07 May 2006

Climate Change May Spread Diseases to New Areas

The Washington Post reported on Friday that a number of experts have found increased links between the spread of infectious diseases and climate change.

"Global warming -- with an accompanying rise in floods and droughts -- is fueling the spread of epidemics in areas unprepared for the diseases, say many health experts worldwide," according to the Post. "Mosquitoes, ticks, mice and other carriers are surviving warmer winters and expanding their range, bringing health threats with them."

Doug Struck, writing in the Post, cites cases of West Nile virus turning up in Canada, and of malaria reaching mountain populations in Africa and Latin America, as well as northern extensions of range for dengue fever and Lyme disease. "West Nile virus," writes Struck, "never seen on this continent until seven years ago, has infected more than 21,000 people in the United States and Canada and killed more than 800."

According to a 2002 report of the World Health Organisation (WHO), "climate change was estimated to be responsible in 2000 for approximately 2.4% of worldwide diarrhoea, and 6% of malaria in some middle-income countries." But that report also noted that "small changes, against a noisy background of ongoing changes in other causal factors, are hard to identify."

Nevertheless, recent findings by the WHO confirm that "the first detectable changes in human health may well be alterations in the geographic range (latitude and altitude) and seasonality of certain infectious diseases -- including vector-borne infections such as malaria and dengue fever, and food-borne infections (e.g. salmonellosis) which peak in the warmer months."

The WHO recognizes there may be additional "public health consequences of the disturbance of natural and managed food-producing ecosystems, rising sea-levels and population displacement for reasons of physical hazard, land loss, economic disruption and civil strife," although these "may not become evident for up to several decades."

As early as 1992, experts have expressed concern about the possible affects of climate shifts on infectious diseases.

According to Robert E. Shope of the Yale Arbovirus Research Unit, "The infections that will spread with climate change have some commonalities. They are focal, and their distribution is limited by the ecology of their reservoir, be it arthropod, snail, or water. They usually have a two- or three-host life cycle, meaning that in addition to infecting people, they infect a vector and frequently also a wild vertebrate animal host."

In such cases, the vector, host or both can be the reservoir, Shope wrote in a chapter of Global Climate Change: Implications, Challenges and Mitigation Measures, published by The Pennsylvania Academy of Science. He noted fourteen years ago that the agents "will probably survive by moving in a polar direction, north in the Northern Hemisphere, in order to find a temperature range that is ecologically permissive."

Still, not everyone agrees there is a relationship between climate change and mosquito-borne diseases. The "Green Consumer Guide" reported that Professor Paul Reiter of the Pasteur Institute and Harvard University, points out "the complex variables regarding diseases such as malaria, dengue and yellow fever."

"'It is naive to attempt to predict the effects of 'global warming' on malaria on the mere basis of temperature,'" Reiter comments. "'The natural history of all the mosquito borne diseases is extraordinarily complex, and the interplay of climate, weather, ecology and the biology of the vector and its hosts defies simple analysis.

A 1998 conference held by the Center for Disease Control and Prevention examined both sides of the argument. Ultimately, according to an article in the journal Emerging Infectious Diseases, there is a need for cooperation in researching the question. They called for a focus "on public health intervention measures that are properly implemented and [that] can mitigate the effect of global climate change on infectious disease incidence and geographic spread."

The Post article adds new voices to the fray, including the Canadian families of victims of West Nile and Dr. Paul Epstein, who worked in Africa and is on the faculty at Harvard Medical School. He suggests that scientists are not "worried enough about the problem." Dr. Epstein's report, which was released last November, suggests that temperature changes are an important factor and that it is a mistake to underestimate the links.

Quoted in the Post, Epstein says, "Things we projected to occur in 2080 are happening in 2006. What we didn't get is how fast and how big it is, and the degree to which the biological systems would respond."

The jury may be out on whether there are direct links between climate change and the spread of disease or how lasting these will be. Meanwhile, however, we may all be wise to increase our protection against mosquitoes as we head into the summer months.

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Anonymous said...

Hey Scott -

It is a complex business predicting climate change and its real impact on the environment. Personally, I am still debating and reading up on the data. In the mean time, I am working with CarbonFund.org to help neutralize the carbon that I do emit into the atmosphere. I figure, every little helps.

The Green Skeptic said...

Thanks, Eric. Yes, there are many carbon counters and offset ideas out there that are worth pursuing. I agree that every little bit helps. But I also hope that the big tipping point is upon us that will make the big things that need to happen -- massive investments in alternatives, energy conservation, etc. -- come tumbling down upon us faster than ice melting off the Arctic shelf...