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A Role for Early-Phase Transmission in the Enzootic Maintenance of Plague
Cedar L Mitchell1, Ashley R Schwarzer1, Adélaïde Miarinjara1
1Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America.
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.
Insights
Yersinia pestis transmission by fleas depends on the transmission mode. Blocked flea transmission is more efficient and can cause plague epizootics in diverse rodent populations.
Area of Science:
- Ecology
- Microbiology
- Epidemiology
Background:
- Plague, caused by Yersinia pestis, is maintained in wild rodent populations and transmitted by fleas.
- Rodent susceptibility and flea vector competence vary, influencing plague epizootic dynamics.
- Understanding factors driving plague epizootics, particularly flea transmission efficiency, remains crucial.
Purpose of the Study:
- To comparatively quantify the transmission efficiency of two Yersinia pestis flea-borne transmission modes.
- To assess the influence of host blood and flea blockage on transmission efficiency.
- To model the conditions under which different transmission modes can drive plague epizootics.
Main Methods:
- Comparative quantification of early-phase and biofilm-dependent transmission by Oropsylla montana.
- Mathematical modeling of Yersinia pestis transmission dynamics in rodent populations.
- Analysis of host blood source effects on transmission efficiency.
Main Results:
- Biofilm-dependent transmission by blocked Oropsylla montana fleas was more efficient and less dependent on host blood characteristics than early-phase transmission.
- Mathematical models predicted that blocked flea transmission could cause epizootics in a wider range of rodent hosts.
- Early-phase transmission, if sublethal, may increase rodent immunity, potentially limiting rapid epizootic spread.
Conclusions:
- Flea vector competence and transmission mechanisms significantly impact Yersinia pestis epizootic potential.
- Blocked flea transmission represents a critical factor for plague outbreaks in diverse wild rodent populations.
- Understanding transmission modes is key to predicting and managing plague dynamics in wildlife.
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