A cruise ship with nearly 150 people aboard is waiting for help off the coast of Cape Verde in the Atlantic Ocean after three passengers died and at least three other people were left seriously ill in a suspected outbreak of the rare hantavirus, according to the World Health Organization and the ship’s operator.

The MV Hondius, a Dutch ship on a weekslong polar cruise from Argentina to Antarctica and several isolated islands in the South Atlantic, had requested help from local health authorities after making its way to the island of Cape Verde, off the West Africa coast.