Vector Control Improves Survival of Three Species of Prairie Dogs (Cynomys) in Areas Considered Enzootic for Plague

Abstract

Plague causes periodic epizootics that decimate populations of prairie dogs (PDs) (Cynomys), but the means by which the causative bacterium (Yersinia pestis) persists between epizootics are poorly understood. Plague epizootics in PDs might arise as the result of introductions of Y. pestis from sources outside PD colonies. However, it remains possible that plague persists in PDs during interepizootic periods and is transmitted at low rates among highly susceptible individuals within and between their colonies. If this is true, application of vector control to reduce flea numbers might reduce mortality among PDs. To test whether vector control enhances PD survival in the absence of obvious plague epizootics, we reduced the numbers of fleas (vectors for Y. pestis) 96-98% (1 month posttreatment) on 15 areas involving three species of PDs (Cynomys leucurus, Cynomys parvidens in Utah, and Cynomys ludovicianus in Montana) during 2000-2004 using deltamethrin dust delivered into burrows as a pulicide. Even during years without epizootic plague, PD survival rates at dusted sites were 31-45% higher for adults and 2-34% higher for juveniles compared to survival rates at nondusted sites. Y. pestis was cultured from 49 of the 851 flea pools tested (6882 total fleas) and antibodies against Y. pestis were identified in serum samples from 40 of 2631 PDs. Although other explanations are possible, including transmission of other potentially fatal pathogens by fleas, ticks, or other ectoparasites, our results suggest that plague might be maintained indefinitely in PD populations in the absence of free epizootics and widespread mortality among these animals. If PDs and their fleas support enzootic cycles of plague transmission, there would be important implications for the conservation of these animals and other species.

Emergence, spread, persistence and fade-out of sylvatic plague in Kazakhstan

“…The mechanism(s) for re-emergence of plague is unknown, although many hypotheses exist [20], including survival of bacteria in the soil [21] or fleas [22], phases with less virulent bacteria in the hosts [22,23] and long-distance transportation by birds or carnivores from areas with ongoing epizootics [24,25]. Recent studies of the plague system in Colorado, USA, indicate a low, but non-zero prevalence of plague in inter-epizootic periods [26,27], supporting the hypothesis that plague circulates among favourable microfoci [28].…”

Assessment of a Recombinant F1-v Fusion Protein Vaccine Intended to Protect Canada Lynx (Lynx Canadensis) From Plague

“…Plague, caused by Yersinia pestis, was introduced into North America in the early 1900s, and its impacts on some native wildlife species since that time have been substantial (Cully, 1993;Wuerthner, 1997;Biggins and Kosoy, 2001;Gasper and Watson, 2001;Biggins et al, 2010). Epizootics in prairie ecosystems have been well documented and probably contributed to the marked declines observed in both prairie dogs (Cynomys spp.)…”

“…Epizootics in prairie ecosystems have been well documented and probably contributed to the marked declines observed in both prairie dogs (Cynomys spp.) and black-footed ferrets (Mustela nigripes) over the last century (Cully, 1993;Biggins et al, 2010). Although less extensively studied, it seems likely that plague has impacted other wildlife species as well (Biggins and Kosoy, 2001;Gasper and Watson, 2001;Biggins et al, 2010).…”

Ectoparasites in Black-footed Ferrets (Mustela nigripes) from the Largest Reintroduced Population of the Conata Basin, South Dakota, USA

“…However, we focus on data only from black-footed ferrets that occupied areas without insecticide application (n5227; Table 1) because these actions are known to reduce flea populations (Biggins et al 2010). Nevertheless, three ectoparasites were found on rare occasions at dusted locations only: Stenoponia americana, Amaradix euphorbia, and Aetheca wagneri.…”

“…Our finding suggests that using the Conata Basin population for translocations is unlikely to introduce novel ectoparasites into new areas but could increase the distribution of plague due to the persistence of the vector, if not actively managed. As such, ectoparasite removal or deltamethrin application in prairie dog burrows to lessen parasite loads of vectors such as O. hirsuta may be necessary to promote the full recovery of black-footed ferrets (Biggins et al 2010).…”