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Asian mosquito approaching UK shores

27 April 2012, by Adele Rackley

Climate change is likely to make northern Europe, including the UK, increasingly hospitable for a mosquito which has potential to transmit a range of infectious diseases.

Asian tiger mosquito

A female Aedes albopictus mosquito feeding on a human host.

New research by the University of Liverpool and the Health Protection Agency used observations and models to see how recent and simulated climate change might make Europe more favourable for the invasive Asian tiger mosquito, Aedes albopictus.

The results suggest that warmer, wetter winters in the future are likely to allow the mosquito to settle further north across Europe. Warmer, drier summers could make southern Europe less suitable. This new study is the first to consider the impact of climate change from 1950 onwards, as well as other environmental factors, on the insect's distribution.

This is the first time a set of regional climate models have been used to map the climate suitability for this mosquito in Europe, explains Dr Cyril Caminade, lead author of the report which is published in the Royal Society's journal Interface.

'This study will help to advise on potential future risks of a range of infectious diseases,' he adds.

A. albopictus first arrived in Europe from south-east Asia in the 1970s. While its presence does not mean disease inevitably follows, A. albopictus was responsible for outbreaks of chikungunya fever in Italy in 2007 and a small number of cases of both chikungunya and dengue fever in France in 2010. It can also transmit other diseases, including West Nile virus, yellow fever, St Louis encephalitis and a parasitic worm that affects animals.


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Asian tiger mosquito

Like other species, the Asian tiger mosquito needs water to breed, but it does not need much – a temporary puddle in a tree hole is good enough in its native environment. This means it can easily spread in urban areas, using water that's gathered in man-made containers, discarded tyres being a particular favourite.

Once deposited, its drought-resistant eggs have been known to survive for around eight months until the arrival of the warm, wet conditions they need to hatch.

While this may still not be long enough to survive a long cold spell between laying and hatching, this resilience has allowed the mosquito to spread rapidly over recent decades with the increase in the world-wide transport of goods, in particular used tyres and plants.

If those goods end up somewhere cold that's the end of the story. But as the climate changes, more countries that used to be too cold are gradually becoming warm enough to give the mosquito a foothold.

To find out just how far and how fast this might happen, the researchers ran three

mosquito distribution models and compared the results with recent measurements of

field observations of the distribution of A. albopictus across Europe. They used the models to see how suitability for the mosquito might change up to 2050.

Today A. albopictus flourishes mainly around the Mediterranean and Adriatic coasts, ranging from eastern Spain, north to southern Switzerland, and west to south-eastern Bulgaria.

The results confirmed that over recent decades the climate has become increasingly favourable over southern UK and other northern European countries but has become less suitable further south, especially during recent droughts in southern Spain.

Future projections show that increased winter rainfall over northern Europe, together with generally higher temperatures, might allow the mosquito to survive European winters that until recently have been far too cold.

Hotter, dryer summers are likely to reduce the risk further south in Europe, but the mosquito can survive in water butts and vases, so the researchers caution that it could survive droughts in urban areas.

Nevertheless, the study does not take into account all the variables that might influence the mosquito's northward march. Factors like vegetation and soil conditions, and climate extremes like storms and dry spells, might limit its spread.