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Mitchell CL, Schwarzer AR, Miarinjara A, Jarrett CO, Luis AD, Hinnebusch BJ. A Role for Early-Phase Transmission in the Enzootic Maintenance of Plague. PLoS Pathog 2022; 18:e1010996. [PMID: 36520713 PMCID: PMC9754260 DOI: 10.1371/journal.ppat.1010996] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2022] [Accepted: 11/10/2022] [Indexed: 12/23/2022] Open
Abstract
Yersinia pestis, the bacterial agent of plague, is enzootic in many parts of the world within wild rodent populations and is transmitted by different flea vectors. The ecology of plague is complex, with rodent hosts exhibiting varying susceptibilities to overt disease and their fleas exhibiting varying levels of vector competence. A long-standing question in plague ecology concerns the conditions that lead to occasional epizootics among susceptible rodents. Many factors are involved, but a major one is the transmission efficiency of the flea vector. In this study, using Oropsylla montana (a ground squirrel flea that is a major plague vector in the western United States), we comparatively quantified the efficiency of the two basic modes of flea-borne transmission. Transmission efficiency by the early-phase mechanism was strongly affected by the host blood source. Subsequent biofilm-dependent transmission by blocked fleas was less influenced by host blood and was more efficient. Mathematical modeling predicted that early-phase transmission could drive an epizootic only among highly susceptible rodents with certain blood characteristics, but that transmission by blocked O. montana could do so in more resistant hosts irrespective of their blood characteristics. The models further suggested that for most wild rodents, exposure to sublethal doses of Y. pestis transmitted during the early phase may restrain rapid epizootic spread by increasing the number of immune, resistant individuals in the population.
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Affiliation(s)
- Cedar L. Mitchell
- Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
| | - Ashley R. Schwarzer
- Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
| | - Adélaïde Miarinjara
- Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
| | - Clayton O. Jarrett
- Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
| | - Angela D. Luis
- Department of Ecosystem and Conservation Sciences, University of Montana, Missoula, Montana, United States of America
| | - B. Joseph Hinnebusch
- Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
- * E-mail:
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2
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Miarinjara A, Eads DA, Bland DM, Matchett MR, Biggins DE, Hinnebusch BJ. Reevaluation of the Role of Blocked Oropsylla hirsuta Prairie Dog Fleas (Siphonaptera: Ceratophyllidae) in Yersinia pestis (Enterobacterales: Enterobacteriaceae) Transmission. JOURNAL OF MEDICAL ENTOMOLOGY 2022; 59:1053-1059. [PMID: 35380675 PMCID: PMC9113170 DOI: 10.1093/jme/tjac021] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Indexed: 05/17/2023]
Abstract
Prairie dogs in the western United States experience periodic epizootics of plague, caused by the flea-borne bacterial pathogen Yersinia pestis. An early study indicated that Oropsylla hirsuta (Baker), often the most abundant prairie dog flea vector of plague, seldom transmits Y. pestis by the classic blocked flea mechanism. More recently, an alternative early-phase mode of transmission has been proposed as the driving force behind prairie dog epizootics. In this study, using the same flea infection protocol used previously to evaluate early-phase transmission, we assessed the vector competence of O. hirsuta for both modes of transmission. Proventricular blockage was evident during the first two weeks after infection and transmission during this time was at least as efficient as early-phase transmission 2 d after infection. Thus, both modes of transmission likely contribute to plague epizootics in prairie dogs.
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Affiliation(s)
- Adélaïde Miarinjara
- Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, NIH, Hamilton, MT, USA
- Department of Environmental Sciences, Emory University, Atlanta, GA, USA
| | - David A Eads
- U.S. Geological Survey, Fort Collins Science Center, Fort Collins, CO, USA
| | - David M Bland
- Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, NIH, Hamilton, MT, USA
| | | | - Dean E Biggins
- U.S. Geological Survey, Fort Collins Science Center, Fort Collins, CO, USA
| | - B Joseph Hinnebusch
- Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, NIH, Hamilton, MT, USA
- Corresponding author, e-mail:
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Russell RE, Walsh DP, Samuel MD, Grunnill MD, Rocke TE. Space matters: host spatial structure and the dynamics of plague transmission. Ecol Modell 2021. [DOI: 10.1016/j.ecolmodel.2021.109450] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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Poché D, Clarke T, Tseveenjav B, Torres-Poché Z. Evaluating the use of a low dose fipronil bait in reducing black-tailed prairie dog ( Cynomys ludovicianus) fleas at reduced application rates. INTERNATIONAL JOURNAL FOR PARASITOLOGY-PARASITES AND WILDLIFE 2020; 13:292-298. [PMID: 33335833 PMCID: PMC7732869 DOI: 10.1016/j.ijppaw.2020.11.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Revised: 11/17/2020] [Accepted: 11/17/2020] [Indexed: 12/04/2022]
Abstract
Plague is a virulent zoonosis, vectored by fleas, posing danger to black-tailed prairie dogs (BTPDs) (Cynomys ludovicianus), black-footed ferrets (Mustela nigripes), and humans in North America. During prior research, a fipronil grain bait (0.005%) applied at rates of 1-½ cup/burrow, reduced flea abundance by > 95–100% when applied three times February–March in northern Colorado. The objective of the current study was to determine the efficacy of fipronil bait against fleas in northern Colorado at reduced application rates (½ cup/burrow) and frequencies (1–2 applications). The field study was conducted in Larimer county, Colorado USA between June-November 2018. Three test plots were selected: two treatment plots (1 vs. 2 fipronil bait applications) and one untreated control. Fipronil was applied at a rate of ½ cup (~95 g)/burrow. Fleas were collected from captured BTPDs and swabs of active burrows prior to bait application and up to 134-days post-treatment. A total of 203 BTPDs and 210 active burrows were sampled. Within the treatment plots, no fleas were collected from BTPDs up to 134-days post-treatment (100% efficacy). Five fleas were recovered from burrows within the one-application plot (<40-days post-application) with efficacy ranging from 97.1 to 100%. No fleas were recovered from burrows within the two-application plot. We caution that while fleas were present within the control plot throughout the study, abundances were low. The efficacy results are supported by those of prior field research conducted in South Dakota and suggest that fipronil bait may be applied at lower rates and frequencies than initially proposed, with potential to sustain flea removal >4-months. Fipronil grain bait fed to black-tailed prairie dogs was effective against fleas. Controlling prairie dog fleas can reduce plague transmission to humans and wildlife. Low application rate could reduce environmental risk and insecticide resistance. One application of bait controlled 100% of prairie dog fleas for more than 4-months.
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Affiliation(s)
- David Poché
- Genesis Laboratories, P.O Box 1195, Wellington, CO, 80549, USA
| | - Tyler Clarke
- Genesis Laboratories, P.O Box 1195, Wellington, CO, 80549, USA
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5
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Bosio CF, Jarrett CO, Scott DP, Fintzi J, Hinnebusch BJ. Comparison of the transmission efficiency and plague progression dynamics associated with two mechanisms by which fleas transmit Yersinia pestis. PLoS Pathog 2020; 16:e1009092. [PMID: 33284863 PMCID: PMC7746306 DOI: 10.1371/journal.ppat.1009092] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2020] [Revised: 12/17/2020] [Accepted: 10/22/2020] [Indexed: 12/19/2022] Open
Abstract
Yersinia pestis can be transmitted by fleas during the first week after an infectious blood meal, termed early-phase or mass transmission, and again after Y. pestis forms a cohesive biofilm in the flea foregut that blocks normal blood feeding. We compared the transmission efficiency and the progression of infection after transmission by Oropsylla montana fleas at both stages. Fleas were allowed to feed on mice three days after an infectious blood meal to evaluate early-phase transmission, or after they had developed complete proventricular blockage. Transmission was variable and rather inefficient by both modes, and the odds of early-phase transmission was positively associated with the number of infected fleas that fed. Disease progression in individual mice bitten by fleas infected with a bioluminescent strain of Y. pestis was tracked. An early prominent focus of infection at the intradermal flea bite site and dissemination to the draining lymph node(s) soon thereafter were common features, but unlike what has been observed in intradermal injection models, this did not invariably lead to further systemic spread and terminal disease. Several of these mice resolved the infection without progression to terminal sepsis and developed an immune response to Y. pestis, particularly those that received an intermediate number of early-phase flea bites. Furthermore, two distinct types of terminal disease were noted: the stereotypical rapid onset terminal disease within four days, or a prolonged onset preceded by an extended, fluctuating infection of the lymph nodes before eventual systemic dissemination. For both modes of transmission, bubonic plague rather than primary septicemic plague was the predominant disease outcome. The results will help to inform mathematical models of flea-borne plague dynamics used to predict the relative contribution of the two transmission modes to epizootic outbreaks that erupt periodically from the normal enzootic background state. Yersinia pestis can be transmitted by fleas within a few days after taking a blood meal from a highly bacteremic host, termed early-phase or mass transmission; and again after it forms a dense biofilm in the foregut of its vector that can eventually block blood feeding. The relative importance of the two transmission modes in the ecology of plague is a matter of current debate, but estimates of transmission rate, efficiency, and other parameters are limited. We compared transmission and disease progression dynamics in mice bitten by groups of fleas three days after their infectious blood meal (early-phase or mass transmission mode) and in mice bitten by individual blocked fleas. In general, a higher percentage of transmissions by blocked fleas led to terminal disease, whereas early-phase transmissions more often led to survival and an immune response, which are nonproductive infections in the sense that the bacteremia required to continue the Y. pestis life cycle did not develop and these animals would be removed from the pool of susceptibles in the host population. The data will be useful in mathematical models of plague dynamics in wild rodent populations.
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Affiliation(s)
- Christopher F. Bosio
- Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
| | - Clayton O. Jarrett
- Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
| | - Dana P. Scott
- Rocky Mountain Veterinary Branch, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
| | - Jonathan Fintzi
- Biostatistics Research Branch, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, United States of America
| | - B. Joseph Hinnebusch
- Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
- * E-mail:
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Liccioli S, Stephens T, Wilson SC, McPherson JM, Keating LM, Antonation KS, Bollinger TK, Corbett CR, Gummer DL, Lindsay LR, Galloway TD, Shury TK, Moehrenschlager A. Enzootic maintenance of sylvatic plague in Canada's threatened black‐tailed prairie dog ecosystem. Ecosphere 2020. [DOI: 10.1002/ecs2.3138] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Affiliation(s)
- Stefano Liccioli
- Grasslands National Park Parks Canada Agency P.O. Box 150 Val Marie Saskatchewan S0N2T0 Canada
| | - Tara Stephens
- Centre for Conservation Research Calgary Zoological Society 1300 Zoo Road N.E. Calgary Alberta T2E 7V6 Canada
| | - Sian C. Wilson
- Centre for Conservation Research Calgary Zoological Society 1300 Zoo Road N.E. Calgary Alberta T2E 7V6 Canada
| | - Jana M. McPherson
- Centre for Conservation Research Calgary Zoological Society 1300 Zoo Road N.E. Calgary Alberta T2E 7V6 Canada
| | - Laura M. Keating
- Centre for Conservation Research Calgary Zoological Society 1300 Zoo Road N.E. Calgary Alberta T2E 7V6 Canada
| | - Kym S. Antonation
- Bioforensics Assay Development and Diagnostics National Microbiology Laboratory Public Health Agency of Canada 1015 Arlington Street Winnipeg Manitoba R3E 3R2 Canada
| | - Trent K. Bollinger
- Department of Veterinary Pathology Canadian Wildlife Health Cooperative 52 Campus Drive Saskatoon Saskatchewan S7N 5B4 Canada
| | - Cindi R. Corbett
- Bioforensics Assay Development and Diagnostics National Microbiology Laboratory Public Health Agency of Canada 1015 Arlington Street Winnipeg Manitoba R3E 3R2 Canada
| | - David L. Gummer
- Natural Resource Management Branch Parks Canada Agency 720 – 220 4 Avenue SE Calgary Alberta T2G 4X3 Canada
| | - L. Robbin Lindsay
- Zoonotic Diseases and Special Pathogens National Microbiology Laboratory Public Health Agency of Canada 1015 Arlington Street Winnipeg Manitoba R3E 3R2 Canada
| | - Terry D. Galloway
- Department of Entomology Faculty of Agricultural and Food Sciences University of Manitoba 12 Dafoe Road Winnipeg Manitoba R3T 2N2 Canada
| | - Todd K. Shury
- Parks Canada Agency 52 Campus Drive Saskatoon Saskatchewan S7N 5B4 Canada
| | - Axel Moehrenschlager
- Centre for Conservation Research Calgary Zoological Society 1300 Zoo Road N.E. Calgary Alberta T2E 7V6 Canada
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D’Ortenzio E, Lemaître N, Brouat C, Loubet P, Sebbane F, Rajerison M, Baril L, Yazdanpanah Y. Plague: Bridging gaps towards better disease control. Med Mal Infect 2018; 48:307-317. [DOI: 10.1016/j.medmal.2018.04.393] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Accepted: 04/13/2018] [Indexed: 01/14/2023]
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8
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Hinnebusch BJ, Jarrett CO, Bland DM. "Fleaing" the Plague: Adaptations of Yersinia pestis to Its Insect Vector That Lead to Transmission. Annu Rev Microbiol 2018; 71:215-232. [PMID: 28886687 DOI: 10.1146/annurev-micro-090816-093521] [Citation(s) in RCA: 64] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Interest in arthropod-borne pathogens focuses primarily on how they cause disease in humans. How they produce a transmissible infection in their arthropod host is just as critical to their life cycle, however. Yersinia pestis adopts a unique life stage in the digestive tract of its flea vector, characterized by rapid formation of a bacterial biofilm that is enveloped in a complex extracellular polymeric substance. Localization and adherence of the biofilm to the flea foregut is essential for transmission. Here, we review the molecular and genetic mechanisms of these processes and present a comparative evaluation and updated model of two related transmission mechanisms.
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Affiliation(s)
- B Joseph Hinnebusch
- Laboratory of Zoonotic Pathogens, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana 59840;
| | - Clayton O Jarrett
- Laboratory of Zoonotic Pathogens, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana 59840;
| | - David M Bland
- Laboratory of Zoonotic Pathogens, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana 59840;
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FLEAS OF BLACK-FOOTED FERRETS (MUSTELA NIGRIPES) AND THEIR POTENTIAL ROLE IN THE MOVEMENT OF PLAGUE. J Wildl Dis 2017; 53:521-531. [DOI: 10.7589/2016-09-202] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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10
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Bahrndorff S, de Jonge N, Skovgård H, Nielsen JL. Bacterial Communities Associated with Houseflies (Musca domestica L.) Sampled within and between Farms. PLoS One 2017; 12:e0169753. [PMID: 28081167 PMCID: PMC5232358 DOI: 10.1371/journal.pone.0169753] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Accepted: 12/21/2016] [Indexed: 11/18/2022] Open
Abstract
The housefly feeds and reproduces in animal manure and decaying organic substances and thus lives in intimate association with various microorganisms including human pathogens. In order to understand the variation and association between bacteria and the housefly, we used 16S rRNA gene amplicon sequencing to describe bacterial communities of 90 individual houseflies collected within and between ten dairy farms in Denmark. Analysis of gene sequences showed that the most abundant classes of bacteria found across all sites included Bacilli, Clostridia, Actinobacteria, Flavobacteria, and all classes of Proteobacteria and at the genus level the most abundant genera included Corynebacterium, Lactobacillus, Staphylococcus, Vagococcus, Weissella, Lactococcus, and Aerococcus. Comparison of the microbiota of houseflies revealed a highly diverse microbiota compared to other insect species and with most variation in species richness and diversity found between individuals, but not locations. Our study is the first in-depth amplicon sequencing study of the housefly microbiota, and collectively shows that the microbiota of single houseflies is highly diverse and differs between individuals likely to reflect the lifestyle of the housefly. We suggest that these results should be taken into account when addressing the transmission of pathogens by the housefly and assessing the vector competence variation under natural conditions.
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Affiliation(s)
- Simon Bahrndorff
- Department of Chemistry and Bioscience, Aalborg University, Aalborg East, Denmark
| | - Nadieh de Jonge
- Department of Chemistry and Bioscience, Aalborg University, Aalborg East, Denmark
| | - Henrik Skovgård
- Department of Agroecology, University of Aarhus, Slagelse, Denmark
| | - Jeppe Lund Nielsen
- Department of Chemistry and Bioscience, Aalborg University, Aalborg East, Denmark
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11
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Hinnebusch BJ, Bland DM, Bosio CF, Jarrett CO. Comparative Ability of Oropsylla montana and Xenopsylla cheopis Fleas to Transmit Yersinia pestis by Two Different Mechanisms. PLoS Negl Trop Dis 2017; 11:e0005276. [PMID: 28081130 PMCID: PMC5230758 DOI: 10.1371/journal.pntd.0005276] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2016] [Accepted: 12/21/2016] [Indexed: 11/19/2022] Open
Abstract
Background Transmission of Yersinia pestis by flea bite can occur by two mechanisms. After taking a blood meal from a bacteremic mammal, fleas have the potential to transmit the very next time they feed. This early-phase transmission resembles mechanical transmission in some respects, but the mechanism is unknown. Thereafter, transmission occurs after Yersinia pestis forms a biofilm in the proventricular valve in the flea foregut. The biofilm can impede and sometimes completely block the ingestion of blood, resulting in regurgitative transmission of bacteria into the bite site. In this study, we compared the relative efficiency of the two modes of transmission for Xenopsylla cheopis, a flea known to become completely blocked at a high rate, and Oropsylla montana, a flea that has been considered to rarely develop proventricular blockage. Methodology/Principal findings Fleas that took an infectious blood meal containing Y. pestis were maintained and monitored for four weeks for infection and proventricular blockage. The number of Y. pestis transmitted by groups of fleas by the two modes of transmission was also determined. O. montana readily developed complete proventricular blockage, and large numbers of Y. pestis were transmitted by that mechanism both by it and by X. cheopis, a flea known to block at a high rate. In contrast, few bacteria were transmitted in the early phase by either species. Conclusions A model system incorporating standardized experimental conditions and viability controls was developed to more reliably compare the infection, proventricular blockage and transmission dynamics of different flea vectors, and was used to resolve a long-standing uncertainty concerning the vector competence of O. montana. Both X. cheopis and O. montana are fully capable of transmitting Y. pestis by the proventricular biofilm-dependent mechanism. The ecology of plague is complex and its epidemiology is enigmatic. Many different flea species are able to transmit Yersinia pestis, the plague bacillus, and they can transmit in two different ways. Early-phase transmission can occur during the first week after a flea has fed on a diseased animal. Thereafter, transmission occurs only as bacterial growth in the flea foregut interferes with and eventually blocks blood feeding. Comparisons of the relative ability of different flea vectors to transmit have been problematic, and contradictory results have been reported for the ability of the ground squirrel flea Oropsylla montana to transmit beyond the early phase. Our results show that O. montana readily develops foregut blockage, and transmission by that mechanism was as good as or better than observed for Xenopsylla cheopis, a flea known to block at a high rate. In contrast, very few bacteria were transmitted in the early phase by either of these fleas compared to later times after infection, suggesting that early-phase transmission is pertinent only to highly susceptible animals. Improved characterization of the transmission patterns of different flea vectors will aid in modeling plague incidence in its various natural settings.
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Affiliation(s)
- B. Joseph Hinnebusch
- Laboratory of Zoonotic Pathogens, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
- * E-mail:
| | - David M. Bland
- Laboratory of Zoonotic Pathogens, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
| | - Christopher F. Bosio
- Laboratory of Zoonotic Pathogens, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
| | - Clayton O. Jarrett
- Laboratory of Zoonotic Pathogens, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
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12
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Richgels KLD, Russell RE, Bron GM, Rocke TE. Evaluation of Yersinia pestis Transmission Pathways for Sylvatic Plague in Prairie Dog Populations in the Western U.S. ECOHEALTH 2016; 13:415-427. [PMID: 27234457 DOI: 10.1007/s10393-016-1133-9] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2015] [Revised: 01/21/2016] [Accepted: 04/15/2016] [Indexed: 06/05/2023]
Abstract
Sylvatic plague, caused by the bacterium Yersinia pestis, is periodically responsible for large die-offs in rodent populations that can spillover and cause human mortalities. In the western US, prairie dog populations experience nearly 100% mortality during plague outbreaks, suggesting that multiple transmission pathways combine to amplify plague dynamics. Several alternate pathways in addition to flea vectors have been proposed, such as transmission via direct contact with bodily fluids or inhalation of infectious droplets, consumption of carcasses, and environmental sources of plague bacteria, such as contaminated soil. However, evidence supporting the ability of these proposed alternate pathways to trigger large-scale epizootics remains elusive. Here we present a short review of potential plague transmission pathways and use an ordinary differential equation model to assess the contribution of each pathway to resulting plague dynamics in black-tailed prairie dogs (Cynomys ludovicianus) and their fleas (Oropsylla hirsuta). Using our model, we found little evidence to suggest that soil contamination was capable of producing plague epizootics in prairie dogs. However, in the absence of flea transmission, direct transmission, i.e., contact with bodily fluids or inhalation of infectious droplets, could produce enzootic dynamics, and transmission via contact with or consumption of carcasses could produce epizootics. This suggests that these pathways warrant further investigation.
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Affiliation(s)
- Katherine L D Richgels
- United States Geological Survey, National Wildlife Health Center, 6006, Schroeder Rd, Madison, WI, USA
- Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin - Madison, Madison, WI, USA
| | - Robin E Russell
- United States Geological Survey, National Wildlife Health Center, 6006, Schroeder Rd, Madison, WI, USA
| | - Gebbiena M Bron
- United States Geological Survey, National Wildlife Health Center, 6006, Schroeder Rd, Madison, WI, USA
- Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin - Madison, Madison, WI, USA
| | - Tonie E Rocke
- United States Geological Survey, National Wildlife Health Center, 6006, Schroeder Rd, Madison, WI, USA.
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13
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Boegler KA, Graham CB, Johnson TL, Montenieri JA, Eisen RJ. Infection Prevalence, Bacterial Loads, and Transmission Efficiency in Oropsylla montana (Siphonaptera: Ceratophyllidae) One Day After Exposure to Varying Concentrations of Yersinia pestis in Blood. JOURNAL OF MEDICAL ENTOMOLOGY 2016; 53:674-680. [PMID: 26843450 PMCID: PMC6555412 DOI: 10.1093/jme/tjw004] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2015] [Accepted: 01/12/2016] [Indexed: 05/28/2023]
Abstract
Unblocked fleas can transmit Yersinia pestis, the bacterium that causes plague, shortly (≤4 d) after taking an infectious bloodmeal. Investigators have measured so-called early-phase transmission (EPT) efficiency in various fleas following infection with highly bacteremic blood (≥108 cfu/ml). To date, no one has determined the lower limit of bacteremia required for fleas to acquire and transmit infection by EPT, though knowing this threshold is central to determining the length of time a host may be infectious to feeding fleas. Here, we evaluate the ability of Oropsylla montana (Baker) to acquire and transmit Y. pestis after feeding on blood containing 103 to 109 cfu/ml. We evaluated the resulting infection prevalence, bacterial loads, and transmission efficiency within the early-phase time period at 1 d postinfection. Fleas acquired infection from bacteremic blood across a wide range of concentrations, but transmission was observed only when fleas ingested highly bacteremic blood.
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Affiliation(s)
- Karen A Boegler
- Centers for Disease Control and Prevention - Division of Vector-Borne Diseases, 3156 Rampart Rd., Fort Collins, CO 80521 (; ; ; ; ) and
| | - Christine B Graham
- Centers for Disease Control and Prevention - Division of Vector-Borne Diseases, 3156 Rampart Rd., Fort Collins, CO 80521 (; ; ; ; ) and
| | - Tammi L Johnson
- Centers for Disease Control and Prevention - Division of Vector-Borne Diseases, 3156 Rampart Rd., Fort Collins, CO 80521 (; ; ; ; ) and
| | - John A Montenieri
- Centers for Disease Control and Prevention - Division of Vector-Borne Diseases, 3156 Rampart Rd., Fort Collins, CO 80521 (; ; ; ; ) and
| | - Rebecca J Eisen
- Centers for Disease Control and Prevention - Division of Vector-Borne Diseases, 3156 Rampart Rd., Fort Collins, CO 80521 (; ; ; ; ) and
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14
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Brown LD, Banajee KH, Foil LD, Macaluso KR. Transmission mechanisms of an emerging insect-borne rickettsial pathogen. Parasit Vectors 2016; 9:237. [PMID: 27117813 PMCID: PMC4847369 DOI: 10.1186/s13071-016-1511-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2016] [Accepted: 04/14/2016] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Vector-borne pathogens must overcome arthropod infection and escape barriers (e.g. midgut and salivary glands) during the extrinsic incubation period (EIP) before subsequent transmission to another host. This particular timespan is undetermined for the etiological agent of flea-borne spotted fever (Rickettsia felis). Artificial acquisition of R. felis by blood-feeding cat fleas revealed dissemination to the salivary glands after seven days; however, this length of time is inconsistent with co-feeding studies that produced infectious cat fleas within 24 h of infection. In the current study, we demonstrated that an alternative mechanism is responsible for the early-phase transmission that typifies flea-borne R. felis spread. METHODS Co-feeding transmission bioassays were constructed to assess temporal dynamics of R. felis amongst cat fleas, including exposure time to produce infectious fleas and association time to transmit infection to naïve fleas. Additional experiments examined the proportion of R. felis-exposed cat fleas with contaminated mouthparts, as well as the likelihood for cat fleas to release R. felis from their mouthparts following exposure to an infectious bloodmeal. The potential for mechanical transmission of R. felis by co-feeding cat fleas was further examined using fluorescent latex beads, as opposed to a live pathogen, which would not require a biological mechanism to achieve transmission. RESULTS Analyses revealed that R. felis-infected cat fleas were infectious to naïve fleas less than 24 h after exposure to the pathogen, but showed no rickettsial dissemination to the salivary glands during this early-phase transmission. Additionally, the current study revealed that R. felis-infected cat fleas must co-feed with naïve fleas for more than 12 h in order for early-phase transmission to occur. Further evidence supported that contaminated flea mouthparts may be the source of the bacteria transmitted early, and demonstrated that R. felis is released from the mouthparts during brief probing events. Moreover, the use of fluorescent latex beads supports the notion that early-phase transmission of R. felis is a mechanical mechanism. CONCLUSIONS Determination of the transmission mechanisms utilized by R. felis is essential to fully understand the vulnerability of susceptible vertebrate hosts, including humans, to this pathogen.
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Affiliation(s)
- Lisa D. Brown
- />Department of Pathobiological Sciences, School of Veterinary Medicine, Louisiana State University, Skip Bertman Drive, SVM-3213, Baton Rouge, LA 70803 USA
| | - Kaikhushroo H. Banajee
- />Department of Pathobiological Sciences, School of Veterinary Medicine, Louisiana State University, Skip Bertman Drive, SVM-3213, Baton Rouge, LA 70803 USA
| | - Lane D. Foil
- />Department of Entomology, Louisiana State University Agricultural Center, LSB-413, Baton Rouge, LA 70803 USA
| | - Kevin R. Macaluso
- />Department of Pathobiological Sciences, School of Veterinary Medicine, Louisiana State University, Skip Bertman Drive, SVM-3213, Baton Rouge, LA 70803 USA
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15
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Graham CB, Eisen RJ, Belthoff JR. Detecting Burrowing Owl Bloodmeals in Pulex irritans (Siphonaptera: Pulicidae). JOURNAL OF MEDICAL ENTOMOLOGY 2016; 53:446-450. [PMID: 26545716 PMCID: PMC5572895 DOI: 10.1093/jme/tjv177] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2015] [Accepted: 10/19/2015] [Indexed: 06/05/2023]
Abstract
Pulex irritans L. is a cosmopolitan flea species that infests a wide variety of hosts. In North America it generally parasitizes large wild mammals, but in the Pacific Northwest an association has emerged between P. irritans and the western burrowing owl (Athene cunicularia hypugaea). While investigators have recognized this association for decades, it has not been clear if P. irritans feeds on burrowing owls, or if the owls serve exclusively as phoretic hosts. Here we describe using a real-time assay that was originally developed to identify bloodmeals in Ugandan cat fleas (Ctenocephalides felis Bouché) to detect burrowing owl DNA in P. irritans collected from burrowing owls in southern Idaho. Of 50 fleas tested, 12 had no detectable vertebrate bloodmeal. The remaining 38 (76%) contained burrowing owl DNA. The assay did not detect vertebrate DNA in unfed fleas exposed to owl or mouse pelts and is therefore unlikely to detect DNA in fleas from vertebrates that have served exclusively as phoretic hosts. We conclude that P. irritans feeds on burrowing owls. We discuss the potential implications of this finding for burrowing owl conservation and enzootic plague dynamics.
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Affiliation(s)
- Christine B Graham
- Bacterial Diseases Branch, Division of Vector-Borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, 3156 Rampart Rd., Fort Collins, CO 80521 (; ),
| | - Rebecca J Eisen
- Bacterial Diseases Branch, Division of Vector-Borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, 3156 Rampart Rd., Fort Collins, CO 80521 (; )
| | - James R Belthoff
- Department of Biological Sciences and Raptor Research Center, Boise State University, 1910 University Dr., Boise, ID 83725
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16
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Mize EL, Britten HB. Detections of Yersinia pestis East of the Known Distribution of Active Plague in the United States. Vector Borne Zoonotic Dis 2016; 16:88-95. [PMID: 26771845 DOI: 10.1089/vbz.2015.1825] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
We examined fleas collected from black-tailed prairie dog (Cynomys ludovicianus) burrows from 2009 through 2011 in five national park units east of the known distribution of active plague across the northern Great Plains for the presence of Yersinia pestis. Across all national park units, Oropsylla tuberculata and Oropsylla hirsuta were the most common fleas collected from prairie dog burrows, 42.4% and 56.9%, respectively, of the 3964 fleas collected from burrow swabbing. Using a nested PCR assay, we detected 200 Y. pestis-positive fleas from 3117 assays. In total, 6.4% of assayed fleas were Y. pestis positive and 13.9% of prairie dog burrows swabbed contained Y. pestis-positive fleas. Evidence of the presence of Y. pestis was observed at all national park units except Devils Tower National Monument in Wyoming. We detected the presence of Y. pestis without large die-offs, i.e., enzootic sylvatic plague, east of the known distribution of active plague and near the eastern edge of the present distribution of black-tailed prairie dogs. This study, in combination with previous work suggests that sylvatic plague likely occurs across the range of black-tailed prairie dogs and should now be treated as endemic across this range.
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Affiliation(s)
- Erica L Mize
- Department of Biology, University of South Dakota , Vermillion, South Dakota
| | - Hugh B Britten
- Department of Biology, University of South Dakota , Vermillion, South Dakota
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17
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Eisen RJ, Dennis DT, Gage KL. The Role of Early-Phase Transmission in the Spread of Yersinia pestis. JOURNAL OF MEDICAL ENTOMOLOGY 2015; 52:1183-92. [PMID: 26336267 PMCID: PMC4636957 DOI: 10.1093/jme/tjv128] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2015] [Accepted: 08/01/2015] [Indexed: 05/28/2023]
Abstract
Early-phase transmission (EPT) of Yersinia pestis by unblocked fleas is a well-documented, replicable phenomenon with poorly defined mechanisms. We review evidence demonstrating EPT and current knowledge on its biological and biomechanical processes. We discuss the importance of EPT in the epizootic spread of Y. pestis and its role in the maintenance of plague bacteria in nature. We further address the role of EPT in the epidemiology of plague.
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Affiliation(s)
- Rebecca J Eisen
- Bacterial Diseases Branch, Division of Vectorborne Diseases, National Center for Emerging Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, CO.
| | | | - Kenneth L Gage
- Bacterial Diseases Branch, Division of Vectorborne Diseases, National Center for Emerging Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, CO
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18
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Earl SC, Rogers MT, Keen J, Bland DM, Houppert AS, Miller C, Temple I, Anderson DM, Marketon MM. Resistance to Innate Immunity Contributes to Colonization of the Insect Gut by Yersinia pestis. PLoS One 2015; 10:e0133318. [PMID: 26177454 PMCID: PMC4503695 DOI: 10.1371/journal.pone.0133318] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2015] [Accepted: 06/25/2015] [Indexed: 01/29/2023] Open
Abstract
Yersinia pestis, the causative agent of bubonic and pneumonic plague, is typically a zoonotic vector-borne disease of wild rodents. Bacterial biofilm formation in the proventriculus of the flea contributes to chronic infection of fleas and facilitates efficient disease transmission. However prior to biofilm formation, ingested bacteria must survive within the flea midgut, and yet little is known about vector-pathogen interactions that are required for flea gut colonization. Here we establish a Drosophila melanogaster model system to gain insight into Y. pestis colonization of the insect vector. We show that Y. pestis establishes a stable infection in the anterior midgut of fly larvae, and we used this model system to study the roles of genes involved in biofilm production and/or resistance to gut immunity stressors. We find that PhoP and GmhA both contribute to colonization and resistance to antimicrobial peptides in flies, and furthermore, the data suggest biofilm formation may afford protection against antimicrobial peptides. Production of reactive oxygen species in the fly gut, as in fleas, also serves to limit bacterial infection, and OxyR mediates Y. pestis survival in both insect models. Overall, our data establish the fruit fly as an informative model to elucidate the relationship between Y. pestis and its flea vector.
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Affiliation(s)
- Shaun C. Earl
- Department of Biology, Indiana University, Bloomington, IN, United States of America
| | - Miles T. Rogers
- Department of Biology, Indiana University, Bloomington, IN, United States of America
| | - Jennifer Keen
- Department of Biology, Indiana University, Bloomington, IN, United States of America
| | - David M. Bland
- Department of Veterinary Pathobiology, University of Missouri, Columbia, Missouri, United States of America
| | - Andrew S. Houppert
- Department of Biology, Indiana University, Bloomington, IN, United States of America
| | - Caitlynn Miller
- Department of Biology, Indiana University, Bloomington, IN, United States of America
| | - Ian Temple
- Department of Biology, Indiana University, Bloomington, IN, United States of America
| | - Deborah M. Anderson
- Department of Veterinary Pathobiology, University of Missouri, Columbia, Missouri, United States of America
| | - Melanie M. Marketon
- Department of Biology, Indiana University, Bloomington, IN, United States of America
- * E-mail:
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19
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Ekanayake AJ, Ekanayake DB. A seasonal SIR metapopulation model with an Allee effect with application to controlling plague in prairie dog colonies. JOURNAL OF BIOLOGICAL DYNAMICS 2014; 9 Suppl 1:262-290. [PMID: 25400201 DOI: 10.1080/17513758.2014.978400] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
For wildlife species living among patchy habitats, disease and the Allee effect (reduced per capita birth rates at low population densities) may together drive a patch's population to extinction, particularly if births are seasonal. Yet local extinction may not be indicative of global extinction, and a patch may become recolonized by migrating individuals. We introduce deterministic and stochastic susceptible, infectious, and immune epidemic models with vector species to study disease in a metapopulation with an Allee effect and seasonal birth and dispersal. We obtain conditions for the existence of a strong Allee effect and existence and stability of a disease-free positive periodic solution. These general models have application to many wildlife diseases. As a case study, we apply them to evaluate dynamics of the sylvatic plague in prairie dog colonies interconnected through dispersal. We further evaluate the effects of control of the vector population and control by immunization on plague eradication.
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Affiliation(s)
- A J Ekanayake
- a Department of Mathematics , Western Illinois University , 1 University Circle, Macomb , IL 61455 , USA
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20
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Johnson TL, Hinnebusch BJ, Boegler KA, Graham CB, MacMillan K, Montenieri JA, Bearden SW, Gage KL, Eisen RJ. Yersinia murine toxin is not required for early-phase transmission of Yersinia pestis by Oropsylla montana (Siphonaptera: Ceratophyllidae) or Xenopsylla cheopis (Siphonaptera: Pulicidae). MICROBIOLOGY-SGM 2014; 160:2517-2525. [PMID: 25187626 DOI: 10.1099/mic.0.082123-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Plague, caused by Yersinia pestis, is characterized by quiescent periods punctuated by rapidly spreading epizootics. The classical 'blocked flea' paradigm, by which a blockage forms in the flea's proventriculus on average 1-2 weeks post-infection (p.i.), forces starving fleas to take multiple blood meals, thus increasing opportunities for transmission. Recently, the importance of early-phase transmission (EPT), which occurs prior to blockage formation, has been emphasized during epizootics. Whilst the physiological and molecular mechanisms of blocked flea transmission are well characterized, the pathogen-vector interactions have not been elucidated for EPT. Within the blocked flea model, Yersinia murine toxin (Ymt) has been shown to be important for facilitating colonization of the midgut within the flea. One proposed mechanism of EPT is the regurgitation of infectious material from the flea midgut during feeding. Such a mechanism would require bacteria to colonize and survive for at least brief periods in the midgut, a process that is mediated by Ymt. Two key bridging vectors of Y. pestis to humans, Oropsylla montana (Siphonaptera: Ceratophyllidae) or Xenopsylla cheopis (Siphonaptera: Pulicidae), were used in our study to test this hypothesis. Fleas were infected with a mutant strain of Y. pestis containing a non-functional ymt that was shown previously to be incapable of colonizing the midgut and were then allowed to feed on SKH-1 mice 3 days p.i. Our results show that Ymt was not required for EPT by either flea species.
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Affiliation(s)
- Tammi L Johnson
- Bacterial Diseases Branch, Division of Vector-borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, USA
| | - B Joseph Hinnebusch
- Laboratory of Zoonotic Pathogens, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, USA
| | - Karen A Boegler
- Bacterial Diseases Branch, Division of Vector-borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, USA
| | - Christine B Graham
- Bacterial Diseases Branch, Division of Vector-borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, USA
| | - Katherine MacMillan
- Bacterial Diseases Branch, Division of Vector-borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, USA
| | - John A Montenieri
- Bacterial Diseases Branch, Division of Vector-borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, USA
| | - Scott W Bearden
- Bacterial Diseases Branch, Division of Vector-borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, USA
| | - Kenneth L Gage
- Bacterial Diseases Branch, Division of Vector-borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, USA
| | - Rebecca J Eisen
- Bacterial Diseases Branch, Division of Vector-borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, USA
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21
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Jones RT, Vetter SM, Gage KL. Short report: Exposing laboratory-reared fleas to soil and wild flea feces increases transmission of Yersinia pestis. Am J Trop Med Hyg 2013; 89:784-7. [PMID: 23939709 DOI: 10.4269/ajtmh.13-0138] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Laboratory-reared Oropsylla montana were exposed to soil and wild-caught Oropsylla montana feces for 1 week. Fleas from these two treatments and a control group of laboratory-reared fleas were infected with Yersinia pestis, the etiological agent of plague. Fleas exposed to soil transmitted Y. pestis to mice at a significantly greater rate (50.0% of mice were infected) than control fleas (23.3% of mice were infected). Although the concentration of Y. pestis in fleas did not differ among treatments, the minimum transmission efficiency of fleas from the soil and wild flea feces treatments (6.9% and 7.6%, respectively) were more than three times higher than in control fleas (2.2%). Our results suggest that exposing laboratory-reared fleas to diverse microbes alters transmission of Y. pestis.
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Affiliation(s)
- Ryan T Jones
- Division of Vector-Borne Disease, Centers for Disease Control and Prevention, Fort Collins, Colorado
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22
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Williams SK, Schotthoefer AM, Montenieri JA, Holmes JL, Vetter SM, Gage KL, Bearden SW. Effects of low-temperature flea maintenance on the transmission of Yersinia pestis by Oropsylla montana. Vector Borne Zoonotic Dis 2013; 13:468-78. [PMID: 23590319 DOI: 10.1089/vbz.2012.1017] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Yersinia pestis, the causative agent of plague, is primarily a rodent-associated, flea-borne zoonosis maintained in sylvatic foci throughout western North America. Transmission to humans is mediated most commonly by the flea vector Oropsylla montana and occurs predominantly in the southwestern United States. With few exceptions, previous studies showed O. montana to be an inefficient vector at transmitting Y. pestis at ambient temperatures, particularly when such fleas were fed on susceptible hosts more than a few days after ingesting an infectious blood meal. We examined whether holding fleas at subambient temperatures affected the transmissibility of Y. pestis by this vector. An infectious blood meal containing a virulent Y. pestis strain (CO96-3188) was given to colony-reared O. montana fleas. Potentially infected fleas were maintained at different temperatures (6°C, 10°C, 15°C, or 23°C). Transmission efficiencies were tested by allowing up to 15 infectious fleas to feed on each of 7 naïve CD-1 mice on days 1-4, 7, 10, 14, 17, and 21 postinfection (p.i.). Mice were monitored for signs of infection for 21 days after exposure to infectious fleas. Fleas held at 6°C, 10°C, and 15°C were able to effectively transmit at every time point p.i. The percentage of transmission to naïve mice by fleas maintained at low temperatures (46.0% at 6°C, 71.4% at 10°C, 66.7% at 15°C) was higher than for fleas maintained at 23°C (25.4%) and indicates that O. montana fleas efficiently transmit Y. pestis at low temperatures. Moreover, pooled percent per flea transmission efficiencies for flea cohorts maintained at temperatures of 10°C and 15°C (8.67% and 7.87%, respectively) showed a statistically significant difference in the pooled percent per flea transmission efficiency from fleas maintained at 23°C (1.94%). This is the first comprehensive study to demonstrate efficient transmission of Y. pestis by O. montana fleas maintained at temperatures as low as 6°C. Our findings further contribute to the understanding of plague ecology in temperate climates by providing support for the hypothesis that Y. pestis is able to overwinter within the flea gut and potentially cause infection during the following transmission season. The findings also might hold implications for explaining the focality of plague in tropical regions.
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Affiliation(s)
- Shanna K Williams
- Bacterial Diseases Branch, Division of Vector-Borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, USA
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23
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Biofilm-dependent and biofilm-independent mechanisms of transmission of Yersinia pestis by fleas. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 954:237-43. [PMID: 22782769 DOI: 10.1007/978-1-4614-3561-7_30] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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24
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Gage KL. Factors Affecting the Spread and Maintenance of Plague. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 954:79-94. [DOI: 10.1007/978-1-4614-3561-7_11] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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25
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Abstract
Flea-borne zoonoses such as plague (Yersinia pestis) and murine typhus (Rickettsia typhi) caused significant numbers of human cases in the past and remain a public health concern. Other flea-borne human pathogens have emerged recently (e.g., Bartonella henselae, Rickettsia felis), and their mechanisms of transmission and impact on human health are not fully understood. Our review focuses on the ecology and epidemiology of the flea-borne bacterial zoonoses mentioned above with an emphasis on recent advancements in our understanding of how these organisms are transmitted by fleas, maintained in zoonotic cycles, and transmitted to humans. Emphasis is given to plague because of the considerable number of studies generated during the first decade of the twenty-first century that arose, in part, because of renewed interest in potential agents of bioterrorism, including Y. pestis.
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Affiliation(s)
- Rebecca J Eisen
- Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado 30333, USA.
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26
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Buhnerkempe MG, Eisen RJ, Goodell B, Gage KL, Antolin MF, Webb CT. Transmission shifts underlie variability in population responses to Yersinia pestis infection. PLoS One 2011; 6:e22498. [PMID: 21799873 PMCID: PMC3143141 DOI: 10.1371/journal.pone.0022498] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2011] [Accepted: 06/28/2011] [Indexed: 11/23/2022] Open
Abstract
Host populations for the plague bacterium, Yersinia pestis, are highly variable in their response to plague ranging from near deterministic extinction (i.e., epizootic dynamics) to a low probability of extinction despite persistent infection (i.e., enzootic dynamics). Much of the work to understand this variability has focused on specific host characteristics, such as population size and resistance, and their role in determining plague dynamics. Here, however, we advance the idea that the relative importance of alternative transmission routes may vary causing shifts from epizootic to enzootic dynamics. We present a model that incorporates host and flea ecology with multiple transmission hypotheses to study how transmission shifts determine population responses to plague. Our results suggest enzootic persistence relies on infection of an off-host flea reservoir and epizootics rely on transiently maintained flea infection loads through repeated infectious feeds by fleas. In either case, early-phase transmission by fleas (i.e., transmission immediately following an infected blood meal) has been observed in laboratory studies, and we show that it is capable of driving plague dynamics at the population level. Sensitivity analysis of model parameters revealed that host characteristics (e.g., population size and resistance) vary in importance depending on transmission dynamics, suggesting that host ecology may scale differently through different transmission routes enabling prediction of population responses in a more robust way than using either host characteristics or transmission shifts alone.
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Affiliation(s)
- Michael G Buhnerkempe
- Department of Biology, Colorado State University, Fort Collins, Colorado, United States of America.
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27
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Schotthoefer AM, Bearden SW, Vetter SM, Holmes J, Montenieri JA, Graham CB, Woods ME, Eisen RJ, Gage KL. Effects of temperature on early-phase transmission of Yersina pestis by the flea, Xenopsylla cheopis. JOURNAL OF MEDICAL ENTOMOLOGY 2011; 48:411-417. [PMID: 21485382 DOI: 10.1603/me10155] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Sharp declines in human and animal cases of plague, caused by the bacterium Yersinia pestis (Yersin), have been observed when outbreaks coincide with hot weather. Failure of biofilm production, or blockage, to occur in the flea, as temperatures reach 30 degrees C has been suggested as an explanation for these declines. Recent work demonstrating efficient flea transmission during the first few days after fleas have taken an infectious blood meal, in the absence of blockage (e.g., early-phase transmission), however, has called this hypothesis into question. To explore the potential effects of temperature on early-phase transmission, we infected colony-reared Xenopsylla cheopis (Rothchild) fleas with a wild-type strain of plague bacteria using an artificial feeding system, and held groups of fleas at 10, 23, 27, and 30 degrees C. Naive Swiss Webster mice were exposed to fleas from each of these temperatures on days 1-4 postinfection, and monitored for signs of infection for 21 d. Temperature did not significantly influence the rates of transmission observed for fleas held at 23, 27, and 30 degrees C. Estimated per flea transmission efficiencies for these higher temperatures ranged from 2.32 to 4.96% (95% confidence interval [CI]: 0.96-8.74). In contrast, no transmission was observed in mice challenged by fleas held at 10 degrees C (per flea transmission efficiency estimates, 0-1.68%). These results suggest that declines in human and animal cases during hot weather are not related to changes in the abilities of X. cheopis fleas to transmit Y. pestis infections during the early-phase period. By contrast, transmission may be delayed or inhibited at low temperatures, indicating that epizootic spread of Y. pestis by X. cheopis via early-phase transmission is unlikely during colder periods of the year.
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Affiliation(s)
- Anna M Schotthoefer
- Bacterial Diseases Branch, Division of Vector Borne Infectious Diseases, National Center for Emerging and Zoonotic, Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, CO 80521, USA.
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28
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Heier L, Storvik GO, Davis SA, Viljugrein H, Ageyev VS, Klassovskaya E, Stenseth NC. Emergence, spread, persistence and fade-out of sylvatic plague in Kazakhstan. Proc Biol Sci 2011; 278:2915-23. [PMID: 21345866 DOI: 10.1098/rspb.2010.2614] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Predicting the dynamics of zoonoses in wildlife is important not only for prevention of transmission to humans, but also for improving the general understanding of epidemiological processes. A large dataset on sylvatic plague in the Pre-Balkhash area of Kazakhstan (collected for surveillance purposes) provides a rare opportunity for detailed statistical modelling of an infectious disease. Previous work using these data has revealed a host abundance threshold for epizootics, and climatic influences on plague prevalence. Here, we present a model describing the local space-time dynamics of the disease at a spatial scale of 20 × 20 km(2) and a biannual temporal scale, distinguishing between invasion and persistence events. We used a Bayesian imputation method to account for uncertainties resulting from poor data in explanatory variables and response variables. Spatial autocorrelation in the data was accounted for in imputations and analyses through random effects. The results show (i) a clear effect of spatial transmission, (ii) a high probability of persistence compared with invasion, and (iii) a stronger influence of rodent abundance on invasion than on persistence. In particular, there was a substantial probability of persistence also at low host abundance.
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Affiliation(s)
- Lise Heier
- Centre for Ecological and Evolutionary Synthesis, Department of Biology, University of Oslo, PO Box 1066 Blindern, 0316 Oslo, Norway
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29
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Franklin HA, Stapp P, Cohen A. Polymerase chain reaction (PCR) identification of rodent blood meals confirms host sharing by flea vectors of plague. JOURNAL OF VECTOR ECOLOGY : JOURNAL OF THE SOCIETY FOR VECTOR ECOLOGY 2010; 35:363-371. [PMID: 21175944 DOI: 10.1111/j.1948-7134.2010.00095.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Elucidating feeding relationships between hosts and parasites remains a significant challenge in studies of the ecology of infectious diseases, especially those involving small or cryptic vectors. Black-tailed prairie dogs (Cynomys ludovicianus) are a species of conservation importance in the North American Great Plains whose populations are extirpated by plague, a flea-vectored, bacterial disease. Using polymerase chain reaction (PCR) assays, we determined that fleas (Oropsylla hirsuta) associated with prairie dogs feed upon northern grasshopper mice (Onychomys leucogaster), a rodent that has been implicated in the transmission and maintenance of plague in prairie-dog colonies. Our results definitively show that grasshopper mice not only share fleas with prairie dogs during plague epizootics, but also provide them with blood meals, offering a mechanism by which the pathogen, Yersinia pestis, may be transmitted between host species and maintained between epizootics. The lack of identifiable host DNA in a significant fraction of engorged Oropsylla hirsuta collected from animals (47%) and prairie-dog burrows (100%) suggests a rapid rate of digestion and feeding that may facilitate disease transmission during epizootics but also complicate efforts to detect feeding on alternative hosts. Combined with other analytical approaches, e.g., stable isotope analysis, molecular genetic techniques can provide novel insights into host-parasite feeding relationships and improve our understanding of the role of alternative hosts in the transmission and maintenance of disease.
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Affiliation(s)
- Heather A Franklin
- Department of Biological Science, California State University, Fullerton, CA 92831, USA
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30
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Maher SP, Ellis C, Gage KL, Enscore RE, Peterson AT. Range-wide determinants of plague distribution in North America. Am J Trop Med Hyg 2010; 83:736-42. [PMID: 20889857 DOI: 10.4269/ajtmh.2010.10-0042] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Plague, caused by the bacterium Yersinia pestis, is established across western North America, and yet little is known of what determines the broad-scale dimensions of its overall range. We tested whether its North American distribution represents a composite of individual host-plague associations (the "Host Niche Hypothesis"), or whether mammal hosts become infected only at sites overlapping ecological conditions appropriate for plague transmission and maintenance (the "Plague Niche Hypothesis"). We took advantage of a novel data set summarizing plague records in wild mammals newly digitized from paper-based records at the Centers for Disease Control and Prevention to develop range-wide tests of ecological niche similarity between mammal host niches and plague-infected host niches. Results indicate that plague infections occur under circumstances distinct from the broader ecological distribution of hosts, and that plague-infected niches are similar among hosts; hence, evidence coincides with the predictions of the Plague Niche Hypothesis, and contrasts with those of the Host Niche Hypothesis. The "plague niche" is likely driven by ecological requirements of vector flea species.
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Affiliation(s)
- Sean P Maher
- Department of Ecology and Evolutionary Biology and Biodiversity Institute, University of Kansas, Lawrence, Kansas 66045, USA.
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31
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Plague outbreaks in prairie dog populations explained by percolation thresholds of alternate host abundance. Proc Natl Acad Sci U S A 2010; 107:14247-50. [PMID: 20660742 DOI: 10.1073/pnas.1002826107] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Highly lethal pathogens (e.g., hantaviruses, hendra virus, anthrax, or plague) pose unique public-health problems, because they seem to periodically flare into outbreaks before disappearing into long quiescent phases. A key element to their possible control and eradication is being able to understand where they persist in the latent phase and how to identify the conditions that result in sporadic epidemics or epizootics. In American grasslands, plague, caused by Yersinia pestis, exemplifies this quiescent-outbreak pattern, because it sporadically erupts in epizootics that decimate prairie dog (Cynomys ludovicianus) colonies, yet the causes of outbreaks and mechanisms for interepizootic persistence of this disease are poorly understood. Using field data on prairie community ecology, flea behavior, and plague-transmission biology, we find that plague can persist in prairie-dog colonies for prolonged periods, because host movement is highly spatially constrained. The abundance of an alternate host for disease vectors, the grasshopper mouse (Onychomys leucogaster), drives plague outbreaks by increasing the connectivity of the prairie dog hosts and therefore, permitting percolation of the disease throughout the primary host population. These results offer an alternative perspective on plague's ecology (i.e., disease transmission exacerbated by alternative hosts) and may have ramifications for plague dynamics in Asia and Africa, where a single main host has traditionally been considered to drive Yersinia ecology. Furthermore, abundance thresholds of alternate hosts may be a key phenomenon determining outbreaks of disease in many multihost-disease systems.
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32
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Vetter SM, Eisen RJ, Schotthoefer AM, Montenieri JA, Holmes JL, Bobrov AG, Bearden SW, Perry RD, Gage KL. Biofilm formation is not required for early-phase transmission of Yersinia pestis. MICROBIOLOGY-SGM 2010; 156:2216-2225. [PMID: 20395271 PMCID: PMC3068684 DOI: 10.1099/mic.0.037952-0] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Early-phase transmission (EPT) is a recently described model of plague transmission that explains the rapid spread of disease from flea to mammal host during an epizootic. Unlike the traditional blockage-dependent model of plague transmission, EPT can occur when a flea takes its first blood meal after initially becoming infected by feeding on a bacteraemic host. Blockage of the flea gut results from biofilm formation in the proventriculus, mediated by the gene products found in the haemin storage (hms) locus of the Yersinia pestis chromosome. Although biofilms are required for blockage-dependent transmission, the role of biofilms in EPT has yet to be determined. An artificial feeding system was used to feed Xenopsylla cheopis and Oropsylla montana rat blood spiked with the parental Y. pestis strain KIM5(pCD1)+, two different biofilm-deficient mutants (ΔhmsT, ΔhmsR), or a biofilm-overproducer mutant (ΔhmsP). Infected fleas were then allowed to feed on naïve Swiss Webster mice for 1–4 days after infection, and the mice were monitored for signs of infection. We also determined the bacterial loads of each flea that fed upon naïve mice. Biofilm-defective mutants transmitted from X. cheopis and O. montana as efficiently as the parent strain, whereas the EPT efficiency of fleas fed the biofilm-overproducing strain was significantly less than that of fleas fed either the parent or a biofilm-deficient strain. Fleas infected with a biofilm-deficient strain harboured lower bacterial loads 4 days post-infection than fleas infected with the parent strain. Thus, defects in biofilm formation did not prevent flea-borne transmission of Y. pestis in our EPT model, although biofilm overproduction inhibited efficient EPT. Our results also indicate, however, that biofilms may play a role in infection persistence in the flea.
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Affiliation(s)
- Sara M Vetter
- Bacterial Diseases Branch, Division of Vector Borne Diseases, National Center for Enteric and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, 3150 Rampart Rd, Fort Collins, CO 80521, USA
| | - Rebecca J Eisen
- Bacterial Diseases Branch, Division of Vector Borne Diseases, National Center for Enteric and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, 3150 Rampart Rd, Fort Collins, CO 80521, USA
| | - Anna M Schotthoefer
- Bacterial Diseases Branch, Division of Vector Borne Diseases, National Center for Enteric and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, 3150 Rampart Rd, Fort Collins, CO 80521, USA
| | - John A Montenieri
- Bacterial Diseases Branch, Division of Vector Borne Diseases, National Center for Enteric and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, 3150 Rampart Rd, Fort Collins, CO 80521, USA
| | - Jennifer L Holmes
- Bacterial Diseases Branch, Division of Vector Borne Diseases, National Center for Enteric and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, 3150 Rampart Rd, Fort Collins, CO 80521, USA
| | - Alexander G Bobrov
- Department of Microbiology, Immunology and Molecular Genetics, University of Kentucky, MS415 Medical Center, Lexington, KY 40536, USA
| | - Scott W Bearden
- Bacterial Diseases Branch, Division of Vector Borne Diseases, National Center for Enteric and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, 3150 Rampart Rd, Fort Collins, CO 80521, USA
| | - Robert D Perry
- Department of Microbiology, Immunology and Molecular Genetics, University of Kentucky, MS415 Medical Center, Lexington, KY 40536, USA
| | - Kenneth L Gage
- Bacterial Diseases Branch, Division of Vector Borne Diseases, National Center for Enteric and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, 3150 Rampart Rd, Fort Collins, CO 80521, USA
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33
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Abu Khweek A, Fetherston JD, Perry RD. Analysis of HmsH and its role in plague biofilm formation. MICROBIOLOGY-SGM 2010; 156:1424-1438. [PMID: 20093287 DOI: 10.1099/mic.0.036640-0] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The Yersinia pestis Hms(+) phenotype is a manifestation of biofilm formation that causes adsorption of Congo red and haemin at 26 degrees C but not at 37 degrees C. This phenotype is required for blockage of the proventricular valve of the oriental rat flea and plays a role in transmission of bubonic plague from fleas to mammals. Genes responsible for this phenotype are located in three separate operons, hmsHFRS, hmsT and hmsP. HmsH and HmsF are outer membrane (OM) proteins, while the other four Hms proteins are located in the inner membrane. According to the Hidden Markov Method-based predictor, HmsH has a large N terminus in the periplasm, a beta-barrel structure with 16 beta-strands that traverse the OM, eight surface-exposed loops, and seven short turns connecting the beta-strands on the periplasmic side. Here, we demonstrate that HmsH is a heat-modifiable protein, a characteristic of other beta-barrel proteins, thereby supporting the bioinformatics analysis. Alanine scanning mutagenesis was used to identify conserved amino acids in the HmsH-like family that are critical for the function of HmsH in biofilm formation. Of 23 conserved amino acids mutated, four residues affected HmsH function and three likely caused protein instability. We used formaldehyde cross-linking to demonstrate that HmsH interacts with HmsF but not with HmsR, HmsS, HmsT or HmsP. Loss-of-function HmsH variants with single alanine substitutions retained their beta-structure and interaction with HmsF. Finally, using a polar hmsH : : mini-kan mutant, we demonstrated that biofilm development is not important for the pathogenesis of bubonic or pneumonic plague in mice.
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Affiliation(s)
- Arwa Abu Khweek
- Department of Microbiology, Immunology, and Molecular Genetics, University of Kentucky, 800 Rose St., Lexington, KY, USA
| | - Jacqueline D Fetherston
- Department of Microbiology, Immunology, and Molecular Genetics, University of Kentucky, 800 Rose St., Lexington, KY, USA
| | - Robert D Perry
- Department of Microbiology, Immunology, and Molecular Genetics, University of Kentucky, 800 Rose St., Lexington, KY, USA
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Stapp P, Salkeld DJ. Inferring host-parasite relationships using stable isotopes: implications for disease transmission and host specificity. Ecology 2010; 90:3268-73. [PMID: 19967881 DOI: 10.1890/08-1226.1] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Identifying the roles of different hosts and vectors is a major challenge in the study of the ecology of diseases caused by multi-host pathogens. Intensive field studies suggested that grasshopper mice (Onychomys leucogaster) help spread the bacterium that causes plague (Yersinia pestis) in prairie dog colonies by sharing fleas with prairie dogs (Cynomys ludovicianus); yet conclusive evidence that prairie dog fleas (Oropsylla hirsuta) feed on grasshopper mice is lacking. Using stable nitrogen isotope analysis, we determined that many blood-engorged O. hirsuta collected from wild grasshopper mice apparently contained blood meals of prairie dogs. These results suggest that grasshopper mice may be infected with Y. pestis via mechanisms other than flea feeding, e.g., early phase or mechanical transmission or scavenging carcasses, and raise questions about the ability of grasshopper mice to maintain Y. pestis in prairie dog colonies during years between plague outbreaks. They also indicate that caution may be warranted when inferring feeding relationships based purely on the occurrence of fleas or other haematophagous ectoparasites on hosts. Stable-isotope analysis may complement or provide a useful alternative to immunological or molecular techniques for identifying hosts of cryptically feeding ectoparasites, and for clarifying feeding relationships in studies of host-parasite interactions.
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Affiliation(s)
- Paul Stapp
- Department of Biological Science, California State University, Fullerton, California 92834-6850, USA.
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35
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36
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Bacterial communities of disease vectors sampled across time, space, and species. ISME JOURNAL 2009; 4:223-31. [PMID: 19865184 DOI: 10.1038/ismej.2009.111] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A common strategy of pathogenic bacteria is to form close associations with parasitic insects that feed on animals and to use these insects as vectors for their own transmission. Pathogens interact closely with other coexisting bacteria within the insect, and interactions between co-occurring bacteria may influence the vector competency of the parasite. Interactions between particular lineages can be explored through measures of alpha-diversity. Furthermore, general patterns of bacterial community assembly can be explored through measures of beta-diversity. Here, we use pyrosequencing (n=115,924 16S rRNA gene sequences) to describe the bacterial communities of 230 prairie dog fleas sampled across space and time. We use these communinty characterizations to assess interactions between dominant community members and to explore general patterns of bacterial community assembly in fleas. An analysis of co-occurrence patterns suggests non-neutral negative interactions between dominant community members (P<0.001). Furthermore, bacterial communities of fleas shift dramatically across years (phylotype-based: R=0.829, P<0.001; phylogenetic-based: R=0.612-0.753, P<0.001), but they also significantly differ across space (phylotype-based: R=0.418, P<0.001; phylogenetic-based: R=0.290-0.328, P<0.001) and between flea species (phylotype-based: R=0.160, P=0.011; phylogenetic-based: not significant). Collectively, our results show that flea-associated bacterial communities are not random assemblages; rather, an individual flea's bacterial community is governed by interactions between bacterial lineages and by the flea's place in space and time.
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Eisen RJ, Eisen L, Gage KL. Studies of vector competency and efficiency of North American fleas for Yersinia pestis: state of the field and future research needs. JOURNAL OF MEDICAL ENTOMOLOGY 2009; 46:737-744. [PMID: 19645275 DOI: 10.1603/033.046.0403] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The etiological agent of plague, Yersinia pestis, is most commonly transmitted by the bite of infectious fleas. To date, at least 28 flea species occurring in North America have been experimentally confirmed as vectors of Y. pestis. Transmission efficiency differs among species and also between different studies of a single species. These differences may, however, in large part reflect nonstandardized experimental conditions used during the first half of the 20th century when such studies were conducted in response to the rapid spread of Y. pestis across the western United States after its introduction at the beginning of this century. The majority of these early transmission studies focused on the blocked flea mechanism of transmission, which typically does not occur until > 2-3 wk after the flea becomes infected. Recent studies have challenged the paradigm that Y. pestis is usually spread by blocked fleas by demonstrating that numerous flea species, including the oriental rat flea Xenopsylla cheopis, which was the focus of the early classical studies on blocked flea transmission, are capable of"early-phase" transmission during the first few days after becoming infected and before a complete blockage can form. The aims of this review are to 1) summarize Y. pestis vector competency and efficiency studies for fleas occurring in North America, 2) discuss the implications of the results of these studies for our understanding of the dynamics of plague epizootics, 3) demonstrate why older transmission studies need to be repeated using a standardized experimental system, and 4) outline future directions for studies of fleas as vectors of Y. pestis.
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Affiliation(s)
- Rebecca J Eisen
- Bacterial Diseases Branch, Division of Vector Borne Infectious Diseases, National Center for Zoonotic, Enteric and Vector-Borne Diseases, Centers for Disease Control and Prevention, 3150 Rampart Rd., Fort Collins, CO 80522, USA.
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Eisen RJ, Gage KL. Adaptive strategies of Yersinia pestis to persist during inter-epizootic and epizootic periods. Vet Res 2009; 40:1. [PMID: 18803931 PMCID: PMC2695026 DOI: 10.1051/vetres:2008039] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2008] [Accepted: 09/18/2008] [Indexed: 11/14/2022] Open
Abstract
Plague is a flea-borne zoonotic bacterial disease caused by Yersinia pestis. It has caused three historical pandemics, including the Black Death which killed nearly a third of Europe's population in the 14th century. In modern times, plague epizootics can extirpate entire susceptible wildlife populations and then disappear for long time periods. Understanding how Y. pestis is maintained during inter-epizootic periods and the factors responsible for transitioning to epizootics is important for preventing and controlling pathogen transmission and ultimately reducing the burden of human disease. In this review, we focus primarily on plague in North American foci and discuss the potential adaptive strategies Y. pestis might employ to ensure not only its survival during inter-epizootic periods but also the rapid epizootic spread and invasion of new territories that are so characteristic of plague and have resulted in major pandemics and establishment of plague foci throughout much of the world.
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Affiliation(s)
- Rebecca J Eisen
- Bacterial Diseases Branch, Division of Vector Borne Infectious Diseases, National Center for Zoonotic, Enteric and Vector-Borne Diseases, Centers for Disease Control and Prevention, 3150 Rampart Road, Fort Collins, Colorado, USA.
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The Yersinia pestis caf1M1A1 fimbrial capsule operon promotes transmission by flea bite in a mouse model of bubonic plague. Infect Immun 2008; 77:1222-9. [PMID: 19103769 DOI: 10.1128/iai.00950-08] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Plague is a zoonosis transmitted by fleas and caused by the gram-negative bacterium Yersinia pestis. During infection, the plasmidic caf1M1A1 operon that encodes the Y. pestis F1 protein capsule is highly expressed, and anti-F1 antibodies are protective. Surprisingly, the capsule is not required for virulence after injection of cultured bacteria, even though it is an antiphagocytic factor and capsule-deficient Y. pestis strains are rarely isolated. We found that a caf-negative Y. pestis mutant was not impaired in either flea colonization or virulence in mice after intradermal inoculation of cultured bacteria. In contrast, absence of the caf operon decreased bubonic plague incidence after a flea bite. Successful development of plague in mice infected by flea bite with the caf-negative mutant required a higher number of infective bites per challenge. In addition, the mutant displayed a highly autoaggregative phenotype in infected liver and spleen. The results suggest that acquisition of the caf locus via horizontal transfer by an ancestral Y. pestis strain increased transmissibility and the potential for epidemic spread. In addition, our data support a model in which atypical caf-negative strains could emerge during climatic conditions that favor a high flea burden. Human infection with such strains would not be diagnosed by the standard clinical tests that detect F1 antibody or antigen, suggesting that more comprehensive surveillance for atypical Y. pestis strains in plague foci may be necessary. The results also highlight the importance of studying Y. pestis pathogenesis in the natural context of arthropod-borne transmission.
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Eisen RJ, Holmes JL, Schotthoefer AM, Vetter SM, Montenieri JA, Gage KL. Demonstration of early-phase transmission of Yersinia pestis by the mouse flea, Aetheca wagneri (Siphonaptera: Ceratophylidae), and implications for the role of deer mice as enzootic reservoirs. JOURNAL OF MEDICAL ENTOMOLOGY 2008; 45:1160-1164. [PMID: 19058643 DOI: 10.1603/0022-2585(2008)45[1160:doetoy]2.0.co;2] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
The role of deer mice and other species of Peromyscus as enzootic reservoirs for plague remains controversial. In this study, we evaluated early-phase vector efficiency of Aetheca wagneri Baker, a common flea species infesting deer mice, to determine the likelihood that Y. pestis could be spread mouse to mouse by this species. We showed that A. wagneri could transmit plague bacteria to laboratory mice as early as 3 d postinfection (p.i.), but transmission efficiency was quite low (1.03%; 95% CI: 0.19-3.34%) 1-4 d p.i. compared with that for the established plague vector Oropsylla montana Baker (10.63%; 95% CI: 4.18-25.91). Using this early-phase transmission efficiency estimate, we determined through parameterization of a simple predictive model that at least 68 A. wagneri per deer mouse would be required to support levels of transmission adequate for enzootic maintenance. Because deer mice typically harbor fewer than three A. wagneri per host, our data do not support the notion of an independent deer mouse--A. wagneri transmission cycle.
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Affiliation(s)
- Rebecca J Eisen
- Bacterial Diseases Branch, Division of Vector Borne Infectious Diseases, National Center for Zoonotic, Enteric and Vector-Borne Diseases, Centers for Disease Control and Prevention, 3150 Rampart Rd., Fort Collins, CO 80522, USA.
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Eisen RJ, Vetter SM, Holmes JL, Bearden SW, Montenieri JA, Gage KL. Source of host blood affects prevalence of infection and bacterial loads of Yersinia pestis in fleas. JOURNAL OF MEDICAL ENTOMOLOGY 2008; 45:933-938. [PMID: 18826038 DOI: 10.1603/0022-2585(2008)45[933:sohbap]2.0.co;2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Yersinia pestis, the etiological agent of plague, is transmitted by multiple flea species. Previous studies have reported wide variability in transmission efficiency among competent vectors. However, it is unclear to what extent such variation is explained by methodological differences among studies. To optimize an artificial feeding system where fleas are infected with controlled numbers of Y. pestis under standardized laboratory conditions that could be used to systematically compare vector efficiency, we sought to test the effect of host bloodmeal source on (1) the flea's ability to remain infected with Y. pestis and (2) bacterial loads in fleas. Here, we demonstrate that both prevalence of infection with a virulent strain of Y. pestis (CO96-3188) and bacterial loads in rock squirrel fleas (Oropsylla montana) are affected by host-associated blood factors. The generality of this observation was confirmed by repeating the study using the rat flea (Xenopsylla cheopis) and a commonly used avirulent laboratory strain of Y. pestis (A1122). Implications of the results for rate of spread of Y. pestis in naturally infected host populations are discussed.
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Affiliation(s)
- Rebecca J Eisen
- Bacterial Diseases Branch, Division of Vector Borne Infectious Diseases, National Center for Zoonotic, Enteric and Vector-Borne Diseases, Centers for Disease Control and Prevention, P.O. Box 2087, Fort Collins, CO 80522, USA.
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