Assembling a safe and effective toolbox for integrated plague mitigation and wildlife conservation

February 1, 2023

Project Collaborators:
U.S. Geological Survey
Prairie Wildlife Research
National Park Service
U.S. Forest Service
U.S. Fish and Wildlife Service
Centers for Disease Control and Prevention
World Wildlife Fund
Lower Brule Sioux Tribe
Arizona Game and Fish Department
Colorado State University
Turner Endangered Species Fund
U.S. Department of Agriculture-APHIS
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Plague is a highly lethal disease of mammalian hosts and flea vectors. The causative agent, Yersinia pestis, was introduced to California in 1900 and spread rapidly to 17 western States. In the grasslands of western North America, Y. pestis poses one of the most significant biological challenges to the conservation of black-footed ferrets (BFF) and prairie dogs (PDs). The pathogen infects mammals of >70 genera and >200 species globally. In populations of colonial, burrowing PDs, plague can erupt during occasional epizootic outbreaks, thereby increasing the risk of transmission to BFFs, eliminating their PD prey, and in some cases, transforming ecosystems. A One Health view of plague is encouraged, recognizing that human, animal, and environmental health are all linked (Eads et al. 2022).
 
U.S. Fish and Wildlife Service (FWS) and colleagues seek to acquire a deeper understanding of plague, and to identify management tools to safely and effectively mitigate the disease. Most commonly in the context of BFF conservation, biologists manage plague using “pulicides” for flea control, including deltamethrin powder, which is infused into PD burrows. Deltamethrin dust has been a mainstay of BFF conservation for decades. That said, experiments conducted by the U.S. Geological Survey (USGS) and many collaborators has demonstrated, fleas can develop resistance to deltamethrin after repeated annual applications (Eads et al. 2018). Moreover, deltamethrin may have unintended, negative impacts on some non-target species (e.g., burrow-dwelling crickets). Therefore, additional tools are needed. 

Over the past decade, USGS and colleagues have evaluated >15 tools for flea control. Encouragingly, an edible grain bait  targeting PDs and laced with fipronil (most widely known as the active ingredient of Frontline flea treatment for dogs and cats), proved effective in controlling PD fleas for 1-2 years or longer in some cases (Eads et al. 2019). PDs eat the grain and the fipronil and metabolites are mostly stored in fat and slowly released into the PD blood stream. Adult fleas are then killed when consuming blood from PDs. Fipronil residues are excreted over time in PD feces and are often deposited in their underground burrow systems and nest chambers where flea eggs hatch into larvae. USGS and partners, including the Centers for Disease Control and Prevention, discovered that flea larvae feed on PD feces, and the flea larvae are killed when they consume (or even contact) feces from PDs that have eaten fipronil-treated bait (Eads et al. 2023). USGS and colleagues found, fipronil residues in PD feces can persist for prolonged periods underground, which may help explain the high degree of flea control observed for 1-2 years after a single treatment with PDs.

Building on those advances, a wildlife biologist with the FWS integrated fipronil into a new bait pellet, dubbed “FipBits”. FWS, USGS, and colleagues discovered, the FipBits are effective in controlling fleas for at least 2 years, or more, in some cases (Eads et al. 2021, Matchett et al. 2023). FipBits may provide a much more affordable and practical means of controlling fleas. In addition, the FWS, USGS, and colleagues are evaluating different active ingredients used to control fleas and ticks on dogs and cats that might be substituted for fipronil in the FipBit model. Rotating active ingredients should prevent fleas from developing resistance to any one active ingredient (Eads et al. 2022).
 
Research is also underway to evaluate potential effects, positive or negative, of fipronil and other pulicides on target species (for example, PDs and BFFs) and non-target species including multiple insects and amphibians. To date, the results are encouraging, and may provide insight into varied ways biologists can minimize unintended impacts on wildlife, again with One Health implications and remembering plague is a devastating disease for both BFFs and PDs. The future appears bright, but much remains to be learned as teammates and partners seek to move BFF conservation toward the species’ recovery.