Human ehrlichioses

Laboratory Blood-Based Testing for Non-Lyme Disease Tick-Borne Infections at a National Reference Laboratory

OBJECTIVES

We evaluated trends in non-Lyme disease tick-borne disease (NLTBI) testing at a national reference laboratory.

METHODS

Testing data performed at Quest Diagnostics during 2010 to 2016 were analyzed nationally and at the state level.

RESULTS

Testing and positivity for most NLTBIs increased dramatically from 2010 through 2016 based on testing from a large reference laboratory. The number of positive cases, though not as stringent as criteria for public health reporting, generally exceeds that reported by the Centers for Disease Control and Prevention. The frequency of NLTBI in the US is seasonal but testing activity and positive test results are observed throughout all months of the year. Positive results for NLTBI testing mostly originated from a limited number of states, indicating the geographic concentration and distribution of NLTBIs reported in this study.

CONCLUSIONS

This report provides an important complementary source of data to best understand trends in and spread of NLTBI.

Prevalence and risk factors for selected canine vector-borne diseases in Greece

Background

Canine vector-borne diseases (CVBDs) represent a wide group of diseases of major significance for canine health. In addition to their veterinary importance, many of these diseases are of great zoonotic concern, posing a risk of potential transmission to humans. To date, there has been scant knowledge regarding the prevalence, distribution and risk factors of CVBDs in Greece. Therefore, the objectives of the present study were to update the current knowledge on the seroprevalence of Dirofilaria immitis, Anaplasma spp., Ehrlichia spp. and Borrelia burgdorferi (sensu lato) in dogs in Greece and, furthermore, to assess possible environmental and any other risk factors associated with these infections. A total of 1000 apparently healthy and randomly selected dogs, presented in veterinary clinics, were involved at the national level (n = 66 municipalities). Serum samples were obtained from each individual dog and were tested using the SNAP^® 4Dx^® Plus kit from IDEXX Laboratories. Possible risk factors were assessed using binary regression models, including dogs’ lifestyle, climatological parameters and the altitude of the region.

Results

Overall, 21.8% (95% CI: 19.4–24.5%) of the sampled dogs were found to be seropositive to at least one of the four pathogens examined. The most prevalent pathogen was Ehrlichia spp. (12.5%, 95% CI: 10.6–14.7) followed by D. immitis (9.0%, 95% CI: 7.8–11.5) and Anaplasma spp. (6.2%, 95% CI: 4.9–7.9). The lowest prevalence (0.1%) was recorded for B. burgdorferi (s.l.) where only one dog was found to be positive. Among the examined risk factors, low mean temperature was found to increase the prevalence of Ehrlichia spp. (P ≤ 0.001) and Anaplasma spp. (P ≤ 0.001), while low minimum temperature increased the prevalence of D. immitis (P ≤ 0.001). In addition, low total annual rainfall had an effect of the prevalence of Ehrlichia spp. (P ≤ 0.01). Altitude also had a significant effect on the prevalence of D. immitis (P ≤ 0.05) and Anaplasma spp. (P ≤ 0.01).

Conclusions

To our knowledge, this is the first large-scale seroepidemiological study of CVBDs in Greece. It has been evidenced that environmental factors such as temperature, rainfall and altitude can influence the prevalence and distribution of CVBDs.

Solution NMR structures of oxidized and reduced Ehrlichia chaffeensis thioredoxin: NMR-invisible structure owing to backbone dynamics

Thioredoxins are small ubiquitous proteins that participate in a diverse variety of redox reactions via the reversible oxidation of two cysteine thiol groups in a structurally conserved active site. Here, the NMR solution structures of a reduced and oxidized thioredoxin from Ehrlichia chaffeensis (Ec-Trx, ECH_0218), the etiological agent responsible for human monocytic ehrlichiosis, are described. The overall topology of the calculated structures is similar in both redox states and is similar to those of other thioredoxins: a five-stranded, mixed β-sheet (β1-β3-β2-β4-β5) surrounded by four α-helices. Unlike other thioredoxins studied by NMR in both redox states, the 1H-15N HSQC spectrum of reduced Ec-Trx was missing eight additional amide cross peaks relative to the spectrum of oxidized Ec-Trx. These missing amides correspond to residues Cys35-Glu39 in the active-site-containing helix (α2) and Ser72-Ile75 in a loop near the active site, and suggest a change in backbone dynamics on the millisecond-to-microsecond timescale associated with the breakage of an intramolecular Cys32-Cys35 disulfide bond in a thioredoxin. A consequence of the missing amide resonances is the absence of observable or unambiguous NOEs to provide the distance restraints necessary to define the N-terminal end of the α-helix containing the CPGC active site in the reduced state. This region adopts a well defined α-helical structure in other reported reduced thioredoxin structures, is mostly helical in oxidized Ec-Trx and CD studies of Ec-Trx in both redox states suggests there is no significant difference in the secondary structure of the protein. The NMR solution structure of reduced Ec-Trx illustrates that the absence of canonical structure in a region of a protein may be owing to unfavorable dynamics prohibiting NOE observations or unambiguous NOE assignments.

Tick-Borne Emerging Infections: Ehrlichiosis and Anaplasmosis

Human ehrlichiosis and anaplasmosis are acute febrile tick-borne infectious diseases caused by various members from the genera Ehrlichia and Anaplasma. Ehrlichia chaffeensis is the major etiologic agent of human monocytotropic ehrlichiosis (HME), while Anaplasma phagocytophilum is the major cause of human granulocytic anaplasmosis (HGA). The clinical manifestations of HME and HGA ranges from subclinical to potentially life-threatening diseases associated with multi-organ failure. Macrophages and neutrophils are the major target cells for Ehrlichia and Anaplasma, respectively. The threat to public health is increasing with newly emerging ehrlichial and anaplasma agents, yet vaccines for human ehrlichioses and anaplasmosis are not available, and therapeutic options are limited. This article reviews recent advances in the understanding of HME and HGA.

SEROLOGICAL EVIDENCE OF EXPOSURE TO Ehrlichia canis IN CATS

Abstract The aim of the present study was to estimate the occurrence of Ehrlichia canis in cats from the semiarid region of Northeast of Brazil. Sera of 101 healthy cats were submitted by Indirect Immunofluorescence Assay (IFA), and considered positive when antibody titers ≥ 40 were obtained. Seroprevalence of 35.6% (36/101) was found, with the following titers: 40 (15 animals); 160 (6); 320 (1); 640 (3), and 2,560 (11). No statistical differences were observed when comparing county of origin, gender, age, breed, and modus vivendi (pet and stray cats), and no ticks were observed in any of the cats. This study revealed exposure to E. canis in cats of the Semiarid Northeast of Brazil.

Ehrlichiosis Induced Aseptic Meningitis and Second-Degree Heart Block in an Adolescent Male

We present a previously healthy 16-year-old male with ehrlichiosis-induced aseptic meningitis and subsequent second-degree heart block.

Type I interferon contributes to noncanonical inflammasome activation, mediates immunopathology, and impairs protective immunity during fatal infection with lipopolysaccharide-negative ehrlichiae

Ehrlichia species are intracellular bacteria that cause fatal ehrlichiosis, mimicking toxic shock syndrome in humans and mice. Virulent ehrlichiae induce inflammasome activation leading to caspase-1 cleavage and IL-18 secretion, which contribute to development of fatal ehrlichiosis. We show that fatal infection triggers expression of inflammasome components, activates caspase-1 and caspase-11, and induces host-cell death and secretion of IL-1β, IL-1α, and type I interferon (IFN-I). Wild-type and Casp1(-/-) mice were highly susceptible to fatal ehrlichiosis, had overwhelming infection, and developed extensive tissue injury. Nlrp3(-/-) mice effectively cleared ehrlichiae, but displayed acute mortality and developed liver injury similar to wild-type mice. By contrast, Ifnar1(-/-) mice were highly resistant to fatal disease and had lower bacterial burden, attenuated pathology, and prolonged survival. Ifnar1(-/-) mice also had improved protective immune responses mediated by IFN-γ and CD4(+) Th1 and natural killer T cells, with lower IL-10 secretion by T cells. Importantly, heightened resistance of Ifnar1(-/-) mice correlated with improved autophagosome processing, and attenuated noncanonical inflammasome activation indicated by decreased activation of caspase-11 and decreased IL-1β, compared with other groups. Our findings demonstrate that IFN-I signaling promotes host susceptibility to fatal ehrlichiosis, because it mediates ehrlichia-induced immunopathology and supports bacterial replication, perhaps via activation of noncanonical inflammasomes, reduced autophagy, and suppression of protective CD4(+) T cells and natural killer T-cell responses against ehrlichiae.

Ehrlichia chaffeensis proliferation begins with NtrY/NtrX and PutA/GlnA upregulation and CtrA degradation induced by proline and glutamine uptake

How the obligatory intracellular bacterium Ehrlichia chaffeensis begins to replicate upon entry into human monocytes is poorly understood. Here, we examined the potential role of amino acids in initiating intracellular replication. PutA converts proline to glutamate, and GlnA converts glutamate to glutamine. E. chaffeensis PutA and GlnA complemented Escherichia coli putA and glnA mutants. Methionine sulfoximine, a glutamine synthetase inhibitor, inhibited E. chaffeensis GlnA activity and E. chaffeensis infection of human cells. Incubation of E. chaffeensis with human cells rapidly induced putA and glnA expression that peaked at 24 h postincubation. E. chaffeensis took up proline and glutamine but not glutamate. Pretreatment of E. chaffeensis with a proline transporter inhibitor (protamine), a glutamine transporter inhibitor (histidine), or proline analogs inhibited E. chaffeensis infection, whereas pretreatment with proline or glutamine enhanced infection and upregulated putA and glnA faster than no treatment or glutamate pretreatment. The temporal response of putA and glnA expression was similar to that of NtrY and NtrX, a two-component system, and electrophoretic mobility shift assays showed specific binding of recombinant E. chaffeensis NtrX (rNtrX) to the promoter regions of E. chaffeensis putA and glnA. Furthermore, rNtrX transactivated E. chaffeensis putA and glnA promoter-lacZ fusions in E. coli. Growth-promoting activities of proline and glutamine were also accompanied by rapid degradation of the DNA-binding protein CtrA. Our results suggest that proline and glutamine uptake regulates putA and glnA expression through NtrY/NtrX and facilitates degradation of CtrA to initiate a new cycle of E. chaffeensis growth.

Human monocytic ehrlichiosis (HME) is one of the most prevalent, life-threatening emerging infectious zoonoses in the United States. HME is caused by infection with E. chaffeensis, an obligatory intracellular bacterium in the order Rickettsiales, which includes several category B/C pathogens, such as those causing Rocky Mountain spotted fever and epidemic typhus. The limited understanding of the mechanisms that control bacterial growth within eukaryotic cells continues to impede the identification of new therapeutic targets against rickettsial diseases. Extracellular rickettsia cannot replicate, but rickettsial replication ensues upon entry into eukaryotic host cells. Our findings will provide insights into a novel mechanism of the two-component system that regulates E. chaffeensis growth initiation in human monocytes. The result is also important because little is known about the NtrY/NtrX two-component system in any bacteria, let alone obligatory intracellular bacteria. Our findings will advance the field’s current conceptual paradigm on regulation of obligatory intracellular nutrition, metabolism, and growth.

Serological survey of Ehrlichia species in dogs, horses and humans: zoonotic scenery in a rural settlement from southern Brazil

The aims of this study were to determine the seroprevalence of Ehrlichia spp. and risk factors for exposure in a restricted population of dogs, horses, and humans highly exposed to tick bites in a Brazilian rural settlement using a commercial ELISA rapid test and two indirect immunofluorescent assays (IFA) with E. canis and E. chaffeensis crude antigens. Serum samples from 132 dogs, 16 horses and 100 humans were used. Fifty-six out of 132 (42.4%) dogs were seropositive for E. canis. Dogs > one year were more likely to be seropositive for E. canis than dogs ≤ one year (p = 0.0051). Ten/16 (62.5%) and 8/16 (50%) horses were seropositive by the commercial ELISA and IFA, respectively. Five out of 100 (5%) humans were seropositive for E. canis and E. chaffeensis. Rhipicephalus sanguineus (n = 291, 97.98%) on dogs and Amblyomma cajennense (n = 25, 96.15%) on horses were the most common ticks found. In conclusion, anti-Ehrlichia spp. antibodies were found in horses; however, the lack of a molecular characterization precludes any conclusion regarding the agent involved. Additionally, the higher seroprevalence of E. canis in dogs and the evidence of anti-Ehrlichia spp. antibodies in humans suggest that human cases of ehrlichiosis in Brazil might be caused by E. canis, or other closely related species.

Ehrlichia moonlighting effectors and interkingdom interactions with the mononuclear phagocyte

Ehrlichia chaffeensis is an obligately intracellular gram negative bacterium with a small genome that thrives in mammalian mononuclear phagocytes by exploiting eukaryotic processes. Herein, we discuss the latest findings on moonlighting tandem repeat protein effectors and their secretion mechanisms, and novel molecular interkingdom interactions that provide insight into the intracellular pathobiology of ehrlichiae.

TLR2 and Nod2 mediate resistance or susceptibility to fatal intracellular Ehrlichia infection in murine models of ehrlichiosis

Our murine models of human monocytic ehrlichiosis (HME) have shown that severe and fatal ehrlichiosis is due to generation of pathogenic T cell responses causing immunopathology and multi-organ failure. However, the early events in the liver, the main site of infection, are not well understood. In this study, we examined the liver transcriptome during the course of lethal and nonlethal infections caused by Ixodes ovatus Ehrlichia and Ehrlichia muris, respectively. On day 3 post-infection (p.i.), although most host genes were down regulated in the two groups of infected mice compared to naïve counterparts, lethal infection induced significantly higher expression of caspase 1, caspase 4, nucleotide binding oligomerization domain-containing proteins (Nod1), tumor necrosis factor-alpha, interleukin 10, and CCL7 compared to nonlethal infection. On day 7 p.i., lethal infection induced highly significant upregulation of type-1 interferon, several inflammatory cytokines and chemokines, which was associated with increased expression levels of Toll-like receptor-2 (TLR2), Nod2, MyD88, nuclear factor-kappa B (NF-kB), Caspase 4, NLRP1, NLRP12, Pycard, and IL-1β, suggesting enhanced TLR signals and inflammasomes activation. We next evaluated the participation of TLR2 and Nod2 in the host response during lethal Ehrlichia infection. Although lack of TLR2 impaired bacterial elimination and increased tissue necrosis, Nod2 deficiency attenuated pathology and enhanced bacterial clearance, which correlated with increased interferon-γ and interleukin-10 levels and a decreased frequency of pathogenic CD8(+) T cells in response to lethal infection. Thus, these data indicate that Nod2, but not TLR2, contributes to susceptibility to severe Ehrlichia-induced shock. Together, our studies provide, for the first time, insight into the diversity of host factors and novel molecular pathogenic mechanisms that may contribute to severe HME.

Neutrophils mediate immunopathology and negatively regulate protective immune responses during fatal bacterial infection-induced toxic shock

Ehrlichia chaffeensis is an obligate intracellular bacterium that infects primarily monocytes and macrophages and causes potentially fatal human monocytic ehrlichiosis (HME) that mimics toxic-shock-like syndrome in immunocompetent hosts. Early recruitment of neutrophils to the sites of infection is critical for the control of bacterial infection and inflammatory responses. We recently observed rapid and sustained neutrophil recruitment at a primary site of infection (peritoneum) following lethal murine ehrlichial infection compared to innocuous ehrlichial infection. We examined here the contribution of neutrophils to protective immunity or immunopathology during infection with monocytic Ehrlichia. Unexpectedly, depletion of neutrophils from lethally infected mice enhanced bacterial elimination, decreased immune-mediated pathology, and prolonged survival. Furthermore, compared to lethally infected sham controls, neutrophil depletion in infected mice resulted in amelioration of pathogenic responses, as evidenced by a decreased number of tumor necrosis factor alpha (TNF-α)-producing CD8(+) T cells, which is known to mediate immunopathology and toxic shock in a murine model of fatal ehrlichiosis. Although neutrophil depletion did not influence the number of CD4(+) Th1 cells and NKT cells producing gamma interferon (IFN-γ), it increased the ratio of IFN-γ- to IL-10-producing NKT cells as well as the ratio of IFN-γ to interleukin 10 (IL-10) transcripts in the liver. This may ameliorate the net suppressive effect of IL-10 on IFN-γ-mediated activation of infected macrophages and thus may account for the enhanced bacterial elimination. Finally, transcriptional analysis of gene expression in the liver indicated that neutrophils contribute to overproduction of cytokines and chemokines during fatal ehrlichiosis. In conclusion, these results revealed an unexpected role of neutrophils in supporting bacterial replication indirectly and promoting immunopathology during severe infection with an intracellular bacterium.

Inhibition of cell death of bone marrow-derived macrophages infected with Ehrlichia muris

Ehrlichia muris is a Gram-negative obligate intracellular bacterium belonging to the family Anaplasmataceae. It preferentially replicates inside macrophages by utilizing nutrients and processes of the host cell. In the present article, we studied the effects of E. muris infection on cell death of bone marrow-derived macrophages (BMDMs). Primary BMDMs were used for accessing E. muris-induced cell death, pro-inflammatory cytokine production and Western blot analysis. Human embryonic kidney cell line 293T (HEK293T) was used to access nuclear factor-kappaB (NF-κB) activity. BMDMs infected with E. muris showed significant inhibition of cell death when compared to uninfected cells. E. muris infection resulted in IκBα degradation, thus activation of NF-κB. In NF-κB reporter gene assay, the HEK293T cells infected with E. muris exhibited robust NF-κB-dependent luciferase activity in a bacterial dose-dependent manner. Furthermore, E. muris-induced inhibition of BMDMs cell death was abolished in the presence of MG132, a proteasome inhibitor that blocks NF-κB activation. Taken together, the results suggest that E. muris infection of BMDMs may have an inhibitory effect on cell death via a mechanism dependent on NF-κB activation.

Expression and immunogenicity of recombinant immunoreactive surface protein 2 of Anaplasma phagocytophilum

Human granulocytic anaplasmosis (HGA), caused by Anaplasma phagocytophilum, is an emerging tick-borne zoonotic disease throughout the world. The first HGA cases in China were documented in 2008, and the greatest challenge posed by the disease is rapid and accurate diagnosis during the acute phage of illness. In this study, we successfully cloned and expressed an A. phagocytophilum immunoreactive surface protein (major surface protein 2 [MSP2]) and demonstrated that this recombinant protein has natural immunogenicity by Western blotting and enzyme-linked immunosorbent assay (ELISA) using human HGA-positive sera and reference rabbit HGA-positive sera. The rabbit antisera against the recombinant protein also reacted actively with the natural antigen of A. phagocytophilum by immunofluorescence assay (IFA). No cross-reaction was observed between the recombinant protein and rabbit antisera against 10 common members of the order Rickettsiales by ELISA when the sera were diluted more than 1:100. We concluded that the recombinant MSP2 protein exhibited excellent antigenicity and specificity, results that should lay the foundation for the development of a simple and rapid diagnostic reagent and a vaccination for anaplasmosis.

Infection prevalences of common tick-borne pathogens in adult lone star ticks (Amblyomma americanum) and American dog ticks (Dermacentor variabilis) in Kentucky

Rocky Mountain spotted fever, Lyme disease, and ehrlichiosis are tick-borne diseases that are reported annually in Kentucky. We conducted a survey to describe infection prevalence of tick-borne pathogens in Amblyomma americanum and Dermacentor variabilis ticks collected in Kentucky. During 2007-2008, we collected 287 ticks (179 D. variabilis and 108 A. americanum) from canine, feral hog, horse, raccoon, white-tailed deer, and human hosts in six counties in Kentucky. Ticks were screened for Rickettsia spp., Borrelia spp., and Ehrlichia spp. by using polymerase chain reaction. Forty-one (14.3%) ticks (31 A. americanum and 10 D. variabilis) were polymerase chain reaction-positive for a Rickettsia spp. Fourteen (4.9%) ticks (6 A. americanum and 8 D. variabilis) were positive for E. chaffeensis, and 4 A. americanum (1.4%) were positive for E. ewingii. One (0.4%) A. americanum was positive for Borrelia lonestari. Although Rocky Mountain spotted fever is diagnosed in Kentucky, no R. rickettsii was found in ticks in this study.

Ehrlichiosis in Brazil

Ehrlichiosis is a disease caused by rickettsial organisms belonging to the genus Ehrlichia. In Brazil, molecular and serological studies have evaluated the occurrence of Ehrlichia species in dogs, cats, wild animals and humans. Ehrlichia canis is the main species found in dogs in Brazil, although E. ewingii infection has been recently suspected in five dogs. Ehrlichia chaffeensis DNA has been detected and characterized in mash deer, whereas E. muris and E. ruminantium have not yet been identified in Brazil. Canine monocytic ehrlichiosis caused by E. canis appears to be highly endemic in several regions of Brazil, however prevalence data are not available for several regions. Ehrlichia canis DNA also has been detected and molecularly characterized in three domestic cats, and antibodies against E. canis were detected in free-ranging Neotropical felids. There is serological evidence suggesting the occurrence of human ehrlichiosis in Brazil but its etiologic agent has not yet been established. Improved molecular diagnostic resources for laboratory testing will allow better identification and characterization of ehrlichial organisms associated with human ehrlichiosis in Brazil.

The interaction between IL-18 and IL-18 receptor limits the magnitude of protective immunity and enhances pathogenic responses following infection with intracellular bacteria

The binding of IL-18 to IL-18Rα induces both proinflammatory and protective functions during infection, depending on the context in which it occurs. IL-18 is highly expressed in the liver of wild-type (WT) C57BL/6 mice following lethal infection with highly virulent Ixodes ovatus ehrlichia (IOE), an obligate intracellular bacterium that causes acute fatal toxic shock-like syndrome. In this study, we found that IOE infection of IL-18Rα(-/-) mice resulted in significantly less host cell apoptosis, decreased hepatic leukocyte recruitment, enhanced bacterial clearance, and prolonged survival compared with infected WT mice, suggesting a pathogenic role for IL-18/IL-18Rα in Ehrlichia-induced toxic shock. Although lack of IL-18R decreased the magnitude of IFN-γ producing type-1 immune response, enhanced resistance of IL-18Rα(-/-) mice against Ehrlichia correlated with increased proinflammatory cytokines at sites of infection, decreased systemic IL-10 production, increased frequency of protective NKT cells producing TNF-α and IFN-γ, and decreased frequency of pathogenic TNF-α-producing CD8(+) T cells. Adoptive transfer of immune WT CD8(+) T cells increased bacterial burden in IL-18Rα(-/-) mice following IOE infection. Furthermore, rIL-18 treatment of WT mice infected with mildly virulent Ehrlichia muris impaired bacterial clearance and enhanced liver injury. Finally, lack of IL-18R signal reduced dendritic cell maturation and their TNF-α production, suggesting that IL-18 might promote the adaptive pathogenic immune responses against Ehrlichia by influencing T cell priming functions of dendritic cells. Together, these results suggested that the presence or absence of IL-18R signals governs the pathogenic versus protective immunity in a model of Ehrlichia-induced immunopathology.

MyD88-dependent signaling contributes to host defense against ehrlichial infection

The ehrlichiae are small Gram-negative obligate intracellular bacteria in the family Anaplasmataceae. Ehrlichial infection in an accidental host may result in fatal diseases such as human monocytotropic ehrlichiosis, an emerging, tick-borne disease. Although the role of adaptive immune responses in the protection against ehrlichiosis has been well studied, the mechanism by which the innate immune system is activated is not fully understood. Using Ehrlichia muris as a model organism, we show here that MyD88-dependent signaling pathways play a pivotal role in the host defense against ehrlichial infection. Upon E. muris infection, MyD88-deficient mice had significantly impaired clearance of E. muris, as well as decreased inflammation, characterized by reduced splenomegaly and recruitment of macrophages and neutrophils. Furthermore, MyD88-deficient mice produced markedly lower levels of IL-12, which correlated well with an impaired Th1 immune response. In vitro, dendritic cells, but not macrophages, efficiently produced IL-12 upon E. muris infection through a MyD88-dependent mechanism. Therefore, MyD88-dependent signaling is required for controlling ehrlichial infection by playing an essential role in the immediate activation of the innate immune system and inflammatory cytokine production, as well as in the activation of the adaptive immune system at a later stage by providing for optimal Th1 immune responses.

First described case of human granulocytic anaplasmosis in a patient in Eastern Austria

A 64-year-old otherwise healthy patient presented with high fever, thrombocytopenia, elevated liver enzymes and an erythema on the belly. The patient remembered a tick bite four weeks ago when walking with his dog before the specific symptoms started. A meningococcal disease or hematological illness was excluded. The serological results for tick-borne diseases showed a high IgG antibody titer for Anaplasma phagocytophila. All symptoms and laboratory parameters normalized after one week of hospitalization. The patient received no treatment and recovered completely. This is the first confirmed case of human granulocytic anaplasmosis (HGA) in Eastern Austria.

Natural killer cells promote tissue injury and systemic inflammatory responses during fatal Ehrlichia-induced toxic shock-like syndrome

Human monocytotropic ehrlichiosis is caused by Ehrlichia chaffeensis, a Gram-negative bacterium lacking lipopolysaccharide. We have shown that fatal murine ehrlichiosis is associated with CD8(+)T cell-mediated tissue damage, tumor necrosis factor-alpha, and interleukin (IL)-10 overproduction, and CD4(+)Th1 hyporesponsiveness. In this study, we examined the relative contributions of natural killer (NK) and NKT cells in Ehrlichia-induced toxic shock. Lethal ehrlichial infection in wild-type mice induced a decline in NKT cell numbers, and late expansion and migration of activated NK cells to the liver, a main infection site that coincided with development of hepatic injury. The spatial and temporal changes in NK and NKT cells in lethally infected mice correlated with higher NK cell cytotoxic activity, higher expression of cytotoxic molecules such as granzyme B, higher production of interferon-gamma and tumor necrosis factor-alpha, increased hepatic infiltration with CD8alphaCD11c(+) dendritic cells and CD8(+)T cells, decreased splenic CD4(+)T cells, increased serum concentrations of IL-12p40, IL-18, RANTES, and monocyte chemotactic protein-1, and elevated production of IL-18 by liver mononuclear cells compared with nonlethally infected mice. Depletion of NK cells prevented development of severe liver injury, decreased serum levels of interferon-gamma, tumor necrosis factor-alpha, and IL-10, and enhanced bacterial elimination. These data indicate that NK cells promote immunopathology and defective anti-ehrlichial immunity, possibly via decreasing the protective immune response mediated by interferon-gamma producing CD4(+)Th1 and NKT cells.

Anaplasma phagocytophilum and Ehrlichia chaffeensis: subversive manipulators of host cells

Anaplasma spp. and Ehrlichia spp. cause several emerging human infectious diseases. Anaplasma phagocytophilum and Ehrlichia chaffeensis are transmitted between mammals by blood-sucking ticks and replicate inside mammalian white blood cells and tick salivary-gland and midgut cells. Adaptation to a life in eukaryotic cells and transmission between hosts has been assisted by the deletion of many genes that are present in the genomes of free-living bacteria (including genes required for the biosynthesis of lipopolysaccharide and peptidoglycan), by the acquisition of a cholesterol uptake pathway and by the expansion of the repertoire of genes encoding the outer-membrane porins and type IV secretion system. Here, I review the specialized properties and other adaptations of these intracellular bacteria.

Strains of Ehrlichia chaffeensis in southern Indiana, Kentucky, Mississippi, and North Carolina

Rates of infection of Amblyomma americanum (L.) by Ehrlichia chaffeensis were compared in 100 ticks collected from sites in each of four states: Indiana, North Carolina, Kentucky, and Mississippi. The overall infection rates were similar among sites, ranging from 1 to 4%. Because pathogenic differences may exist between E. chaffeensis strains, nested polymerase chain reaction (PCR) amplification of the variable-length PCR target (VLPT), and sequencing of the amplicons were performed to differentiate between strains. The most common infecting strains at all sites exhibited a repeat profile of 1,2,3,4 (corresponding to the Arkansas/Jax/Osceola and Liberty strains). To determine whether the minimum infection rates (MIRs) or the most common infecting strain were changing over time in southern Indiana sites, 2765 ticks from six counties in 2000 and 837 ticks from seven counties in 2004 also were examined in pools of five ticks per pool. The MIRs for 2000 and 2004 were 3.5 and 4.2% respectively, suggesting that the overall MIRs remained low. At two sites, in Pike and Harrison counties, however, infection rates more than doubled from 2000 to 2004 (7 to 16% and 0.3 to 2.7% respectively). Across all sites, the most common infecting strains (Arkansas/Jax/Osceola and Liberty) did not significantly change (68% in 2000; 79% in 2004).

Host surveys, ixodid tick biology and transmission scenarios as related to the tick-borne pathogen, Ehrlichia canis

The ehrlichioses have been subject to increasing interest from veterinary and public health perspectives, but experimental studies of these diseases and their etiologic agents can be challenging. Ehrlichia canis, the primary etiologic agent of canine monocytic ehrlichiosis, is relatively well characterized and offers unique advantages and opportunities to study interactions between a monocytotropic pathogen and both its vertebrate and invertebrate hosts. Historically, advances in tick-borne disease control strategies have typically followed explication of tick-pathogen-vertebrate interactions, thus it is reasonable to expect novel, more sustainable approaches to control of these diseases as the transmission of their associated infections are investigated at the molecular through ecological levels. Better understanding of the interactions between E. canis and its canine and tick hosts would also elucidate similar interactions for other Ehrlichia species as well as the potential roles of canine sentinels, reservoirs and models of tick-borne zoonoses. This article summarizes natural exposure studies and experimental investigations of E. canis in the context of what is understood about biological vectors of tick-borne Anaplasmataceae.

Ehrlichioses in humans: epidemiology, clinical presentation, diagnosis, and treatment

Human ehrlichioses are emerging tickborne infections. "Human ehrlichiosis" describes infections with at least 5 separate obligate intracellular bacteria in 3 genera in the family Anaplasmataceae. Since 1986, these agents and infections (human monocytic ehrlichiosis [HME], caused by Ehrlichia chaffeensis; human granulocytic anaplasmosis [HGA], caused by Anaplasma phagocytophilum; and human ewingii ehrlichiosis, caused by Ehrlichia ewingii) are the causes of most human ehrlichioses. Their prevalence and incidence are increasing where the appropriate tick vectors are found. The diseases generally present as undifferentiated fever, but thrombocytopenia, leukopenia, and increased serum transaminase activities are important laboratory features. Despite clinical similarities, each disease has unique features: a greater severity and a higher case-fatality rate for HME and a higher prevalence of opportunistic infections for HGA. Once an ehrlichiosis is suspected on historical and clinical grounds, doxycycline treatment should be initiated concurrently with attempts at etiologic confirmation using laboratory methods such as blood smear examination, polymerase chain reaction, culture, and serologic tests.

Ehrlichiosis: Making the Diagnosis in the Acute Setting

Human monocytic ehrlichiosis (HME) is a tick-borne disease transmitted during the summer months in the mid-Atlantic, southeastern and south-central United States. A large proportion of patients presenting with ehrlichiosis must be hospitalized because of the severity of their presenting signs, symptoms and lab abnormalities. We report a case of HME presenting with negative serologies and positive DNA PCR for Ehrlichia chaffeensis during the acute illness. The patient was empirically treated with doxycycline before the availability of diagnostic test results and had a rapid recovery. This report summarizes the common findings of ehrlichiosis on presentation, diagnostic strategies, and treatment options. This case emphasizes the importance of considering tick-borne diseases in the differential diagnosis for patients presenting with nonspecific febrile syndromes in endemic areas and using the clinical scenario to determine whether empiric treatment for a tick-borne disease is necessary. Delaying treatment while awaiting confirmatory tests is unnecessary, and may result in a less favorable patient outcome.

Relative importance of T-cell subsets in monocytotropic ehrlichiosis: a novel effector mechanism involved in Ehrlichia-induced immunopathology in murine ehrlichiosis

Infection with gram-negative monocytotropic Ehrlichia strains results in a fatal toxic shock-like syndrome characterized by a decreased number of Ehrlichia-specific CD4(+) Th1 cells, the expansion of tumor necrosis factor alpha (TNF-alpha)-producing CD8(+) T cells, and the systemic overproduction of interleukin-10 (IL-10) and TNF-alpha. Here, we investigated the role of CD4(+) and CD8(+) T cells in immunity to Ehrlichia and the pathogenesis of fatal ehrlichiosis caused by infection with low- and high-dose (10(3) and 10(5) bacterial genomes/mouse, respectively) ehrlichial inocula. The CD4(+) T-cell-deficient mice showed exacerbated susceptibility to a lethal high- or low-dose infection and harbored higher bacterial numbers than did wild-type (WT) mice. Interestingly, the CD8(+) T-cell-deficient mice were resistant to a low dose but succumbed to a high dose of Ehrlichia. The absence of CD8(+) T cells abrogated TNF-alpha and IL-10 production, reduced tissue injury and bacterial burden, restored splenic CD4(+) T-cell numbers, and increased the frequency of Ehrlichia-specific CD4(+) Th1 cells in comparison to infected WT mice. Although fatal disease is perforin independent, our data suggested that perforin played a critical role in controlling bacterial burden and mediating liver injury. Similar to WT mice, mortality of infected perforin-deficient mice was associated with CD4(+) T-cell apoptosis and a high serum concentration of IL-10. Depletion of IL-10 restored the number of CD4(+) and CD8(+) T cells in infected WT mice. Our data demonstrate a novel mechanism of immunopathology in which CD8(+) T cells mediate Ehrlichia-induced toxic shock, which is associated with IL-10 overproduction and CD4(+) T-cell apoptosis.

Structures and Functions of Microbial Lipid Antigens Presented by CD1

The CD1 family of proteins has evolved to bind a range of endogenous and foreign lipids and present these at the cell surface for antigen-specific recognition by T cells. The distinct intracellular trafficking pathways of CD 1 molecules indicate that collectively, they have the potential to survey the endocytic system widely for antigen, consistent with a role in the presentation of lipids derived from intracellular microbial pathogens. In keeping with this idea, CDla, CDlb, CDlc and CDld have now been shown to present foreign lipid antigens derived from mycobacteria, Gram-negative bacteria and also protozoan species to T cells. These antigens are extremely diverse chemically, and include naturally occurring lipopeptide, glycolipid and phospholipid structures that are distinct from mammalian lipids. CD1-restricted mycobacterial lipids defined to date derive from the highly complex microbial cell envelope. They play a variety of physiological roles for the microbe, including formation of the plasma membrane and protective cell wall and as metabolic intermediates in iron-scavenging pathways. In each case, alkyl chains of CD 1-restricted lipid antigens are accommodated within a deep hydrophobic groove in the membrane-distal alphal-alpha2 domains of the CD1 molecule, with hydrophilic elements solvent-exposed and accessible for recognition by the T cell receptor. Variation in the number, length and saturation of alkyl chains, and the precise chemistry and chirality of the lipid headgroup, clearly exert dominant influences on antigenicity, mediated by effects on CD1 binding and T cell receptor recognition. In the context of structural studies of CD1-lipid complexes, these data suggest that the CD1 isoforms have evolved binding specificities for different classes of foreign lipids, and strongly support a model for antigen recognition involving fine discrimination of lipid headgroup components by the alpha beta T cell receptor. In this review, we summarise our current knowledge of foreign lipid antigens bound by CD 1, focusing on the roles their distinct structural features play in presentation and T cell antigen recognition, and their likely function in antimicrobial T cell responses.

Human monocytic ehrlichiosis in a renal transplant patient

Human ehrlichiosis is an emerging pathogen in immunocompromised patients, potentially leading to increased morbidity compared to immunocompetent patients. A high index of suspicion is imperative and early treatment with doxycycline can be life-saving. We report the case of an immunosuppressed renal transplant patient who was diagnosed with human monocytic ehrlichiosis and successfully treated with doxycycline.

The clinical assessment, treatment, and prevention of lyme disease, human granulocytic anaplasmosis, and babesiosis: clinical practice guidelines by the Infectious Diseases Society of America

Evidence-based guidelines for the management of patients with Lyme disease, human granulocytic anaplasmosis (formerly known as human granulocytic ehrlichiosis), and babesiosis were prepared by an expert panel of the Infectious Diseases Society of America. These updated guidelines replace the previous treatment guidelines published in 2000 (Clin Infect Dis 2000; 31[Suppl 1]:1-14). The guidelines are intended for use by health care providers who care for patients who either have these infections or may be at risk for them. For each of these Ixodes tickborne infections, information is provided about prevention, epidemiology, clinical manifestations, diagnosis, and treatment. Tables list the doses and durations of antimicrobial therapy recommended for treatment and prevention of Lyme disease and provide a partial list of therapies to be avoided. A definition of post-Lyme disease syndrome is proposed.

Invariant natural killer T cells in the response to bacteria: the advent of specific antigens

Invariant natural killer T (iNKT) cells are a unique subset of T lymphocytes that have been implicated in diverse immune reactions, ranging from self-tolerance and development of autoimmunity to responses to pathogens and tumors. Although some degree of autoreactivity of iNKT cells has been shown, it remained controversial whether the T-cell antigen receptor expressed by these cells could recognize microbial antigens, hampering the investigation of their physiological role during tolerance and immunity. Several recent publications have now defined natural antigens for the majority of iNKT cells in some Proteobacteria and in Borrelia burgdorferi, demonstrating specificity of these cells for microbes in addition to self-reactivity. The characterization of natural antigens from bacteria, and the iNKT cell response to bacteria containing them, are decisive steps toward the clarification of the natural role of iNKT cells in host defense against pathogens, and will likely spur numerous findings in the near future.

Clinical Diagnosis and Treatment of Human Granulocytotropic Anaplasmosis

Tick-borne rickettsiae in the genera Ehrlichia and Anaplasma are intracellular bacteria that infect wild and domestic mammals and, more recently, man. The increased desire of humans for recreational activities outdoors has increased the exposure to potential human pathogens that previously cycled almost exclusively within natural, nonhuman enzootic hosts. Anaplasma phagocytophilum causes an acute, nonspecific febrile illness of humans previously known as human granulocytotropic ehrlichiosis (HGE) and now called human granulocytotropic anaplasmosis (HGA). The first patient to have recognized HGA was hospitalized at St Mary's Hospital in Duluth, Minnesota, USA in 1990. However, the clinical and laboratory presentation of this infection remained undefined until 1994, when Bakken and collaborators published their experience with 12 patients who had HGA. By the end of December 2004, at least 2,871 cases of HGA had been reported from 13 U.S. states to the Centers for Disease Control and Prevention (CDC). A limited number of laboratory-confirmed cases have been reported from countries in Europe, including Austria, Italy, Latvia, the Netherlands, Norway, Poland, Slovenia, Spain, and Sweden. Ixodes persulcatus-complex ticks are the arthropod hosts for Borrelia burgdorferi, the agent of Lyme borreliosis, and are also the arthropod hosts for A. phagocytophilum. Most cases of HGA have been contracted in geographic regions that are endemic for Lyme borreliosis. Male patients outnumber female patients by a factor of 3 to 1 and as many as 75% of patients with HGA have had a tick bite prior to their illness. Seroepidemiologic studies have demonstrated that HGA for the most part is a mild or even asymptomatic illness. However, older individuals and patients who are immunocompromised by natural disease processes or medications may develop an acute, influenza-like illness characterized by high fever, rigors, generalized myalgias, and severe headache. Local skin reactions at the site of the tick bite have not been described, and nonspecific skin rashes have been reported only occasionally. Anaplasmosis is associated with variable but suggestive changes in routine laboratory test parameters. Most patients develop transient reductions in total leukocyte and platelet concentrations. Relative granulocytosis accompanied by a left shift and lymphopenia during the first week of illness has been reported frequently. Serum hepatic transaminase concentrations usually increase two- to fourfold, and inflammatory markers, such as C-reactive protein and the erythrocyte sedimentation rate, rise during the acute phase. Abnormal laboratory findings may return toward normal range for patients who have been ill for more than 7 days, which may obfuscate the clinical decision making. Characteristic clusters of bacteria (morulae) are observed in the cytoplasm of peripheral blood granulocytes in 20% to 80% of infected patients during the acute phase of illness. The clinical diagnosis may be confirmed retrospectively by specific laboratory tests, which include positive polymerase chain reaction (PCR), identification of A. phagocytophilum in culture of acute-phase blood, or the detection of specific antibodies to A. phagocytophilum in convalescent serum. Virtually all patients have developed serum antibodies to A. phagocytophilum after completion of antibiotic therapy, and demonstration of seroconversion by indirect immunofluorescent antibody testing of acute-phase and convalescent-phase serum samples is currently the most sensitive and specific tool for laboratory confirmation of HGA. Treatment with doxycycline usually results in rapid improvement and cure. Most patients with HGA have made an uneventful recovery even without specific antibiotic therapy. However, delayed diagnosis in older and immunocompromised patients may place those individuals at risk for an adverse outcome, including death. Thus, prompt institution of antibiotic therapy is advocated for any patient who is suspected to have HGA and for all patients who have confirmed HGA.

An intradermal environment promotes a protective type-1 response against lethal systemic monocytotropic ehrlichial infection

Immune responses against monocytotropic ehrlichiosis during infection with a strain of Ehrlichia from Ixodes ovatus (IOE) were evaluated using a model that closely reproduces the pathology and immunity associated with tick-transmitted human monocytotropic ehrlichiosis. C57BL/6 mice were inoculated intradermally or intraperitoneally with high-dose highly virulent IOE or intraperitoneally with mildly virulent Ehrlichia muris. Intradermal (i.d.) infection with IOE established mild, self-limited disease associated with minimal hepatic apoptosis, and all mice survived past 30 days. Intraperitoneal (i.p.) infection with IOE resulted in acute, severe toxic shock-like syndrome and severe multifocal hepatic apoptosis and necrosis, and all mice succumbed to disease. Compared to i.p. infection with IOE, intradermally infected mice had a 100- to 1,000-fold lower bacterial load in the spleen with limited dissemination. Compared to mice infected intraperitoneally with IOE, i.d. infection stimulated a stronger protective type-1 cell-mediated response on day 7 of infection, characterized by increased percentages of both CD4+ and CD8+ splenic T cells, generation of a greater number of IOE-specific, gamma interferon-producing CD4+ Th1 cells, and higher levels of tumor necrosis factor (TNF-alpha) in the spleen but lower concentrations of serum TNF-alpha and interleukin-10. These data suggest that under the conditions of natural route of challenge (i.e., i.d. inoculation), the immune response has the capacity to confer complete protection against monocytotropic ehrlichiosis, which is associated with a strong cell-mediated type-1 response and decreased systemic production of pro- and anti-inflammatory cytokines.

Lymph node hemophagocytosis in rickettsial diseases: a pathogenetic role for CD8 T lymphocytes in human monocytic ehrlichiosis (HME)?

BACKGROUND

Human monocytic ehrlichiosis (HME) and Rocky Mountain spotted fever (RMSF) are caused by Ehrlichia chaffeensis and Rickettsia rickettsii, respectively. The pathogenesis of RMSF relates to rickettsia-mediated vascular injury, but it is unclear in HME.

METHODS

To study histopathologic responses in the lymphatic system for correlates of immune injury, lymph nodes from patients with HME (n = 6) and RMSF (n = 5) were examined. H&E-stained lymph node tissues were examined for five histopathologic features, including hemophagocytosis, cellularity, necrosis, and vascular congestion and edema. The relative proportions of CD68 macrophages, CD8 and CD4 T lymphocytes, and CD20 B lymphocytes were evaluated by immunohistochemical staining.

RESULTS

Hemophagocytosis was similar in HME and RMSF, and was greater than in control cases (p = .015). Cellularity in HME was not different from controls, whereas RMSF lymph nodes were markedly less cellular (p < 0.002). E. chaffeensis-infected mononuclear phagocytes were infrequent compared to R. rickettsii-infected endothelial cells. More CD8 cells in lymph nodes were observed with HME (p < .001), but no quantitative differences in CD4 lymphocytes, macrophages, or B lymphocytes were identified.

CONCLUSION

Hemophagocytosis, CD8 T cell expansion, and the paucity of infected cells in HME, suggest that E. chaffeensis infection leads to macrophage activation and immune-mediated injury.

Balancing protective immunity and immunopathology: a unifying model of monocytotropic ehrlichiosis

Interactions among pathogens, antigen-presenting cells (APCs) and lymphocytes are critical in maintaining balance in the daily challenges to the immune system. Monocytotropic ehrlichiosis, caused by Ehrlichia chaffeensis, is a multisystem inflammatory ailment. A complex interaction between Ehrlichia and the immune systems of a number of mammalian hosts, in human disease and animal models, has been described. The presence of an overwhelming ehrlichial infection in immunocompromised individuals suggests that severe tissue damage is most likely due to direct bacterial effect. However, clinical and experimental observations indicate that this is an oversimplified concept. First, immunocompetent patients with severe ehrlichiosis have a low bacterial burden. Second, severe and fatal murine ehrlichiosis in immunocompetent animals, which mimics human disease, is associated with a low bacterial burden in different organs and late systemic and local overproduction of TNF-alpha by T cells. In order to counterbalance overshooting immune responses, T cells and APCs secrete anti-inflammatory cytokines that are key for maintaining a healthy balance between protection and immunopathology. CD4+ T cell-mediated immunity and antibody responses of a Th1 phenotype play critical roles in protection against Ehrlichia. Of particular importance for the generation of protective immunity is the induction of activation programs in APCs directly by pathogens or by T cell-derived factors. In this study, we consider the roles of innate and adaptive immune responses in terms of protection from severe ehrlichiosis and their potential roles in immunopathology.

Glycolipids for natural killer T cells

Natural killer T cells (NKT cells) play a central role in regulating immune responses influencing conditions ranging from autoimmune to infectious diseases. NKT cell responses are induced by recognition of glycolipid antigens presented by CD1d, an antigen presentation protein. In the last 10 years great strides have been made in understanding the types of glycolipids recognized by NKT cells. These advances have included determination of the lipid and carbohydrate recognition requirements for stimulation and identification of "natural" antigens for these cells.

Role of tumor necrosis factor alpha (TNF-alpha) and interleukin-10 in the pathogenesis of severe murine monocytotropic ehrlichiosis: increased resistance of TNF receptor p55- and p75-deficient mice to fatal ehrlichial infection

Intraperitoneal (i.p.) infection with a high dose of a highly virulent Ehrlichia strain (IOE) results in a toxic shock-like syndrome characterized by severe liver injury and systemic overproduction of tumor necrosis factor alpha (TNF-alpha) by CD8+ T cells. We examined the role of TNF-alpha and TNF receptors in high-dose-IOE-induced shock/liver injury. TNF receptor (TNFR) I/II-/- mice lacking both the p55 and p75 receptors for this cytokine were more resistant to IOE-induced liver injury than their wild-type background controls. TNFR I/II-/- mice survived longer, dying between 15 and 18 days, with evidence of mild liver necrosis/apoptosis. In contrast, wild-type mice were not rescued from the lethal effect of IOE by TNF-alpha neutralization. TNF-alpha-depleted mice developed severe liver injury and succumbed to disease between days 9 and 11 postinfection, similar to sham-treated, infected wild-type mice. Although IFN-gamma production in the spleens of IOE-infected TNFR I/II-/- and TNF-alpha-depleted mice was higher than that detected in wild-type controls, these mice had higher bacterial burdens than infected controls. Following high-dose IOE challenge, TNFR I/II-/- and TNF-alpha-depleted mice have an early increase in IL-10 levels in sera and spleens, which was produced mainly by adherent spleen cells. In contrast, a late burst of interleukin-10 (IL-10) was observed in control mice. Nonadherent spleen cells were the major source of IL-10 in IOE-infected wild-type mice. We conclude that TNFR I/II and TNF-alpha participate in Ehrlichia-induced shock and host defense by regulating liver injury and controlling ehrlichial burden. Our data suggest that fatal ehrlichiosis could be a multistep process, where TNF-alpha is not solely responsible for mortality.

Co-infection of White-Tailed Deer with Multiple Strains ofEhrlichia chaffeensis

We investigated the effect of exposing deer to multiple strains of Ehrlichia chaffeensis that differed in number of tandem repeats in either the variable-length PCR target (VLPT) gene or 120 kDa antigen gene. We hypothesized that infection with one strain would provide immunity to infection with other strains of E. chaffeensis. All deer initially exposed to strain A (604-2) became PCR and culture positive by 10 days post-infection (DPI). Three deer infected with strain A and subsequently inoculated with strain B (623-4) became infected with strain B. Two deer infected with strain A and subsequently inoculated with strain C (125B) became infected with strain C. Of three deer, each infected with strain B and subsequently inoculated with strain C, one was PCR positive for strain C. Of three deer previously inoculated with both strains A and B, and subsequently inoculated with strain C, one showed delayed evidence of strain C. Western blot analysis demonstrated that deer sera reacted differently to antigens from each exposed strain. A complementary in vitro study demonstrated that exposure to two strains differing in VLPT repeats may lead to co-infection of DH82 cells. These results complement a previous study and further show that deer can become sequentially infected with up to three strains of E. chaffeensis. This suggests that competitive exclusion, a phenomenon described in related organisms such as Anaplasma marginale whereby infection with one strain precludes subsequent infection by a second, distinct strain of the same species, may not occur with E. chaffeensis.

Ehrlichia infection of the central nervous system

Ehrlichiosis in the United States is caused by three closely related bacterial species (Ehrlichia chaffeensis, Ehrlichia ewingii, and Anaplasma phagocytophilum), all transmitted through tick bite. Although there is variation with respect to geography and tick vector, the clinical manifestations are similar, and treatment of these infections is identical. Ehrlichiosis can present with a spectrum of neurologic manifestations, ranging in severity from headache to meningoencephalitis. Treatment is straightforward if the diagnosis is suspected, but antibiotic therapy should not be delayed pending laboratory confirmation. Doxycycline, the treatment of choice for adults and children with suspected ehrlichiosis, has high bioavailability and can be administered orally in most cases. Therapy is typically continued at least 3 days after the last documented fever. Although there have been no studies specifically evaluating duration or dosing of doxycycline for Ehrlichia meningoencephalitis, anecdotal reports suggest 100 mg doxycycline administered twice daily is effective, despite limited penetration into the cerebrospinal fluid. Because doxycycline interacts with CYP3A4 enzymes, there is potential for drug interactions with a number of medications. In endemic areas, documentation of coinfection with Borrelia burgdorferi, the etiologic agent of Lyme disease, may require prolonging the duration of doxycycline therapy.

Tick modulation of the in-vitro expression of adhesion molecules by skin-derived endothelial cells

As a tick feeds, its saliva induces innate and acquired immune responses in the host, including leucocyte infiltration into the bite site. Tick salivary glands produce molecules, however, that counteract many host defences against blood feeding. The effects of salivary-gland extracts (SGE) of Dermacentor andersoni and Ixodes scapularis on the expression of various adhesion molecules [E-selectin, P-selectin, intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1)] by the sEND.1 cell line (which is based on cells from the subcutaneous tissue of mice) have now been investigated in vitro. The effects were found to differ with the tick species. The SGE of D. andersoni significantly down-regulated the expression of ICAM-1, whereas a similar extract prepared from I. scapularis significantly reduced the expression of P-selectin and VCAM-1. Tick salivary proteins therefore appear to have direct effects on adhesion-molecule expression, in addition to their previously established roles in down-regulating the pro-inflammatory cytokines that activate endothelial cells. It remains unclear exactly how the reduction of adhesion-molecule expression in the host's endothelial cells benefits the feeding tick but it may alter leucocyte migration to the bite site and/or reduce antigen presentation by the endothelial cells. It may also modulate the interactions between the host's leucocytes and any tick-borne pathogens, during initial infection of the endothelium.

Is Lyme disease always poly microbial? – The jigsaw hypothesis

Lyme disease is considered to be caused by Borrelia species of bacteria but slowly evidence is accumulating which suggests that Lyme disease is a far more complex condition than Borreliosis alone. This hypothesis suggests that it may be more appropriate to regard Lyme disease as a tick borne disease complex. Over recent years numerous different microbes have been found in ticks which are known to be zoonotic and can coinfect the human host. The hypothesis suggests that multiple coinfections are invariably present in the clinical syndromes associated with Lyme disease and it is suggested that these act synergistically in complex ways. It may be that patterns of coinfection and host factors are the main determinants of the variable clinical features of Lyme disease rather than Borrelia types. An analogy with a jigsaw puzzle is presented with pieces representing Borreliae, coinfections and host factors. It is suggested that many pieces of the puzzle are missing and our knowledge of how the pieces fit together is rudimentary. It is hoped that the hypothesis will help our understanding of this complex, enigmatic condition.

Experimental Ehrlichia canis infection in the dog does not cause immunosuppression

A carrier state develops in some Ehrlichia canis-infected dogs due to ineffective host defenses. The subsequent development of immune-mediated diseases or opportunistic infections in chronic ehrlichiosis suggests dysregulation of immunity; however, the immunobiology of this infection has not been well characterized. In this study, eight dogs were infected with E. canis, and changes in seroreactivity, serum immunoglobulin (Ig) concentrations, peripheral blood T cell subsets, lymphocyte blastogenesis (LBT), and lymphokine-activated killer (LAK) activity were evaluated over 4 months. Infection, which was documented by seroconversion, polymerase chain reaction, and blood culture, caused self-limiting fever and thrombocytopenia. Infected dogs developed an anti-E. canis antibody response but were not immune to re-infection. Serum IgM, IgG, and IgA concentrations were unaffected by E. canis. The percentage of circulating CD4(+) T cells was similar in uninfected and infected dogs at all points. Infected dogs developed a CD8(+) lymphocytosis 6 weeks after inoculation that subsequently subsided, despite organism persistence. Functional defects of cell-mediated immunity, measured as suppression of LAK activity or mitogen-driven LBT, were not observed. These results suggest that immune responses are not grossly impaired in young dogs during the first several months following experimental E. canis infection.

Anaplasma and Ehrlichia Infection

Human and animal infections by Anaplasmataceae are increasingly recognized as important and potentially fatal arthropod-transmitted diseases. Since the first recognition and implementation of diagnostic methods for human infection by Ehrlichia chaffeensis and Anaplasma phagocytophilum, the incidence of infections has linearly increased. Moreover, diagnostic and epidemiological testing indicates that "ehrlichia" infections are globally distributed and suggests that additional agents of human and veterinary "ehrlichiosis" will be identified. With increasing disease identification has come recognition that the infections can be severe, with approximately one-half of patients requiring hospitalization for complications including respiratory distress, myocarditis, neurological complications, hepatitis, a septic or toxic shock-like disease, opportunistic infections, and death in 0.5 to 3.0%. An understanding of the diseases, pathophysiology, pathogenesis, control, and management will best be developed through fundamental investigations. Advances in comprehension as to the separate contributions of bacteria and host are crucial since most data now suggest that alterations in host neutrophil function and protection from innate and adaptive immunity also contribute to disease manifestations. It is reasonable to operate from the hypothesis that these host cell functional changes ultimately benefit bacterial survival while inadvertently eliciting clinical disease in poorly adapted hosts. A firmer basis for the scientific understanding of Anaplasmataceae biology will allow logical and rational approaches toward infection control, prevention, and treatment.

Transstadial and intrastadial experimental transmission of Ehrlichia canis by male Rhipicephalus sanguineus

The acquisition and transmission of rickettsial pathogens by different tick developmental stages has important epidemiological implications. The purpose of this study was to determine if male Rhipicephalus sanguineus can experimentally acquire and transmit Ehrlichia canis in the absence of female ticks. Two trials were performed where nymphal and male R. sanguineus were simultaneously acquisition fed on the same infected donor hosts, and transstadially or intrastadially exposed male ticks were fed on separate pathogen-free dogs as a test for transmission. A single-step p30-based PCR assay was used to test canine and tick hosts for E. canis infections before and after tick feeding. E. canis was detected after either intrastadial or transstadial passage in male ticks, the organism remained detectable in both tick groups after transmission feeding, and both tick groups transmitted the rickettsia to susceptible dogs. Infection of dogs via tick feeding resulted in milder clinical signs and lower antibody titers than intravenous inoculation of carrier blood, but further investigation is needed to understand the mechanisms responsible for this observation. These results demonstrate that male R. sanguineus can take multiple feedings, and that they can both acquire and transmit E. canis in the absence of female ticks. This tick development stage could be important in transmission of E. canis, and perhaps related pathogens, between vertebrate hosts under natural and experimental conditions.

Training room management of medical conditions: infectious diseases

Management of infectious diseases in athletes encompasses a wide range of pathogens, clinical presentations, and treatment options. Certain athletic activities and training regimens may predispose athletes to increased risk of contracting infectious diseases, some of which may limit athletic participation and pose the threat of significant morbidity. The sports medicine physician plays an important role as a first line of defense in preventing, recognizing, and appropriately treating infectious diseases in athletes.

Exogenous and endogenous glycolipid antigens activate NKT cells during microbial infections

CD1d-restricted natural killer T (NKT) cells are innate-like lymphocytes that express a conserved T-cell receptor and contribute to host defence against various microbial pathogens. However, their target lipid antigens have remained elusive. Here we report evidence for microbial, antigen-specific activation of NKT cells against Gram-negative, lipopolysaccharide (LPS)-negative alpha-Proteobacteria such as Ehrlichia muris and Sphingomonas capsulata. We have identified glycosylceramides from the cell wall of Sphingomonas that serve as direct targets for mouse and human NKT cells, controlling both septic shock reaction and bacterial clearance in infected mice. In contrast, Gram-negative, LPS-positive Salmonella typhimurium activates NKT cells through the recognition of an endogenous lysosomal glycosphingolipid, iGb3, presented by LPS-activated dendritic cells. These findings identify two novel antigenic targets of NKT cells in antimicrobial defence, and show that glycosylceramides are an alternative to LPS for innate recognition of the Gram-negative, LPS-negative bacterial cell wall.