Dynamics of the plague–wildlife–human system in Central Asia are controlled by two epidemiological thresholds
- aDepartment of Statistics, Northwestern University, Evanston, IL 60208;
- bCentre for Ecological and Evolutionary Synthesis (CEES), University of Oslo, N-0316 Oslo, Norway;
- cTheoretical Epidemiology, Faculty of Veterinary Medicine, Utrecht University, 3584 CL, Utrecht, The Netherlands;
- dKazakh Scientific Centre for Quarantine and Zoonotic Diseases, Almaty 050054, Republic of Kazakhstan;
- eInstitute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB, United Kingdom; and
- fDepartment of Statistics and Actuarial Science, University of Iowa, Iowa City, IA 52242
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Edited* by Rita R. Colwell, University of Maryland, College Park, MD, and approved July 6, 2011 (received for review October 24, 2010)

Abstract
Plague (caused by the bacterium Yersinia pestis) is a zoonotic reemerging infectious disease with reservoirs in rodent populations worldwide. Using one-half of a century of unique data (1949–1995) from Kazakhstan on plague dynamics, including data on the main rodent host reservoir (great gerbil), main vector (flea), human cases, and external (climate) conditions, we analyze the full ecoepidemiological (bubonic) plague system. We show that two epidemiological threshold quantities play key roles: one threshold relating to the dynamics in the host reservoir, and the second threshold relating to the spillover of the plague bacteria into the human population.
- climate forcing
- generalized threshold model
- wildlife reservoir of Yersinia pestis
- spillover to the human population
Footnotes
- 1To whom correspondence may be addressed. E-mail: n-samia{at}northwestern.edu or n.c.stenseth{at}bio.uio.no.
Author contributions: N.I.S. and N.C.S. designed research; N.I.S., H.H., M.B., and N.C.S. performed research; N.I.S. analyzed data; N.I.S., K.L.K., H.H., V.A., M.B., K.-S.C., and N.C.S. wrote the paper; and N.I.S. and H.H. derived the two threshold quantities.
The authors declare no conflict of interest.
↵*This Direct Submission article had a prearranged editor.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1015946108/-/DCSupplemental.
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