Polymorphism and transcription at the p44-1/p44-18 genomic locus in Anaplasma phagocytophilum strains from diverse geographic regions

Epidemiology, genetic variants and clinical course of natural infections with Anaplasma phagocytophilum in a dairy cattle herd

Background

Anaplasma phagocytophilum is an obligate intracellular, tick-transmitted bacterium that causes granulocytic anaplasmosis in humans and several mammalian species including domestic ruminants where it is called tick-borne fever (TBF). Different genetic variants exist but their impact with regard to putative differences in host associations and pathogenicity are not yet completely understood.

Methods

Natural infections with A. phagocytophilum in a dairy cattle herd in Germany were investigated over one pasture season by using serology, haematology, blood chemistry and polymerase chain reaction (PCR). Sequence analysis of partial 16S rRNA, groEL, msp2 and msp4 genes of A. phagocytophilum was carried out in order to trace possible genetic variants and their relations between cattle, roe deer (Capreolus capreolus) and ticks (Ixodes ricinus) in this area.

Results

In total 533 samples from 58 cattle, 310 ticks, three roe deer and one wild boar were examined. Our results show (i) typical clinical symptoms of TBF in first-time infected heifers, such as high fever, reduced milk yield, lower limb oedema and typical haematological and biochemical findings such as severe leukopenia, erythropenia, neutropenia, lymphocytopenia, monocytopenia, a significant increase in creatinine and bilirubin and a significant decrease in serum albumin, γ-GT, GLDH, magnesium and calcium; (ii) a high overall prevalence of A. phagocytophilum infections in this herd as 78.9% (15/19) of the naïve heifers were real-time PCR-positive and 75.9% (44/58) of the entire herd seroconverted; and (iii) a high level of sequence variation in the analysed genes with five variants of the 16S rRNA gene, two variants of the groEL gene, three variants of the msp2 gene and four variants in the msp4 gene with certain combinations of these variants.

Conclusions

In cattle particular combinations of the genetic variants of A. phagocytophilum occurred, whereas three roe deer showed different variants altogether. This is indicative for a sympatric circulation of variants in this small geographical region (< 1 km²). Both re- and superinfections with A. phagocytophilum were observed in five cattle showing that infection does not result in sterile immunity. For prevention of clinical cases we suggest pasturing of young, not pregnant heifers to reduce economical losses.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2570-1) contains supplementary material, which is available to authorized users.

Molecular characterization of Msp2/P44 of Anaplasma phagocytophilum isolated from infected patients and Haemaphysalis longicornis in Laizhou Bay, Shandong Province, China

Molecular characterization of the MSP2/P44 protein of Anaplasma phagocytophilum may determine not only if the bacterium is capable of invading hosts but also whether it generates antigenic variation for the purpose of escaping the host immune response, resulting in various pathologic injuries and serious clinical outcomes. Chinese anaplasmosis patients usually present with serious manifestations, and the fatality rate is as high as 26.5%. In this study, we amplified, cloned and sequenced the msp2/p44 genes of three Chinese A. phagocytophilum isolates from Laizhou Bay, Shandong Province, where human granulocytic anaplasmosis (HGA) patients present severe clinical manifestations, and analyzed their genetic characterization and structural features. We also compared them with the HZ and Webster A. phagocytophilum strains. The sequences for both strains are available in GenBank. Analyses indicated that Chinese A. phagocytophilum isolates were significantly different from the HZ and Webster strains in terms of nucleotide sequences, amino acid sequences and protein secondary and tertiary structures. Moreover, the number of immunologic B-cell epitopes (19) of the MSP2 protein of the Chinese isolates was higher than that of the A. phagocytophilum strains HZ (16) and Webster (9). This genetic diversity of the MSP2/P44 protein of Chinese A. phagocytophilum isolates might be relevant and might have serious clinical outcomes. This observation could provide a clue to further understand the pathogenesis of Chinese A. phagocytophilum.

Genetic variants of Anaplasma phagocytophilum from 14 equine granulocytic anaplasmosis cases

Background

Equine Granulocytic Anaplasmosis (EGA) is caused by Anaplasma phagocytophilum, a tick-transmitted, obligate intracellular bacterium. In Europe, it is transmitted by Ixodes ricinus. A large number of genetic variants of A. phagocytophilum circulate in nature and have been found in ticks and different animals. Attempts have been made to assign certain genetic variants to certain host species or pathologies, but have not been successful so far. The purpose of this study was to investigate the causing agent A. phagocytophilum of 14 cases of EGA in naturally infected horses with molecular methods on the basis of 4 partial genes (16S rRNA, groEL, msp2, and msp4).

Results

All DNA extracts of EDTA-blood samples of the horses gave bands of the correct nucleotide size in all four genotyping PCRs. Sequence analysis revealed 4 different variants in the partial 16S rRNA, groEL gene and msp2 genes, and 3 in the msp4 gene. One 16S rRNA gene variant involved in 11 of the 14 cases was identical to the "prototype" variant causing disease in humans in the amplified part [GenBank: U02521]. Phylogenetic analysis revealed as expected for the groEL gene that sequences from horses clustered separately from roe deer. Sequences of the partial msp2 gene from this study formed a separate cluster from ruminant variants in Europe and from all US variants.

Conclusions

The results show that more than one variant of A. phagocytophilum seems to be involved in EGA in Germany. The comparative genetic analysis of the variants involved points towards different natural cycles in the epidemiology of A. phagocytophilum, possibly involving different reservoir hosts or host adaptation, rather than a strict species separation.

Mechanisms of obligatory intracellular infection with Anaplasma phagocytophilum

Anaplasma phagocytophilum persists in nature by cycling between mammals and ticks. Human infection by the bite of an infected tick leads to a potentially fatal emerging disease called human granulocytic anaplasmosis. A. phagocytophilum is an obligatory intracellular bacterium that replicates inside mammalian granulocytes and the salivary gland and midgut cells of ticks. A. phagocytophilum evolved the remarkable ability to hijack the regulatory system of host cells. A. phagocytophilum alters vesicular traffic to create an intracellular membrane-bound compartment that allows replication in seclusion from lysosomes. The bacterium downregulates or actively inhibits a number of innate immune responses of mammalian host cells, and it upregulates cellular cholesterol uptake to acquire cholesterol for survival. It also upregulates several genes critical for the infection of ticks, and it prolongs tick survival at freezing temperatures. Several host factors that exacerbate infection have been identified, including interleukin-8 (IL-8) and cholesterol. Host factors that overcome infection include IL-12 and gamma interferon (IFN-γ). Two bacterial type IV secretion effectors and several bacterial proteins that associate with inclusion membranes have been identified. An understanding of the molecular mechanisms underlying A. phagocytophilum infection will foster the development of creative ideas to prevent or treat this emerging tick-borne disease.

Global proteomic analysis of two tick-borne emerging zoonotic agents: anaplasma phagocytophilum and ehrlichia chaffeensis

Anaplasma phagocytophilum and Ehrlichia chaffeensis are obligatory intracellular α-proteobacteria that infect human leukocytes and cause potentially fatal emerging zoonoses. In the present study, we determined global protein expression profiles of these bacteria cultured in the human promyelocytic leukemia cell line, HL-60. Mass spectrometric (MS) analyses identified a total of 1,212 A. phagocytophilum and 1,021 E. chaffeensis proteins, representing 89.3 and 92.3% of the predicted bacterial proteomes, respectively. Nearly all bacterial proteins (≥99%) with known functions were expressed, whereas only approximately 80% of “hypothetical” proteins were detected in infected human cells. Quantitative MS/MS analyses indicated that highly expressed proteins in both bacteria included chaperones, enzymes involved in biosynthesis and metabolism, and outer membrane proteins, such as A. phagocytophilum P44 and E. chaffeensis P28/OMP-1. Among 113 A. phagocytophilum p44 paralogous genes, 110 of them were expressed and 88 of them were encoded by pseudogenes. In addition, bacterial infection of HL-60 cells up-regulated the expression of human proteins involved mostly in cytoskeleton components, vesicular trafficking, cell signaling, and energy metabolism, but down-regulated some pattern recognition receptors involved in innate immunity. Our proteomics data represent a comprehensive analysis of A. phagocytophilum and E. chaffeensis proteomes, and provide a quantitative view of human host protein expression profiles regulated by bacterial infection. The availability of these proteomic data will provide new insights into biology and pathogenesis of these obligatory intracellular pathogens.

An entropy-optimized multilocus approach for characterizing the strains of Anaplasma phagocytophilum infecting horses in the Czech Republic

Anaplasma phagocytophilum is a tick-borne rickettsial pathogen that has measurable genetic heterogeneity across its geographical range and reservoir spectrum. In the present study, publicly available sequences of the genes that have prevailingly been used for typing A. phagocytophilum were analysed to identify the segments giving the highest resolution with respect to the predictability of host and geographical provenances of the strains. Selected partial sequences of 16S rRNA, groL, msp4 and ank genes were then employed in a tentative multilocus typing scheme used to characterize the strains causing equine granulocytic anaplasmosis (EGA). We were able to both identify alleles characteristic for equine strains of A. phagocytophilum and distinguish two unique genetic variants infecting horses in the Czech Republic. This resolution far exceeded the discriminatory potential of any of the four sequenced genes when used singly. The two novel A. phagocytophilum variants appeared to be phylogenetically closer to the strains reported as causing human disease in Slovenia than to strains thus far isolated from other European EGA cases. A decline in the quality of recently deposited A. phagocytophilum sequences was also demonstrated.

Anaplasma phagocytophilum p44 mRNA expression is differentially regulated in mammalian and tick host cells: involvement of the DNA binding protein ApxR

The natural life cycle of Anaplasma phagocytophilum, an obligatory intracellular bacterium that causes human granulocytic anaplasmosis, consists of alternate infection of two distinct hosts, ticks and mammals, in which bacterial surface proteins are expected to have a critical role. The present study investigated regulation of A. phagocytophilum p44 genes, which encode the P44 major surface proteins. Quantitative real-time reverse transcription-PCR analysis revealed that the amount of p44 mRNA obtained from spleens of A. phagocytophilum-infected SCID mice was approximately 10-fold greater than the amount obtained from salivary glands of A. phagocytophilum-infected Ixodes scapularis nymphs. Similarly, the amount of p44 mRNA obtained from A. phagocytophilum-infected HL-60 cells per bacterium was significantly greater than the amount obtained from infected ISE6 tick cells. The relative amount of p44 mRNA was approximately threefold higher in A. phagocytophilum-infected HL-60 cells cultured at 37 degrees C than in A. phagocytophilum-infected HL-60 cells cultured at 28 degrees C. Although there are more than 100 p44 paralogs, we observed expression mainly from the p44 expression locus (p44E) in various host environments. Interestingly, transcription of the A. phagocytophilum gene encoding the DNA binding protein ApxR was also significantly greater in A. phagocytophilum-infected HL-60 cells than in infected ISE6 tick cells. Gel mobility shift and DNase I protection assays revealed recombinant ApxR binding to the promoter regions of p44E and apxR. ApxR also transactivated the p44E and apxR promoter regions in a lacZ reporter assay. These results indicate that p44 genes and apxR are specifically up-regulated in the mammalian host environment and suggest that ApxR not only is positively autoregulated but also acts as a transcriptional regulator of p44E.

High-resolution genetic fingerprinting of European strains of Anaplasma phagocytophilum by use of multilocus variable-number tandem-repeat analysis

Anaplasma phagocytophilum is a widely distributed tick-borne pathogen of humans, livestock, and companion animals. We used in silico methods to identify 10 variable-number tandem-repeat (VNTR) loci within the genome sequence of the A. phagocytophilum HZ strain and used these data to develop a multilocus VNTR-based typing scheme for the species. Having confirmed the stability of four of the loci in replicates of the A. phagocytophilum strain that had been subjected to different numbers of passages through cell cocultures in vitro, we then used this typing scheme to discriminate between 20 A. phagocytophilum strains of diverse geographical and host provenances. Extensive diversity was found at each of the four loci studied, with total allele numbers ranging from 13 to 18 and Hunter-Gaston discriminatory index values ranging from 0.93 to 0.99. Only 2 of the 20 strains examined shared alleles at all four loci. The discriminatory power of VNTR analysis was found to be greater than that of either partial msp4 or 16S rRNA gene sequence comparison. The extremely high sensitivity of this novel approach to the genetic fingerprinting of A. phagocytophilum strains should serve well in molecular epidemiological studies of infection transmission, particularly when fine-scale strain delineation is required.

New findings on members of the family Anaplasmataceae of veterinary importance

Members of the family Anaplasmataceae are obligate intracellular Gram-negative bacteria that naturally infect a variety of wild and domestic animal species, the spillover of which may lead to zoonosis. I discuss new findings on members of the family Anaplasmataceae of veterinary importance and therefore, I will describe the recent findings on Neorickettsia risticii in the trematode and related Neorickettsia species. I also will review the recent progress on Aegyptianella pullorum and other Aegyptianella sp., "Candidatus Neoehrlichia mikurensis" and Anaplasma phagocytophilum strains in various hosts. The whole genome sequences of two important veterinary pathogens-Anaplasma marginale, the bovine anaplasmosis agent, and Ehrlichia (formerly Cowdria) ruminantium, the agent of heartwater of ruminants-have been published. Taken together, these advances in research of the family Anaplasmataceae in the veterinary field provide us with insights into the evolution, reservoir, and transmission of these organisms in nature and their pathogenesis in natural and accidental hosts. It is through this work that surveillance, diagnosis, preventive measures, and treatment of ehrlichioses of both animals and humans can be improved.

Porin activity of Anaplasma phagocytophilum outer membrane fraction and purified P44

Anaplasma phagocytophilum, an obligatory intracellular bacterium that causes human granulocytic anaplasmosis, has significantly less coding capacity for biosynthesis and central intermediary metabolism than do free-living bacteria. Thus, A. phagocytophilum needs to usurp and acquire various compounds from its host. Here we demonstrate that the isolated outer membrane of A. phagocytophilum has porin activity, as measured by a liposome swelling assay. The activity allows the diffusion of L-glutamine, the monosaccharides arabinose and glucose, the disaccharide sucrose, and even the tetrasaccharide stachyose, and this diffusion could be inhibited with an anti-P44 monoclonal antibody. P44s are the most abundant outer membrane proteins and neutralizing targets of A. phagocytophilum. The P44 protein demonstrates characteristics consistent with porins of gram-negative bacteria, including detergent solubility, heat modifiability, a predicted structure of amphipathic and antiparallel beta-strands, an abundance of polar residues, and a C-terminal phenylalanine. We purified native P44s under two different nondenaturing conditions. When reconstituted into proteoliposomes, both purified P44s exhibited porin activity. P44s are encoded by approximately 100 p44 paralogs and go through extensive antigenic variation. The 16-transmembrane-domain beta-strands consist of conserved P44 N- and C-terminal regions. By looping out the hypervariable region, the porin structure is conserved among diverse P44 proteins yet enables antigenic variation for immunoevasion. The tricarboxylic acid (TCA) cycle of A. phagocytophilum is incomplete and requires the exogenous acquisition of L-glutamine or L-glutamate for function. Efficient diffusion of L-glutamine across the outer membrane suggests that the porin feeds the Anaplasma TCA cycle and that the relatively large pore size provides Anaplasma with the necessary metabolic intermediates from the host cytoplasm.

Evaluation of white-tailed deer (Odocoileus virginianus) as natural sentinels for Anaplasma phagocytophilum

Anaplasma phagocytophilum, the causative agent of human granulocytotropic anaplasmosis, can infect white-tailed deer (WTD; Odocoileus virginianus), and this species is a crucial host for adult Ixodes scapularis, the primary vector of A. phagocytophilum. The goal of this study was to determine the geographic distribution of A. phagocytophilum among WTD across a 19 state region and to evaluate the utility of WTD as natural sentinels. Serologic testing using the indirect fluorescent antibody (IFA) assay was conducted on WTD serum samples and molecular and xenodiagnostic tests were performed to confirm serologic results. The surveillance system was assessed through examination of vital attributes including WTD age and gender associations with serologic status, sample size adequacy for accurate infection status classification, and presence of the vector, I. scapularis. Six hundred thirty-three of 2,666 (24%) WTD in 17 states tested positive for antibodies (>or=128) when tested by IFA assay. Testing for p44 and/or 16S rRNA gene targets identified 73 (16%) PCR positive WTD among 458 animals tested, all of which originated from seropositive populations. Attempts to culture A. phagocytophilum from WTD were unsuccessful; however, xenodiagnostic mice inoculated with blood from 3 WTD became infected. Seroprevalence did not differ by deer age or gender; however, WTD<or=0.75 years old had a higher prevalence of PCR positivity. Using seroprevalence data, a sample size of 6-9 animals per population was projected to be adequate for identifying seropositive populations. The presence of I. scapularis was significantly associated with A. phagocytophilum antibodies in WTD. Collectively, the results of this study demonstrate that WTD would be suitable natural sentinels for this emerging zoonotic pathogen.

Two monoclonal antibodies with defined epitopes of P44 major surface proteins neutralize Anaplasma phagocytophilum by distinct mechanisms

Anaplasma phagocytophilum is an obligatory intracellular bacterium that causes human granulocytic anaplasmosis. The polymorphic 44-kDa major outer membrane proteins of A. phagocytophilum are dominant antigens recognized by patients and infected animals. However, the ability of anti-P44 antibody to neutralize the infection has been unclear due to a mixture of P44 proteins with diverse hypervariable region amino acid sequences expressed by a given bacterial population and lack of epitope-defined antibodies. Monoclonal antibodies (MAbs) 5C11 and 3E65 are directed to different domains of P44 proteins, the N-terminal conserved region and P44-18 central hypervariable region, respectively. Passive immunization with either MAb 5C11 or 3E65 partially protects mice from infection with A. phagocytophilum. In the present study, we demonstrated that the two monoclonal antibodies recognize bacterial surface-exposed epitopes of naturally folded P44 proteins and mapped these epitopes to specific peptide sequences. The two MAbs almost completely blocked the infection of the A. phagocytophilum population that predominantly expressed P44-18 in HL-60 cells by distinct mechanisms: MAb 5C11 blocked the binding, but MAb 3E65 did not block binding or internalization. Instead, MAb 3E65 inhibited internalized A. phagocytophilum to develop into microcolonies called morulae. Some plasma from experimentally infected horses and mice reacted with these two epitopes. Taken together, these data indicate the presence of at least two distinct bacterial surface-exposed neutralization epitopes in P44 proteins. The results indicate that antibodies directed to certain epitopes of P44 proteins have a critical role in inhibiting A. phagocytophilum infection of host cells.

Comparative genomics of emerging human ehrlichiosis agents

Anaplasma (formerly Ehrlichia) phagocytophilum, Ehrlichia chaffeensis, and Neorickettsia (formerly Ehrlichia) sennetsu are intracellular vector-borne pathogens that cause human ehrlichiosis, an emerging infectious disease. We present the complete genome sequences of these organisms along with comparisons to other organisms in the Rickettsiales order. Ehrlichia spp. and Anaplasma spp. display a unique large expansion of immunodominant outer membrane proteins facilitating antigenic variation. All Rickettsiales have a diminished ability to synthesize amino acids compared to their closest free-living relatives. Unlike members of the Rickettsiaceae family, these pathogenic Anaplasmataceae are capable of making all major vitamins, cofactors, and nucleotides, which could confer a beneficial role in the invertebrate vector or the vertebrate host. Further analysis identified proteins potentially involved in vacuole confinement of the Anaplasmataceae, a life cycle involving a hematophagous vector, vertebrate pathogenesis, human pathogenesis, and lack of transovarial transmission. These discoveries provide significant insights into the biology of these obligate intracellular pathogens.

Ehrlichiosis is an acute disease that triggers flu-like symptoms in both humans and animals. It is caused by a range of bacteria transmitted by ticks or flukes. Because these bacteria are difficult to culture, however, the organisms are poorly understood. The genomes of three emerging human pathogens causing ehrlichiosis were sequenced. A database was designed to allow the comparison of these three genomes to sixteen other bacteria with similar lifestyles. Analysis from this database reveals new species-specific and disease-specific genes indicating niche adaptations, pathogenic traits, and other features. In particular, one of the organisms contains more than 100 copies of a single gene involved in interactions with the host(s). These comparisons also enabled a reconstruction of the metabolic potential of five representative genomes from these bacteria and their close relatives. With this work, scientists can study these emerging pathogens in earnest.