Officials study virus link to birth defects

US health officials are stepping up efforts to study the link between infections from a mosquito-borne virus and birth defects in infants.

They are investigating the Zika virus amid predictions that it will circulate widely in the United States during warmer months.

The National Institutes of Health called on Tuesday for the intensified efforts, citing a study estimating that the virus could reach regions where 60 percent of the US population lives.