No evidence for enzootic plague within black‐tailed prairie dog (Cynomys ludovicianus) populations

Abstract

Yersinia pestis, causative agent of plague, occurs throughout the western United States in rodent populations and periodically causes epizootics in susceptible species, including black‐tailed prairie dogs (Cynomys ludovicianus). How Y. pestis persists long‐term in the environment between these epizootics is poorly understood but multiple mechanisms have been proposed, including, among others, a separate enzootic transmission cycle that maintains Y. pestis without involvement of epizootic hosts and persistence of Y. pestis within epizootic host populations without causing high mortality within those populations. We live‐trapped and collected fleas from black‐tailed prairie dogs and other mammal species from sites with and without black‐tailed prairie dogs in 2004 and 2005 and tested all fleas for presence of Y. pestis. Y. pestis was not detected in 2126 fleas collected in 2004 but was detected in 294 fleas collected from multiple sites in 2005, before and during a widespread epizootic that drastically reduced black‐tailed prairie dog populations in the affected colonies. Temporal and spatial patterns of Y. pestis occurrence in fleas and genotyping of Y. pestis present in some infected fleas suggest Y. pestis was introduced multiple times from sources outside the study area and once introduced, was dispersed between several sites. We conclude Y. pestis likely was not present in these black‐tailed prairie dog colonies prior to epizootic activity in these colonies. Although we did not identify likely enzootic hosts, we found evidence that deer mice (Peromyscus maniculatus) may serve as bridging hosts for Y. pestis between unknown enzootic hosts and black‐tailed prairie dogs.

Plague risk in the western United States over seven decades of environmental change

“…Yersinia pestis can infect hundreds of rodent species (Mahmoudi et al, 2020), and some species once considered key to maintain endemic plague are now known to be spillover hosts from unknown reservoirs (Colman et al, 2021;Danforth et al, 2018). Rodent habitat use adds another dimension to the problem: synanthropic and "wild" reservoirs may have very different richness hotspots (Sun et al, 2019), which may explain some differences between the geography of maintenance and spillover (as, alternately, could the geography of domestic cat and dog ownership (Campbell et al, 2019)).…”

“…Though the plague “niche” may largely transcend any individual host species (Maher et al, 2010 ), in future, our understanding of these mechanisms might be further refined by exploring more granular variation among the species involved. Identifying “true reservoirs” is a nontrivial task in disease ecology (Becker et al, 2020 ; Viana et al, 2014 ); Yersinia pestis can infect hundreds of rodent species (Mahmoudi et al, 2020 ), and some species once considered key to maintain endemic plague are now known to be spillover hosts from unknown reservoirs (Colman et al, 2021 ; Danforth et al, 2018 ). Rodent habitat use adds another dimension to the problem: synanthropic and “wild” reservoirs may have very different richness hotspots (Sun et al, 2019 ), which may explain some differences between the geography of maintenance and spillover (as, alternately, could the geography of domestic cat and dog ownership (Campbell et al, 2019 )).…”

A big data–model integration approach for predicting epizootics and population recovery in a keystone species

“…We inferred plague epizootics and population recovery from annual changes in colony data. To distinguish between plague‐induced die‐offs and mortality due to predation, drought, or other natural processes, we defined plague epizootics as catastrophic declines of greater than 50% loss in colony area between consecutive years (Colman et al, 2021; Johnson et al, 2011). Thus, within colonies that suffered greater than 50% loss in area between years, we classified raster cells that transitioned from occupied by BTPDs to unoccupied as extinction events due to plague.…”

Deltamethrin reduces survival of non-target small mammals

“…Epizootics are characterised by catastrophic population collapses (≥90% mortality over a large area within a short time span), with enzootic plague encompassing the remaining broad spectrum of mortality rates, time scales, and temporal scales (Biggins et al 2021a). Part of the ongoing discussion over enzootic plague (Colman et al 2021) might be resolved with more articulate definitions. Because survival of several target mammals has increased when enzootic and epizootic plague is reduced via application of deltamethrin in the western US (Biggins et al 2010(Biggins et al , 2021a(Biggins et al , 2021bMatchett et al 2010;Tripp et al 2017;Goldberg et al 2021a), we hypothesised that similar vector-control measures would increase the survival of non-target small mammals.…”