Sunday, June 29, 2008

Will global warming create new 'hot zones'? Maybe … Will a warmer world also lead to more infectious diseases? Yes and no. Politicians and reporters hate an answer like that, but it really depends on what disease, and where, and sometimes who you ask.

For example, there was a recent surge in the number of cases of tick-borne encephalitis in the former Soviet states of Latvia, Estonia and Lithuania. The first impulse was to blame a warming climate for the increase in ticks, which led to more tick bites and more disease. But the real reason seems to have been the fall of communism.

…In Africa, a warming climate may accelerate the spread of deserts. The dry dusty air may, in turn, lead to the expansion of the Meningitis Belt, which is a vast area of sub-Saharan Africa known for annual epidemics of infectious meningitis. The dusty air carries the bacteria from infected patients to the cracked and dried mucus membranes of other people. More than 50,000 meningitis cases were reported during the 2006-2007 season.

…Recently, African dust blowing north into Europe - and Europe's own warming weather - may have combined to spread a virus-carrying insect (midge) into new parts of the continent. The result has been outbreaks of Blue Tongue Disease among sheep and other ruminant animals. According to European scientists, higher temperatures increased the overall range of the infected midges, the virus development in the midges, the number of virus-infected midges and the ability to transmit the virus to other midge species.

….In January of this year, two infectious disease experts wrote an article suggesting global warming may allow a tropical disease called dengue to become established in the U.S. Dengue is a viral infection that can be carried and transmitted by the Asian Tiger mosquito. The Asia Tiger arrived in the U.S. in 1983 in shipments of used tires. Since then it has spread to 36 states without the help of global warming and without spreading dengue among U.S. citizens. Why?

….Predictions about climate change sparking epidemics around the world are just that: predictions. Many of those predictions have been made with "soft data" and derided by many disease experts as "simplistic thinking" and "gloom and doom speculation."

Still, the planet is warming up and it is difficult to know what all of the consequences of that warming will be for us. There will be surprises. In April, some Dutch infectious disease experts wrote, "it is difficult to foresee which arthropod-borne diseases will appear in the Netherlands due to climate change … but continued vigilance is necessary…" That's good advice for the Netherlands, the U.S. and other evolving "Hot Zones."

This virus causes dengue fever, Wikimedia Commons

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