A latest study suggested that the Zika virus could have first spread in Brazil around a couple of years before the first reported cases. The mosquito-borne virus may possibly have reached the country in 2013, between May and December.

Though Brazilian health officials observed a cluster of illnesses identified by fever and rash towards the end of 2014, they didn't diagnose the patients with the less-known Zika virus officially before May last year.

As per an analysis of many Zika virus genomes appeared on Thursday in Science, international travel might have spread Zika to Brazil from French Polynesia, which was hit by Zika outbreak during the time period from 2013 to 2014.

Scientists can draw estimation on the arrival of Zika in a nation by observing the location of reported cases, studying mutations in the virus and making a count in back direction in time, on the basis of how quickly mutations generally occur.

Zika has been associated with the birth defect microcephaly, which leads to tiny heads and brain damage in babies. Besides, it has also been connected with infant eye abnormalities and Guillain-Barre Syndrome, a neurological disorder that can result into temporary paralysis. Zika has no cure so far, and there is no microcephaly treatment too.

The authors of the study noted that the number of air travel passengers to Brazil has gone up steadily from late 2012 till last year, partially due to famous sports events.

Scott Weaver, director of the Institute for Human Infections and Immunity and scientific director of the Galveston National Laboratory in Texas, said the process of detecting how the virus could have flown under the radar for one year or more is easy.