People who have visited or live in the Busselton area in the state's South-West are being asked to be alert to the risk of measles following confirmation of an additional case in the region.
Children and adults who have been inadvertently exposed are at risk of developing measles if they are not already immune.
Individuals should remain vigilant for the onset of measles symptoms throughout the next 18 days if they attended:
Vasse Coles and surrounds in the afternoon or evenings of July 21, 22, 23 and 24 and Vasse McDonald's on the evening of July 24.
According to the WA Country Health Services Dr Tania Wallace, measles is a serious and highly contagious viral illness that spreads when infected people cough and sneeze.
"Being in the same room around the same time as someone with measles can result in infection in people who are not immune," she said.
"People with measles typically develop symptoms approximately 10 to 18 days after exposure.
"Early symptoms include fever, cough, runny nose and sore eyes, followed by a red blotchy rash three or four days later.
"The rash usually starts on the face and spreads to the rest of the body," she added.
Dr Wallace said complications following measles can be serious and include ear infections and pneumonia in about 10 per cent of cases.
Parents are urged to make sure their children receive their measles vaccinations.
People who are concerned they may have measles and require medical advice after hours can contact Healthdirect on 1800 022 222.
