Researchers have traced the outbreak of Zika virus in South America back to a canoeing championship event held in Rio de Janiero in 2014.
But there are concerns the study, published in journal PLOS Neglected Tropical Diseases, hasn't done enough to prove the hypothesis.
Brazilian and German scientists tested blood samples from 119 confirmed Zika patients in Rio, none of which had recently travelled. Of those, 11 percent had first shown signs of infection before the first reported Brazilian outbreak in the northeast of the country, suggesting that wasn't the origin of the present pandemic.
They tested 10 randomly selected virus samples, and found their genome sequence resembled those found in Asian Zika strains.
"This suggests that the virus was introduced to Brazil from Asia and supports the hypothesis of initial transmission from Pacific Island teams participating in a 2014 canoe championship in Rio," the researchers said in a statement.
There were minor outbreaks of Zika in the Pacific Islands in 2014.
Michael Baker of the Department of Public Health at the University of Otago says it is a speculative conclusion, but if accurate, suggests how easily Zika may be transmitted across the globe.
"The large number of visitors to Rio during the Summer Olympics in August may increase the dissemination of Zika to new locations across the globe.
"This is another reason why it is important that public health officials in Rio take action to control this epidemic and visitors take measures to protect themselves from mosquito bites."
Philip Hill, co-director of the Centre for International Health and the Otago Global Health Institute, says the study proves nothing.
"It is just speculation as they have done none of the work required to get a genetic fingerprint match for the virus present in any Pacific country," he says.
"My guess is that this study shows that the virus they have found in this small population in Brazil likely originated from Asia-Pacific somewhere and it found its way into this group of people around 2014/15, but it could easily have started off in Asia a long time before then and come from another part of Brazil in 2014/15.
"You can't be more specific than that."
Zika was declared a public health emergency of international concern by the World Health Organisation in February. The Centers for Disease Control in the US warned yesterday it could be more dangerous than initially thought.
"Most of what we've learned is not reassuring," Dr Anne Schuchat told USA Today.
"Everything we look at with this virus seems to be a bit scarier than we initially thought."
Newshub.
