Nils Chr. Stenseth, Dr.philos.8 University of Oslo
Plague, caused by the bacterium Yersinia pestis, is found on all continents except Antarctica and Australia (Figure 2-10). The plague bacillus causes a rapidly progressing, serious illness that, in its bubonic form, is likely to lead to death by septicemia (40 to 70 percent mortality). Without prompt antibiotic treatment, pneumonic and bubonic plagues are nearly always fatal. For these reasons the plague bacterium Y. pestis is considered one of the most pathogenic bacteria for humans (Gage and Kosoy, 2005). Throughout history, it has played a dramatic role, and it continues to be a threat worldwide (Figure 2-10), particularly in Africa (Figure 2-11).
Plague is currently recognized as a reemerging disease increasing in frequency throughout the world (Duplantier et al., 2005; Schrag and Wiener, 1995; Stenseth et al., 2008; WHO, 2003, 2005) as well as being a potential agent of bioterrorism (Inglesby et al., 2000; Koirala, 2006). Throughout its geographic distribution, its main reservoir is composed of a variety of wild (and in some cases commensal) rodents and the bacterium is transmitted between individual hosts primarily by flea vectors (see "The (Full) Plague Eco-Epidemiological System" below). Understanding what determines the dynamics of plague necessitates an understanding of the dynamic rodent-flea-bacterium system in the wild.
The dynamics of the reservoir species are known to be profoundly influenced by climate variation (see Stenseth, 1999; Stenseth et al., 2002, 2006). Here, I summarize our findings from the analysis of long-term data monitoring in Kazakhstan. I both address what might happen should the climate change as expected (IPCC, 2007) and assess whether there has been a climate component underpinning the past plague pandemics.
Plague has given rise to at least three major pandemics. The first ("the Justinian plague") spread around the Mediterranean Sea in the sixth century A.D., the second ("the Black Death") started in Europe in the fourteenth century and
8Founding Chair of the Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biology, University of Oslo, PO Box 1066 Blindern, N-0316 Oslo, Norway.
FIGURE 2-10 The global distribution of plague. The map shows countries with a known presence of plague in wild reservoir species (black) (after WHO, 2005 ). For the United States, only the mainland below 50°N is shown. SOURCE: Stenseth et al. (2008).
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