Infectious diseases can be spread by a ship's crew, passengers and visitors.
Unless diseases are identified and contained quickly, they could potentially infect large numbers of people.
Masters of ships must notify Newport City Council, as the port health authority, of any suspected infectious disease or death on board other than by an accident.
The presence of animals or captive birds and any illness or death in those animals or birds must also be reported.
Read more from the Port Health Association.
Visit the World Health Organisation for information on international emergencies.