Climate changes increase risk of plague

“A temperature increase of one degree Celsius in spring may lead to a 50 percent increase in the prevalence of the plague bacterium,” he stated to Uniforum, the University of Oslo’s own news bulletin.

Climate changes cannot lead to any new Black Death, but it is quite clear that a small increase in temperature may create more cases of bubonic plague than we have today,” said Professor Stenseth, who heads the international top-notch Centre for Ecological and Evolutionary Synthesis (CEES) at the University of Oslo. Using field data from a national surveillance programme which monitored the stock of gerbils in Kazakhstan from 1949-1995, and using new statistical techniques, Stenseth and his team found a clear connection between the prevalence of the bacterium Yersina pestis in gerbils and climate variations.

“Samples from the annual rings of trees in Kazakhstan revealed that when the Black Death broke out there in the 14th century, the springs were warm and the summers were wet. Conditions were the same at the onset of the plague of the 1800’s in the same region,” he explained. Stenseth obtained these figures from the Swiss researcher Jan Esper, one of the co-authors of the article. He is pleased that the researchers were given access to data from the health authorities’ surveillance programme in Kazakhstan.

After Kazakhstan initiated this surveillance programme in 1949, the cases of plague here decreased from over 100 cases a year to a few cases a year. In the past Stenseth and his colleagues have been close to finding out why the prevalence of the bacterium varies from year to year.

“In an article we wrote on this bacterium in Science in 2004, I had a feeling that there was a part of the variation which we couldn’t explain adequately. But we could have explained it, had we included climate as a cause of variation in the prevalence of this bacteria,” Stenseth said to Uniforum.

Hence, one of the candidates of co-author Noelle I. Samia from the University of Iowa was given the task of running all the data of the surveillance programme through an advanced statistical analysis.

“The results of this work enabled us to write this article and conclude that climate changes have affected the prevalence of the bacterium which causes plague,” Stenseth said. He was not sure what the conclusions would be after the investigations were finished.

“In the US, researchers have studied infectious diseases that are passed on among humans, indicating a similar connection between the prevalence of bacteria and climate changes, but this is the first time anyone has found a clear connection between the prevalence of the plague bacteria carried by gerbils and climate change,” he stated.

“It was precisely in this area that the genetic and climatic conditions which brought on the Black Death and the Asian flu, emerged”, he said.

It is the prevalence of the bacterium Yersina pestis which has been the subject of study for Nils Chr. Stenseth and his colleagues from the Universities of Norway, Kazakhstan, Switzerland, Denmark, Belgium, UK and the US. This bacterium lives in gerbils in the semideserts and steppes of Central Asia, and it is passed from gerbils to other animals and humans through flea bites. The gerbils themselves are not infected by the plague bacterium, they merely serve as hosts.

“In central Asia people can also catch the plague through infected camel meat, as camels often lay in places with gerbil burrows,” Stenseth explained.