A cruise ship carrying hundreds of passengers is expected to dock in the Canary Islands tonight following an outbreak of hantavirus. The virus, which can cause severe respiratory illness, has already infected at least 12 people on board. Authorities are scrambling to prepare an emergency evacuation.

The ship, the MS Aurora, is operated by British cruise line Oceanic Cruises. It left Southampton two weeks ago. The outbreak was first detected five days ago when a passenger complained of fever and muscle aches. Since then, cases have multiplied.

Hantavirus is not typically associated with cruise ships. It is usually spread through contact with rodent droppings. Health officials are baffled. "We do not yet know the source," said Dr. Helena Costa, the regional health director. "But we are taking every precaution."

The ship was due to stop in Tenerife for a scheduled port call. Instead, it will dock at a remote pier on Gran Canaria. The area will be cordoned off. Medical teams in full protective gear will board.

Passengers are being kept in their cabins. They have been told not to leave. "It is very frightening," said Sarah Thompson, a passenger from Manchester. "We are locked in. They bring food to the door. No one tells us anything."

The crew has been instructed to wear masks and gloves. The ship's ventilation system has been shut down to prevent airborne spread. Health officials are contacting passengers from the previous voyage.

Dr. Costa confirmed that the hantavirus strain involved is the Sin Nombre virus. This is the most dangerous type. It has a mortality rate of up to 40 percent. "We are dealing with a serious situation," she said. "Our priority is to isolate the sick and prevent further spread."

The evacuation will begin as soon as the ship docks. Passengers will be disembarked one by one. Those with symptoms will be taken to a local hospital. Others will be quarantined in a nearby hotel.

The British Embassy is on standby. A spokesman said: "We are providing consular assistance. We urge calm."

Oceanic Cruises has issued a statement. It says the company is "fully cooperating with health authorities". It adds: "The safety of our passengers and crew is our highest priority."

But questions remain. How did the virus get on board? Could it have been prevented? And what about the rest of the cruise season? The Canary Islands are a popular winter destination.

Local authorities are worried about the economic impact. Tourism is a key industry. "This could be devastating," said a hotel owner who asked not to be named. "We rely on cruise ships."

For now, all eyes are on the MS Aurora. The ship is due to arrive at 10 p.m. local time. The evacuation is expected to last through the night.

Dr. Costa confirmed that all passengers will be screened before being released. The quarantine period is 21 days. That means a long wait for the 800 people on board.

Meanwhile, the World Health Organization has been alerted. It is monitoring the situation. This is a test of global health security. How we respond will set a precedent.

Alastair Vance, reporting for The British Wire.