Bad microbes on the move

Since the 1950s, when scientists first identified the mosquito-borne tropical disease known as chikungunya, its reach has been limited to countries near the Indian Ocean. But in August, chikungunya broke out in Italy. Now World Health Organization officials are calling it the first example of a tropical disease, aided by global warming, causing an epidemic in a developed European country. The outbreak should spur efforts both to curb greenhouse gases and to prepare public health defenses against infections spread by climate change.
By itself, chikungunya is rarely fatal, but it causes a high fever, a rash, and debilitating joint pains that can last for months. In the Italian outbreak, about 300 residents in towns near Ravenna fell ill. Investigators traced the virus to an Italian who had brought it back from a visit to the state of Kerala in India. In Europe, the carrier for the virus is the Asian tiger mosquito, which first came to Italy in the 1990s and has steadily worked its way northward with warming temperatures. Without mosquitoes, there is no human-to-human transmission of the disease.

Until recently, the carrier for the virus was a different mosquito, but one genetic mutation allowed chikungunya to piggyback on tiger mosquitoes, which exist in the United States and as far north as Germany in Europe, and are expanding their range with warmer temperatures. Recently, scientists from the University of Texas reported that their tests had confirmed that the mutated chikungunya virus could thrive in tiger mosquitoes. Chikungunya is related to the more serious mosquito-borne disease dengue fever, which scientists fear will also be moving from the tropics to temperate regions.

The migration of tropical diseases is likely to be less catastrophic than some other effects of global warming – rising sea levels, droughts, dramatic weather events. But the illnesses are serious and require concerted preventive action.

Boston Globe