Oral Sylvatic Plague Vaccine Does Not Adequately Protect Prairie Dogs (Cynomys spp.) for Endangered Black-Footed Ferret (Mustela nigripes) Conservation

Abstract

The plague bacterium Yersinia pestis is lethal to endangered black-footed ferrets ( Mustela nigripes , BFF) and the prairie dogs ( Cynomys spp., PD) on which they depend for habitat and prey. We assessed the effectiveness of an oral sylvatic plague vaccine delivered in baits to black-tailed PD ( Cynomys ludovicianus , BTPD) from 2013 to 2017 on the Charles M. Russell National Wildlife Refuge (CMR) in northcentral Montana. We permanently marked BTPD on four paired vaccine ( N = 1,349 individuals) and placebo plots ( N = 926; 7,027 total captures). We analyzed capture–recapture data under a Cormack–Jolly–Seber model to estimate annual apparent survival. Overall, survival averaged 0.05 lower on vaccine plots than on paired placebo plots. Immediately before noticeable die-offs and detecting plague on pairs CMR1 and CMR2, 89% of BTPD sampled on vaccine plots had consumed at least one bait and the immune systems of 40% were likely boosted by consuming baits over multiple years. Survival to the following year was 0.16 and 0.05 on the vaccine plots and 0.19 and 0.06 on the placebo plots for pairs CMR1 and CMR2, respectively. These rates were markedly lower than 0.63, the overall average estimate on those same plots during the previous 3 years. PD populations subjected to such large die-offs would not be expected to sustain a BFF population. An overriding limitation to achieving sufficient protection rests with vaccine delivery constraints. Late summer/fall bait distribution results in the highest bait uptake rates. However, the PD birth pulse each spring can double the size of populations in most years, greatly reducing the proportion of vaccinates in populations and diminishing potential herd immunity benefits. In addition to nonvaccinated juveniles and PD that do not consume bait, incomplete vaccine protection and time required for immunity to develop leaves a large majority of PD populations vulnerable to plague for 6–7 months or more each year.

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

“…As stated earlier in the Methods section, we acknowledge that population fluctuations in BTPDs did not necessarily equate to disease dynamics, as we did not have concomitant disease data during each colony die-off. Although we were confident that large-scale extinctions were due to plague in our study, this confidence may be restricted to our study area (i.e., central Great Plains), where much work has confirmed the pattern of spread and effects of plague on BTPD colonies (e.g., Cully et al, 2010;Johnson et al, 2011;Matchett et al, 2021). Thus, researchers should exercise caution when applying our model to grasslands outside of our study area, such as more southern grasslands where drought can result in colony contractions (e.g., Ceballos et al, 2010;Facka et al, 2010).…”

“…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. We were confident that these large‐scale extinction events were primarily attributable to plague because plague is the only disease known to cause extensive die‐offs among BTPDs over short time periods (Barnes, 1993), and no other mechanism (e.g., predation, drought) is likely to cause the extreme population reductions that could be confused with the effects of plague (e.g., Colman et al, 2021; Cully et al, 2010; Johnson et al, 2011; Matchett et al, 2021). Indeed, serological testing of BTPD carcasses and fleas collected in and around burrows confirmed the presence of the plague bacterium at all eight of our study sites (Cully et al, 2010; Johnson et al, 2011; Savage et al, 2011; Thiagarajan et al, 2008).…”

Flea Control on Prairie Dogs (Cynomys Spp.) With Fipronil Bait Pellets: Potential Plague Mitigation Tool for Rapid Field Application and Wildlife Conservation

“…We recommend fipronil bait treatments in mid-to late summer for BTPDs because Abbott et al (2018) and Matchett et al (2021) showed high levels of bait uptake under those conditions, while Eads et al ( , 2020Eads et al ( , 2021 showed effective flea control on BTPDs with fipronil bait treatments during the same time periods. We recommend similar treatment timing for GPDs, Utah PDs (Cynomys parvidens) and white-tailed PDs (Cynomys leucurus), considering that treatments need to be completed before the onset of hibernation.…”

“…Trap effort and sampling procedures were identical and simultaneous on paired treated and nontreated plots. Detailed PD handling methods can be found in Eads et al ( , 2020Eads et al ( , 2021 and Matchett et al (2021). Briefly, we live-trapped PDs using cage traps (Tomahawk Live Trap, Hazelhurst, Wisconsin, USA in South Dakota and Arizona; Tru-Catch Traps, Belle Fourche, South Dakota in Montana) baited with a rolled corn, oats, barley, and molasses livestock feed (laced with small amounts of peanut butter in South Dakota).…”

“…A priority action item in the current BFF Recovery Plan (US Fish and Wildlife Service 2013, p. 101) is to “Develop and implement as appropriate prophylactic methods for controlling sylvatic plague.” A variety of insecticides has been used with varying degrees of cost and success to control fleas and minimize the effects of plague on PDs and other mammals (e.g., Hoogland et al 2004, 2018; Biggins et al 2010, 2021a, 2021b; Eads and Biggins 2019; Eads et al 2019, 2021; Enscore et al 2021; Goldberg et al 2021). Given the need to minimize plague effects at BFF reintroduction sites, there have been intensive and extensive efforts to manage plague (e.g., Biggins et al 2010, 2021a; Matchett et al 2010, 2021; Rocke et al 2017; Tripp et al 2017). Such efforts continue with the development and testing of fipronil-laced bait pellets herein that have the potential to drastically reduce the cost of mitigating plague with flea control compared to other methods.…”