global warming can lead to more cases of plague, warns a recent study. Warmer springs and more moist summers may create conditions for Yersina pestis -- the plague bacterium -- to proliferate in parts of Central Asia, it claims.
"A temperature increase of 1c in spring may lead to a 50 per cent increase in the prevalence of the plague bacterium," says Nils C Stenseth, professor of biology at the University of Oslo, Norway, who is the lead author of the paper. Using data from a national surveillance programme to monitor the stock of great gerbils (Rhombomys opmus) -- a rodent -- in Kazakhstan from 1949-1995, and new statistical methods, Stenseth and colleagues found a clear link between the prevalence of Y pestis in gerbils and climate variations. The study appeared in the Proceedings of National Academy of Sciences (Vol 103, No 35, August 29, 2006).
Gerbils in the semi-deserts and steppes of Central Asia carry the microbe, which is passed to other animals and humans through flea bites. The gerbils are not infected by Y pestis, they merely serve as hosts. "In Central Asia, people can also catch the plague through infected camel meat," says Stenseth. "When we wrote an article on this bacterium in Science in 2004, I had a feeling that there was a part of the variation in its prevalence which we couldn't explain adequately. But we could have explained it, had we included climate as a factor," he adds.
The researchers found that spring temperature is the most important environmental factor determining the germ's prevalence level warmer spring conditions lead to an elevated vector-host ratio, which leads to a higher prevalence level in the gerbil host population. Moreover, a warmer climate that favours increased prevalence among gerbils, also favours increased gerbil populations.This means that the threshold density conditions for plague will be reached more often, thus increasing the probability of plague. Overall, the researchers model suggests that warmer springs (and wetter summers) can trigger a cascading effect on the occurrence and level of plague prevalence.
Plague is not the only disease that may be on the rise with climate change. The World Health Organization estimated in its World Health Report 2002 that climate change was responsible in 2000 for about 2.4 per cent of worldwide diarrhoea cases, six per cent malaria cases in some middle-income countries and seven per cent dengue fever cases in some industrialised countries.
As per the Intergovernmental Panel on Climate Change report, overall climate change is projected to increase threats to human health, particularly in lower income populations predominantly within tropical subtropical countries. Climate change can affect human health through multiple pathways, including direct affects (such as increased heat stress, loss of life in floods) and indirect effects that operate through changes in the ranges of disease vectors (example mosquitoes), water-borne pathogens, water quality, air quality, food availability and quality among other things.
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