Genetic and antigenic diversities of major immunoreactive proteins in globally distributed Ehrlichia canis strains

Immuno- and expression analysis of Ehrlichia canis immunoreactive proteins

Ehrlichia canis is the primary etiologic agent of canine monocytic ehrlichiosis, a serious and sometimes fatal hemorrhagic disease of dogs. Diagnosis of E. canis infection is often retrospectively confirmed by serologic detection of antibodies by immunofluorescent microscopy. Our laboratory previously identified numerous major immunoreactive proteins with species-specific linear antibody epitopes that are useful for immunodiagnosis of CME. More recently, we have defined the entire antibody-reactive immunome of E. canis, substantially increasing the number of major immunoreactive proteins known to exist. In this study, we analyzed and compared seven recently identified antibody reactive E. canis proteins with established diagnostic antigens including tandem repeat proteins TRP19, TRP36 and TRP140 and observed comparable immunoreactivity. Many of these proteins were conserved in different E. canis strains. Multiple linear antibody epitopes were mapped in a highly conserved TRP (Ecaj_0126), including within the tandem repeat domain. Temporal antibody responses were examined, and multiple proteins reacted with antibodies in sera as early as 21 days post experimental infection. Host-specific expression of the proteins was examined which revealed that some proteins exhibited higher expression in mammalian cells, while others in tick cells. This study has identified new immunodiagnostic candidates that exhibit different host expression patterns, information which may be useful for developing ultrasensitive immunodiagnostics and effective vaccines for CME.

Antibody reactive immunomes of Ehrlichia chaffeensis and E. canis are diverse and defined by conformational antigenic determinants

For decades, the defined antibody reactive proteins of Ehrlichia chaffeensis and E. canis were limited to a small group with linear antibody epitopes. Recently, our laboratory has utilized an immunomics-based approach to rapidly screen and identify undefined Ehrlichia chaffeensis and E. canis antigenic proteins and antibody epitopes. In this study, we analyzed the remaining portion (~50%) of the E. chaffeensis and E. canis proteomes (n = 444 and n = 405 proteins, respectively), that were not examined in previous studies, to define the complete immunomes of these important pathogens. Almost half of the E. chaffeensis proteins screened (196/444) reacted with antibodies in convalescent HME patient sera, while only 43 E. canis proteins reacted with CME dog sera. New major immunoreactive proteins were identified in E. chaffeensis (n = 7) and E. canis (n = 1), increasing the total number of E. chaffeensis (n = 14) and E. canis proteins (n = 18) that exhibited antibody reactivity comparable to well-defined major antigenic proteins (TRP120 and TRP19). All of the E. chaffeensis but only some E. canis major immunoreactive proteins contained major conformation-dependent antibody epitopes. The E. chaffeensis immunoreactive proteins were generally small (< 250 amino acids; ~27kDa) and the E. canis proteins were slightly larger (> 320 amino acids; ~35 kDa). The majority of these new Ehrlichia major immunoreactive proteins were predicted to be type I secreted effectors, some of which contained transmembrane domains. Characterization of the immunomes of E. chaffeensis and E. canis and understanding the host specific Ehrlichia immune responses will facilitate identification of protective antigens and define the biophysical epitope characteristics vital to effective vaccine development for the ehrlichioses.

Molecular occurrence and genetic diversity of Ehrlichia canis in naturally infected dogs from Thailand

Canine monocytic ehrlichiosis is cause by Ehrlichia canis resulting in hematologic disorders and severe clinical signs. The aim of this study was to scrutinize the molecular detection and genetic diversity of E. canis based on the trp36 gene in dogs from Thailand's northern and central regions. A total of 120 dogs blood samples were amplified for trp36 gene of E. canis using the polymerase chain reaction (PCR). Forty-seven out of 120 dog blood samples (39.16%, 47/120) were positive for E. canis the trp36 DNA with 790 bp of PCR amplicon size. The factor significantly associated with E. canis infection is animal housing status (p < 0.05). Sequence and phylogenetic analysis showed that E. canis trp36 gene of Thailand isolates was clustered into 1st clade with similarity ranging from 95.65 to 100% together with the US genogroup. The 14 haplotypes of the trp36 gene shown in TCS network exhibited that haplotype #1-4 was found in Thailand. The entropy analysis of the trp36 gene illustrated 751 polymorphic sites and 271 entropy peaks of nucleic and amino acid sequences, respectively. Hence, these findings are crucial for better understanding the epidemiology of Ehrlichia infection and could be helpful for implementing control measures in Thailand.

Costa Rican Genotype of Ehrlichia canis: A Current Concern

Canine monocytic ehrlichiosis (CME) is endemic to Brazil, and studies have verified that dogs have been exposed to different genotypes of Ehrlichia canis. This genetic divergence can influence the clinical response of the animals. We aimed to describe clinical and hematological changes in 125 dogs that reacted to BrTRP36, USTRP36, and CRTRP36 genotypes through enzyme immunoassays and to highlight the current concern regarding infection by the Costa Rican genotype. The results showed that 52.0% reacted to the Brazilian genotype, 22.4% reacted to the Costa Rican genotype, and 16.0% reacted to the American genotype, and some co-reactions were observed. Dogs reactive to BrTRP36 were 1.24% more likely to present with medullary regeneration in cases of anemia and 3% less likely to manifest hyperproteinemia, while dogs reactive to CRTRP36 were 0.7% less likely to present with medullary regeneration. Febrile illness and neurological alterations were also statistically associated, with an 85.7% and 231.2% increased likelihood, respectively, to occur in dogs that reacted to USTRP36. The dogs with the American genotype developed clinical manifestations related to systemic inflammation, while those with the Brazilian genotype of E. canis were more dispersed in the region studied, showing greater adaptation to the hosts. We highlight the significant serocurrence of the Costa Rican genotype, which has already been described to have zoonotic potential and which showed less adaptation.

Molecular characterization of Ehrlichia canis and Babesia vogeli reveals multiple genogroups associated with clinical traits in dogs from urban areas of Colombia

Ehrlichia canis and Babesia vogeli are vector-borne pathogens that infect blood cells and produce the diseases Canine Monocytic Ehrlichiosis (CME) and Babesiosis in dogs. Considering the lack of studies on these pathogens in Colombia, this study aims to determine the molecular prevalence and genetic characterization of E. canis and Babesia spp., in dogs from the Metropolitan Area of Bucaramanga (MAB), Santander, a region with one of the greatest pet densities in Colombia. One hundred eighty-five dogs were surveyed and analyzed through molecular, clinical, and hematological approaches. The molecular detection of E. canis and Babesia spp., was performed by conventional PCR targeting the dsb and 18S rRNA genes, respectively. To identify genogroups, E. canis positive samples underwent a hemi-nested PCR of the trp36 gene, and the PCR products were subsequently sequenced. Molecular analyses showed a prevalence of 13% (24/185; CI 95%, 8.1 - 18.0%) and 1.09% (2/185; CI 95,% -0.43 - 2.6%) for E. canis and B. vogeli respectively, as well as the presence of the genogroups US (USA), BR (Brazil), and CR (Costa Rica), in 62.5, 16.6, and 16.6% of E. canis positive samples, respectively. Values of hematocrit, hemoglobin, platelets, erythrocytes, white blood cell (WBC) count, lymphocytes, and eosinophils showed significant differences between animals infected with the different genogroups of E. canis (p< 0.05). In contrast, hematocrit values, hemoglobin, platelets, red blood cells, and creatine kinase MB isoenzyme (CK-MB) were lower in B. vogeli positive animals. Statistical analysis indicated that E. canis infection was associated with specific socioeconomic sectors as well as with some household features (p< 0.05). In conclusion, our results present evidence of the circulation of multiple genogroups of E. canis in the MAB, which is associated with different geographical origins and clinical traits. Epidemiological analyses suggest a need to increase molecular surveillance and prevention campaigns especially in lower socioeconomic sectors.

Ehrlichia canis: Molecular characterization and genetic diversity based on the p28 and trp36 genes

Ehrlichia canis is a common tick-borne intracellular pathogen causing canine monocytic ehrlichiosis (CME) in dogs worldwide. The aims of this study were to investigate the genetic diversity and antigenicity of E. canis based on the p28 and trp36 genes in dogs in Thailand. The E. canis p28 and trp36 genes were amplified by the polymerase chain reaction (PCR) and cloned for sequencing and bioinformatic analyses. 36% (44/120) of dog blood samples were positive for E. canis DNA consisting of p28 (31%, 14/44) and trp36 (69%, 30/44) genes with 792 and 882 bp of PCR products size, respectively. The E. canis TRP36 from all Thailand sequences exhibited encoded nine amino acids (TEDSVSAPA) with 11 copies of tandem repeats along the sequences. The phylogenetic trees of E. canis, using the p28 and trp36 genes, exhibited that the Thailand isolates fell into two clades and one clade with similarity ranging from 55.95 to 100% and 100%, respectively. The results of diversity analysis revealed 10 and 20 haplotypes of the p28 and trp 36 genes, respectively. The entropy analysis of the p28 and trp36 nucleic acid sequences showed 442 and 1321 high entropy peaks respectively, whereas those of the P28 and TRP36 amino acid sequences showed 477 and 388 high entropy peaks, respectively. For B-cell epitopes analysis, the conserved amino acid of P28 and TRP36 sequences has been also demonstrated. Therefore, the results could be utilized to improve the understanding of phylogenetic relationship, genetic diversity and antigenicity of E. canis Thailand isolates.

Novel Ehrlichia canis genogroup in dogs with canine ehrlichiosis in Cuba

Background

Canine monocytic ehrlichiosis (CME) is caused by the tick-borne pathogen Ehrlichia canis, an obligate intracellular Gram-negative bacterium of the family Anaplasmataceae with tropism for canine monocytes and macrophages. The trp36 gene, which encodes for the major immunoreactive protein TRP36 in E. canis, has been successfully used to characterize the genetic diversity of this pathogen in different regions of the world. Based on trp36 sequence analysis, four E. canis genogroups, United States (US), Taiwan (TWN), Brazil (BR) and Costa Rica (CR), have been identified. The aim of this study was to characterize the genetic diversity of E. canis in Cuba based on the trp36 gene.

Methods

Whole blood samples (n = 8) were collected from dogs found to be infested with the tick vector Rhipicephalus sanguineus sensu lato (s.l.) and/or presenting clinical signs and symptoms of CME. Total DNA was extracted from the blood samples and trp36 fragments were amplified by PCR. Nucleotide and protein sequences were compared using alignments and phylogenetic analysis.

Results

Four of the trp36 sequences obtained (n = 8) fall within the phylogenetic cluster grouping the US genogroup E. canis strains. The other E. canis trp36 sequences formed a separate and well-supported clade (94% bootstrap value) that is phylogenetically distant from the other major groups and thus represents a new genogroup, herein designated as the ‘Cuba (CUB) genogroup’. Notably, dogs infected with the CUB genogroup presented frequent hemorrhagic lesions.

Conclusions

The results of this study suggest that genetic diversification of E. canis in Cuba is associated with the emergence of E. canis strains with increased virulence.

Recombinant Ehrlichia canis GP19 Protein as a Promising Vaccine Prototype Providing a Protective Immune Response in a Mouse Model

Simple summary

One of the limitations of vaccine development against E. canis infection is the indefinite knowledge of the protective immunity in the host. In this study, recombinant protein GP19 was produced as a vaccine prototype, rGP19, for inducing protective immune responses in a mouse model against E. canis. Antibody responses against E. canis were evaluated and revealed that the immunized mice with rGP19 showed higher antibody levels than in adjuvant-immunized and naive mice, both pre- and post-challenging with E. canis. DNA from blood, liver, and spleen were extracted to determine ehrlichial loads. The rGP19-immunized mice showed significantly lower ehrlichial loads in blood, liver, and spleen DNA compared with adjuvant-immunized mice. This study also detected IFN-γ-producing CD4+ T cells in the rGP19-immunized mice and then were later infected with E. canis on day 14 of the post-infection period using flow cytometry. Additionally, Cytokine mRNA expression was investigated and revealed up-regulation of IFNG and IL1 mRNA expression in rGP19-immunized mice. The present study provides evidence of rGP19 that can eliminate E. canis by manipulating both humoral and cell-mediated immune responses in the laboratory animal model.

Abstract

The intracellular bacterium Ehrlichia canis is the causative pathogen of canine monocytic ehrlichiosis (CME) in dogs. Despite its veterinary and medical importance, there is currently no available vaccine against this pathogen. In this study, the recombinant GP19 (rGP19) was produced and used as a recombinant vaccine prototype in a mouse model against experimental E. canis infection. The efficacy of the rGP19 vaccine prototype in the part of stimulating B and T cell responses and conferring protection in mice later challenged with E. canis pathogen were evaluated. The rGP19-specific antibody response was evaluated by ELISA after E. canis challenge exposure (on days 0, 7, and 14 post-challenge), and demonstrated significantly higher mean antibody levels in rGP19-immunized mice compared with adjuvant-immunized and naive mice. Significantly lower ehrlichial loads in blood, liver, and spleen DNA samples were detected in the immunized mice with rGP19 by qPCR. The up-regulation of IFNG and IL1 mRNA expression were observed in mice immunized with rGP19. In addition, this study detected IFN-γ-producing memory CD4+ T cells in the rGP19-immunized mice and later infected with E. canis on day 14 post-infection period using flow cytometry. The present study provided a piece of evidence that rGP19 may eliminate E. canis by manipulating Th1 and B cell roles and demonstrated a promising strategy in vaccine development against E. canis infection in the definitive host for further study.

Exposure of Domestic Cats to Distinct Ehrlichia canis TRP Genotypes

Cats naturally exposed to Ehrlichia canis have been described in different regions of the world, but little is known about the genotypes associated with infection in these animals. To detect E. canis-specific antibodies and investigate the E. canis TRP genotypes in cats, serum samples from 76 domestic cats reactive to crude E. canis antigens by the indirect fluorescence antibody test (IFAT) were analyzed by ELISA, using E. canis-specific peptides (i.e., TRP19 and TRP36 /BR/US/CR). Of these, 25 (32.9%) cats reacted to at least one TRP peptide, confirming their specific exposure to E. canis. Eighteen (23.7%) cats reacted to TRP19, 15 (19.8%) to BRTRP36, and 11 (14.5%) to USTRP36, but none of them reacted to CRTRP36. Eight (10.5%) cats reacted to TRP19 but not to any TRP36 genotype, demonstrating the possible existence of a new E. canis genotype infecting felines. Nevertheless, this study provides the first report of anti-E. canis-specific antibodies in domestic cats.

Effect of GP19 Peptide Hyperimmune Antiserum on Activated Macrophage during Ehrlichia canis Infection in Canine Macrophage-like Cells

In terms of its veterinary importance, vaccine development against Ehrlichia canis is needed. However, the effect of developing vaccines on humoral immune response against E. canis infection is still unknown. Novel GP19_4-43 was synthesized according to E. canis GP19 epitope prediction. To restrict any loss and/or illness in the host animal, rabbits were used in this study to produce GP19_4-43 hyperimmune sera. The effect of GP19_4-43 hyperimmune sera on neutralization was examined in vitro by determining the inhibition of E. canis infection of the macrophage-like cell line (DH82) in the presence of the sera. Four groups of DH82 cells received differing treatments. These included E. canis experimentally infected DH82 cells, E. canis-infected DH82 cells with control rabbit serum (untreated group), E. canis-infected DH82 cells with GP19_4-43 rabbit antiserum (treated group) and uninfected cells (negative control group), respectively. The treated group developed a decrease (p < 0.01) in the percentage of E. canis infected cells after 3 days post-infection at 48.57 ± 1.28. In addition, real-time PCR analyses of cytokine mRNA expression involved with the macrophage, humoral, and cellular immune responses were conducted. The findings revealed an upregulated expression of IFNG in the treated group during the infection. This study demonstrated neutralization in the GP19_4-43 peptide hyperimmune sera of immunized rabbits. Notably, IFN-γ production could be effectively promoted in canine macrophages in relation to the activation of macrophages and adaptive immune responses. The results of this study indicate the potential for the use of this immunogen in further investigations involving immunized and infected dogs as E. canis host species.

Serological evidence of Ehrlichia minasensis infection in Brazilian dogs

Ehrlichia spp. are important tick-borne pathogens of animals in Brazil, and Ehrlichia canis is the most prevalent species infecting dogs. Moreover, Ehrlichia minasensis has also recently been identified as a novel ehrlichial agent that infects cattle in Brazil. The objective of this study was to determine whether dogs could be infected by E. minasensis. To investigate this possibility, sera (n = 429) collected from dogs in the Pantanal region were retrospectively analyzed for the presence of antibodies against E. canis and E. minasensis. Canine sera were screened by two isolates of E. canis in indirect immunofluorescence assay (IFA) and the majority (n = 298; 69.4%) had antibodies with endpoint titers ranging from 80 to 327,680. In order to further confirm E. canis-specific antibodies, IFA positive sera were analyzed by ELISA using E. canis-specific peptides (i.e. TRP19 and TRP36 US/BR/CR), which detected E. canis antibodies in 80.2% (239/298) of the dog sera. Fifty-nine (13.7%) samples had detectable antibodies to E. canis by IFA but were negative by E. canis peptide ELISA. These sera were then tested by E. minasensis IFA (Cuiaba strain) as antigen and 67.8% (40/59) were positive (titers ranging from 80 to 20,480). Eleven sera had antibody titers against E. minasensis at least two-fold higher than observed for E. canis and suggests that these dogs were previously infected with E. minasensis. The results of the present study suggest that multiple ehrlichial agents infect dogs in Brazil, which highlights the need to consider different Ehrlichia spp. in Brazilian dogs, particularly in areas where dogs are frequently exposed to multiple tick species. This investigation is the first to provide serologic evidence of E. minasensis infection in dogs from Brazil.

Seroprevalence and Genotypic Analysis of Ehrlichia canis Infection in Dogs and Humans in Cauca, Colombia

Ehrlichia canis infections have been reported in humans in Venezuela and Costa Rica. In this study, 506 healthy residents and 114 dogs from four municipalities (Cauca, Colombia) were surveyed and blood samples collected. Antibodies to E. canis in human and canine sera were evaluated using the Tandem repeat protein 19 (TRP19) peptide ELISA and indirect immunofluorescence assay (IFA). Ehrlichia canis TRP19 antibodies were detected in only 1/506 human sera, but the single positive sample was negative by IFA. The majority (75/114; 66%) of dogs surveyed had antibodies to the E. canis TRP19 peptide by ELISA, and eight randomly selected sera were further confirmed by E. canis IFA. Genomic DNA samples obtained from 73 E. canis TRP19 ELISA-positive dog blood samples were examined by PCR targeting the 16S ribosomal ribonucleic acid (rRNA) gene. Ehrlichia canis 16S rRNA was amplified in 30 (41%) of the dogs, and 16 amplicons were selected for DNA sequencing, which confirmed that all were E. canis. A second PCR was performed on the 16 confirmed E. canis 16S rRNA PCR-positive samples to determine the TRP36 genotype by amplifying the trp36 gene. TRP36 PCR amplicon sequencing identified nine dogs infected with the U.S. E. canis TRP36 genotype (56%), one dog with the Brazilian genotype (6%), and six dogs with the Costa Rican genotype (38%). Moreover, these molecular genotype signatures were consistent with serologic analysis using TRP36 genotype-specific peptides. Notably, there was no serologic evidence of E. canis infection in humans, suggesting that E. canis infection in dogs in Cauca is not associated with zoonotic human infection.

Genetic variability of Ehrlichia canis TRP36 in ticks, dogs, and red foxes from Eurasia

Ehrlichia canis is among the most prevalent tick-borne pathogens infecting dogs worldwide, being primarily vectored by brown dog ticks, Rhipicephalus sanguineus sensu lato (s.l.). The genetic variability of E. canis has been assessed by analysis of different genes (e.g., disulfide bond formation protein gene, glycoprotein 19, tandem repeat protein 36 - TRP36) in the Americas, Africa, Asia, and in a single dog sample from Europe (i.e., Spain). This study was aimed to assess the variations in the TRP36 gene of E. canis detected in naturally infected canids and R. sanguineus s.l. ticks from different countries in Asia and Europe. DNA samples from dogs (n = 644), foxes (n = 146), and R. sanguineus s.l. ticks (n = 658) from Austria, Italy, Iran, Pakistan, India, Indonesia, Malaysia, the Philippines, Singapore, Thailand, Vietnam, and Taiwan were included in this study. Ehrlichia canis 16S rRNA positive samples (n = 115 from the previous studies; n = 14 from Austria in this study) were selected for molecular examination by analyses of TRP36 gene. Out of 129 E. canis 16S rRNA positive samples from dogs (n = 88), foxes (n = 7), and R. sanguineus s.l. ticks (n = 34), the TRP36 gene was successfully amplified from 52. The phylogenetic analysis of the TRP36 pre-repeat, tandem repeat, and post repeat regions showed that most samples were genetically close to the United States genogroup, whereas two samples from Austria and one from Pakistan clustered within the Taiwan genogroup. TRP36 sequences from all samples presented a high conserved nucleotide sequence in the tandem repeat region (from 6 to 20 copies), encoding for nine amino acids (i.e., TEDSVSAPA). Our results confirm the US genogroup as the most frequent group in dogs and ticks tested herein, whereas the Taiwan genogroup was present in a lower frequency. Besides, this study described for the first time the US genogroup in red foxes, thus revealing that these canids share identical strains with domestic dogs and R. sanguineus s.l. ticks.

Canonical correlative analyses among an enzyme-linked immunosorbent assay using synthetic peptides, an indirect fluorescent antibody test, and hematologic measurements in dogs infected with Ehrlichia canis

BACKGROUND

Immunoreactive tandem repeat proteins (TRPs) in amino acid sequences were identified and employed in the serologic diagnosis of canine monocytic ehrlichiosis (CME).

OBJECTIVES

This study evaluated using TRP19 and TRP36 synthetic protein antigens with enzyme-linked immunosorbent assays (ELISAs) and compared the results with an indirect fluorescent antibody test (IFAT) to diagnose CME in the serum of dogs with suspected CME.

METHODS

The sera of 243 dogs that exhibited clinical and hematologic signs suggestive of CME had IFATs performed. An ELISA with synthetic TRP19 and TRP36 antigens from two E canis genotypes (USTRP36 and BrTRP36) that circulate in Brazil were also performed. Canonical correlations and chi-square tests were evaluated on the results of these tests.

RESULTS

Among the 243 dogs, 179 (73.6%) were reactive at an IFAT ≥ 40, 167 (68.72%) reacted at the cut-off ≥160, and 149 (61.31%) reacted at ≥640. The ELISA revealed that 172 (70.8%) dogs reacted to TRP19 peptide, 163 (67.1%) reacted to USTRP36, and 114 (46.9%) reacted to BrTRP36. The canonical correlation analyses showed that the TRP19 ELISA was the most effective diagnostic method. Serum total protein levels showed strong positive correlations with the USTRP36 peptide. Qualitative analyses revealed an association between the TRP19 peptide and the presence of anemia, thrombocytopenia, and hyperproteinemia. The IFAT results at titers of ≥160 and ≥640 were associated with thrombocytopenia.

CONCLUSIONS

The results of this study indicated that the TRP19 peptide was an excellent antigen and that the IFAT was diagnostically important in confirming the diagnosis of CME in serum samples.

Geographic Distribution of Ehrlichia canis TRP Genotypes in Brazil

Tandem repeat proteins (TRPs) are major immunoreactive proteins of Ehrlichia canis, which have been used in the serological diagnosis of different genotypes of the microorganism. TRP19 is preserved among different E. canis isolates expressed on both reticulate and dense-core cells and observed in the extracellular matrix or associated with the morula membrane. TRP36 is differentially expressed only on the surface of the dense-core form of the bacterium and exhibits more divergence among isolates. The aim of this study was to evaluate the distribution of the American (USTRP36), Brazilian (BrTRP36) and Costa Rican (CRTRP36) genotypes of E. canis in Brazil, using ELISA assays. Serum samples of 814 dogs from 49 municipalities from all over Brazil were analyzed. Our results showed that 33.9% of the samples were reactive to the USTRP36 genotype and 32.6% to the BrTRP36 genotype. The two genotypes appeared to occur equally throughout Brazil, although the frequency of seropositivity was lower in the south than in the country's other regions. Dogs that reacted to at least one of the synthetic peptides (TRP19 and TRP36) were 456 (56%). A few dogs (n = 5; 0.6%) reactive to the E. canis TRP36 genotype (CRTRP36) were also detected in the northeast and southern regions. We concluded that the American and Brazilian genotypes of E. canis are distributed evenly in Brazil, especially in the tropical region, while the temperate region in the south presented the lowest prevalence rates. This study offers the first report of dogs seropositive for the Costa Rican genotype in Brazil.

Development of a Loop-Mediated Isothermal Amplification (LAMP) Assay Targeting the Citrate Synthase Gene for Detection of Ehrlichia canis in Dogs

Canine monocytic ehrlichiosis caused by Ehrlichia canis is one of the leading tick-borne diseases of dogs, particularly in tropical countries. A highly sensitive and specific diagnostic method is essential for early detection to facilitate treatment. This study was conducted to develop E. canis loop-mediated isothermal amplification (LAMP) assay, a highly sensitive yet simple molecular technique, targeting the citrate synthase (gltA) gene of E. canis. Canine blood samples were subjected to conventional PCR targeting E. canis gltA. After analysis of the sequences of PCR amplicons, LAMP primers were generated. The optimum temperature and time for the LAMP assay were determined using eight samples—after which, the effectiveness and reproducibility of LAMP were verified by testing 40 samples, which included PCR-positive and negative samples. The detection limit was also established. The optimal condition for the assay was 61 °C for 60 min. Compared to PCR, the LAMP assay had a relative sensitivity and specificity of 92.5 and 100%, respectively. Statistical analysis using McNemar’s test showed that the E. canis LAMP assay has no significant difference with PCR. Therefore, the LAMP assay developed in this study may be used as an alternative to PCR in the detection of E. canis.

Molecular Detection and Characterization of the mecA and nuc Genes From Staphylococcus Species (S. aureus, S. pseudintermedius, and S. schleiferi) Isolated From Dogs Suffering Superficial Pyoderma and Their Antimicrobial Resistance Profiles

Canine superficial pyoderma (CSP) is a bacterial infection secondary to several skin diseases of the dog. Staphylococcus pseudintermedius, which is a commensal bacterium of the dog's skin, is the leading agent found in dogs affected by CSP, which can progress to deep pyoderma. It is also of clinical significance because S. pseudintermedius strains carry antimicrobial resistance genes, mainly the mecA gene. In this descriptive longitudinal study, molecular characterization of bacterial isolates from dogs affected by CSP was performed in addition to phenotyping, antimicrobial profiling, and assessment of resistance carriage status. Fifty dogs (24 females and 26 males) attending the CES University Veterinary Teaching Hospital were included in the study. CSP was confirmed according to clinical signs and cytological examination. Swabs were taken from active skin lesions for bacterial culture, and phenotyping and antimicrobial resistance profiles were assessed using API-Staph phenotyping and the Kirby–Bauer method, respectively. We also performed molecular detection and characterization of the mecA and nuc encoding gene of coagulase-positive Staphylococci. The mecA gene frequency was established by qPCR amplification of a 131bp gene fragment. Data were evaluated by descriptive statistics. Erythema, peeling, pruritus, and alopecia were the predominant symptoms (72, 56, and 46%, respectively). We isolated bacteria compatible with Staphylococcus species from all samples tested. API phenotyping showed 83.1 to 97.8% compatibility with S. pseudintermedius. PCR-genotyping resulted in 15, 3, and 1 isolates positive for S. pseudintermedius, S. aureus, and S. schleiferi, respectively. Isolated strains showed high susceptibility to Imipenem, Ampicillin/Sulbactam, and Rifampicin (100, 94, and 92%, respectively). The highest resistance was against Vancomycin and Trimethoprim/Sulfamethoxazole (98 and 74%, respectively). S. pseudintermedius, S. aureus, and S. schleiferi isolates were cloned and shared 96% sequence homology. Finally, we found 62% carriage status of the mecA gene in isolates of CSP patients, although only 36% of the isolates were methicillin-resistant. Identification of three Staphylococcus species causing CSP, high-level resistance against conventional antimicrobials, and carriage of the mecA gene highlight the importance of performing molecular characterization of bacteria causing dermatological conditions in dogs.

Detection of specific IgM and IgG antibodies in acute canine monocytic ehrlichiosis that recognize recombinant gp36 antigens

The efficacy of antibody detection tools for all stages of Ehrlichia canis infections and for various genotypes remains unclear. We produced recombinant gp36 (rgp36) antigens from different isolates of Thai E. canis to confirm the immunoreactivities to these recombinant proteins from naturally infected dogs. Sera and blood samples were taken from 21 dogs naturally infected with E. canis and in the clinical stages of acute phase ehrlichiosis. The expression vectors and competent E. coli produced two isolates of rgp36. These two major rgp36s were recognized by the dogs' sera in Western blotting, with both anti-dog IgM and IgG used as secondary antibodies. The two different genotypes of these local recombinant immunoreactive proteins were gp36 subgroup A (isolate 1055) and subgroup B (isolate 533). The Western blot analyses successfully identified both specific IgM and IgG from the dogs' sera. Of all 21 cases, five dogs presented specific IgM, twenty dogs presented specific IgG, and the commercial test used found fifteen seropositive dogs. There were four dogs that presented both specific IgM and IgG. Only one dog presented specific IgM only. This report is the first identification of a specific IgM in dogs in response to acute infections with E. canis. The recombinant gp36 isolates may be useful as potential antigenic material for subsequent serological tests that have a high possibility for differentiating between acute, chronic, primary, and nonprimary infections with E. canis.

Molecular detection and genetic variability of Ehrlichia canis in pet dogs in Xinjiang, China

BACKGROUND AND AIM

As a tick-borne zoonotic pathogen, Ehrlichia canis has already posed a threat to public health and safety. This study aimed to clarify the prevalence and molecular characteristics of E. canis in pet dogs in Xinjiang, China.

MATERIALS AND METHODS

A total of 297 blood samples of pet dogs and 709 skin ticks (Rhipicephalus sanguineus sensu lato) were subjected to molecular detection using PCR for E. canis 16S rRNA gene, and then, positive samples were amplified, sequenced, and phylogenetically analyzed for E. canis gp36 gene.

RESULTS

The PCR detection showed that the positive rate of PCR was 12.12% (36/297) in blood samples and 15.23% (108/709) in tick samples, respectively. Based on the phylogenetic analysis of E. canis gp36 protein, these E. canis strains in different geographical regions of the world can be divided into Genogroup I and Genogroup II. Among them, the Xinjiang epidemic strain XJ-6 and 533, 36, 1055, Kasur1, and Jake strains were clustered into subgroup 1.1 of Genogroup I, while the XJ-2, XJ-21, and XJ-35 strains and the TWN1, TWN4, CM180, and CM196 strains were closely related and belonged to subgroup 2.2 of Genogroup II, displaying high genetic diversity.

CONCLUSION

This is the first study focusing on the molecular epidemiology of E. canis infection in pet dogs, which revealed that E. canis infection had been occurred in Xinjiang, China. More importantly, this study confirmed that the substantial variability in immunoreactive protein gp36 from E. canis strains circulating in pet dogs.

Ehrlichia canis TRP36 diversity in naturally infected-dogs from an urban area of Colombia

Ehrlichia canis is the etiologic agent of a highly prevalent tick-borne disease, canine monocytic ehrlichiosis (CME). Four defined E. canis genotypes based on the trp36 gene sequences have been reported, three of them identified in North or South America. The diversity of E. canis has been investigated using genetic and serologic approaches based on distinct 36 kDa tandem repeat protein (trp36) gene sequences that have been reported. The main objectives of this study were to determine the prevalence of E. canis infection in dogs from Medellín, Colombia by PCR and determine the E. canis diversity using molecular and serologic approaches. Blood was collected from dogs (n = 300) with clinical signs of CME for PCR detection of E. canis 16S rRNA, dsb and trp36 DNA. Phylogenetic analysis of trp36 gene sequences was performed using MEGA. A serological evaluation was performed using immunofluorescence microscopy and ELISA with species-specific peptides from E. canis TRP19 and TRP36 (3 genotypes) and E. chaffeensis (TRP32). E. canis DNA (16S rRNA and/or dsb) was detected in 18 % (53/300) of dogs by PCR amplification. The trp36 gene was amplified and sequenced from 35/53 16S rRNA/dsb PCR positive samples revealing three genotypes: United States (US; n = 21), Costa Rica (CR; n = 11), and Brazil (BR; n = 3). Most dogs (33/35) with detectable trp36 DNA had anti-E. canis TRP19 and TRP36 peptide antibodies that corresponded to the genotype detected by PCR. Dogs that had antibodies to the TRP19 peptide (82/300; 38 %), also had antibodies to one or more genotype-specific TRP36 peptides. Based on TRP36 serology, the dogs exhibited highest frequency of infection with the US genogroup (US = 26), followed by the CR genogroup (CR = 19) and the BR genogroup (BR = 11). Notably, 26/53 trp36 PCR positive dogs had detectable antibodies to multiple E. canis genotypes (US/BR/CR = 8, BR/CR = 7, US/CR = 6 and US/BR = 5) suggesting coinfection or multiple sequential infections with different genotypes. Colombian dogs did not have antibodies to E. chaffeensis as determined by a TRP32 species-specific ELISA. Our results demonstrate the presence of three previously defined genotypes in North and South America in Colombian dogs (US, BR, CR). These results also demonstrate that TRP19 and TRP36 serology can provide valuable information regarding E. canis exposure and the potential genotype(s) involved in infection.

Ehrlichia chaffeensis Outer Membrane Protein 1-Specific Human Antibody-Mediated Immunity Is Defined by Intracellular TRIM21-Dependent Innate Immune Activation and Extracellular Neutralization

Antibodies are essential for immunity against Ehrlichia chaffeensis, and protective mechanisms involve blocking of ehrlichial attachment or complement and Fcγ-receptor-dependent destruction. In this study, we determined that major outer membrane protein 1 (OMP-19) hypervariable region 1 (HVR1)-specific human monoclonal antibodies (huMAbs) are protective through conventional extracellular neutralization and, more significantly, through a novel intracellular TRIM21-mediated mechanism.

Antibodies are essential for immunity against Ehrlichia chaffeensis, and protective mechanisms involve blocking of ehrlichial attachment or complement and Fcγ-receptor-dependent destruction. In this study, we determined that major outer membrane protein 1 (OMP-19) hypervariable region 1 (HVR1)-specific human monoclonal antibodies (huMAbs) are protective through conventional extracellular neutralization and, more significantly, through a novel intracellular TRIM21-mediated mechanism. Addition of OMP-1-specific huMAb EHRL-15 (IgG1) prevented infection by blocking attachment/entry, a mechanism previously reported; conversely, OMP-1-specific huMAb EHRL-4 (IgG3) engaged intracellular TRIM21 and initiated an immediate innate immune response and rapid intracellular degradation of ehrlichiae. EHRL-4-TRIM21-mediated inhibition was significantly impaired in TRIM21 knockout THP-1 cells. EHRL-4 interacted with cytosolic Fc receptor TRIM21, observed by confocal microscopy and confirmed by co-immunoprecipitation. E. chaffeensis-EHRL-4-TRIM21 complexes caused significant upregulation of proinflammatory cytokine/chemokine transcripts and resulted in rapid (<30 min) nuclear accumulation of NF-κB and TRIM21 and ehrlichial destruction. We investigated the role of TRIM21 in the autophagic clearance of ehrlichiae in the presence of EHRL-4. Colocalization between EHRL-4-opsonized ehrlichiae, polyubiquitinated TRIM21, autophagy regulators (ULK1 and beclin 1) and effectors (LC3 and p62), and lysosome-associated membrane protein 2 (LAMP2) was observed. Moreover, autophagic flux defined by conversion of LC3I to LC3II and accumulation and degradation of p62 was detected, and EHRL-4-mediated degradation of E. chaffeensis was abrogated by the autophagy inhibitor 3-methyladenine. Our results demonstrate that huMAbs are capable of inhibiting E. chaffeensis infection by distinct effector mechanisms: extracellularly by neutralization and intracellularly by engaging TRIM21, which mediates a rapid innate immune response that mobilizes the core autophagy components, triggering localized selective autophagic degradation of ehrlichiae.

Genetic diversity of Ehrlichia canis in dogs from Turkey inferred by TRP36 sequence analysis and phylogeny

Canine monocytic ehrlichiosis, an important tick-borne disease caused by Ehrlichia canis, is cosmopolitan but particularly prevalent in tropical and subtropical regions. In Turkey, the genetic diversity of E. canis remains undefined. The aim of this study was to characterize E. canis in naturally infected dogs from Turkey by sequencing and phylogenetic analysis of the Tandem Repeat Protein 36 (TRP36) encoded by the trp36 gene. A total of 167 archived blood samples randomly collected from municipal shelter dogs in three distinct geographic regions were analyzed for E. canis. Only ten samples (5.98%) were found positive by PCR assays target regions of the trp36 and 16S rRNA genes. Sequence analysis of Turkish E. canis TRP36 revealed five Tanden Repeat sequences (TRs) resulting to three TR genotypes: i) the previously reported US genotype composed exclusively from TRs of "TEDSVSAPA" sequence (14 or 8 TRs), ii) the previously Brazilian genotype composed exclusively from TRs of ASVVPEAE sequence (13 TRs), and iii) a novel genotype. In addition, phylogenetic analysis based on the entire sequences of TRP36 revealed that these genotypes correspond to four distinct genogroups (US genogroups I and II, Brazilian genogroup and Costa Rica-Turkey genogroup), all containing Turkish genotypes amongst other geographically distant E. canisgenotypes.

Low genetic diversity of Ehrlichia canis associated with high co-infection rates in Rhipicephalus sanguineus (s.l.)

BACKGROUND

Rhipicephalus sanguineus sensu lato (s.l.) is the most widely distributed ixodid tick and is a vector of major canine and human pathogens. High-throughput technologies have revealed that individual ticks carry a high diversity of pathogens, including bacteria, protozoa and viruses. Currently, it is accepted that co-infections (multiple pathogen species within an individual) are very common in ticks and influence pathogen acquisition and transmission as well as host infection risk. However, little is known on the impact of the genetic diversity of pathogens on the incidence of co-infections. Herein, we studied the frequency of co-infections in R. sanguineus (s.l.) and their association with the genetic diversity of Ehrlichia canis.

METHODS

Rhipicephalus sanguineus (s.l.) female ticks (n = 235) were collected from healthy farm dogs in three districts of Pakistan. Microfluidic real-time PCR, a powerful nanotechnology for high-throughput molecular detection of pathogens, was used to test the presence of 25 bacterial and seven parasitic species in individual ticks. The genetic diversity of E. canis was evaluated by characterizing the trp36 gene.

RESULTS

A total of 204 ticks were infected with at least one pathogen and 109 co-infected with two (80%) or three (20%) pathogens. Rickettsia massiliae (human pathogen) and E. canis (zoonotic dog pathogen) were the most common pathogens co-infecting (30.4%) ticks. Furthermore, all identified co-infections included R. massiliae and/or E. canis. Multiple correspondence analysis (MCA) revealed that single infections did not show clear regional association whereas some co-infections were restricted to certain geographical regions. The sequence analysis of trp36 in representative samples allowed the identification of three E. canis strains with low genetic diversity, and the strain found in Muzaffargarh district appeared to be more adapted to co-infection with R. massiliae.

CONCLUSIONS

Rhipicephalus sanguineus (s.l.) harbors multiple co-infections with human and dog pathogens of zoonotic potential. Findings of this study suggest that genetic diversity of E. canis may favor co-infections with different pathogens.

Molecular characterization of Ehrlichia canis from naturally infected dogs from the state of Rio de Janeiro

The aim of the present study was to evaluate the genetic diversity of Ehrlichia canis in naturally infected dogs from six mesoregions of Rio de Janeiro state. E. canis was diagnosed with a real-time polymerase chain reaction (qPCR) targeting a 93 base pair (bp) fragment of the 16S rDNA gene. To evaluate the genetic diversity of the parasite, we amplified a positive sample from each mesoregion by distinct conventional PCR assays with targets in the gp19 (414 bp), gp36 (814 bp), and p28 (843 bp) genes. A total of 267 samples were collected from dogs in Rio de Janeiro state. Among the samples analyzed, 42.3% (n = 113/267) were 16S rDNA-qPCR positive. When performing PCR for the gp19 and gp36 genes, 100% (n = 113/113) and 5.3% (n = 6/113) of the samples amplified fragments of 414 bp and 814 bp, respectively. The six PCR-positive samples for the gp36 gene also amplified the p28 gene fragment. The characterization based on the gp19 gene demonstrated that it is highly conserved. In protein analysis (TRP36), all samples showed a tandem repeat protein (TRP) that comprised 11 replicates. Seven high-entropy amino acid sites were distributed throughout the gp36 gene. Eleven high-entropy amino acid sites were found throughout the p28 gene. There is a positive selection pressure in both genes (p ≤ 0.05). Comparing and characterizing an organism are useful for providing important information about the host's immune response and identifying new antigenic targets, as well as essential characteristics for the development of vaccines and new diagnostic tools.

Use of an automated system for detection of canine serum antibodies against Ehrlichia canis glycoprotein 36

Ehrlichia canis is the most common cause of monocytotropic ehrlichiosis in dogs around the world. The purpose of the present study was to validate a new automated fluorescence system (Accuplex4™ BioCD system; Antech Diagnostics, Lake Success, New York) to detect antibodies against the E. canis immunodominant glycoprotein 36 (gp36). Sera and blood samples (ethylenediamine tetra-acetic acid) were collected from mixed sex beagles ( n = 8) on days 0, 3, 7, 10, 14, 17, 21, 28, 42, 49, 56, 63, 70, 77, 84, and 98 after intravenous inoculation with culture-derived E. canis. Sera were assayed using the Accuplex4 BioCD system (Accuplex4), an E. canis indirect fluorescent antibody test (IFAT), and a commercially available kit. A complete blood cell count and a proprietary E. canis polymerase chain reaction (PCR) were performed on each blood sample. On the day thrombocytopenia was first detected for each dog, E. canis DNA was amplified from blood of all dogs. At those times, E. canis antibodies were detected in 7 of 8 dogs by the Accuplex4, 1 of 8 dogs by the commercial kit, and 4 of 8 dogs by IFAT. Ehrlichia canis DNA was amplified from blood before seroconversion in any antibody assay for 6 dogs. Antibodies against gp36 were detected by Accuplex4 within 3 days of PCR-positive test results and were detected up to 25 days sooner than the commercial kit. After starting doxycycline treatment, E. canis DNA was no longer amplified by PCR assay, but serum antibodies remained detectable by all assays.

Molecular detection and phylogenetic analysis of Ehrlichia canis in a Philippine dog

Canine monocytic ehrlichiosis (CME), caused by a rickettsial bacterium, Ehrlichia canis, is distributed worldwide, particularly in tropical and subtropical regions. Transmission of E. canis is primarily mediated by the vector tick, Rhipicephalus sanguineus sensu lato and the bacteria then infect and replicate in monocytes and macrophages. Many cases are seen in veterinary hospitals and treated routinely; however, the genetic variation of E. canis strains found in the Philippines has been poorly investigated to date. In this study, the 16S rRNA gene and the gp200 gene of E. canis were detected by polymerase chain reaction from an infected dog in the Philippines, and the deduced amino acid sequence of the gp200 gene was subjected to a phylogenetic analysis. The Philippine genotype formed a cluster with the Taiwan genotype, and was somewhat divergent from the USA and Brazil strains. This suggested that E. canis underwent evolution in East and Southeast Asia, confirming the utility of the gp200 gene for the assessment of genetic relationships among strains.

Association of Ehrlichia canis, Hemotropic Mycoplasma spp. and Anaplasma platys and severe anemia in dogs in Thailand

Canine tick-borne bacteria; Ehrlichia canis, hemotropic Mycoplasma spp. and Anaplasma spp., are organisms transmitted by Rhipicephalus sanguineus ticks. However, only a few clinical studies evaluating dogs infected with these organisms and anemia condition have been published. In this study, the potential tick-borne bacteria linked to anemia were investigated in eighty-one blood samples selected from anemic dogs using a broad range nested-PCR of the 16S rRNA gene. Positive results were shown in 12/81 blood specimens (14.81%). Nucleotide sequences from the PCR products were analyzed using BLAST and resulted in identification of Ehrlichia canis (8), Candidatus Mycoplasma haematoparvum (1) and Anaplasma platys (3). Two other PCR assays were used to detect and identify the positive results of these pathogens including a specific PCR for Ehrlichia canis (gp36) and a specific nested-PCR for hemoplasma species (16S rRNA) and the phylogenetic analyses of E. canis and canine hemoplasmas were performed using these two loci. These specific PCRs revealed co-infection of E. canis and Mycoplasma haemocanis in two cases. These two male dogs had presented with jaundice, severe hemolytic anemia, severe thrombocytopenia, leukocytosis, mild azotemia and hepatitis. Ehrlichia canis was detected in a significantly greater number of severe anemia cases (PCV<15%) than moderate or mild anemia cases (PCV 16-29%) (P<0.05) and these severe anemia cases were 7-fold more at risk of having E. canis infections (odds ratio: 7.11, p=0.020). However, no statistical differences were detected between E. canis detection and degrees of thrombocytopenia or leukopenia. From the results of this study, we conclude that the severity of anemia is associated with E. canis infections rather than the severity of thrombocytopenia.

Detection of genotype-specific Ehrlichia canis exposure in Brazilian dogs by TRP36 peptide ELISA

We recently characterized a novel genotype of Ehrlichia canis based on the tandem repeat (TR) sequence of the TRP36 gene in Brazil. The TR amino acid sequence of the Brazilian (Br) genotype (ASVVPEAE) was divergent from the previously described US genotype (TEDSVSAPA) of E. canis. In this study, we developed an ELISA based on TRP36 TR synthetic peptides from both Br and US E. canis TRP36 genotypes to serologically detect and distinguish infections caused by these genotypes. Sera from 30 Brazilian dogs naturally infected with E. canis, sera from dogs experimentally infected E. canis (Jake and Cuiabá #1 strains) and E. chaffeensis (Arkansas strain) and 12 seronegative E. canis dogs were evaluated. Fifteen naturally infected Brazilian dogs had antibodies that reacted with the US TRP36 (n=9) or Br TRP36 (n=6) only, and 13 dogs had antibodies that reacted with both TPR36 peptides suggesting that these dogs were exposed to both genotypes. Most dogs (n=28) had antibodies that reacted with the highly conserved E. canis TRP19 peptide; however, two dogs had antibodies to E. canis TRP19, but did not have TRP36 antibodies, raising the possibility that another novel TRP36 genotype is circulating in Brazil. Our results demonstrate that synthetic peptides based on the TR region of E. canis TRP36 can be used to serologically distinguish infections or identify coinfections by different genotypes, and to determine the seroprevalence of various E. canis genotypes in Brazil.

Recombinant gp19 as a potential antigen for detecting anti-Ehrlichia canis antibodies in dog sera

The canine monocytic ehrlichiosis, caused by Ehrlichia canis, is endemic in several regions of Brazil. Some serological diagnostic techniques using immunodominant proteins of E. canis as antigens are available, but their specificities and sensitivities are questionable. Based on this, the objective of this study was to test the antigenic potential of the recombinant gp19 protein (rGP19) for subsequent use in diagnostic tests. The rGP19 expressed in the Escherichia coli strain BL21 (DE3) C41 was recognized in the sera from experimentally infected dogs using ELISA and Western blotting. Thus, it was possible to obtain a promising antigen with the ability to differentiate between E. canis-positive and -negative animals, even 1 week after infection.

Mini-review: Strategies for Variation and Evolution of Bacterial Antigens

Across the eubacteria, antigenic variation has emerged as a strategy to evade host immunity. However, phenotypic variation in some of these antigens also allows the bacteria to exploit variable host niches as well. The specific mechanisms are not shared-derived characters although there is considerable convergent evolution and numerous commonalities reflecting considerations of natural selection and biochemical restraints. Unlike in viruses, mechanisms of antigenic variation in most bacteria involve larger DNA movement such as gene conversion or DNA rearrangement, although some antigens vary due to point mutations or modified transcriptional regulation. The convergent evolution that promotes antigenic variation integrates various evolutionary forces: these include mutations underlying variant production; drift which could remove alleles especially early in infection or during life history phases in arthropod vectors (when the bacterial population size goes through a bottleneck); selection not only for any particular variant but also for the mechanism for the production of variants (i.e., selection for mutability); and overcoming negative selection against variant production. This review highlights the complexities of drivers of antigenic variation, in particular extending evaluation beyond the commonly cited theory of immune evasion. A deeper understanding of the diversity of purpose and mechanisms of antigenic variation in bacteria will contribute to greater insight into bacterial pathogenesis, ecology and coevolution with hosts.

Isolation, in vitro propagation, genetic analysis, and immunogenic characterization of an Ehrlichia canis strain from southeastern Brazil

Amplification of the 16S rRNA gene from a blood sample obtained from a dog in southeastern Brazil was used to confirm a naturally acquired Ehrlichia (E.) canis infection. Following isolation and culturing of the new bacterial strain called Uberlândia, partial sequences of the dsb and p28 genes were obtained. The dsb partial sequence of the novel strain was 100% similar to dsb gene sequences of E. canis obtained from different geographic areas around the world. Conversely, the p28 partial sequence for the E. canis Uberlândia strain differed at several nucleotides from other sequences available in GenBank. To confirm the antigenic profile of the Uberlândia strain, an indirect immunofluorescence assay against E. canis antigens was performed using dog sera collected from two different areas in Brazil (Uberlândia and São Paulo). The results suggest that both antigens were able to identify animals seropositive for E. canis in Brazil since these Brazilian strains appear to be highly conserved.

Genetic diversity of Ehrlichia canis in Brazil

Canine monocytic ehrlichiosis is a highly prevalent disease in Brazil, where the genetic diversity of Ehrlichia canis remains undefined. In this study, we used the TRP36 gene to examine the genetic diversity of E. canis strains from naturally infected dogs residing in five distinct geographic regions in Brazil. E. canis DNA was detected in 82/126 (65%) dogs by dsb-specific PCR and E. canis was isolated in cell culture from 13 dogs. Sequences obtained from dsb genes amplified from the isolates were identical to the US E. canis strain. An extended molecular characterization based on the TRP36 gene identified two major genogroups based on differences among eight isolates. Isolates with tandem repeat amino acid sequence (TEDSVSAPA) identical to the previously reported TRP36 sequence were found in the midwest, northeast and southeast regions of Brazil, and classified into the US genogroup. A novel Brazilian genotype with a different tandem repeat sequence (ASVVPEAE) was also identified in midwest, northern and southern regions. Similarity in the N-terminal sequence of a US genogroup member with the Brazilian genogroup suggested that genomic recombination between the two genogroups may have occurred. Other subtypes within the Brazilian genogroup were also identified using C-terminal amino acid divergence. We identified two distinct major Brazilian genogroups and several subtypes based on analysis of TRP36, and such information will be useful for further genotyping and possible associations with disease severity, understanding of the genetic and antigenic variability of E. canis, and for developing strain-specific vaccines and diagnostic methods based on TRP36.

New species of Ehrlichia isolated from Rhipicephalus (Boophilus) microplus shows an ortholog of the E. canis major immunogenic glycoprotein gp36 with a new sequence of tandem repeats

Background

Ehrlichia species are the etiological agents of emerging and life-threatening tick-borne human zoonoses that inflict serious and fatal infections in companion animals and livestock. The aim of this paper was to phylogeneticaly characterise a new species of Ehrlichia isolated from Rhipicephalus (Boophilus) microplus from Minas Gerais, Brazil.

Methods

The agent was isolated from the hemolymph of Rhipicephalus (B.) microplus engorged females that had been collected from naturally infested cattle in a farm in the state of Minas Gerais, Brazil. This agent was then established and cultured in IDE8 tick cells. The molecular and phylogenetic analysis was based on 16S rRNA, groEL, dsb, gltA and gp36 genes. We used the maximum likelihood method to construct the phylogenetic trees.

Results

The phylogenetic trees based on 16S rRNA, groEL, dsb and gltA showed that the Ehrlichia spp isolated in this study falls in a clade separated from any previously reported Ehrlichia spp. The molecular analysis of the ortholog of gp36, the major immunoreactive glycoproteins in E. canis and ortholog of the E. chaffeensis gp47, showed a unique tandem repeat of 9 amino acids (VPAASGDAQ) when compared with those reported for E. canis, E. chaffeensis and the related mucin-like protein in E. ruminantium.

Conclusions

Based on the molecular and phylogenetic analysis of the 16S rRNA, groEL, dsb and gltA genes we concluded that this tick-derived microorganism isolated in Brazil is a new species, named E. mineirensis (UFMG-EV), with predicted novel antigenic properties in the gp36 ortholog glycoprotein. Further studies on this new Ehrlichia spp should address questions about its transmissibility by ticks and its pathogenicity for mammalian hosts.

Evaluation of an attenuated strain of Ehrlichia canis as a vaccine for canine monocytic ehrlichiosis

Canine monocytic ehrlichiosis is an important tick-borne disease worldwide. No commercial vaccine for the disease is currently available and tick control is the main preventive measure against the disease. The aim of this study was to evaluate the potential of a multi-passaged attenuated strain of Ehrlichia canis to serve as a vaccine for canine monocytic ehrlichiosis, and to assess the use of azithromycin in the treatment of acute ehrlichiosis. Twelve beagle dogs were divided into 3 groups of 4 dogs. Groups 1 and 2 were inoculated (vaccinated) with an attenuated strain of E. canis (#611A) twice or once, respectively. The third group consisted of naïve dogs which served as controls. All 3 groups were challenged with a wild virulent strain of E. canis by administering infected dog-blood intravenously. Transient thrombocytopenia was the only hematological abnormality observed following inoculation of dogs with the attenuated strain. Challenge with the virulent strain resulted in severe disease in all 4 control dogs while only 3 of 8 vaccinated dogs presented mild transient fever. Furthermore, the mean blood rickettsial load was significantly higher in the control group (27-92-folds higher during days 14-19 post challenge with the wild the strain) as compared to the vaccinated dogs. The use of azithromycin was assessed as a therapeutic agent for the acute disease. Four days treatment resulted in further deterioration of the clinical condition of the dogs. Molecular comparison of 4 genes known to express immunoreactive proteins and virulence factors (p30, gp19, VirB4 and VirB9) between the attenuated strain and the challenge wild strain revealed no genetic differences between the strains. The results of this study indicate that the attenuated E. canis strain may serve as an effective and secure future vaccine for canine ehrlichiosis.

First detection and molecular characterization of Ehrlichia canis from dogs in Nigeria

The present study aimed to detect the presence of Ehrlichia canis in naturally infected dogs in Nigeria, using a combination of PCR and sequence analysis of the 16S rRNA gene and two genes encoding the tandem repeat-containing proteins (TRPs), TRP19 and TRP36. Out of a total of 100 blood samples collected from domestic dogs presented to veterinary hospitals in Jos, the capital city of Plateau State of Nigeria, 11 were positive in nested PCR for E. canis. Sequencing results for these amplicons showed that all of the 16S rDNA sequences (1623 bp) or the TRP19 coding sequences (414 bp) were identical to each other and had very high similarities (99.3-100%) with those from other E. canis strains accessible in GenBank. The TRP36 gene sequences derived from the 11 Nigerian isolates were identical to each other except for the number of the 27-bp repeat unit in a tandem repeat region, which was found to be 8, 12 or 18. Without considering the number of tandem repeats, these sequences had 100% identity to that of the reported Cameroon 71 isolate, but distinctly differed from those obtained from other geographically distant E. canis strains previously published. A phylogenetic tree of E. canis based on the TRP36 amino acid sequences showed that the Nigerian isolates and the Cameroon 71 isolate fell into a separate clade, indicating that they may share a common ancestor. Overall, this study not only provides the first molecular evidence of E. canis infections in dogs from Nigeria but also highlights the value of the TRP36 gene as a tool to classify E. canis isolates and to elucidate their phylogeographic relationships.

Neorickettsia risticii surface-exposed proteins: proteomics identification, recognition by naturally-infected horses, and strain variations

Neorickettsia risticii is the Gram-negative, obligate, and intracellular bacterial pathogen responsible for Potomac horse fever (PHF): an important acute systemic disease of horses. N. risticii surface proteins, critical for immune recognition, have not been thoroughly characterized. In this paper, we identified the 51-kDa antigen (P51) as a major surface-exposed outer membrane protein of older and contemporary strains of N. risticii through mass spectrometry of streptavidin-purified biotinylated surface-labeled proteins. Western blot analysis of sera from naturally-infected horses demonstrated universal and strong recognition of recombinant P51 over other Neorickettsia recombinant proteins. Comparisons of amino acid sequences for predicted secondary structures of P51, as well as Neorickettsia surface proteins 2 (Nsp2) and 3 (Nsp3) among N. risticii strains from horses with PHF during a 26-year period throughout the United States revealed that the majority of variations among strains were concentrated in regions predicted to be external loops of their β-barrel structures. Large insertions or deletions occurred within a tandem-repeat region in Ssa3. These data demonstrate patterns of geographical association for P51 and temporal associations for Nsp2, Nsp3, and Ssa3, indicating evolutionary trends for these Neorickettsia surface antigen genes. This study showed N. risticii surface protein population dynamics, providing groundwork for designing immunodiagnostic targets for PHF.

Tyrosine-phosphorylated Ehrlichia chaffeensis and Ehrlichia canis tandem repeat orthologs contain a major continuous cross-reactive antibody epitope in lysine-rich repeats

A small subset of major immunoreactive proteins have been identified in Ehrlichia chaffeensis and Ehrlichia canis, including three molecularly and immunologically characterized pairs of immunoreactive tandem repeat protein (TRP) orthologs with major continuous species-specific epitopes within acidic tandem repeats (TR) that stimulate strong antibody responses during infection. In this study, we identified a fourth major immunoreactive TR-containing ortholog pair and defined a major cross-reactive epitope in homologous nonidentical 24-amino-acid lysine-rich TRs. Antibodies from patients and dogs with ehrlichiosis reacted strongly with recombinant TR regions, and epitopes were mapped to the N-terminal TR region (18 amino acids) in E. chaffeensis and the complete TR (24 amino acids) in E. canis. Two less-dominant epitopes were mapped to adjacent glutamate/aspartate-rich and aspartate/tyrosine-rich regions in the acidic C terminus of E. canis TRP95 but not in E. chaffeensis TRP75. Major immunoreactive proteins in E. chaffeensis (75-kDa) and E. canis (95-kD) whole-cell lysates and supernatants were identified with TR-specific antibodies. Consistent with other ehrlichial TRPs, the TRPs identified in ehrlichial whole-cell lysates and the recombinant proteins migrated abnormally slow electrophoretically a characteristic that was demonstrated with the positively charged TR and negatively charged C-terminal domains. E. chaffeensis TRP75 and E. canis TRP95 were immunoprecipitated with anti-pTyr antibody, demonstrating that they are tyrosine phosphorylated during infection of the host cell.

Sequence and phylogenetic analysis of the gp200 protein of Ehrlichia canis from dogs in Taiwan

Ehrlichia (E.) canis is a Gram-negative obligate intracellular bacterium responsible for canine monocytic ehrlichiosis. Currently, the genetic diversity of E. canis strains worldwide is poorly defined. In the present study, sequence analysis of the nearly full-length 16S rDNA (1,620 bp) and the complete coding region (4,269 bp) of the gp200 gene, which encodes the largest major immunoreactive protein in E. canis, from 17 Taiwanese samples was conducted. The resultant 16S rDNA sequences were found to be identical to each other and have very high homology (99.4~100%) with previously reported E. canis sequences. Additionally, phylogenetic analysis of gp200 demonstrated that the E. canis Taiwanese genotype was genetically distinct from other reported isolates obtained from the United States, Brazil, and Israel, and that it formed a separate clade. Remarkable variations unique to the Taiwanese genotype were found throughout the deduced amino acid sequence of gp200, including 15 substitutions occurring in two of five known species-specific epitopes. The gp200 amino acid sequences of the Taiwanese genotype bore 94.4~94.6 identities with those of the isolates from the United States and Brazil, and 93.7% homology with that of the Israeli isolate. Taken together, these results suggest that the Taiwanese genotype represents a novel strain of E. canis that has not yet been characterized.

Progress and obstacles in vaccine development for the ehrlichioses

Ehrlichia are tick-borne obligately intracellular bacteria that cause significant diseases in veterinary natural hosts, including livestock and companion animals, and are now considered important zoonotic pathogens in humans. Vaccines are needed for these veterinary and zoonotic human pathogens, but many obstacles exist that have impeded their development. These obstacles include understanding genetic and antigenic variability, influence of the host on the pathogen phenotype and immunogenicity, identification of the ehrlichial antigens that stimulate protective immunity and those that elicit immunopathology, development of animal models that faithfully reflect the immune responses of the hosts and understanding molecular host-pathogen interactions involved in immune evasion or that may be blocked by the host immune response. We review the obstacles and progress in addressing barriers associated with vaccine development to protect livestock, companion animals and humans against these host defense-evasive and cell function-manipulative, vector-transmitted pathogens.

Detection and characterization of four novel genotypes of Ehrlichia canis from dogs

The genetic diversity of Ehrlichia canis strains worldwide is currently poorly defined. The present study aimed to characterize E. canis strains in naturally infected dogs in Taiwan, using a combination of PCR and sequence analysis of the 16S rDNA and two antigen-encoding genes, gp19 and gp36. Genomic DNA was extracted from 34 parasitemic dogs and the genes of the pathogen were separately amplified, sequenced, and aligned with corresponding sequences available in GenBank. All 16S rDNA sequences (1623 bp) amplified from the Taiwanese isolates were identical and had very high similarity (99.4-100%) with previously reported E. canis sequences. Nevertheless, most of the gp19 gene sequences (414 bp) from the Taiwanese isolates had three specific nucleotide substitutions at positions 9, 323 and 371 that resulted in three amino acid changes. The gp36 gene of the Taiwanese isolates consists of three regions: a 5' end pre-repeat region (426 bp), a tandem repeat region with variable numbers of the 27-bp repeat unit depending on the isolate, and a 3' end region (87 bp). The nucleotide sequences of the 5' end region of gp36 from Taiwanese isolates were identical to each other, but unexpectedly, quite distinct from the sequences of eleven other E. canis strains previously published, with 86.7-87.2% identities only. A phylogenetic tree of E. canis strains based on the gp36 amino acid sequences showed that the Taiwanese isolates fell into a separate clade, indicating the presence of a novel strain that had not yet been characterized.

Major species-specific antibody epitopes of the Ehrlichia chaffeensis p120 and E. canis p140 orthologs in surface-exposed tandem repeat regions

Ehrlichia chaffeensis and E. canis have a small subset of tandem repeat (TR)-containing protein orthologs, including p120/p140, which elicit strong antibody responses. The TR regions of these protein orthologs are immunoreactive, but the molecular characteristics of the p120/p140 epitopes have not been determined. In this study, the immunodeterminants of the E. chaffeensis p120 and E. canis p140 were identified and molecularly defined. Major antibody epitope-containing regions of both p120 and p140 were localized to the TR regions, which reacted strongly by Western immunoblotting with antibodies in sera from E. chaffeensis-infected dogs or patients and E. canis-infected dogs, respectively. Single continuous species-specific major epitopes within the E. chaffeensis p120 and E. canis p140 TRs were mapped to homologous surface-exposed glutamate/aspartate-rich regions (19 to 22 amino acids). In addition, minor cross-reactive epitopes were localized to homologous N- and C-terminal regions of p120 and p140. Furthermore, although the native and recombinant p120 and p140 proteins exhibited higher-than-predicted molecular masses, posttranslational modifications were not present on abnormally migrating p120 and p140 TR recombinant proteins as determined by matrix-assisted laser desorption ionization-time of flight mass spectrometry.