THE HAGUE, Netherlands (AP) — Countries around the world are preparing to deal with the more than 140 passengers and crew members on board a hantavirus-stricken cruise ship headed for the Canary Islands. The vessel is expected to reach the Spanish island of Tenerife, off the coast of West Africa, early Sunday.At least three passengers have died, and several other people have been infected.Hantavirus is usually spread by the inhalation of contaminated rodent droppings and isn’t easily transmitted between people. Some scientists believe the Andes virus implicated in the cruise ship outbreak may be able to spread between people in rare cases. But the World Health Organization says the risk to the wider public from the outbreak is low. Symptoms usually show between one and eight weeks after exposure. Authorities and the cruise operator have been providing updates, but some key information is still lacking. Here’s what we don’t know:

Where the outbreak originatedArgentine investigators suspect a Dutch couple may have first contracted the virus while on a bird-watching trip before they boarded the cruise ship in Argentina on April 1. But no organization has confirmed where or how they acquired the disease. Argentina’s Health Ministry has zeroed in on the nation’s southernmost town, Ushuaia. Officials plan to travel there in the coming days, according to a written statement to The Associated Press.