Factsheet

What are mosquitoes?
Mosquitoes are flying insects. They have two sets of wings and are quite small, generally between 4 and 10 millimetres in length. They have a specially developed proboscis (a feeding mouth part) that they use to bite through skin to suck blood. Mosquitoes feed on a range of birds and mammals including man. They are known as "vectors" because they can carry certain communicable diseases.

What diseases do mosquitoes carry?
In the tropics and warmer countries, mosquitoes can carry a range of infections including malaria, yellow fever, West Nile virus, chikungunya fever and Dengue. Mosquitoes pass on disease when they bite a person to feed on their blood. If they have been recently feeding on an animal or person infected with a virus or parasite, they can pass this on to the next person during feeding. In this way they inject the infection into the person.

Have we mosquitoes in Ireland?
We have mosquitoes in Ireland, the commonest being Culex pipiens. They can be seen hovering over water and marshy places in the late summer and early autumn, especially in the south and east of the country.

Do Irish mosquitoes carry disease?
Irish mosquitoes have not been demonstrated to carry any human infections. The reasons for this are:

1. There are not enough mosquitoes in Ireland to carry infected blood. You need large numbers of mosquitoes to be sure that you can sustain spread of infection.
2. It is our weather, which in winter kills off mosquitoes, that protects us. At the beginning of each summer, the mosquito numbers are very small and will not grow quickly enough over the summer to produce the large numbers needed to sustain infection.
3. In addition, there are not enough people or animals whose blood is infected. You need large numbers of infected animals or birds or people to ensure that mosquitoes, when they feed, are becoming infected and carrying the virus to infect others.

Could new types of mosquito be introduced into Ireland?
As our climate warms (see Met Eireann's Community Climate Change Consortium for Ireland) conditions become progressively more favourable for novel types of arthropods (insect like creatures) to multiply across Europe (see here and here). West Nile virus has encroached around the Danube basin and was introduced for the first time to the US in 1999.  In Italy, there have been outbreaks of chikungunya fever, not previously seen, and thought to be, in part, related to increasing temperature. Dengue and Chikungunya fever could potentially become established in Europe. Asian tiger mosquitoes (Aedes albopictus) are now established in Southern Europe and are better adapted to lower temperatures than the usual vector (Aedes aegypti) of the chikungunya and dengue viruses.

What is being done about this?
The Health Protection Surveillance Centre undertakes surveillance for the types of diseases that are carried by mosquitoes. If such diseases began to appear in Ireland in patients who had not been out of the country, this would be an important clue that the disease could be becoming established in Ireland. However, the only cases of tropical vectorborne disease seen in Ireland have been imported from tropical countries. In addition, there are a number of initiatives to monitor the types of mosquito in the country and to be alert to the possibility of the appearance of new types of mosquito not before seen in Ireland (such as the Asian tiger mosquito). To date, the only types of mosquitoes seen in Ireland in general are local ones that pose no human threat. The European Centre for Disease Prevention and Control considers this issue to be a priority and has included mosquito surveillance and control among its work programs and is monitoring the distribution of Aedes albopictus in Europe.

Updated: 13th July 2010