Publications

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quantitative competitive pcr as a technique for exploring flea-yersina pestis dynamics.we used a quantitative competitive polymerase chain reaction assay to quantify yersinia pestis loads in fleas and bacteremia levels in mice that were used as sources of infectious blood meals for feeding the fleas. xenopsylla cheopis, the oriental rat flea, achieved higher infection rates, developed greater bacterial loads, and became infectious more rapidly than oropsylla montana, a ground squirrel flea. both flea species required about 10(6) y. pestis cells per flea to be able to transmit to m ...200011289663
flea, rodent, and plague ecology at chuchupate campground, ventura county, california.chuchupate campground in ventura county, california, was closed to the public for 18 years (1982 to 2000) because of uncontrolled vector fleas and persistent plague antibody titers in rodents. the primary purpose of this study was to clarify the plague ecology of chuchupate campground by identifying involved rodents and their vector fleas and by determining many of their ecological parameters: abundance, flea and host preferences and diversities, and flea seasonality. rodents and fleas were iden ...200212125863
analysis of genetic algorithm for rule-set production (garp) modeling approach for predicting distributions of fleas implicated as vectors of plague, yersinia pestis, in california.more than 20 species of fleas in california are implicated as potential vectors of yersinia pestis. extremely limited spatial data exist for plague vectors-a key component to understanding where the greatest risks for human, domestic animal, and wildlife health exist. this study increases the spatial data available for 13 potential plague vectors by using the ecological niche modeling system genetic algorithm for rule-set production (garp) to predict their respective distributions. because the a ...200616506453
early-phase transmission of yersinia pestis by unblocked fleas as a mechanism explaining rapidly spreading plague epizootics.plague is a highly virulent disease believed to have killed millions during three historic human pandemics. worldwide, it remains a threat to humans and is a potential agent of bioterrorism. dissemination of yersinia pestis, the etiological agent of plague, by blocked fleas has been the accepted paradigm for flea-borne transmission. however, this mechanism, which requires a lengthy extrinsic incubation period before a short infectious window often followed by death of the flea, cannot sufficient ...200617032761
temporal dynamics of early-phase transmission of yersinia pestis by unblocked fleas: secondary infectious feeds prolong efficient transmission by oropsylla montana (siphonaptera: ceratophyllidae).plague, a flea-borne zoonotic disease, is characterized by rapidly spreading epizootics. rate of infectious spread is thought to be related to daily biting rate of the vector, the extrinsic incubation period, vector efficiency, and the duration of infectivity. a recent study of oropsylla montana (baker) (siphonaptera: ceratophyllidae), the primary vector of yersinia pestis (yersin) to humans in north america, revealed that this flea feeds readily on a daily basis, has a very short extrinsic incu ...200717695024
source of host blood affects prevalence of infection and bacterial loads of yersinia pestis in fleas.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 ef ...200818826038
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.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: ...200819058643
biofilm formation is not required for early-phase transmission of yersinia pestis.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 storag ...201020395271
plague studies in california: a review of long-term disease activity, flea-host relationships and plague ecology in the coniferous forests of the southern cascades and northern sierra nevada mountains.we review 28 years of long-term surveillance (1970-1997) for plague activity among wild rodents from ten locations within three coniferous forest habitat types in the northern sierra nevada and the southern cascade mountains of northeastern california. we identify rodent hosts and their fleas and document long-term plague activity in each habitat type. the highest seroprevalence for yersinia pestis occurred in the chipmunks, tamias senex and t. quadrimaculatus, and the pine squirrel, tamiasciuru ...201020618641
seasonal and among-site variation in the occurrence and abundance of fleas on california ground squirrels (otospermophilus beecheyi).an improved understanding of the ecology of fleas on california ground squirrels, otospermophilus beecheyi, is warranted given the role of fleas in the transmission, and perhaps persistence, of the plague-causing bacterium yersinia pestis. we sampled o. beecheyi on a seasonal basis from three study sites, each representing a different land use type (preserve, pasture, and agriculture) in the san joaquin valley, ca. overall, the abundance of fleas on squirrels was greatest in spring at the preser ...201121635649
evaluation of the effect of host immune status on short-term yersinia pestis infection in fleas with implications for the enzootic host model for maintenance of y. pestis during interepizootic periods.plague, a primarily flea-borne disease caused by yersinia pestis, is characterized by rapidly spreading epizootics separated by periods of quiescence. little is known about how and where y. pestis persists between epizootics. it is commonly proposed, however, that y pestis is maintained during interepizootic periods in enzootic cycles involving flea vectors and relatively resistant host populations. according to this model, while susceptible individuals serve as infectious sources for feeding fl ...201425276941
yersinia pestis infection and laboratory conditions alter flea-associated bacterial communities.we collected oropsylla montana from rock squirrels, spermophilus varigatus, and infected a subset of collected fleas with yersinia pestis, the etiological agent of plague. we used bar-tagged dna pyrosequencing to characterize bacterial communities of wild, uninfected controls and infected fleas. bacterial communities within y. pestis-infected fleas were substantially more similar to one another than communities within wild or control fleas, suggesting that infection alters the bacterial communit ...201222895162
comparative ability of oropsylla montana and xenopsylla cheopis fleas to transmit yersinia pestis by two different mechanisms.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 ...201728081130
[advance to the research of the climate factor effect on the distribution of plague].plague is an anthropozoonotic disease caused by the yersinia pestis ,which developed by many factors including local climate factors. in recent years, more and more studies on the effects of climate on plague were conducted. according to the researches, climate factors (mainly the rainfall and temperature) affected the development and distribution of plague by influencing the abundance of plague host animals and fleas index. the climate also affected the epidemic dynamics and the scope of plague ...201627141906
infection prevalence, bacterial loads, and transmission efficiency in oropsylla montana (siphonaptera: ceratophyllidae) one day after exposure to varying concentrations of yersinia pestis in blood.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 (≥10(8 )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 ...201626843450
yersinia murine toxin is not required for early-phase transmission of yersinia pestis by oropsylla montana (siphonaptera: ceratophyllidae) or xenopsylla cheopis (siphonaptera: pulicidae).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. whil ...201425187626
short report: exposing laboratory-reared fleas to soil and wild flea feces increases transmission of yersinia pestis.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 treatment ...201323939709
effects of low-temperature flea maintenance on the transmission of yersinia pestis by oropsylla montana.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 ho ...201323590319
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