Last data update: May 06, 2024. (Total: 46732 publications since 2009)
Records 1-8 (of 8 Records) |
Query Trace: Holmes JL[original query] |
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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
Graham CB , Woods ME , Vetter SM , Petersen JM , Montenieri JA , Holmes JL , Maes SE , Bearden SW , Gage KL , Eisen RJ . J Med Entomol 2014 51 (5) 1079-1086 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 fleas and subsequently die of infection, resistant hosts survive infection, develop antibodies to the plague bacterium, and continue to provide bloodmeals to infected fleas. For Y. pestis to persist under this scenario, fleas must remain infected after feeding on hosts carrying antibodies to Y. pestis. Studies of other vector-borne pathogens suggest that host immunity may negatively impact pathogen survival in the vector. Here, we report infection rates and bacterial loads for fleas (both Xenopsylla cheopis (Rothschild) and Oropsylla montana (Baker)) that consumed an infectious bloodmeal and subsequently fed on an immunized or age-matched naive mouse. We demonstrate that neither the proportion of infected fleas nor the bacterial loads in infected fleas were significantly lower within 3 d of feeding on immunized versus naive mice. Our findings thus provide support for one assumption underlying the enzootic host model of interepizootic maintenance of Y. pestis. |
Effects of low-temperature flea maintenance on the transmission of Yersinia pestis by Oropsylla montana
Williams SK , Schotthoeffer AM , Montenieri JA , Holmes JL , Vetter SM , Gage KL , Bearden SW . Vector Borne Zoonotic Dis 2013 13 (7) 468-78 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 degrees C, 10 degrees C, 15 degrees C, or 23 degrees C). Transmission efficiencies were tested by allowing up to 15 infectious fleas to feed on each of 7 naive 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 degrees C, 10 degrees C, and 15 degrees C were able to effectively transmit at every time point p.i. The percentage of transmission to naive mice by fleas maintained at low temperatures (46.0% at 6 degrees C, 71.4% at 10 degrees C, 66.7% at 15 degrees C) was higher than for fleas maintained at 23 degrees 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 degrees C and 15 degrees 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 degrees 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 degrees 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. |
Combining real-time polymerase chain reaction using SYBR Green I detection and sequencing to identify vertebrate bloodmeals in fleas.
Graham CB , Black WC , Boegler KA , Montenieri JA , Holmes JL , Gage KL , Eisen RJ . J Med Entomol 2012 49 (6) 1442-52 Programs that aim to control vector-borne zoonotic diseases require information on zoonotic hosts and on the feeding behavior of bridging vectors that are capable of transmitting pathogens from those hosts to humans. Here we describe an assay developed to identify bloodmeals in field-collected cat fleas (Ctenocephalides felis Bouche) to assess this species' potential role as a Yersinia pestis bridging vector in a plague-endemic region of Uganda. Our assay uses a single primer set and SYBR Green I-based real-time polymerase chain reaction to amplify a segment of the 12S mitochondrial ribosomal RNA gene for identification by sequencing. The assay capitalizes on the sensitivity of real-time polymerase chain reaction and the specificity of sequencing and can be used to differentiate vertebrate bloodmeals to the genus or species level without a priori knowledge of the host community. Because real-time assays that detect vertebrate DNA are highly sensitive to human DNA contamination, we analyzed detection in artificially fed and unfed fleas to establish a Ct cutoff that optimized specificity without completely sacrificing sensitivity. Using the established cutoff, our assay detected human, rat, and goat DNA in artificially fed C. felis up to 72 h postfeeding. |
Evaluation of the infectiousness to mice of soil contaminated with Yersinia pestis-infected blood
Boegler KA , Graham CB , Montenieri JA , Macmillan K , Holmes JL , Petersen JM , Gage KL , Eisen RJ . Vector Borne Zoonotic Dis 2012 12 (11) 948-52 Plague, an often-fatal zoonotic disease caused by Yersinia pestis, is characterized by epizootic and quiescent periods. How Y. pestis is maintained during inter-epizootic periods is poorly understood, but soil has been implicated as a potential reservoir. Although previous studies have suggested that Y. pestis is able to survive in soil for weeks or months, it is unclear whether or not it is infectious to susceptible hosts. Here we investigate the potential for Y. pestis to infect mice through close contact with contaminated soil under laboratory conditions. In an attempt to approximate the natural conditions under which animals would be exposed to Y. pestis-contaminated soil, mouse cages filled with soil from a plague-endemic region were held at temperature and humidity ranges observed in ground squirrel burrows. These laboratory "burrows" were contaminated with highly bacteremic blood (>10(8) cfu/mL) to simulate the introduction of infectious material from a dying animal during an epizootic. Outbred Swiss-Webster mice with scarified skin patches were held on contaminated soil for 10 days and monitored for signs of illness. Following exposure to contaminated soil, one animal of 104 became infected with Y. pestis. None of the remaining animals seroconverted following a 21-day holding period. Under our experimental conditions, which maximized the likelihood of contact between susceptible mice and contaminated soil, transmission efficiency from soil to mice was 0.96% (95% CI 0.17, 5.25%). This suggests that although transmission of Y. pestis from contaminated soils is possible, it is not likely a major transmission route under natural conditions. |
Evaluation and modification of off-host flea collection techniques used in Northwest Uganda: laboratory and field studies
Borchert JN , Eisen RJ , Holmes JL , Atiku LA , Mpanga JT , Brown HE , Graham CB , Babi N , Montenieri JA , Enscore RE , Gage KL . J Med Entomol 2012 49 (1) 210-214 Quantifying the abundance of host-seeking fleas is critical for assessing risk of human exposure to flea-borne disease agents, including Yersinia pestis, the etiological agent of plague. Yet, reliable measures of the efficacy of existing host-seeking flea collection methods are lacking. In this study, we compare the efficacy of passive and active methods for the collection of host-seeking fleas in both the laboratory and human habitations in a plague-endemic region of northwest Uganda. In the laboratory, lighted "Kilonzo" flea traps modified with either blinking lights, the creation of shadows or the generation of carbon dioxide were less efficient at collecting Xenopsylla cheopis Rothchild and Ctenocephalides felis Bouché fleas than an active collection method using white cotton socks or cotton flannel. Passive collection using Kilonzo light traps in the laboratory collected significantly more X. cheopis than C. felis and active collection, using white socks and flannel, collected significantly more C. felis than X. cheopis. In field studies conducted in Uganda, Kilonzo traps using a flashlight were similar in their collection efficacy to Kilonzo traps using kerosene lamps. However, in contrast to laboratory studies, Kilonzo flea traps using flashlights collected a greater number of fleas than swabbing. Within human habitations in Uganda, Kilonzo traps were especially useful for collecting C. felis, the dominant species found in human habitations in this area. |
Effects of temperature on the transmission of Yersinia pestis by the flea, Xenopsylla cheopis, in the late phase period
Schotthoefer AM , Bearden SW , Holmes JL , Vetter SM , Montenieri JA , Williams SK , Graham CB , Woods ME , Eisen RJ , Gage KL . Parasit Vectors 2011 4 191 BACKGROUND: Traditionally, efficient flea-borne transmission of Yersinia pestis, the causative agent of plague, was thought to be dependent on a process referred to as blockage in which biofilm-mediated growth of the bacteria physically blocks the flea gut, leading to the regurgitation of contaminated blood into the host. This process was previously shown to be temperature-regulated, with blockage failing at temperatures approaching 30 degrees C; however, the abilities of fleas to transmit infections at different temperatures had not been adequately assessed. We infected colony-reared fleas of Xenopsylla cheopis with a wild type strain of Y. pestis and maintained them at 10, 23, 27, or 30 degrees C. Naive mice were exposed to groups of infected fleas beginning on day 7 post-infection (p.i.), and every 3-4 days thereafter until day 14 p.i. for fleas held at 10 degrees C, or 28 days p.i. for fleas held at 23-30 degrees C. Transmission was confirmed using Y. pestis-specific antigen or antibody detection assays on mouse tissues. RESULTS: Although no statistically significant differences in per flea transmission efficiencies were detected between 23 and 30 degrees C, efficiencies were highest for fleas maintained at 23 degrees C and they began to decline at 27 and 30 degrees C by day 21 p.i. These declines coincided with declining median bacterial loads in fleas at 27 and 30 degrees C. Survival and feeding rates of fleas also varied by temperature to suggest fleas at 27 and 30 degrees C would be less likely to sustain transmission than fleas maintained at 23 degrees C. Fleas held at 10 degrees C transmitted Y. pestis infections, although flea survival was significantly reduced compared to that of uninfected fleas at this temperature. Median bacterial loads were significantly higher at 10 degrees C than at the other temperatures. CONCLUSIONS: Our results suggest that temperature does not significantly effect the per flea efficiency of Y. pestis transmission by X. cheopis, but that temperature is likely to influence the dynamics of Y. pestis flea-borne transmission, perhaps by affecting persistence of the bacteria in the flea gut or by influencing flea survival. Whether Y. pestis biofilm production is important for transmission at different temperatures remains unresolved, although our results support the hypothesis that blockage is not necessary for efficient transmission. |
Biofilm formation is not required for early-phase transmission of Yersinia pestis
Vetter SM , Eisen RJ , Schotthoefer AM , Monteneri JA , Holmes JL , Bobrov AG , Bearden SW , Perry RD , Gage KL . Microbiology (Reading) 2010 156 2216-2225 Our study investigated whether hms-mediated biofilm formation was necessary for early-phase transmission (EPT) of Yersinia pestis. In addition to the biofilm-dependent blockage model of plague transmission from flea to mammal, an EPT model of transmission, has been described where fleas transmit Y. pestis to a host up to 4 days post infection, which is insufficient time for blockages to form in flea foreguts. An artificial feeding system was used to feed Xenopsylla cheopis and Oropsylla montana rat blood spiked with either the parental Y. pestis strain KIM5(pCD1)+, two different biofilm-mutants (DeltahmsT , DeltahmsR), or a biofilm-overproducer mutant (DeltahmsP ). Infected fleas were then allowed to feed on naive Swiss Webster mice 1-4 days after infection and the mice were monitored for signs of infection up to three weeks post-exposure. The biofilm-defective mutants were transmitted from X. cheopis and O. montana as efficiently as the parent strain, whereas the transmission efficiency of fleas fed the biofilm-overproducer was significantly less than either the parent or biofilm-deficient strains. The bacterial loads in fleas infected with a biofilm-deficient strain harbored lower bacterial loads 4 days post infection when compared to fleas infected with the parent strain. Thus defects in biofilm formation did not prevent flea-borne transmission of Y. pestis in our EPT model and biofilm over-production inhibited efficient EPT, however biofilm may play a role in infection persistence in the flea. |
Climatic predictors of the intra- and inter-annual distributions of plague cases in New Mexico based on 29 years of animal-based surveillance data
Brown HE , Ettestad P , Reynolds PJ , Brown TL , Hatton ES , Holmes JL , Glass GE , Gage KL , Eisen RJ . Am J Trop Med Hyg 2010 82 (1) 95-102 Within the United States, the majority of human plague cases are reported from New Mexico. We describe climatic factors involved in intra- and inter-annual plague dynamics using animal-based surveillance data from that state. Unlike the clear seasonal pattern observed at lower elevations, cases occur randomly throughout the year at higher elevations. Increasing elevation corresponded with delayed mean time in case presentation. Using local meteorological data (previous year mean annual precipitation, total degrees over 27 degrees C 3 years before and maximum winter temperatures 4 years before) we built a time-series model predicting annual case load that explained 75% of the variance in pet cases between years. Moreover, we found a significant correlation with observed annual human cases and predicted pet cases. Because covariates were time-lagged by at least 1 year, intensity of case loads can be predicted in advance of a plague season. Understanding associations between environmental and meteorological factors can be useful for anticipating future disease trends. |
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