Humans adapting to climate change help mosquitoes spread disease

Yahoo News 27 Jan 09;

PARIS (AFP) – Humans adjusting to water shortages caused by global warming could help a dengue fever-carrying mosquito expand into new parts of Australia, according to a study released Tuesday.

People hoarding water in ever-more parched swathes of the country already affected by climate change inadvertently create perfect breeding grounds for the potentially deadly insects, the study found.

Once confined to Africa, Aedes aegypti also carries viruses that cause yellow fever and the painful joint inflammation called chikungunya, and is today found throughout the tropics.

Its closely-related cousin, Aedes albopictus, spreads the same diseases, and has recently been found in southern Europe, finding new habitat in warmer climes.

A. aegypti first showed up in Australia in the 19th century. By the 1960s, eradication efforts reduced its range to the continent's northeastern state of Queensland.

Concerned about the potential impact of climate change on the species, a team of researchers led by Michael Kearney of the University of Melbourne designed a computer model to simulate its potential spread.

They looked at two habitats -- a 3,600-litre (9,500 gallons) water tank, and a 20-litre (five-gallon) bucket -- in different temperature conditions, one with near-total shade and another with very little.

Slight increases in average temperature would not by themselves expand the range in which the mosquitoes could easily survive, they found.

But when changes in human behaviour spurred by global warming were taken into account, the danger was suddenly multiplied many times over.

"In many Australian cities and towns, a major impact of climate change is reduced rainfall, resulting in a dramatic increase in domestic rainwater storage and other forms of water hoarding," explained Kearney in a press statement.

The still or stagnant water in such open-air containers provide an ideal spot for mosquitoes to lay eggs, the most vulnerable stage of their life cycle.

If conditions are too cold or too dry, the eggs will not develop into larvae.

"This indirect effect of climate change via human adaptation could dramatically re-expand the mosquito's current range," said Kearney.

The study, published in Functional Ecology, a journal of the British Ecological Society (BES), also factored in the capacity of the mosquitoes to evolve, a variable not previously included in such models.

Based on earlier research on fruit flies and other insects, the scientists conclude that A. aegypti would adapt through the process of natural selection, accelerating its spread into new areas where it cannot survive today.

"Evolution happens all the time in nature and can be very rapid, taking only a few generations to influence the fitness of populations," said co-author Ary Hoffmann, a professor of genetics at the University of Melbourne.

"Our results show that evolution can make a very large difference when predicting changes in species ranges under climate change."

The study recommended water hygiene education campaigns be set up in the regions most at risk.

The UN's Intergovernmental Panel on Climate Change, gathering top scientists, warned in a landmark report in 2007 that climate change could spur the spread of mosquito-borne diseases, especially malaria and dengue.