"We were quite surprised," said Stefania Salmaso, director of Italy's Center for Epidemiology at the National Health Institute. "Nobody was expecting that such an unusual event was going to happen."
While the mostly nonfatal outbreak was largely the result of increasingly global trade and travel ties, some experts believe it is a sign of how global warming is creating new breeding grounds for diseases long confined to subtropical climates.
Officials at the European Centre for Disease Prevention and Control (ECDC) said the particularly mild winter in Italy allowed mosquitoes to start breeding earlier than usual, giving the insect population a boost.
"This outbreak is most important as a warning signal," said Diarmid Campbell-Lendrum, a climate change expert at the World Health Organization (WHO). "Climate change affects the breeding of every mosquito on earth."
"With more movement of people and a changing climate, there will be shifting patterns of disease," Campbell-Lendrum said. "We need to be prepared for more surprises like this in the future."
Chikungunya to Dengue?
Italian officials first grew suspicious in July, when dozens of people in the country's northeast complained of fevers, joint pain, headaches, and rashes. Local doctors thought they had been bitten by sand flies, but lab tests confirmed chikungunya fever.
Officials believe the virus arrived when an Indian tourist brought the virus to the Italian province of Ravenna. The Asian tiger mosquito, which can spread the disease, had reached Italy nearly two decades earlier.
Experts are also nervous because the tiger mosquito might be capable of spreading more dangerous diseases like dengue fever and yellow fever (see a photo of the tiger mosquito).