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Tiger mosquitoes bring tropical disease to Europe

September 6, 2007 By Emiliano Feresin This article courtesy of Nature News.

Invasive species could cause Chikungunya to become endemic.

The arrival of a tropical mosquito-borne disease in Italy has experts worried that such illnesses may become endemic in Europe.

Local authorities in Bologna, Italy, this week ordered parts of the city to implement mosquito-control measures prevent the spread of the flu-like viral disease, Chikungunya. The disease is carried by the tiger mosquito (Aedes albopictus) and is more usually found in African and Asian countries.

Chikungunya hit two villages, some 80 kilometres east of Bologna, this summer. Nearly 200 people are thought to have been infected and one has died of complications. The number of new cases is now decreasing, but suspected cases have started to appear in the city.

The tiger mosquito is a relative newcomer in Europe, which has spread to Italy, France, Belgium, the Netherlands and the Balkan region over the past decades. It lives in urban areas and feeds mostly on human blood. The bites are painful, but, until now, have usually been harmless.

Experts fear that the recent spate of disease may allow Chikungunya to become endemic in this area — or, even worse, the more dangerous dengue virus that the tiger mosquito can also carry.

European first

The Italian outbreak started in early July, but was at first mistaken for simple flu. Authorities now think that a tourist returning from India imported the Chikungunya virus to Italy, where it spread among the dense population of tiger mosquitoes.

Chikungunya means 'that which bends up' in Makonde, a local language of Tanzania and Mozambique, describing the joint pain that accompanies the illness's high fever. In 2005, the disease affected hundreds of thousands of people in the Indian Ocean islands and later spread throughout India, where it had not been seen for several decades (see ''Disease outbreaks highlight India's poor mosquito control'').

"Isolated cases of imported Chikungunya disease have occurred in Europe," says Hervé Zeller, virologist at the Institute Pasteur of Lyon, France. "But this is the first time that transmission from local mosquitoes has occurred here".

Uncertain spread

Scientists say they don't yet know enough to say for sure whether the disease will spread from northern Italy to other European countries infested with the tiger mosquitoes. "We don't even know why West Nile disease became endemic in North America but not in Europe, even though the virus and the vector are present on both continents," says Evelyn Depoortere, an epidemiologist at the European Centre for Disease Prevention and Control in Stockholm. "We need a lot more research on the environmental factors that affect how insect-borne viruses spread," Says Zeller.

They point out that although the current outbreak is damping down, thanks to efficient control measures and cooling temperatures, it could re-occur next year. Recent research in tropical areas has shown that infected female tiger mosquitoes transmit the Chikungunya virus to their eggs. Mosquito eggs easily survive mild Mediterranean winters.

Officials at the World Health Organization (WHO) in Geneva, Switzerland, doubt that it will be possible to eradicate the mosquitoes. "They are very persistent," says Michael Nathan, an entomologist at WHO. Italy and France have already spent a lot of money trying — to little effect, he says. "But since we don't have a vaccine or drugs against the Chikungunya virus, the only option we have is efficient mosquito control."

In Bologna, doctors have been told to take special care in diagnosing flu-like illnesses. "We are fighting to keep Chikungunya out of our territory," says a local government official.

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