Chikungunya: It's Tyres, Not Global Warming
Climate Change, Environment, Frontier Centre, Worth A Look October 4, 2007
A World Health Organization official has claimed that the current chikungunya outbreak in Northern Italy is the result of climate change: this widely reported absurdity undermines rational debate at a time when world leaders were negotiating climate policy in New York and Washington.
Not far from Graceland, Elvis Presley's home, is a quiet cemetery that dates back to the American Civil War. In the middle is a large mound like a megalithic tomb and underneath are the bones of more than 6,000 people who died in the terrible Yellow Fever epidemic in 1878. More than 20,000 people were infected in Memphis alone, and more than 120,000 throughout the United States, as far north as Ohio.
The virus and the mosquito that transmitted it were first imported from Africa in the 17th century. The mosquito bred in shipboard barrels of water. The virus circulated among the slaves. Many died. The mosquito is now present from South Carolina to Buenos Aires and it remained a scourge in many cities until the advent of DDT–although it still lurks in the rainforests of South America.
Twenty-five years ago, working on another mosquito-borne virus in another Memphis cemetery, I was astonished to find another mosquito from distant shores. The species had never, ever, been found on the American side of the Pacific Ocean, yet two years later I was sent to Houston, Texas, where the biting was so bad that people were even abandoning their barbecues. I found the city littered with discarded tyres that contained rainwater infested with the stripey Aedes albopictus, now dubbed the Asian Tiger mosquito.
Even more surprisingly, I chanced upon several people gathering these tyres for a company that shipped them–with the mosquitoes–to Mexico and Guatemala. Next surprise: the company supplemented the scavenged tyres by importing thousands more from Japan. Finally, I was amazed to find that there was (and still is) a large international commerce in used tyres. Millions are shipped to and from nearly all countries of the world.
The Tiger is now well-settled from New York to Buenos Aires, in twelve European countries and in at least three African countries. It arrived in Italy in the 1990s in tyres from Atlanta, Georgia and is ubiquitous from the Alps to Naples, bringing misery from early spring to late autumn. In our studies in America we confirmed that the Tiger originated in Japan and was splendidly adapted to cold winters. At present its northern limit is Holland, but I suspect it will soon go at least as far north as Denmark. It will doubtless adapt to the southern, warmer parts of Europe by natural selection.
Just as with Yellow Fever, the virus has followed the Tiger. Its exotic name–chikungunya–means "bent double" in Swahili. Endemic in Africa, massive pandemics occasionally sweep through Asia. With unpleasant 'flu-like symptoms, it causes painful arthritis that can last for months, even years, and it is incurable.
Three years ago, something new happened. Chikungunya hit Mauritius, Reunion and the Seychelles, not because of any mysterious climate change but because an infected person had boarded an airplane, landed in those islands and transferred the virus to the local Tigers. It had never occurred there before, so the virus swept through the population like wild-fire.
So the globalization of mosquitoes and mosquito-borne diseases is nothing new and we can expect further surprises in the future. There is also nothing new about mosquito-borne disease in Europe. Until DDT, malaria was endemic and common in many regions as far north as Russia, with 13 million cases a year in the 1920s: at Archangel, on the edge of the Arctic Circle, 10,000 people died in one year. In Italy the highest incidence was in the Po valley, in exactly the same area now hit by chikungunya. Dengue, another so-called tropical virus, infected a million people in Greece in the 1920s.
Despite all this, a WHO official has claimed that warming allowed this cold-weather mosquito to settle in Italy. Whether this is ignorance or deliberate mis-information, it diverts attention from the real cause: the increasing globalization of disease as a result of modern transportation.
World leaders have just been discussing far-reaching policies at the UN's High Level Event and at President Bush's Meeting of Major Economies on Climate Change and Energy Security, where they were bombarded with this kind of distortion.
The public will surely soon get fed up with constant hype about global warming. Sadly, when they realize that the alarmists were crying wolf, it is confidence in science and scientists that will suffer: we have to stick to the science and nothing but the science.
Professor Paul Reiter is Director of the Insects and Infectious Diseases Unit of the Institut Pasteur, Paris. He worked for the US Centers for Disease Control for over 20 years.