Long-term persistence of virulent Yersinia pestis in soil

Abstract

Plague is characterized by geographical foci from which it re-emerges after decades of silence, a fact currently explained by enzootic and epizootic cycles between plague-susceptible and plagueresistant rodents. To assess the potential role of soil in plague epidemiology, we experimentally investigated whether Yersinia pestis could persist alive and virulent in soil. Sterilized soil inoculated with virulent Y. pestis biotype Orientalis was regularly sampled for 40 weeks in duplicate. Each sample was observed by acridine orange staining and immunofluorescence using an anti-Y. pestis polyclonal antibody, and DNA was extracted for PCR amplification and sequencing of the Y. pestis ureD, caf1 and pla genes. All samples were inoculated onto selective agar, and samples from soil that had been incubated for 10, 60, 165, 210 and 280 days were also inoculated into each of two BALB/c female mice. The mouse experiment was performed in triplicate. Non-inoculated, sterilized soil samples were used as negative controls. Microorganisms fluorescing orange and detected by immunofluorescence were identified as Y. pestis in all samples. They were recovered in pure agar cultures for up to 30 weeks but thereafter were contaminated with Pseudomonas spp. Soil that had been inoculated with Y. pestis proved to be fully virulent in mice, which died with Y. pestis septicaemia and multiple organ involvement. Negative control mice showed no signs of disease. These data indicate that Y. pestis biotype Orientalis can remain viable and fully virulent after 40 weeks in soil. This study is a first step on which to base further investigations of a potential telluric reservoir for Y. pestis, which could represent an alternative mechanism for the maintenance of plague foci.

Range-wide Determinants of Plague Distribution in North America

“…[9][10][11][12][13][14][15] Plague bacteria also may survive outside living hosts on carcasses or in the soil, but only limited evidence exists to suggest that such mechanisms are important for long-term survival in nature. 9,16,17 Plague likely evolved in Asia, 9,18,19 and has since spread broadly by various means, 18 including the transport of infected hosts and fleas along overland trade routes or aboard rat-infested ships during the three historically documented pandemics. The third of these pandemics and that most relevant to this study introduced plague to North American ports in the late nineteenth century; where it afterwards "escaped" into native rodent populations, eventually spreading east through the Rocky Mountains to the western edge of the Great Plains.…”

Predicting small mammal and flea abundance using landform and soil properties in a plague endemic area in Lushoto District, Tanzania

“…Some literature indicates that plague persistence in natural foci has a root cause in soils (Breneva et al, 2006;Eisen et al, 2008). This indication has been supported by the evidence that Y. pestis can survive in natural soil conditions from 24 days to 40 weeks (Ayyadurai et al, 2008). Additionally, there is a long standing hypothesis linking enzootic and epizootic plague cycles with soil micro-organisms like amoeba and soil organic matter (Anisimov, 2002) which come in contact with burrowing rodents.…”

Rodent and Flea Abundance Fail to Predict a Plague Epizootic in Black-Tailed Prairie Dogs

“…Low overall rates of plague exposure during and preceding epizootics among rodent (Stapp et al 2008) and nonrodent (Brinkerhoff et al 2009) mammalian species point to a nonmammalian source of Y. pestis infection to prairie dogs. Recent demonstrations of Y. pestis persistence in soils (Ayyadurai et al 2008, Eisen et al 2008b indicate that a mammalian reservoir may not be required for epizootic initiation, although it has not been demonstrated that soils contaminated with Y. pestis can initiate epizootic events in prairie dogs.…”