A tropical virus moves north

An unusual virus known as chikungunya sickened at least 200 people and contributed to the death of a man in northeastern Italy this year, marking the first time the tropical virus has caused a disease outbreak in a temperate climate, researchers reported this month.

The chikungunya virus, whose name derives from a word in an African language meaning “to become contorted,” arrived in the Emilia Romagna region in June with a visitor from India and was spread through Asian tiger mosquitoes, researchers found.

Tropical tiger mosquitoes are not native to Italy, but they have been found there since the 1990s, presumably because of higher temperatures resulting from global warming.

“This is a clear example of what we have been speculating 10 years about -- that climate change could move certain diseases north,” said Dr. Roberto Bertollini, a senior public health and environment advisor at the World Health Organization.

European travelers have brought malaria, dengue and other tropical diseases home before, but local outbreaks were never larger than two or three people, he said.

The concern in this case, Bertollini said, is that Europe’s winters are becoming “milder and milder and therefore the mosquitoes carrying disease can survive the winter. This might transform the occasional type of event to endemic disease.”

The outbreak also shows the increasing connection among disparate places through family ties, tourism and commerce, said Dr. Antonio Cassone, chief of the infectious-diseases department at the National Health Institute in Rome and a senior author on the paper describing the Italian outbreak. “All developed countries must be prepared and not think this only happens in Africa or southern India,” he said.

Chikungunya has expanded its range in the last few years because the virus has mutated to transmit easily through the Asian tiger mosquito, Aedes albopictus, said Stephen Higgs, a vector biologist at the University of Texas Medical Branch, who was not involved in the Italian study.

The tiger mosquito can survive in cooler climates than the mosquito that historically transmitted the disease, Higgs said.

Chikungunya typically causes fever, intense joint pain, rash and fatigue. The virus was discovered in 1952 in Tanzania.

Chikungunya fever has broken out sporadically in Africa and Southeast Asia for decades, but it was not considered fatal until a 2005 outbreak on several islands in the Indian Ocean. The largest occurred on Reunion, a French island east of Madagascar, where about 266,000 people fell ill. More than 200 died.

A related strain of chikungunya caused a larger outbreak in India. The WHO says 1.4 million Indians fell ill in 2006; it has not reported the number of fatalities.

Hundreds of travelers from Europe brought the infection home and at least 37 cases in travelers were logged in the United States, but no widespread local transmission occurred in those areas.

Italian health officials, who detailed their work in the journal Lancet, suspected about 300 local cases of chikungunya fever and confirmed 204 between July and September.

The area around Castiglione di Cervia and Castiglione di Ravenna proved particularly hospitable to spreading the disease because it typically explodes with “clouds of mosquitoes” in the summer, Cassone said.

The warm climate also provided an extended season for mosquitoes, and the houses in the villages tend to be close together, he said.

All but one patient recovered after a few months, Cassone said. The 83-year-old man who died had underlying health problems, including diabetes, he said.

An outbreak like Italy’s could occur anywhere with the right mosquitoes and people without immunity to chikungunya, said Ann M. Powers, chief of the alphavirus lab at the U.S. Centers for Disease Control and Prevention. “This could include the Southern United States and most of Latin America,” she said.

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jia-rui.chong@latimes.com