Temporal and spatial patterns of Bartonella infection in black-tailed prairie dogs (Cynomys ludovicianus)

Epidemiological survey and genetic diversity of Bartonella in fleas collected from rodents in Fujian Province, Southeast China

BACKGROUND

Fleas, considered to be the main transmission vectors of Bartonella, are highly prevalent and show great diversity. To date, no investigations have focused on Bartonella vectors in Southeast China. The aim of this study was to investigate the epidemiological and molecular characteristics of Bartonella in fleas in Southeast China.

METHODS

From 2016 to 2022, flea samples (n = 1119) were collected from 863 rodent individuals in seven inland and coastal cities in Southeast China. Flea species, region, gender, host species and habitat were recorded. The DNA samples from each individual flea were screened by real-time PCR for the Bartonella ssrA gene. All positive samples were confirmed by PCR based on the presence of the gltA gene and sequenced. The factors associated with Bartonella infection were analyzed by the Chi-square test and Fisher's exact test. ANOVA and the t-test were used to compare Bartonella DNA load.

RESULTS

Bartonella DNA was detected in 26.2% (293/1119) of the flea samples, including in 27.1% (284/1047) of Xenopsylla cheopis samples, 13.2% (5/38) of Monopsyllus anisus samples, 8.3% (2/24) of Leptopsylla segnis samples and 20.0% (2/10) of other fleas (Nosopsyllus nicanus, Ctenocephalides felis, Stivalius klossi bispiniformis and Neopsylla dispar fukienensis). There was a significant difference in the prevalence of Bartonella among flea species, sex, hosts, regions and habitats. Five species of Bartonella fleas were identified based on sequencing and phylogenetic analyses targeting the gltA gene: B. tribocorum, B. queenslandensis, B. elizabethae, B. rochalimae and B. coopersplainsensis.

CONCLUSIONS

There is a high prevalence and diversity of Bartonella infection in the seven species of fleas collected in Southeast China. The detection of zoonotic Bartonella species in this study, including B. tribocorum, B. elizabethae and B. rochalimae, raises public health concerns.

Emerging rodent-associated Bartonella: a threat for human health?

Background

Species of the genus Bartonella are facultative intracellular alphaproteobacteria with zoonotic potential. Bartonella infections in humans range from mild with unspecific symptoms to life threatening, and can be transmitted via arthropod vectors or through direct contact with infected hosts, although the latter mode of transmission is rare. Among the small mammals that harbour Bartonella spp., rodents are the most speciose group and harbour the highest diversity of these parasites. Human–rodent interactions are not unlikely as many rodent species live in proximity to humans. However, a surprisingly low number of clinical cases of bartonellosis related to rodent-associated Bartonella spp. have thus far been recorded in humans.

Methods

The main purpose of this review is to determine explanatory factors for this unexpected finding, by taking a closer look at published clinical cases of bartonellosis connected with rodent-associated Bartonella species, some of which have been newly described in recent years. Thus, another focus of this review are these recently proposed species.

Conclusions

Worldwide, only 24 cases of bartonellosis caused by rodent-associated bartonellae have been reported in humans. Possible reasons for this low number of cases in comparison to the high prevalences of Bartonella in small mammal species are (i) a lack of awareness amongst physicians of Bartonella infections in humans in general, and especially those caused by rodent-associated bartonellae; and (ii) a frequent lack of the sophisticated equipment required for the confirmation of Bartonella infections in laboratories that undertake routine diagnostic testing. As regards recently described Bartonella spp., there are presently 14 rodent-associated Candidatus taxa. In contrast to species which have been taxonomically classified, there is no official process for the review of proposed Candidatus species and their names before they are published. This had led to the use of malformed names that are not based on the International Code of Nomenclature of Prokaryotes. Researchers are thus encouraged to propose Candidatus names to the International Committee on Systematics of Prokaryotes for approval before publishing them, and only to propose new species of Bartonella when the relevant datasets allow them to be clearly differentiated from known species and subspecies.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05162-5.

Molecular detection and genetic characterization of small rodents associated Bartonella species in Zhongtiao Mountain, China

The prevalence and molecular characteristics of Bartonella infections in small rodents in the Zhongtiao Mountain, China have been explored. In this study, the liver, spleen and kidney tissues of captured rodents were used for Bartonella spp. detection and identification by combination of real-time PCR of transfer-mRNA (ssrA) gene and traditional PCR and sequencing of citrate synthase (gltA) gene. It was shown that 49.52% of the rodents (52/105) were positive for Bartonella spp.. The infection rate in different gender (χ2 = 0.079, P = 0.778) and tissues (χ2 = 0.233, P = 0.890) of small rodents did not have statistical difference, but that in different small rodents (Fisher's exact test, P < 0.001) and habitats (χ2 = 5.483, P = 0.019) had statistical difference. And, the sequencing data suggests that Bartonella sequences (n = 31) were identified into three species, including 14 of B. grahamii, 3 of B. queenslandensis and 14 of unknown Bartonella species. Phylogenetic analysis showed that B. grahamii sequences were clustered with the isolates from South Korea and China, and B. queenslandensis sequences were mainly closely related to the isolates from China and Thailand. The genetic diversity analysis showed that B. grahamii and B. queenslandensis sequences exhibited noticeable intraspecies diversity. Taken together our data demonstrates the high prevalence and genetic diversity of Bartonella infections in small rodents in the Zhongtiao Mountain, especially a potential novel Bartonella specie was detected, which could benefit the prevention and control of rodent-Bartonella species in this area.

Ecology of Ixodes pacificus Ticks and Associated Pathogens in the Western United States

Lyme disease is the most important vector-borne disease in the United States and is increasing in incidence and geographic range. In the Pacific west, the western black-legged tick, Ixodes pacificus Cooley and Kohls, 1943 is an important vector of the causative agent of Lyme disease, the spirochete, Borrelia burgdorferi. Ixodes pacificus life cycle is expected to be more than a year long, and all three stages (larva, nymph, and adult) overlap in spring. The optimal habitat consists of forest cover, cooler temperatures, and annual precipitation in the range of 200–500 mm. Therefore, the coastal areas of California, Oregon, and Washington are well suited for these ticks. Immature stages commonly parasitize Western fence lizards (Sceloporus occidentalis) and gray squirrels (Sciurus griseus), while adults often feed on deer mice (Peromyscus maniculatus) and black-tailed deer (Odocoileus h. columbianus). Ixodes pacificus carry several pathogens of human significance, such as Borrelia burgdorferi, Bartonella, and Rickettsiales. These pathogens are maintained in the environment by many hosts, including small mammals, birds, livestock, and domestic animals. Although a great deal of work has been carried out on Ixodes ticks and the pathogens they transmit, understanding I. pacificus ecology outside California still lags. Additionally, the dynamic vector–host–pathogen system means that new factors will continue to arise and shift the epidemiological patterns within specific areas. Here, we review the ecology of I. pacificus and the pathogens this tick is known to carry to identify gaps in our knowledge.

Fine-Scale Spatial Structure of Soil Microbial Communities in Burrows of a Keystone Rodent Following Mass Mortality

Soil microbial communities both reflect and influence biotic and abiotic processes occurring at or near the soil surface. Ecosystem engineers that physically alter the soil surface, such as burrowing ground squirrels, are expected to influence the distribution of soil microbial communities. Black-tailed prairie dogs (Cynomys ludovicianus) construct complex burrows in which activities such as nesting, defecating, and dying are partitioned spatially into different chambers. Prairie dogs also experience large-scale die-offs due to sylvatic plague, caused by the bacterium Yersinia pestis, which lead to mass mortality events with potential repercussions on microbial communities. We used 16S sequencing to examine microbial communities in soil that was excavated by prairie dogs from different burrow locations, and surface soil that was used in the construction of burrow entrances, in populations that experienced plague die-offs. Following the QIIME2 pipeline, we assessed microbial diversity at several taxonomic levels among burrow regions. To do so, we computed community similarity metrics (Bray–Curtis, Jaccard, and weighted and unweighted UniFrac) among samples and community diversity indexes (Shannon and Faith phylogenetic diversity indexes) within each sample. Microbial communities differed across burrow regions, and several taxa exhibited spatial variation in relative abundance. Microbial ecological diversity (Shannon index) was highest in soil recently excavated from within burrows and soils associated with dead animals, and was lowest in soils associated with scat. Phylogenetic diversity varied only marginally within burrows, but the trends paralleled those for Shannon diversity. Yersinia was detected in four samples from one colony, marking the first time the genus has been sampled from soil on prairie dog colonies. The presence of Yersinia was a significant predictor of five bacterial families and eight microbial genera, most of which were rare taxa found in higher abundance in the presence of Yersinia, and one of which, Dictyostelium, has been proposed as an enzootic reservoir of Y. pestis. This study demonstrates that mammalian modifications to soil structure by physical alterations and by mass mortality can influence the distribution and diversity of microbial communities.

Longitudinal Study of Bacterial Infectious Agents in a Community of Small Mammals in New Mexico

Background and Objectives: Vector-borne bacterial diseases represent a substantial public health burden and rodents have been recognized as important reservoir hosts for many zoonotic pathogens. This study investigates bacterial pathogens in a small mammal community of the southwestern United States of America. Methods: A total of 473 samples from 13 wild rodent and 1 lagomorph species were tested for pathogens of public health significance: Bartonella, Brucella, Yersinia, Borrelia, Rickettsia spp., and Anaplasma phagocytophilum. Results: Three animals were positive for Yersinia pestis, and one Sylvilagus audubonii had a novel Borrelia sp. of the relapsing fever group. No Brucella, Rickettsia, or A. phagocytophilum infections were detected. Bartonella prevalence ranged between 0% and 87.5% by animal species, with 74.3% in the predominant Neotoma micropus and 78% in the second most abundant N. albigula. The mean duration of Bartonella bacteremia in mark-recaptured N. micropus and N. albigula was 4.4 months, ranging from <1 to 18 months, and differed among Bartonella genogroups. Phylogenetic analysis of the Bartonella citrate synthase gene (gltA) revealed 9 genogroups and 13 subgroups. Seven genogroups clustered with known or previously reported Bartonella species and strains while two were distant enough to represent new Bartonella species. We report, for the first time, the detection of Bartonella alsatica in North America in Sylvilagus audubonii and expand the known host range of Bartonella washoensis to include Otospermophilus variegatus. Interpretation and Conclusion: This work broadens our knowledge of the hosts and geographic range of bacterial pathogens that could guide future surveillance efforts and improves our understanding of the dynamics of Bartonella infection in wild small mammals.

Expanding our view of Bartonella and its hosts: Bartonella in nest ectoparasites and their migratory avian hosts

BACKGROUND

Bartonella is a genus of Gram-negative facultative intracellular Alphaproteobacteria of public health importance. Although they are known to mainly infect mammalian hosts with some blood-feeding arthropods having been confirmed as vectors, there is some evidence of Bartonella association with non-mammalian hosts including birds.

METHODS

Here we used high-throughput sequencing of 16S rRNA and Sanger sequencing of the citrate synthase (gltA) genes to test for the presence of Bartonellaceae in the blood of three migratory cavity nesting bird species, purple martins (Progne subis), tree swallows (Tachycineta bicolor) and eastern bluebirds (Sialia sialis) and their most prevalent and abundant nest ectoparasites, Dermanyssus prognephilus (mite), Ceratophyllus idius (flea) and Protocalliphora sialia (bird blow fly larva). We constructed maximum likelihood phylogenetic trees to verify the placement of the resulting sequences in the Bartonellaceae.

RESULTS

We found evidence of Bartonella in all three bird species and all three arthropod species tested. We report multiple instances of identical Bartonella sequences in both birds and parasites, leading to the likely hypothesis that these ectoparasites are potential vectors of Bartonella. Our phylogenetic analysis suggests that 'avian Bartonella' may form its own sub-clade within the genus Bartonella.

CONCLUSIONS

To the best of our knowledge, we provide the first confirmation of overlapping Bartonella strains among bird hosts and various species of nest-associated ectoparasites from the same system, suggesting a possible Bartonella host-vector relationship between these arthropods and a non-mammalian host. Our study adds to the growing appreciation of the Bartonellaceae as a phylogenetically diverse group with a wide range of hosts.

Prevalence of zoonotic Bartonella among prairie rodents in Illinois

Bartonella is a genus of gram-negative bacteria that includes a variety of human and veterinary pathogens. These pathogens are transmitted from reservoirs to secondary hosts through the bite of arthropod vectors including lice and fleas. Once in the secondary host, the bacteria cause a variety of pathologies including cat-scratch disease, endocarditis, and myocarditis. Reservoirs of these bacteria are numerous and include several species of large mammals, mesocarnivores, and small mammals. Research on reservoirs of these bacteria has focused on western North America, Europe, and Asia, with little focus on the eastern and central United States. We assessed the prevalence of zoonotic Bartonella species among prairie-dwelling rodent species in the midwestern United States. Tissue samples (n = 700) were collected between 2015 and 2017 from five rodent species and screened for the presence of Bartonella DNA via PCR and sequencing of two loci using Bartonella-specific primers. Bartonella were prevalent among all five species, with 13-lined ground squirrels (Ictidomys tridecemlineatus) serving as a likely reservoir of the pathogen B. washoensis, and other rodents serving as reservoirs of the pathogens B. grahamii and B. vinsonii subsp. arupensis. These results demonstrate the value of studies of disease ecology in grassland systems, particularly in the context of habitat restoration and human–vector interactions.

EVALUATING THE IMPACTS OF COINFECTION ON IMMUNE SYSTEM FUNCTION OF THE DEER MOUSE ( PEROMYSCUS MANICULATUS) USING SIN NOMBRE VIRUS AND BARTONELLA AS MODEL PATHOGEN SYSTEMS

:  Simultaneous infections with multiple pathogens can alter the function of the host's immune system, often resulting in additive or synergistic morbidity. We examined how coinfection with the common pathogens Sin Nombre virus (SNV) and Bartonella sp. affected aspects of the adaptive and innate immune responses of wild deer mice ( Peromyscus maniculatus). Adaptive immunity was assessed by measuring SNV antibody production; innate immunity was determined by measuring levels of C-reactive protein (CRP) in blood and the complement activity of plasma. Coinfected mice had reduced plasma complement activity and higher levels of CRP compared to mice infected with either SNV or Bartonella. However, antibody titers of deer mice infected with SNV were more than double those of coinfected mice. Plasma complement activity and CRP levels did not differ between uninfected deer mice and those infected with only Bartonella, suggesting that comorbid SNV and Bartonella infections act synergistically, altering the innate immune response. Collectively, our results indicated that the immune response of deer mice coinfected with both SNV and Bartonella differed substantially from individuals infected with only one of these pathogens. Results of our study provided unique, albeit preliminary, insight into the impacts of coinfection on immune system function in wild animal hosts and underscore the complexity of the immune pathways that exist in coinfected hosts.

Elucidating transmission dynamics and host-parasite-vector relationships for rodent-borne Bartonella spp. in Madagascar

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At least five distinct species of Bartonella infect R. rattus rodents and their ectoparasites in Madagascar.

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Infection dynamics for zoonotic B. elizabethae are consistent with an SIS or SIR model in rodent hosts.

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Infection dynamics for non-zoonotic B. phoceensis & rattimassiliensis are consistent with an SI model in rodent hosts.

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Transmission of B. elizabethae and B. phoceensis & rattimassiliensis, respectiviely, are affected by S. fonquerniei & X. cheopsis fleas and Polyplax spp. lice.

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S. fonquerniei/X. cheopsis fleas may vector B. elizabethae and Polyplax spp. lice vector B. phoceensis/rattimassiliensis.

Bartonella spp. are erythrocytic bacteria transmitted via arthropod vectors, which infect a broad range of vertebrate hosts, including humans. We investigated transmission dynamics and host-parasite-vector relationships for potentially zoonotic Bartonella spp. in invasive Rattus rattus hosts and associated arthropod ectoparasites in Madagascar. We identified five distinct species of Bartonella (B. elizabethae 1, B. elizabethae 2, B. phoceensis 1, B. rattimassiliensis 1, and B. tribocorum 1) infecting R. rattus rodents and their ectoparasites. We fit standard epidemiological models to species-specific age-prevalence data for the four Bartonella spp. with sufficient data, thus quantifying age-structured force of infection. Known zoonotic agents, B. elizabethae 1 and 2, were best described by models exhibiting high forces of infection in early age class individuals and allowing for recovery from infection, while B. phoceensis 1 and B. rattimassiliensis 1 were best fit by models of lifelong infection without recovery and substantially lower forces of infection. Nested sequences of B. elizabethae 1 and 2 were recovered from rodent hosts and their Synopsyllus fonquerniei and Xenopsylla cheopsis fleas, with a particularly high prevalence in the outdoor-dwelling, highland-endemic S. fonquerniei. These findings expand on force of infection analyses to elucidate the ecological niche of the zoonotic Bartonella elizabethae complex in Madagascar, hinting at a potential vector role for S. fonquerniei. Our analyses underscore the uniqueness of such ecologies for Bartonella species, which pose a variable range of potential zoonotic threats.

Bartonella infection in rodents and their flea ectoparasites: an overview

Epidemiological studies worldwide have reported a high prevalence and a great diversity of Bartonella species, both in rodents and their flea parasites. The interaction among Bartonella, wild rodents, and fleas reflects a high degree of adaptation among these organisms. Vertical and horizontal efficient Bartonella transmission pathways within flea communities and from fleas to rodents have been documented in competence studies, suggesting that fleas are key players in the transmission of Bartonella to rodents. Exploration of the ecological traits of rodents and their fleas may shed light on the mechanisms used by bartonellae to become established in these organisms. The present review explores the interrelations within the Bartonella-rodent-flea system. The role of the latter two components is emphasized.

Declines in large wildlife increase landscape-level prevalence of rodent-borne disease in Africa

Populations of large wildlife are declining on local and global scales. The impacts of this pulse of size-selective defaunation include cascading changes to smaller animals, particularly rodents, and alteration of many ecosystem processes and services, potentially involving changes to prevalence and transmission of zoonotic disease. Understanding linkages between biodiversity loss and zoonotic disease is important for both public health and nature conservation programs, and has been a source of much recent scientific debate. In the case of rodent-borne zoonoses, there is strong conceptual support, but limited empirical evidence, for the hypothesis that defaunation, the loss of large wildlife, increases zoonotic disease risk by directly or indirectly releasing controls on rodent density. We tested this hypothesis by experimentally excluding large wildlife from a savanna ecosystem in East Africa, and examining changes in prevalence and abundance of Bartonella spp. infection in rodents and their flea vectors. We found no effect of wildlife removal on per capita prevalence of Bartonella infection in either rodents or fleas. However, because rodent and, consequently, flea abundance doubled following experimental defaunation, the density of infected hosts and infected fleas was roughly twofold higher in sites where large wildlife was absent. Thus, defaunation represents an elevated risk in Bartonella transmission to humans (bartonellosis). Our results (i) provide experimental evidence of large wildlife defaunation increasing landscape-level disease prevalence, (ii) highlight the importance of susceptible host regulation pathways and host/vector density responses in biodiversity-disease relationships, and (iii) suggest that rodent-borne disease responses to large wildlife loss may represent an important context where this relationship is largely negative.

Natural history of Bartonella-infecting rodents in light of new knowledge on genomics, diversity and evolution

Among the 33 confirmed Bartonella species to date, more than half are hosted by rodent species, and at least five of them have been involved in human illness causing diverse symptoms including fever, myocarditis, endocarditis, lymphadenitis and hepatitis. In almost all countries, wild rodents are infected by extremely diverse Bartonella strains with a high prevalence. In the present paper, in light of new knowledge on rodent-adapted Bartonella species genomics, we bring together knowledge gained in recent years to have an overview of the impact of rodent-adapted Bartonella infection on humans and to determine how diversity of Bartonella helps to understand their mechanisms of adaptation to rodents and the consequences on human health.

Experimental infection of laboratory mice with two Bartonella tribocorum strains from wild Mus species: a homologous host-bacteria model system at the genus level

To date no experimental infection studies have been conducted in laboratory mice using Mus spp. bartonella strains. Therefore we designed a study to evaluate the in vivo infection characteristics of 2 Bartonella tribocorum strains from wild Mus spp. in laboratory mice with the aim of developing a mouse model that reproduces characteristics of naturally acquired bartonella infections in rodents. Groups of outbred CD1 female mice were subcutaneously inoculated with low doses of 2 mouse bartonella strains (10, 100, and 1000 bacteria/mouse). Blood was collected weekly for 27 weeks to evaluate bacteraemia kinetics in infected mice. Mouse urine collected during weeks 3-6 post-inoculation was also tested for viable bacteria to determine whether urine might serve as a source of bacterial transmission. Mice were susceptible to infection with both strains. Bacteraemias in mice lasted up to 25 weeks, sometimes with abacteraemic intervals, and achieved levels up to 107 cfu/ml of blood. Temporal lags in bacteraemia onset of up to 19 weeks in length were noted at different inoculum doses. No viable bacteria were detected in mouse urine. Bacteraemic mice displayed characteristics of infection similar to those observed in natural rodent hosts during longitudinal field studies. This mouse model of persistent bacteraemia should be suitable for a variety of experimental uses.

Interactions among symbionts of Oropsylla spp. (Siphonoptera: Ceratophyllidae)

We used high-throughput DNA sequencing to explore bacterial communities of three species of Oropyslla fleas [Oropsylla hirsuta (Baker), Oropsylla montana (Baker), and Oropsylla tuberculata cynomuris (Jellison)] and detected seven bacterial lineages related to known insect symbionts. No significant co-occurrence patterns were detected among bacterial lineages, but relative abundance data suggest that the two most common lineages (Bartonella and Rickettsiales) interact negatively. Furthermore, presence of these two lineages significantly reduced bacterial diversity within fleas.

Intruders below the radar: molecular pathogenesis of Bartonella spp

Bartonella spp. are facultative intracellular pathogens that employ a unique stealth infection strategy comprising immune evasion and modulation, intimate interaction with nucleated cells, and intraerythrocytic persistence. Infections with Bartonella are ubiquitous among mammals, and many species can infect humans either as their natural host or incidentally as zoonotic pathogens. Upon inoculation into a naive host, the bartonellae first colonize a primary niche that is widely accepted to involve the manipulation of nucleated host cells, e.g., in the microvasculature. Consistently, in vitro research showed that Bartonella harbors an ample arsenal of virulence factors to modulate the response of such cells, gain entrance, and establish an intracellular niche. Subsequently, the bacteria are seeded into the bloodstream where they invade erythrocytes and give rise to a typically asymptomatic intraerythrocytic bacteremia. While this course of infection is characteristic for natural hosts, zoonotic infections or the infection of immunocompromised patients may alter the path of Bartonella and result in considerable morbidity. In this review we compile current knowledge on the molecular processes underlying both the infection strategy and pathogenesis of Bartonella and discuss their connection to the clinical presentation of human patients, which ranges from minor complaints to life-threatening disease.

Persistent infection or successive reinfection of deer mice with Bartonella vinsonii subsp. arupensis

Bartonella infections are common in rodents. From 1994 to 2006, longitudinal studies of a rodent community, consisting mainly of deer mice (Peromyscus maniculatus), were conducted in southwestern Colorado to study hantaviruses. Blood samples from deer mice captured one or more times during the period 2003 to 2006 (n = 737) were selected to study bartonellae in deer mice. Bartonellae were found to be widely distributed in that population, with an overall prevalence of 82.4% (607/737 mice). No correlation was found between bartonella prevalence and deer mouse weight or sex. Persistent or successive infections with bartonellae were observed in deer mice captured repeatedly, with a prevalence of 83.9% (297/354), and the infection appeared to last for more than 1 year in some of them. Persistent infection with bartonellae may explain the high prevalence of these bacteria in deer mice at this site and, perhaps, elsewhere. Genetic analysis demonstrated that deer mouse-borne bartonella isolates at this site belong to the same species, B. vinsonii subsp. arupensis, demonstrating a specific relationship between B. vinsonii subsp. arupensis and deer mice.

An immunocompromised murine model of chronic Bartonella infection

Bartonella are ubiquitous gram-negative pathogens that cause chronic blood stream infections in mammals. Two species most often responsible for human infection, B. henselae and B. quintana, cause prolonged febrile illness in immunocompetent hosts, known as cat scratch disease and trench fever, respectively. Fascinatingly, in immunocompromised hosts, these organisms also induce new blood vessel formation leading to the formation of angioproliferative tumors, a disease process named bacillary angiomatosis. In addition, they cause an endothelial-lined cystic disease in the liver known as bacillary peliosis. Unfortunately, there are as yet no completely satisfying small animal models for exploring these unique human pathologies, as neither species appears able to sustain infection in small animal models. Therefore, we investigated the potential use of other Bartonella species for their ability to recapitulate human pathologies in an immunodeficient murine host. Here, we demonstrate the ability of Bartonella taylorii to cause chronic infection in SCID/BEIGE mice. In this model, Bartonella grows in extracellular aggregates, embedded within collagen matrix, similar to previous observations in cat scratch disease, bacillary peliosis, and bacillary angiomatosis. Interestingly, despite overwhelming infection later in disease, evidence for significant intracellular replication in endothelial or other cell types was not evident. We believe that this new model will provide an important new tool for investigation of Bartonella-host interaction.

Bacterial communities of disease vectors sampled across time, space, and species

A common strategy of pathogenic bacteria is to form close associations with parasitic insects that feed on animals and to use these insects as vectors for their own transmission. Pathogens interact closely with other coexisting bacteria within the insect, and interactions between co-occurring bacteria may influence the vector competency of the parasite. Interactions between particular lineages can be explored through measures of alpha-diversity. Furthermore, general patterns of bacterial community assembly can be explored through measures of beta-diversity. Here, we use pyrosequencing (n=115,924 16S rRNA gene sequences) to describe the bacterial communities of 230 prairie dog fleas sampled across space and time. We use these communinty characterizations to assess interactions between dominant community members and to explore general patterns of bacterial community assembly in fleas. An analysis of co-occurrence patterns suggests non-neutral negative interactions between dominant community members (P<0.001). Furthermore, bacterial communities of fleas shift dramatically across years (phylotype-based: R=0.829, P<0.001; phylogenetic-based: R=0.612-0.753, P<0.001), but they also significantly differ across space (phylotype-based: R=0.418, P<0.001; phylogenetic-based: R=0.290-0.328, P<0.001) and between flea species (phylotype-based: R=0.160, P=0.011; phylogenetic-based: not significant). Collectively, our results show that flea-associated bacterial communities are not random assemblages; rather, an individual flea's bacterial community is governed by interactions between bacterial lineages and by the flea's place in space and time.

Ecological fitness and strategies of adaptation of Bartonella species to their hosts and vectors

Bartonella spp. are facultative intracellular bacteria that cause characteristic hostrestricted hemotropic infections in mammals and are typically transmitted by blood-sucking arthropods. In the mammalian reservoir, these bacteria initially infect a yet unrecognized primary niche, which seeds organisms into the blood stream leading to the establishment of a long-lasting intra-erythrocytic bacteremia as the hall-mark of infection. Bacterial type IV secretion systems, which are supra-molecular transporters ancestrally related to bacterial conjugation systems, represent crucial pathogenicity factors that have contributed to a radial expansion of the Bartonella lineage in nature by facilitating adaptation to unique mammalian hosts. On the molecular level, the type IV secretion system VirB/VirD4 is known to translocate a cocktail of different effector proteins into host cells, which subvert multiple cellular functions to the benefit of the infecting pathogen. Furthermore, bacterial adhesins mediate a critical, early step in the pathogenesis of the bartonellae by binding to extracellular matrix components of host cells, which leads to firm bacterial adhesion to the cell surface as a prerequisite for the efficient translocation of type IV secretion effector proteins. The best-studied adhesins in bartonellae are the orthologous trimeric autotransporter adhesins, BadA in Bartonella henselae and the Vomp family in Bartonella quintana. Genetic diversity and strain variability also appear to enhance the ability of bartonellae to invade not only specific reservoir hosts, but also accidental hosts, as shown for B. henselae. Bartonellae have been identified in many different blood-sucking arthropods, in which they are typically found to cause extracellular infections of the mid-gut epithelium. Adaptation to specific vectors and reservoirs seems to be a common strategy of bartonellae for transmission and host diversity. However, knowledge regarding arthropod specificity/restriction, the mode of transmission, and the bacterial factors involved in arthropod infection and transmission is still limited.