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Plague-Positive Mouse Fleas on Mice Before Plague Induced Die-Offs in Black-Tailed and White-Tailed Prairie Dogs.

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Bron GM 1, 2, Malavé CM 1, Boulerice JT 3, Osorio JE 2, Rocke TE 1.

Author information:
1. 1 U.S. Geological Survey National Wildlife Health Center, Madison, Wisconsin.
2. 2 Department of Pathobiological Sciences, University of Wisconsin-Madison, School of Veterinary Medicine, Madison, Wisconsin.
3. 3 Wyoming Game and Fish Department, Laramie, Wyoming.

Abstract

Plague is a lethal zoonotic disease associated with rodents worldwide. In the western United States, plague outbreaks can decimate prairie dog (Cynomys spp.) colonies. However, it is unclear where the causative agent, Yersinia pestis, of this flea-borne disease is maintained between outbreaks, and what triggers plague-induced prairie dog die-offs. Less susceptible rodent hosts, such as mice, could serve to maintain the bacterium, transport infectious fleas across a colony, or introduce the pathogen to other colonies, possibly facilitating an outbreak. Here, we assess the potential role of two short-lived rodent species, North American deer mice (Peromyscus maniculatus) and Northern grasshopper mice (Onychomys leucogaster) in plague dynamics on prairie dog colonies. We live-trapped short-lived rodents and collected their fleas on black-tailed (Cynomys ludovicianus, Montana and South Dakota), white-tailed (Cynomys leucurus, Utah and Wyoming), and Utah prairie dog colonies (Cynomys parvidens, Utah) annually, from 2013 to 2016. Plague outbreaks occurred on colonies of all three species. In all study areas, deer mouse abundance was high the year before plague-induced prairie dog die-offs, but mouse abundance per colony was not predictive of plague die-offs in prairie dogs. We did not detect Y. pestis DNA in mouse fleas during prairie dog die-offs, but in three cases we found it beforehand. On one white-tailed prairie dog colony, we detected Y. pestis positive fleas on one grasshopper mouse and several prairie dogs live-trapped 10 days later, months before visible declines and plague-confirmed mortality of prairie dogs. On one black-tailed prairie dog colony, we detected Y. pestis positive fleas on two deer mice 3 months before evidence of plague was detected in prairie dogs or their fleas and also well before a plague-induced die-off. These observations of plague positive fleas on mice could represent early spillover events of Y. pestis from prairie dogs or an unknown reservoir, or possible movement of infectious fleas by mice.

Prairie Dogs, Persistent Plague, Flocking Fleas, and Pernicious Positive Feedback.

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1. Front Vet Sci. 2019 Mar 28;6:75. doi: 10.3389/fvets.2019.00075. eCollection 2019.
Biggins DE 1, Eads DA 1, 2.

Author information:
1. United States Geological Survey, Fort Collins Science Center, Fort Collins, CO, United States.
2. Department of Biology, Colorado State University, Fort Collins, CO, United States.

Abstract

Plague (caused by the bacterium Yersinia pestis) is a deadly flea-borne disease that remains a threat to public health nearly worldwide and is particularly disruptive ecologically where it has been introduced. We review hypotheses regarding maintenance and transmission of Y. pestis, emphasizing recent data from North America supporting maintenance by persistent transmission that results in sustained non-epizootic (but variable) rates of mortality in hosts. This maintenance mechanism may facilitate periodic epizootic eruptions “in place” because the need for repeated reinvasion from disjunct sources is eliminated. Resulting explosive outbreaks that spread rapidly in time and space are likely enhanced by synergistic positive feedback (PFB) cycles involving flea vectors, hosts, and the plague bacterium itself. Although PFB has been implied in plague literature for at least 50 years, we propose this mechanism, particularly with regard to flea responses, as central to epizootic plague rather than a phenomenon worthy of just peripheral mention. We also present new data on increases in flea:host ratios resulting from recreational shooting and poisoning as possible triggers for the transition from enzootic maintenance to PFB cycles and epizootic explosions. Although plague outbreaks have received much historic attention, PFB cycles that result in decimation of host populations lead to speculation that epizootic eruptions might not be part of the adaptive evolutionary strategy of Y. pestis but might instead be a tolerated intermittent cost of its modus operandi. We also speculate that there may be mammal communities where epizootics, as we define them, are rare or absent. Absence of plague epizootics might translate into reduced public health risk but does not necessarily equate to inconsequential ecologic impact.

PMCID: PMC6447679 Free PMC Article

Effects of Deltamethrin Treatment on Small Mammal and Ectoparasite Population Dynamics and Plague Prevalence in a North American Mixed-Grass Prairie System.

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Maestas LP1, Britten HB1.

Author information

Department of Biology, University of South Dakota, Vermillion, South Dakota.

Abstract

Sylvatic plague affects many species in North American prairie ecosystems. Deltamethrin is commonly used to manage fleas in potential outbreak areas. Understanding the role of small mammals and their ectoparasites in sylvatic plague maintenance is pertinent to understanding the ecology of plague and its persistence in nature. This study examined the effects of plague management using deltamethrin on communities of small mammals, their flea faunas, and Yersinia pestis prevalence. We trapped small mammals from 2014 to 2016 on the Lower Brule Indian Reservation (LOBR), South Dakota, and analyzed the effects of deltamethrin treatment on small mammal populations, flea loads, and Y. pestis prevalence. We collected higher flea loads from small mammals on sites not treated with deltamethrin (1.10 fleas per animal) than from deltamethrin-treated sites (1.03 fleas per animal). We observed significant negative trends in mean flea load per animal between pre- and post-treatment collections. We detected no significant effects of deltamethrin treatment on animal captures pre- and post-treatment, but observed significant differences in animal captures by experimental unit. We detected no serological evidence for the presence of Y. pestis antibodies in small mammals and 1.2% Y. pestis prevalence across all sampled fleas. Although there is little overlap in the species of fleas infesting small mammals and prairie dogs, the occurrence of flea spillover has been documented. In our study, treatment with deltamethrin reduced flea loads on small mammals by up to 49%. Our data suggest that although the efficacy of deltamethrin on the LOBR-a mixed-grass system-may not be as high as that found in a comparable study in a short-grass system, deltamethrin is still a useful tool in the management of plague.

KEYWORDS:

; South Dakota; deltamethrin; fleas; plague management; small mammals

Third cat tests positive for bubonic plague in Wyoming

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For the third time in recent months, a cat has tested positive for bubonic plague in Wyoming, the state’s Department of Health reports. No human cases have been identified, but health officials warn the disease can be passed to people from infected animals.

 The most recent case involved a cat in the small town of Kaycee. Officials said the animal was known to wander outdoors. The disease was confirmed by the Wyoming State Veterinary Laboratory in Laramie.

Read more:  Wyoming

Evaluation of Five Pulicides to Suppress Fleas on Black-Tailed Prairie Dogs:

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1. Vector Borne Zoonotic Dis. 2019 Jan 8. doi: 10.1089/vbz.2018.2339. [Epub ahead of

print]
Evaluation of Five Pulicides to Suppress Fleas on Black-Tailed Prairie Dogs:
Encouraging Long-Term Results with Systemic 0.005% Fipronil.
Eads DA(1), Biggins DE(2), Bowser J(2), Broerman K(2), Livieri TM(3), Childers
E(4), Dobesh P(5), Griebel RL(5).
Author information:
(1)1 Department of Biology, Colorado State University, Fort Collins, Colorado.
(2)2 U.S. Geological Survey, Fort Collins Science Center, Fort Collins, Colorado.
(3)3 Prairie Wildlife Research, Wellington, Colorado.
(4)4 National Park Service, Badlands National Park, Interior, South Dakota.
(5)5 U.S. Forest Service, Wall, South Dakota.
Plague, a flea-borne disease, hampers efforts to restore populations of
black-footed ferrets (Mustela nigripes), which occupy colonies of prairie dogs
(Cynomys spp.) in North America. Plague is managed by infusing prairie dog
burrows with DeltaDust® 0.05% deltamethrin, a pulicide that kills fleas.
Experiments are needed to identify pulicides that can be used in rotation with
DeltaDust for integrated plague management. In South Dakota, USA, we tested the
efficacy of four pulicide dusts when applied at a rate of 8
g per burrow on
colonies of black-tailed prairie dogs (Cynomys ludovicianus): Sevin® 5% carbaryl;
Dusta-cide® 6% malathion; Alpine® 0.25% dinotefuran with 95% diatomaceous earth;
and Tri-Die® 1% pyrethrum with 40% amorphous silica and 10% piperonyl butoxide.
We also tested systemic 0.005% fipronil, which was distributed as
½
cup of laced
grain per burrow. We sampled prairie dogs on 3294 occasions and detected 10,041
fleas. Sevin and Dusta-cide suppressed fleas but only for 1 month. Neither Alpine
nor Tri-Die had any noticeable, consistent effect on fleas. Fipronil suppressed
fleas by 97-100% for 3 months. The residual effect of fipronil persisted for
∼
12
months. Efficacy of fipronil seems comparable with DeltaDust, which exhibited a
residual effect for
∼
10 months in prior studies. Continued research is needed to
optimize fipronil treatments for plague management on prairie dog colonies.
DOI: 10.1089/vbz.2018.2339
PMID: 30620249
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