Two cases of measles have been confirmed following ferry journeys between Aberdeen and Shetland.
Passengers and crew members who were aboard journeys travelling from Aberdeen to Shetland on October 19 and southbound back to the city on October 20 have been contacted.
Those who travelled northbound to Shetland on October 21 have also been advised.
The ferry called at Kirkwall in Orkney on October 19 and passengers who were on board may also have come into contact with the virus.
Anyone who travelled on any of these routes is asked to stay vigilant and contact their GP or public health team by phone if they develop a fever of 38C or higher (100.4F), have a generalised rash and either a cough, blocked nose and/or conjunctivitis.
The highly infectious viral illness is most common in young children but can be contracted by anyone.
It has cold-like symptoms, which appear around 10 days after infection.
It usually clears in around seven to 10 days, but can lead to serious and life-threatening complications in some people, such as pneumonia and encephalitis.
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Captain John Strathearn, operations director for Serco NorthLink Ferries, said: “We are continuing to work closely with NHS Shetland to follow NHS protocols and instructions.
“This includes informing all relevant passengers and crew to ensure they have the required information.”
The World Health Organisation confirmed the UK eliminated measles in 2016.
The NHS health board in Shetland has already begun an immediate programme of vaccination for all children, women of child-bearing age, healthcare workers, social care workers and other young adults who have not had two doses of MMR vaccines or a measles-containing vaccine.
NHS Shetland public health principal Elizabeth Robinson said the only way to prevent against measles is to have a vaccination.
She added: “Measles is a highly infectious disease.
“It is possible that subsequent cases of measles could arise in susceptible passengers who have not been vaccinated against the disease who travelled on the same ferry journeys.
“We are aware that there may be increased demand for the MMR vaccine over the next few weeks and we are working to ensure sufficient stocks can be made available as soon as possible.”