Black-footed ferrets (Mustela nigripes) require extensive prairie dog colonies (Cynomys spp.) to provide habitat and prey. Epizootic plague kills both prairie dogs and ferrets and is a major factor limiting recovery of the highly endangered ferret. In addition to epizootics, we hypothesized that enzootic plague, that is, presence of disease-causing Yersinia pestis without any noticeable prairie dog die off, may also affect ferret survival…
Vector control improves survival of three species of prairie dogs (Cynomys) in areas considered enzootic for plague
Biggins, D.E., J.L. Godbey, K.L. Gage, L.G. Carter, and J.A. Montenieri
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 high susceptible individuals within and between their colonies…
A review of plague persistence with special emphasis on fleas
Sylvatic plague is highly prevalent during infrequent epizootics that ravage the landscape of western North America. During these periods, plague dissemination is very efficient. Epizootics end when rodent and flea populations are decimated and vectored transmission declines. A second phase (enzootic plague) ensues when plague is difficult to detect from fleas, hosts or the environment, and presents less of a threat to public health.
Recently, researchers have hypothesized that the bacterium (Yersinia pestis) responsible for plague maintains a continuous state of high virulence and thus only changes in transmission efficiency explain the shift between alternating enzootic and epizootic phases. However, if virulent transmission becomes too inefficient, strong selection might favor an alternate survival strategy. Another plausible non-exclusive hypothesis, best supported from Asian field studies, is that Y. pestis persists (locally) at foci by maintaining a more benign relationship within adapted rodents during the long expanses of time between outbreaks. From this vantage, it can revert to the epizootic (transmission efficient) form. Similarly, in the United States (US), enzootic plague persistence has been proposed to develop sequestered within New World rodent carriers. However, the absence of clear support for rodent carriers in North America has encouraged a broader search for alternative explanations. A telluric plague existence has been proposed. However, the availability of flea life stages and their hosts could critically supplement environmental plague sources, or fleas might directly represent a lowlevel plague reservoir.
Here, we note a potentially pivotal role for fleas. These epizootic plague vectors should be closely studied with newer more exacting methods to determine their potential to serve as participants in or accomplices to a plague persistence reservoir.
Evidence of enzootic plague impacts on black-footed ferret survival in Montana
Rocke, T.E., M.R. Matchett, and D.E. Biggins
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Unpublished paper presented at the 56th Aunual Meeting of the Wildlife Disease Assocation, 12-17 August 2007, Estes Park, Colorado
Transmission of plague by small mammals at Badlands National Park
A prairie dog guarding his burrow
This Hispid pocket mouse is one of the most common species found at the Badlands site last summer
Plague was first detected in the southwest corner of Badlands National Park (BADL), and spread northeastward, reaching the northeast corner in 2011. Multiple prairie dog colonies in BADL and Conata Basin have had population collapses from plague since its arrival in the park. Plague is now common throughout BADL (NPS and USFS, unpublished data), and threatens efforts to preserve and manage the federally endangered black-footed ferret in BADL, which were reintroduced into the park in 1994. Although plague management in BADL and elsewhere has specifically targeted black-footed ferrets and prairie dogs, this disease is transmitted within a larger community of small mammals. This study will serve as an exploratory effort to gain insight into which species of small mammals and their fleas are primary participants in the plague cycle; which are secondary participants, which are bystanders. We will conduct a field experiment based on a randomized complete block design to investigate whether small mammals are chronically affected by enzootic levels of plague and which are potential hosts that may function as short-term reservoirs in the flea-borne transmission of plague in black-tailed prairie dog colonies and surrounding environments in BADL. Our study will encompass a minimum of 6 consecutive months in 2 randomly selected paired dog colonies (study sites) that experienced an epizootic plague outbreak in 2011-2012. Within the two colonies, we will utilize 3 experimental treatment groups on 2.25-ha plots. One plot will receive deltamethrin insecticide applications to control the fleas that are vectors for plague, all animals will be vaccinated with an experimental plague vaccine on a second plot, and the third plot will not be treated. We will capture and mark small mammals on all plots on a monthly basis. Survival during the resulting 5 intervals (based on 6 trapping sessions) will be analyzed for each species via multiple logistic regression and Cormack-Jolly-Seber models in program MARK. By doing the above items, we will be able to: 1. Determine the role of small mammal species in maintenance of enzootic plague. 2. Determine whether small mammal species harbor fleas that carry the bacterium (Y. pestis) and function as short-term reservoir hosts of plague. 3. Assess efficacy and longevity of deltamethrin insecticide for plague vector control on small mammals.