arriving for the 2014 soccer World Cup, which was played in host cities all over Brazil in June to July that year, or for the Va’a World Sprints, a set of outrigger canoe races held in Rio de Janeiro in mid-August of that year.

Source: http://www.nytimes.com/2016/03/25/health/one-traveler-may-have-brought-zika-to-the-americas-in-2013.html?ref=health&_r=2