Singapore: A virus from Africa, a mosquito from Asia and a tourist from India met this summer on the Italian seaside, showing how globalization hastens the spread of disease from one continent to another.
More than 250 people in Italy’s province of Ravenna have been infected with chikungunya—a virus that causes fever, rashes and joint pains—since it arrived with a tourist three months ago. The outbreak was caused by the same viral strain that sickened about 235,000 people on Reunion island in the Indian Ocean last year, says an Italian virologist investigating the episode.
Now Italy is threatened by a contagious illness that may also spread elsewhere in Europe and North America the same way it got to Ravenna—through an infected traveller. There were 2.1 billion airplane passengers last year, driving the spread of new diseases that are emerging at “an unprecedented rate”, the World Health Organization (WHO) had said last month.
“We are in a world where things are whizzing around so fast, we inevitably are
going to see more and more of this kind of thing happening,” said Paul Reiter, director of the insects and infectious diseases unit at the Pasteur Institute in Paris.
Fatal carrier: An Aedes albopictus, or Asian Tiger mosquito. Trade in used tyres, which harbour insect larvae in trapped rainwater, has allowed the Asian tiger mosquito to colonize areas such as ?the French? Riviera, Florida and the Caribbean over the past 30 years.
At least 39 new pathogens have been identified during the past 40 years, WHO had said in its 2007 World Health Report last month. They include the HIV virus that causes AIDS, Ebola haemorrhagic fever, Marburg fever and SARS—a respiratory infection.
Bugs that have infected people for “thousands of years” in local areas are now causing disease on an international scale, says Duane Gubler, director of the University of Hawaii’s Asia-Pacific Institute of Tropical Medicine and Infectious Diseases. Epidemics resulting from “globalization are going to be progressively more expensive,” he adds.
First described by doctors in Tanzania in 1953, chikungunya regularly causes epidemics in 23 countries in Africa, Asia and the Pacific. Until last month, Europe had only recorded cases in travellers who returned with the infection and didn’t pass it on.
Scientists say chikungunya, for which there is no vaccine or specific treatment, could become established in parts of Europe and the Americas as a result of travel and commerce. Trade in used tyres, which harbour insect larvae in trapped rainwater, has allowed the Asian tiger mosquito, which can transmit the virus, to colonize areas such as the French Riviera, Florida and the Caribbean over the past 30 years.
Tyres from a single source in Atlanta may have introduced the insect, known scientifically as Aedes albopictus, to the north-eastern Italian city of Padua in 1991, according to the US Centers for Disease Control and Prevention.
The species is now in nine of Italy’s 21 regions, proving a receptive host for chikungunya, dengue—a more serious disease that can cause lethal haemorrhaging—and at least five other viruses.
Italy’s chikungunya outbreak probably started with a man who arrived on 21 June and developed symptoms two days later when he was in the north-eastern town of Castiglione di Cervia, the European Centre for Disease Prevention and Control in Stockholm said in a report this month.
His arrival coincided with “a very hot summer” that favoured mosquito-breeding, said Isabelle Schuffenecker, a biologist with France’s national reference centre for arboviruses and viral haemorrhagic fevers in Lyon.
Genetic sequencing traced the virus to an outbreak in India that had caused more than 1.25 million suspected cases last year, and before that to an epidemic in a group of islands in the western Indian Ocean that began in late 2004, said Loredana Nicoletti, a virologist who helped diagnose more than 100 chikungunya cases for Italy’s health ministry.
Tests results are pending on samples from the most recent suspected cases in Italy, and the epidemic won’t be declared for at least two more weeks, Nicoletti said Monday.
Efforts to control mosquito-breeding, aided by cooler winter weather, and closer surveillance of chikungunya cases may break the chain of transmission over the next few months, Schuffenecker said.
“At least this year, we will be able to contain transmission, but what of next summer?” Schuffenecker said. “That’s the question.”