resistance to tick-borne francisella tularensis by tick-sensitized rabbits: allergic klendusity.mammals become hypersensitive to ticks that feed upon them. that hypersensitivity was thought responsible for an observation that a large number of francisella tularensis-infected dermacentor variabilis failed to infect a rabbit previously exposed to ticks of that species. in a series of tests of that hypothesis, rabbits sensitized to ticks were often significantly more resistant than control animals to tick-borne tularemia. the conditions that determine the klendusity are thought to be variable ...1979484770
tick-borne tularemia. an outbreak of lymphadenopathy in children.between june 1 and july 15, 1984, twenty persons with glandular tularemia were identified on the lower brule and crow creek indian reservations in south dakota. the median age of the patients was 6 years (range, 2 to 20 years). the clinical illness was mild, consisting of fever, headache, and lymphadenopathy. all lymphadenopathy was in the head and neck area. dermacentor variabilis ticks were identified as the vector. although the mild clinical illness suggested francisella tularensis, type b, w ...19854057512
an outbreak of human tularemia associated with the american dog tick, dermacentor variabilis. 19665949558
clinically mild tularemia associated with tick-borne francisella tularensis.between may 9 and july 3, 1979, 12 cases of glandular or ulceroglandular tularemia occurred in residents of the crow indian reservation in southcentral montana; only 13 cases had been reported from this geographic area in the preceding 25 years. the illness was mild, characterized by fever and cervical or occipital adenopathy. systemic symptoms were self-limited although residual lymphadenopathy was common. francisella tularensis was isolated from ticks (dermacentor variabilis), the suspected ve ...19836886487
genotypic diversity of francisella tularensis infecting dermacentor variabilis ticks on martha's vineyard, massachusetts.martha's vineyard, mass., has been the site of two outbreaks of tularemia (1978 and 2000). although most patients from both outbreaks presented with pneumonic disease and although aerosol transmission has been suggested, the bite of a dog tick and exposure to rabbits remain the only proven modes of transmission. the factors that precipitated the tularemia outbreaks or the proximal determinants of human risk remain undescribed. we sought to test the hypothesis that the ongoing outbreak is due to ...200415528681
a call for renewed research on tick-borne francisella tularensis in the arkansas-missouri primary national focus of tularemia in humans.arkansas-missouri has emerged as the primary u.s. focus of tularemia, which is caused by the national institute of allergy and infectious diseases category a priority pathogen francisella tularensis, over the past 30 yr. there are several pieces of indirect evidence suggesting that a key role of ticks in the transmission of f. tularensis to humans in arkansas-missouri is the primary reason why tularemia has remained a prominent disease of humans in this two-state area while fading away from othe ...200717547223
nonrandom distribution of vector ticks (dermacentor variabilis) infected by francisella tularensis.the island of martha's vineyard, massachusetts, is the site of a sustained outbreak of tularemia due to francisella tularensis tularensis. dog ticks, dermacentor variabilis, appear to be critical in the perpetuation of the agent there. tularemia has long been characterized as an agent of natural focality, stably persisting in characteristic sites of transmission, but this suggestion has never been rigorously tested. accordingly, we sought to identify a natural focus of transmission of the agent ...200919247435
subolesin expression in response to pathogen infection in ticks.ticks (acari: ixodidae) are vectors of pathogens worldwide that cause diseases in humans and animals. ticks and pathogens have co-evolved molecular mechanisms that contribute to their mutual development and survival. subolesin was discovered as a tick protective antigen and was subsequently shown to be similar in structure and function to akirins, an evolutionarily conserved group of proteins in insects and vertebrates that controls nf-kb-dependent and independent expression of innate immune res ...201020170494
quantum of infection of francisella tularensis tularensis in host-seeking dermacentor variabilis.the american dog tick, dermacentor variabilis, is fundamental to the perpetuation of francisella tularensis tularensis on martha's vineyard, massachusetts, u.s.a. although infected ticks are relatively common on the island, human cases deriving from tick bite are rare. it may be that the quantum of bacteria within these naturally infected ticks is frequently too small to cause disease. accordingly, we quantified the amount of f.t. tularensis bacteria in host-seeking ticks from the island. contra ...201020563231
deep mitochondrial dna lineage divergences within alberta populations of dermacentor albipictus (acari: ixodidae) do not indicate distinct species.the winter tick dermacentor albipictus (packard) has a single-host life cycle that allows it to reach severe infestation levels on ungulates, particularly moose. genotypic variation within these and related ticks has been a source of taxonomic confusion, although the continuity in their morphology and life history has generally been interpreted as indicating the existence of a single species. to further investigate this variation, we sequenced regions of two mitochondrial dna (mtdna) genes (coi ...201020695271
transmission dynamics of francisella tularensis subspecies and clades by nymphal dermacentor variabilis (acari: ixodidae).in the united states, the american dog tick, dermacentor variabilis (say) is considered an important biological vector of francisella tularensis, the etiologic agent of tularemia. in this study, we evaluated the vector efficiency of nymphal d. variabilis infected as larvae with differing clades and subspecies (a1b, a2, and type b) of f. tularensis. in all cases, d. variabilis larvae were able to acquire, maintain, and transstadially transmit f. tularensis. significant replication of the bacteria ...201020810833
differential mortality of dog tick vectors due to infection by diverse francisella tularensis tularensis genotypes.abstract the factors involved in the long-term perpetuation of francisella tularensis tularensis in nature are poorly understood. martha's vineyard, massachusetts, has become a site of sustained transmission of type a tularemia, with nearly 100 human cases reported from 2000 to 2010. we have identified a stable focus of f. tularensis transmission there, where the annual prevalence in host-seeking dermacentor variabilis is about 3%, suggesting that this tick perpetuates the agent. however, labora ...201121612530
association of different genetic types of francisella-like organisms with the rocky mountain wood tick (dermacentor andersoni) and the american dog tick (dermacentor variabilis) from localities near their northern distributional limits.dermacentor andersoni and dermacentor variabilis from allopatric and sympatric populations near their northern distributional limits were examined for the presence of francisella species using molecular techniques that targeted 373 bp of the 16s ribosomal rna gene. although there was no evidence for the presence of francisella tularensis in any tick, francisella-like endosymbionts (fles) were common in d. andersoni and d. variabilis adults and immatures. a significantly greater proportion of fem ...201122179251
transmission efficiency of francisella tularensis by adult american dog ticks (acari: ixodidae).the american dog tick, dermacentor variabilis (say) (acari: ixodidae), has been implicated as a potential bridging vector to humans of francisella tularensis, the etiological agent of tularemia. since the initial studies evaluating vector competency of d. variabilis were conducted, f. tularensis has been subdivided into subspecies and clades that differ in their geographical distribution in the united states and in the severity of infections caused in humans. here, we demonstrate that d. variabi ...201121845949
amblyomma americanum as a bridging vector for human infection with francisella tularensis.the γ-proteobacterium francisella tularensis causes seasonal tick-transmitted tularemia outbreaks in natural rabbit hosts and incidental infections in humans in the south-central united states. although dermacentor variabilis is considered a primary vector for f. tularensis, amblyomma americanum is the most abundant tick species in this endemic region. a systematic study of f. tularensis colonization of a. americanum was undertaken to better understand its potential to serve as an overwintering ...201526121137
factors associated with tick bites and pathogen prevalence in ticks parasitizing humans in georgia, usa.the incidence and emergence of tick-borne diseases has increased dramatically in the united states during the past 30 years, yet few large-scale epidemiological studies have been performed on individuals bitten by ticks. epidemiological information, including disease development, may provide valuable information regarding effectiveness of tick bite prevention education, pathogen transmission, human-disease dynamics, and potential implications for under reporting of tick-borne diseases.201626935205
prevalence of rickettsia species in dermacentor variabilis ticks from ontario, canada.relatively little is known about the prevalence of rickettsial species in dermacentor ticks in eastern canada. in this study, dermacentor ticks from the province of ontario, canada, were tested for the presence of spotted fever group rickettsial (sfgr) species, coxiella burnetii and francisella tularensis. rickettsia rickettsii was not detected in any ticks tested, but r. montanensis was detected at a prevalence of 2.2% in d. variabilis (17/778). two other sfgr species, r. parkeri and candidatus ...201627318438
reproducible and quantitative model of infection of dermacentor variabilis with the live vaccine strain of francisella tularensis.pathogen life cycles in mammalian hosts have been studied extensively, but studies with arthropod vectors represent considerable challenges. in part this is due to the difficulty of delivering a reproducible dose of bacteria to follow arthropod-associated replication. we have established reproducible techniques to introduce known numbers of francisella tularensis strain lvs from mice into dermacentor variabilis nymphs. using this model infection system, we performed dose-response infection exper ...201425362054
biology of francisella tularensis subspecies holarctica live vaccine strain in the tick vector dermacentor variabilis.the γ-proteobacterium francisella tularensis is the etiologic agent of seasonal tick-transmitted tularemia epizootics in rodents and rabbits and of incidental infections in humans. the biology of f. tularensis in its tick vectors has not been fully described, particularly with respect to its quanta and duration of colonization, tissue dissemination, and transovarial transmission. a systematic study of the colonization of dermacentor variabilis by the f. tularensis subsp. holarctica live vaccine ...201222530023
ticks and tick-borne pathogens and putative symbionts of black bears (ursus americanus floridanus) from georgia and florida.ticks were collected from 38 black bears (ursus americanus floridanus) from northwestern florida (n = 18) from 2003 to 2005 and southern georgia (n = 20) in 2006. five species (amblyomma americanum, a. maculatum, dermacentor variabilis, ixodes scapularis, and i. affinis) were collected from florida bears, and 4 species (a. americanum, a. maculatum, d. variabilis, i. scapularis) were collected from bears in georgia. ixodes scapularis was the most frequently collected tick, followed by d. variabil ...200919413369
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