Wednesday 18 September 2019

Could invading mosquitoes leave more than just an itch?

The transmission of mosquito-borne viruses, such as dengue and chikungunya, is now a major public health concern in Europe.
The transmission of mosquito-borne viruses, such as dengue and chikungunya, is now a major public health concern in Europe.

Brian Bourke

While enjoying warm summer evenings, we may well find ourselves distracted by the buzzing sound of overzealous mosquitos. It is during this season that mosquitoes are most active and abundant.

Mosquitoes, like many insects, rely on nectar as their main source of food. However, it is the female mosquito's additional desire for blood that has shaped the mosquito's reputation throughout the world.

Blood is necessary for egg development and so females are armed with a long and sharp mouthpart, called a proboscis, which is used to penetrate the skin of a host animal and feed on its blood.

It is difficult to say how many species are native to Ireland but previous studies have put the number at 18. Most are quite selective of the host animals they feed on.

The most common (Culex pipiens) feeds on birds, while others (like Anopheles claviger) favour other animals including humans. Fortunately, Irish mosquitoes pose no greater a problem than being a biting nuisance in localities where they are abundant.

Mosquitos encountered overseas, however, can present a major threat to public health.

The most dangerous are found in Africa, where Anopheles gambiae mosquitoes transmit the parasites that cause human malaria, which kills more than half a million people (mainly children) annually.

Worryingly, many mosquito species of public health importance are now invading new areas worldwide due to global warming. The tiger mosquito (Aedes albopictus, pictured above) is perhaps the most successful of these and has recently established populations through much of Europe. It is now involved in the transmission of the dengue and chikungunya viruses in France, Italy, Croatia and Madeira. There are currently no preventative medicines available for these viruses and so avoiding mosquito bites is the only way to prevent infection.

Although the tiger mosquito has not yet reached Ireland, a suitable climate now exists in the country and it will become more favourable in the future due to global warming. It is likely that a successful invasion would primarily occur, as elsewhere, through the trade in used tyres (standing water in car tyres provides ideal mosquito larval habitat) and, to a lesser degree, exotic plants.

Once established, the species would colonise urban areas and, in the presence of sufficient numbers of infected travellers returning to Ireland, raise concerns of viral outbreaks and local transmission.

The transmission of mosquito-borne viruses, such as dengue and chikungunya, is now a major public health concern in Europe. Effective health service response will see a drive for effective preventative medicines. It will also rely on effective mosquito surveillance and control strategies.

Given the tiger mosquitoes' invasion history, an understanding of the used tyre trade is vital. The trade in Ireland relies primarily on importation from European countries where the tiger mosquito is already present.

It will therefore be essential to establish a system to identify and monitor the origin, transport routes and destination of imported used tyres as well as suitable habitats around Irish ports of entry.

It will also be necessary to design effective tiger mosquito control measures in affected areas. Such strategies will function as a safeguard against the establishment of populations and viral outbreaks, as is occurring in other parts of Europe.

Dr Brian Bourke, a graduate of Waterford IT, is currently based in the University of Sao Paulo Brazil, where he is researching mosquitoes.

Irish Independent

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