FCM PB 2016/2

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"Brazil’s soccer team celebrated its victory in the Confederations Cup tournament in Rio de Janeiro in June 2013. In a study of the Zika virus’s genome, scientists noted that it was possible the virus arrived during the tournament. Credit: Michael Regan/Getty Images‖

"The Zika virus is 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 on Thursday in the journalScience. 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 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 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 or tourists arriving for the 2014 soccer World Cup, which was played in host cities all over Brazil from June to July that year. Those assumptions were based on air traffic patterns, not on viral sequencing. Oliver G. Pybus, a disease geneticist at Oxford University and one of the paper’s authors, said that the virus’s arrival during the Confederations Cup was ―within the range of possibilities, but not something you can capture scientifically."

Until this year, however, few doctors had even heard of Zika, and it was often misdiagnosed as dengue or other diseases."

(Adapted from: http://www.nytimes.com/2016/03/25/health)