India, May 13 -- A hantavirus outbreak linked to a cruise ship has put 18 Americans under medical monitoring across the United States, raising urgent questions about how the virus spreads and whether it could be the next major public health threat.

As of Tuesday, one passenger is being monitored at a biocontainment unit at the University of Nebraska, while 15 others are quarantining at the university's National Quarantine Center. Two more passengers, including one showing symptoms have been sent to a biocontainment unit at Emory University in Atlanta. That symptomatic individual has tested negative for the Andes variant of hantavirus which is the only known strain capable of spreading from person to person, according to USA Today.

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