When a cluster of hantavirus infections struck the cruise ship MV Hondius , about two dozen American passengers were on board. At least seven disembarked before health authorities were informed of the outbreak and headed home to the United States; 17 others remained on the ship for several weeks and have only just been repatriated. Meanwhile, a few Americans who had never been on the ship may have been exposed to the virus while on board an international flight.

Officials with the World Health Organization (WHO) say they've been in consistent communication with the U.S. Centers for Disease Control and Prevention (CDC), coordinating plans for the American passengers and exchanging technical information about hantaviruses.…