Threshold Conditions for the Persistence of Plague Transmission in Urban Rats

Durham, David P.; Casman, Elizabeth A.

doi:10.1111/j.1539-6924.2009.01309.x

Cited by 5 publications

(4 citation statements)

References 43 publications

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“…However, a feature of flea-borne transmission in nature is that several infected fleas feeding simultaneously on a single host in the early-phase window, or a blocked flea making repeated feeding attempts in succession can produce an augmented, cumulative transmission efficiency. For example, a blocked flea will bite continuously and persistently in the few days before it dies from starvation; and blocked flea transmission efficiency estimates based on single, short term exposure trials are acknowledged to be underestimates [ 8 , 28 ]. The probability of a blocked flea cumulatively transmitting significant numbers of CFUs in repeated bites likely approaches 100%.…”

Section: Discussionmentioning

confidence: 99%

A Role for Early-Phase Transmission in the Enzootic Maintenance of Plague

et al. 2022

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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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Section: Discussionmentioning

confidence: 99%

A Role for Early-Phase Transmission in the Enzootic Maintenance of Plague

et al. 2022

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“…In our experiments, blocked fleas were given only a single one-hour feeding opportunity. Importantly, as has been noted, this underestimates the effective natural transmission efficiency of a blocked flea, which likely approaches 100% because the cumulative number of bites and extended time over which it attempts to feed act as a force multiplier for transmission [22,23]. For example, in one case a single blocked flea transmitted to three separate bite sites during the 1-hour challenge period (S5 Table).…”

Section: Plos Pathogensmentioning

confidence: 97%

Comparison of the transmission efficiency and plague progression dynamics associated with two mechanisms by which fleas transmit Yersinia pestis

et al. 2020

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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.

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“…Wild rodents that are relatively resistant to plague, as well as fleas that are able to transmit the bacteria, are thought to maintain the infection in established foci of plague from which commensal rodents can become periodically infected . However, modeling studies of plague in urban rats suggest the disease can also be maintained in their populations without introduction from another source (Keeling and Gilligan, 2000a, b;Durham and Casman, 2010). According to these models, plague circulates within rat populations when the proportion of susceptible rats is between 25 and 50 percent, and these circumstances pose little risk of causing an epidemic among humans (Keeling and Gilligan, 2000a, b).…”

Section: Commensal Ratsmentioning

confidence: 99%

“…Another modeling study concluded that enzootic plague in rats of a specified area depends on the "critical flea index," a statistical tipping point related to the rat population. When flea density of the area is greater than the critical flea index, plague will become enzootic in urban rats (Durham and Casman, 2010).…”

Section: Commensal Ratsmentioning

confidence: 99%