"As in several European countries, the Aedes albopictus species of mosquito has now been identified for the first time in Portugal in the North," the DGS said in a statement.

However, the DGS said that so far "there is no evidence of increased risk to the health of the population."

"The director general of Health and the president of the Dr Ricardo Jorge National Institute of Health will continue to inform the population of developments and the measures taken," added the DGS statement.

The dengue virus is transmitted through the bite of mosquitoes of the genus Aedes infected with the virus, and person-to-person transmission does not occur. The vectors exist in extensive areas of the world, particularly in tropical and subtropical regions.

Symptoms of the disease include fever, headaches, muscle and joint pains, vomiting and red spots on the skin and, more rarely, haemorrhaging.

The primary prevention measure is individual protection against mosquito bites as there is no vaccine against the disease.