New Delhi, May 20 -- Argentine investigators searching for the source of a deadly hantavirus outbreak on a cruise last month were trapping rodents in the forests surrounding the southernmost city of Ushuaia on Tuesday, with the aim of detecting the possible presence of the rat-borne virus in an area previously thought unaffected.

The scientists, wearing bright blue gloves and surgical masks, checked the 150 box traps they had set out the previous night, dropping dead rats into black plastic bags that they hoisted into pickup trucks bound for a makeshift lab where they said they'd draw blood samples.

Tuesday's rat-trapping marks the start of fieldwork within Argentina's wider investigation into the origin of the contagion that struck the...