Zika virus outbreaks in parts of Africa and Asia.

 Zika virus outbreaks in parts of Africa and Asia; two billion people could be at risk

mosquito socking blood from human body.

More than two billion people could be at risk Zika virus outbreaks in parts of Africa and Asia, according to scientists writing in The Lancet Infectious Diseases.

Populations in India, Indonesia and Nigeria are some of the most vulnerable to transmission, the researchers said.They used data on air traveler numbers to help model their predictions.However, they acknowledge that immunity to the virus could already exist in some areas and could reduce the risk.The research team, from the London School of Hygiene and Tropical Medicine, Oxford University and the University of Toronto, Canada, said "vast numbers" of people were living in environments where it would be hard to prevent, detect and respond to the virus.

They looked at factors such as the numbers of people who traveled from Zika-affected areas in South America to Africa and Asia, the presence of mosquitoes that can pass on the virus, and the climate in the regions to assess which countries could be most at risk from an outbreak.