Mosquitoes gathering in UK gardens

21 May 2014 by Alex Peel

Two species of mosquito, responsible for spreading malaria and West Nile virus elsewhere, are gathering in Britain's gardens, say scientists.

Asian tiger mosquitoNew research, published in PLOS ONE, says the warm, moist environment of water storage containers provide an ideal habitat for the insects throughout spring and summer.

Although neither species currently spread infections to humans in the UK, there is a risk that they could exacerbate an outbreak of a mosquito-borne disease if one were to arrive on British shores.

Its authors say the scenario is likely to be repeated in towns and cities throughout the world, and could be particularly dangerous in areas already affected by infectious mosquitoes.

"There is increasing pressure on water resources around the world, and people are responding to this by storing water on their property," says Dr Amanda Callaghan of the University of Reading, one of the study's authors.

"Water storage containers make an ideal habitat for some species of mosquito and this is going to bring them into ever-closer contact with dense human populations."

The researchers put black plastic dustbins in the gardens of volunteers throughout Reading and surrounding rural villages.

At the moment there are no mosquito-borne human diseases in Britain. But if ever there are, then this is something that we would want to be aware of

- Dr Amanda Callaghan, University of Reading

The bins were filled to about two thirds with tap water. Some ground-up beetles and decomposing leaves were added in for food and they were sampled for mosquitoes every week from April to October in both 2011 and 2012.

The urban bins contained a higher number of mosquito larvae, but fewer species than their rural counterparts.

Callaghan says the scarcity of city habitats and the urban heat island effect, which on average boosted temperatures in Reading by 0·8°C, are probably to blame.

"In urban areas, there are few other habitats available to the mosquitoes, so they tend to gather in higher numbers, and the populations tend to be dominated by just a few species," she says.

The species Culex Pipiens was particularly abundant in urban containers, accounting for 97 per cent of larvae in 2011, and 85 per cent in 2012.

Culex Pipiens was implicated in a US outbreak of West Nile virus (WNV) in 2012, which infected more than 5,000 people and took almost 300 lives. The UK version doesn't bite people, but there is some evidence to suggest that they are spreading the disease among birds.

More worryingly, the scientists also spotted a number of Anophelinae plumbeus larvae. This is a vicious human-biting mosquito, active in daylight hours, and is known to spread both WNV and malaria in other parts of the world.

Thanks to advances in prevention and treatment measures, global rates of malaria are gradually falling. But according to the World Health Organization, there were more than 207 million cases of the disease in 2012, claiming more than 600,000 lives.

A recent study said that warming temperatures were extending the disease's reach into higher altitudes in the tropics. There have been fears that global warming could also cause malaria to spread into higher latitudes, but for now the evidence remains unclear.

The UK experienced outbreaks as recently as the years following World War One, but malaria was effectively wiped out in Britain by the 1950s.

"It's something that we need to keep an eye on," says Callaghan. "At the moment there are no mosquito-borne human diseases in Britain. But if ever there are, then this is something that we would want to be aware of."

'British Container Breeding Mosquitoes: The Impact of Urbanisation and Climate Change on Community Composition and Phenology' - Susannah Townroe and Amanda Callaghan, PLOS ONE, 2014.