Biomedical subjects

Kenneth L Gage

Publications and source records attributed to Kenneth L Gage.

At least 19 recordsLinked to original sources

PubMed2007

Phenotypic and molecular characterizations of Yersinia pestis isolates from Kazakhstan and adjacent regions.

Recent interest in characterizing infectious agents associated with bioterrorism has resulted in the development of effective pathogen genotyping systems, but this information is rarely combined with phenotypic data. Yersinia pestis, the aetiological agent of plague, has been well defined genotypically on local and worldwide scales using multi-locus variable number tandem repeat analysis (MLVA), with emphasis on evolutionary patterns using old isolate collections from countries where Y. pestis has existed the longest. Worldwide MLVA studies are largely based on isolates that have been in long-term laboratory culture and storage, or on field material from parts of the world where Y. pestis has potentially circulated in nature for thousands of years. Diversity in these isolates suggests that they may no longer represent the wild-type organism phenotypically, including the possibility of altered pathogenicity. This study focused on the phenotypic and genotypic properties of 48 Y. pestis isolates collected from 10 plague foci in and bordering Kazakhstan. Phenotypic characterization was based on diagnostic tests typically performed in reference laboratories working with Y. pestis. MLVA was used to define the genotypic relationships between the central-Asian isolates and a group of North American isolates, and to examine Kazakh Y. pestis diversity according to predefined plague foci and on an intermediate geographical scale. Phenotypic properties revealed that a large portion of this collection lacks one or more plasmids necessary to complete the blocked flea/mammal transmission cycle, has lost Congo red binding capabilities (Pgm-), or both. MLVA analysis classified isolates into previously identified biovars, and in some cases groups of isolates collected within the same plague focus formed a clade. Overall, MLVA did not distinguish unique phylogeographical groups of Y. pestis isolates as defined by plague foci and indicated higher genetic diversity among older biovars.

Animals↗

PubMed2006

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 sufficiently explain the rapid rate of spread that typifies plague epidemics and epizootics. Inconsistencies between the expected rate of spread by blocked rat fleas and that observed during the Black Death has even caused speculation that plague was not the cause of this medieval pandemic. We used the primary vector to humans in North America, Oropsylla montana, which rarely becomes blocked, as a model for studying alternative flea-borne transmission mechanisms. Our data revealed that, in contrast to the classical blocked flea model, O. montana is immediately infectious, transmits efficiently for at least 4 d postinfection (early phase) and may remain infectious for a long time because the fleas do not suffer block-induced mortality. These factors match the criteria required to drive plague epizootics as defined by recently published mathematical models. The scenario of efficient early-phase transmission by unblocked fleas described in our study calls for a paradigm shift in concepts of how Y. pestis is transmitted during rapidly spreading epizootics and epidemics, including, perhaps, the Black Death.

Animals↗

PubMed2006

Classic flea-borne transmission does not drive plague epizootics in prairie dogs.

We lack a clear understanding of the enzootic maintenance of the bacterium (Yersinia pestis) that causes plague and the sporadic epizootics that occur in its natural rodent hosts. A key to elucidating these epidemiological dynamics is determining the dominant transmission routes of plague. Plague can be acquired from the bites of infectious fleas (which is generally considered to occur via a blocked flea vector), inhalation of infectious respiratory droplets, or contact with a short-term infectious reservoir. We present results from a plague modeling approach that includes transmission from all three sources of infection simultaneously and uses sensitivity analysis to determine their relative importance. Our model is completely parameterized by using data from the literature and our own field studies of plague in the black-tailed prairie dog (Cynomys ludovicianus). Results of the model are qualitatively and quantitatively consistent with independent data from our field sites. Although infectious fleas might be an important source of infection and transmission via blocked fleas is a dominant paradigm in the literature, our model clearly predicts that this form of transmission cannot drive epizootics in prairie dogs. Rather, a short-term reservoir is required for epizootic dynamics. Several short-term reservoirs have the potential to affect the prairie dog system. Our model predictions of the residence time of the short-term reservoir suggest that other small mammals, infectious prairie dog carcasses, fleas that transmit plague without blockage of the digestive tract, or some combination of these three are the most likely of the candidate infectious reservoirs.

Animals↗

PubMed2005

Persistent Yersinia pestis antigens in ischemic tissues of a patient with septicemic plague.

In November 2002, a couple from New Mexico traveled to New York where both had fever and unilateral inguinal adenopathy. The husband was in septic shock when he sought medical care and was admitted to an intensive care unit, where he developed ischemic necrosis of his feet which later required bilateral amputation. Yersinia pestis was grown from his blood. Immunohistochemical assays using anti-Y pestis antibodies demonstrated multiple bacteria and granular antigens in and around vessels of the ischemic amputation tissues obtained 20 days after initiation of antibiotics; however, no evidence of Y pestis was present in viable tissues. Immunohistochemical evidence of Y pestis inside vessels of gangrenous feet in this patient underscores the importance of adequate excision of necrotic or partially necrotic tissues because antibiotics cannot be effectively delivered to necrotic and poorly perfused tissues.

Amputation, Surgical↗

PubMed2005

Detection of Rickettsia felis in a New World flea species, Anomiopsyllus nudata (Siphonaptera: Ctenophthalmidae).

The flea and rodent samples studied in this project were collected from field study sites in New Mexico from winter 1998 to spring 2001. During this period, 155 small rodents (14 different species) were live-trapped and combed for the presence of fleas. A total of 253 fleas were collected, comprising 21 species. Two of the 253 fleas collected were polymerase chain reaction (PCR) positive for the Rickettsia 17-kDa protein gene. These two fleas were both Anomiopsyllus nudata Baker, each collected from an individual Neotoma albigula Hartley, on two occasions. Individual fleas positive for the Rickettsia 17-kDa protein gene were then tested with primers targeting the rickettsial genes for citrate synthase (gltA) and two major outer membrane proteins (ompA and ompB). The nucleotide sequences of the PCR products of these two fleas were identical to each other and were 100% (394/394), 100% (1150/1150), 99.8% (469/470), and 99.3% (818/824) similar to the corresponding sequences of the 17-kDa, gltA, ompA, and ompB genes of Rickettsia felis, respectively. Flea homogenates of individual PCR-positive fleas were inoculated into shell vials seeded with Vero cells, and the Gimenez stain technique was used to demonstrate the presence of Rickettsia-like organisms in detached cells found in aspirated medium 19 d after inoculation. These cells were harvested and tested by PCR, targeting portions of the 17-kDa and gltA genes, resulting in products 100% identical to R. felis. This work comprises the first report of R. felis detection in a flea species (A. nudata) endemic to the New World.

Animals↗

PubMed2005

Identifying sources of human exposure to plague.

Yersinia pestis, the etiologic agent of plague, has shaped the course of human history, killing millions of people in three major pandemics. This bacterium is still endemic in parts of Asia, Africa, and the Americas, where it poses a natural disease threat to human populations. Y. pestis has also recently received attention as a possible bioterrorism agent. Thus, rapid methods to distinguish between bioterrorism and naturally occurring plague infections are of major importance. Our study is the first to demonstrate that variable-number tandem repeats (VNTRs) in the Y. pestis genome can link human case isolates to those obtained from suspected environmental sources of infection. We demonstrate the valuable utility of VNTR markers in epidemiological investigations of naturally occurring plague and the forensic analysis of possible bioterrorism events.

Animals↗

PubMed2005

Natural history of plague: perspectives from more than a century of research.

For more than a century, scientists have investigated the natural history of plague, a highly fatal disease caused by infection with the gram-negative bacterium Yersinia pestis. Among their most important discoveries were the zoonotic nature of the disease and that plague exists in natural cycles involving transmission between rodent hosts and flea vectors. Other significant findings include those on the evolution of Y. pestis; geographic variation among plague strains; the dynamics and maintenance of transmission cycles; mechanisms by which fleas transmit Y. pestis; resistance and susceptibility among plague hosts; the structure and typology of natural foci; and how landscape features influence the focality, maintenance, and spread of the disease. The knowledge gained from these studies is essential for the development of effective prevention and control strategies.

Animals↗

PubMed2004

Methods for enhanced culture recovery of Francisella tularensis.

Francisella tularensis is found in a wide variety of hosts and extrahost environments, making culture recovery a diagnostic challenge. Here we demonstrate improved recovery times and good sensitivity (90%) when cultures were inoculated on the site of an investigation using fresh tissues. For contaminated specimens, antibiotic supplementation of enriched cysteine heart agar blood culture medium improved recovery of F. tularensis by 81.1%. For transport of tissues, immediate freezing yielded culture recovery rates as high as 94%.

Animals↗

PubMed2004

An outbreak of Francisella tularensis in captive prairie dogs: an immunohistochemical analysis.

An immunohistochemical assay was developed and tested for detection of Francisella tularensis lipopolysaccaride antigen in tissues of captive prairie dogs (Cynomys ludovicianus). Tissues from 59 cases of F. tularensis were examined by this technique, which was corroborated by direct fluorescent antibody assay and direct isolation of the organism. In infected prairie dogs, studies indicated multiple, severe, necroprurulent foci occurring in the liver, lung, spleen, terminal ileum, and mandibular lymph node. Immunohistochemical analysis of the same formalin-fixed tissues indicated the presence of F. tularensis antigen in neutrophils and macrophages of these lesions and occurring extracellularly in areas of necrosis. This report demonstrates that immunohistochemical analysis is a rapid procedure that can be used to determine the pathogenesis of F. tularensis in rodent populations.

Animals↗

PubMed2004

Laboratory analysis of tularemia in wild-trapped, commercially traded prairie dogs, Texas, 2002.

Oropharyngeal tularemia was identified as the cause of a die-off in captured wild prairie dogs at a commercial exotic animal facility in Texas. From this point source, Francisella tularensis-infected prairie dogs were traced to animals distributed to the Czech Republic and to a Texas pet shop. F. tularensis culture isolates were recovered tissue specimens from 63 prairie dogs, including one each from the secondary distribution sites. Molecular and biochemical subtyping indicated that all isolates were F. tularensis subsp. holarctica (Type B). Microagglutination assays detected antibodies against F. tularensis, with titers as great as 1:4,096 in some live animals. All seropositive animals remained culture positive, suggesting that prairie dogs may act as chronic carriers of F. tularensis. These findings demonstrate the need for additional studies of tularemia in prairie dogs, given the seriousness of the resulting disease, the fact that prairie dogs are sold commercially as pets, and the risk for pet-to-human transmission.

Animals↗

PubMed2004

First reported prairie dog-to-human tularemia transmission, Texas, 2002.

A tularemia outbreak, caused by Francisella tularensis type B, occurred among wild-caught, commercially traded prairie dogs. F. tularensis microagglutination titers in one exposed person indicated recent infection. These findings represent the first evidence for prairie-dog-to-human tularemia transmission and demonstrate potential human health risks of the exotic pet trade.

Adult↗

PubMed2004

Prevalence and diversity of Bartonella in rodents of northern Thailand: a comparison with Bartonella in rodents from southern China.

We report results of the first study to investigate the distribution and diversity of Bartonella in rodents from Thailand. Whole blood from 195 rodents, representing six species, was tested for the presence of Bartonella species using standard culture techniques. Isolates were obtained from 17 (8.7%) of the samples, and 14 of those isolates represented distinct strains, based upon partial sequencing of the citrate synthase (gltA) gene. Phylogenetic analysis of the isolates and other Bartonella species indicated that five unique isolates from Bandicota indica form a cluster that may represent a new Bartonella species. Two additional isolates from B. indica clustered together, and were nearly identical to an isolate from Apodemus draco collected in southern China. Importantly, a number of the isolates from Thailand rodents are closely related to B. grahamii and B. elizabethae, species which have been associated with human illness.

Animals↗

PubMed2003

Molecular characterization of the sucB gene encoding the immunogenic dihydrolipoamide succinyltransferase protein of Bartonella vinsonii subsp. berkhoffii and Bartonella quintana.

Members of the genus Bartonella have historically been connected with human disease, such as cat scratch disease, trench fever, and Carrion's disease, and recently have been recognized as emerging pathogens causing other clinical manifestations in humans. However, because little is known about the antigens that elicit antibody production in response to Bartonella infections, this project was undertaken to identify and molecularly characterize these immunogens. Immunologic screening of a Bartonella vinsonii subsp. berkhoffii genomic expression library with anti-Bartonella antibodies led to the identification of the sucB gene, which encodes the enzyme dihydrolipoamide succinyltransferase. Antiserum from a mouse experimentally infected with live Bartonella was reactive against recombinant SucB, indicating the mounting of an anti-SucB response following infection. Antigenic cross-reactivity was observed with antiserum against other Bartonella spp. Antibodies against Coxiella burnetti, Francisella tularensis, and Rickettsia typhi also reacted with our recombinant Bartonella SucB. Potential SucB antigenic cross-reactivity presents a challenge to the development of serodiagnostic tests for other intracellular pathogens that cause diseases such as Q fever, rickettsioses, brucelloses, tularemia, and other bartonelloses.

Acyltransferases↗

PubMed2003

Bartonella strains from ground squirrels are identical to Bartonella washoensis isolated from a human patient.

The most likely animal source of a human case of cardiac disease in Washoe County, Nev., was identified by comparison of DNA sequences of three genes (citrate synthase gltA, 60-kDa heat shock protein gene groEL, and 16S rRNA gene) of Bartonella washoensis cultured from the human patient in question and of Bartonella isolates obtained from the following Nevada rodents: Peromyscus maniculatus (17 isolates), Tamias minimus (11 isolates), Spermophilus lateralis (3 isolates), and Spermophilus beecheyi (7 isolates). Sequence analyses of gltA amplicons obtained from Bartonella from the rodents demonstrated considerable heterogeneity and resulted in the identification of 16 genetic variants that were clustered within three groups in phylogenetic analysis. Each of the three groups was associated with a rodent genus, Peromyscus, Tamias, or Spermophilus: The gltA, 16S rRNA gene, and groEL sequences of a Bartonella isolate obtained from a California ground squirrel (S. beecheyi) were completely identical to homologous sequences of B. washoensis, strongly suggesting that these animals were the source of infection in the human case.

Animal Diseases↗

PubMed2003

Detection of novel Bartonella strains and Yersinia pestis in prairie dogs and their fleas (Siphonaptera: Ceratophyllidae and Pulicidae) using multiplex polymerase chain reaction.

We developed a multiplex polymerase chain reaction (PCR) assay that simultaneously detects three types of flea-associated microorganisms. Targets for the assay were sequences encoding portions of the gltA, a 17-kDa antigen, and pla genes of Bartonella spp. Strong et al., Rickettsia spp. da Rocha-Lima, and Yersinia pestis Yersin, respectively. A total of 260 flea samples containing bloodmeal remnants were analyzed from fleas collected from abandoned prairie dog (Cynomys ludovicianus) burrows at the site of an active plague epizootic in Jefferson County, CO. Results indicated that 34 (13.1%) fleas were positive for Bartonella spp., 0 (0%) were positive for Rickettsia spp., and 120 (46.2%) were positive for Y. pestis. Twenty-three (8.8%) of these fleas were coinfected with Bartonella spp. and Y. pestis. A second group of 295 bloodmeal-containing fleas was collected and analyzed from abandoned burrows in Logan County, CO, where a prairie dog die-off had occurred 2-4 mo before the time of sampling. Of these 295 fleas, 7 (2.4%) were positive for Bartonella spp., 0 (0%) were positive for Rickettsia spp., and 46 (15.6%) were positive for Y. pestis. Coinfections were not observed in fleas from the Logan County epizootic site. The multiplex PCR also was used to identify Y. pestis and Bartonella in prairie dog blood and tissues. This report represents the first identification of Bartonella from prairie dogs and their fleas. Prairie dog fleas were tested with PCR, and the Bartonella PCR amplicons produced were sequenced and found to be closely related to similar sequences amplified from Bartonella that had been isolated from prairie dog blood samples. Phylogenetic analyses indicate that the sequences of bartonellae from prairie dogs and prairie dog fleas cluster tightly within a clade that is distinct from those containing other known Bartonella genotypes.

Animals↗

PubMed2003

Treatment of black-tailed prairie dog burrows with deltamethrin to control fleas (Insecta: Siphonaptera) and plague.

Burrows within black-tailed prairie dog (Cynomys ludovicianus) colonies on the Rocky Mountain Arsenal National Wildlife Refuge, Colorado, were dusted with deltamethrin insecticide to reduce flea (Insecta: Siphonaptera) abundance. Flea populations were monitored pre- and posttreatment by combing prairie dogs and collecting fleas from burrows. A single application of deltamethrin significantly reduced populations of the plague vector Oropsylla hirsuta, and other flea species on prairie dogs and in prairie dog burrows for at least 84 d. A plague epizootic on the Rocky Mountain Arsenal National Wildlife Refuge caused high mortality of prairie dogs on some untreated colonies, but did not appear to affect nearby colonies dusted with deltamethrin.

Animals↗

PubMed2002

Predicting membrane oxygenator pressure drop using computational fluid dynamics.

Three-dimensional computational fluid dynamic (CFD) simulations of membrane oxygenators should allow prediction of spatially dependent variables and subsequent shape optimization. Fiber bed complexity and current computational limitations require the use of approximate models to predict fiber drag effects in complete device simulations. A membrane oxygenator was modified to allow pressure measurement along the fiber bundle in all cardinal axes. Experimental pressure drop information with water perfusion was used to calculate the permeability of the fiber bundle. A three-dimensional CFD model of a commercial membrane oxygenator was developed to predict pressure drops throughout the device. Darcy's Law was used to account for the viscous drag of the fibers and was incorporated as a momentum loss term in the conservation equations. Close agreement was shown between experimental and simulated pressure drops at lower flow rates, but the simulated pressure drops were lower than experimental results at higher flows. Alternate models of fiber drag effects and flow field visualization are suggested as means to potentially improve the accuracy of the flow simulation. Computational techniques coupled with experimental verification offer insight into model validity and show promise for the development of accurate three-dimensional simulations of membrane oxygenators.

Artificial Organs↗

PubMed2002

Modeling relationships between climate and the frequency of human plague cases in the southwestern United States, 1960-1997.

The relationships between climatic variables and the frequency of human plague cases (1960-1997) were modeled by Poisson regression for two adjoining regions in northeastern Arizona and northwestern New Mexico. Model outputs closely agreed with the numbers of cases actually observed, suggesting that temporal variations in plague risk can be estimated by monitoring key climatic variables, most notably maximum daily summer temperature values and time-lagged (1 and 2 year) amounts of late winter (February-March) precipitation. Significant effects also were observed for time-lagged (1 year) summer precipitation in the Arizona model. Increased precipitation during specific periods resulted in increased numbers of expected cases in both regions, as did the number of days above certain lower thresholds for maximum daily summer temperatures (80 degrees F in New Mexico and 85 degrees F in Arizona). The number of days above certain high-threshold temperatures exerted a strongly negative influence on the numbers of expected cases in both the Arizona and New Mexico models (95 degrees F and 90 degrees F, respectively). The climatic variables found to be important in our models are those that would be expected to influence strongly the population dynamics of the rodent hosts and flea vectors of plague.

Arizona↗