Tick-Borne Encephalitis Virus Adaptation in Different Host Environments and Existence of Quasispecies

A highly virulent strain (Hypr) of tick-borne encephalitis virus (TBEV) was serially subcultured in the mammalian porcine kidney stable (PS) and Ixodes ricinus tick (IRE/CTVM19) cell lines, producing three viral variants. These variants exhibited distinct plaque sizes and virulence in a mouse model. Comparing the full-genome sequences of all variants, several nucleotide changes were identified in different genomic regions. Furthermore, different sequential variants were revealed to co-exist within one sample as quasispecies. Interestingly, the above-mentioned nucleotide changes found within the whole genome sequences of the new variants were present alongside the nucleotide sequence of the parental strain, which was represented as a minority quasispecies. These observations further imply that TBEV exists as a heterogeneous population that contains virus variants pre-adapted to reproduction in different environments, probably enabling virus survival in ticks and mammals.

Anaplasma phagocytophilum modifies tick cell microRNA expression and upregulates isc-mir-79 to facilitate infection by targeting the Roundabout protein 2 pathway

The microRNAs (miRNAs) are a class of small noncoding RNAs that have important regulatory roles in multicellular organisms including innate and adaptive immune pathways to control bacterial, parasite and viral infections, and pathogens could modify host miRNA profile to facilitate infection and multiplication. Therefore, understanding the function of host miRNAs in response to pathogen infection is relevant to characterize host-pathogen molecular interactions and to provide new targets for effective new interventions for the control infectious diseases. The objective of this study was to characterize the dynamics and functional significance of the miRNA response of the tick vector Ixodes scapularis in response to Anaplasma phagocytophilum infection, the causative agent of human and animal granulocytic anaplasmosis. To address this objective, the composition of tick miRNAs, functional annotation, and expression profiling was characterized using high throughout RNA sequencing in uninfected and A. phagocytophilum-infected I. scapularis ISE6 tick cells, a model for tick hemocytes involved in pathogen infection. The results provided new evidences on the role of tick miRNA during pathogen infection, and showed that A. phagocytophilum modifies I. scapularis tick cell miRNA profile and upregulates isc-mir-79 to facilitate infection by targeting the Roundabout protein 2 (Robo2) pathway. Furthermore, these results suggested new targets for interventions to control pathogen infection in ticks.

Exosomes serve as novel modes of tick-borne flavivirus transmission from arthropod to human cells and facilitates dissemination of viral RNA and proteins to the vertebrate neuronal cells

Molecular determinants and mechanisms of arthropod-borne flavivirus transmission to the vertebrate host are poorly understood. In this study, we show for the first time that a cell line from medically important arthropods, such as ticks, secretes extracellular vesicles (EVs) including exosomes that mediate transmission of flavivirus RNA and proteins to the human cells. Our study shows that tick-borne Langat virus (LGTV), a model pathogen closely related to tick-borne encephalitis virus (TBEV), profusely uses arthropod exosomes for transmission of viral RNA and proteins to the human- skin keratinocytes and blood endothelial cells. Cryo-electron microscopy showed the presence of purified arthropod/neuronal exosomes with the size range of 30 to 200 nm in diameter. Both positive and negative strands of LGTV RNA and viral envelope-protein were detected inside exosomes derived from arthropod, murine and human cells. Detection of Nonstructural 1 (NS1) protein in arthropod and neuronal exosomes further suggested that exosomes contain viral proteins. Viral RNA and proteins in exosomes derived from tick and mammalian cells were secured, highly infectious and replicative in all tested evaluations. Treatment with GW4869, a selective inhibitor that blocks exosome release affected LGTV loads in both arthropod and mammalian cell-derived exosomes. Transwell-migration assays showed that exosomes derived from infected-brain-microvascular endothelial cells (that constitute the blood-brain barrier) facilitated LGTV RNA and protein transmission, crossing of the barriers and infection of neuronal cells. Neuronal infection showed abundant loads of both tick-borne LGTV and mosquito-borne West Nile virus RNA in exosomes. Our data also suggest that exosome-mediated LGTV viral transmission is clathrin-dependent. Collectively, our results suggest that flaviviruses uses arthropod-derived exosomes as a novel means for viral RNA and protein transmission from the vector, and the vertebrate exosomes for dissemination within the host that may subsequently allow neuroinvasion and neuropathogenesis.

An Ixodes scapularis cell line with a predominantly neuron-like phenotype

The Ixodes scapularis embryo-derived cell line ISE6 is the most widely utilized tick-derived cell line due to its susceptibility to a wide variety of tick- and non-tick-vectored pathogens. Little is known about its tissue origin or biological background. Protein expression of ISE6 cells was compared with that of another I. scapularis-derived cell line, IDE12, and dissected tick synganglia. Results demonstrated the presence of a neuronal marker protein, type 3 β-tubulin, in all three samples, as well as other shared and unique neuronal and immune response-associated proteins. Of neuronal proteins shared between the two cell lines, ISE6 expressed several in significantly greater quantities than IDE12. Stimulation of ISE6 cells by in vivo exposure to the hemocoel environment in unfed larval and molting nymphal ticks, but not unfed nymphal ticks, resulted in the development of neuron-like morphologic characteristics in the implanted cells.

First detection and molecular identification of Borrelia garinii spirochete from Ixodes ovatus tick ectoparasitized on stray cat in Taiwan

Borrelia garinii spirochete was detected for the first time in Ixodes ovatus tick ectoparasitized on stray cat in Taiwan. The genetic identity of this detected spirochete was determined by analyzing the gene sequence amplified by genospecies-specific polymerase chain reaction assays based on the 5S-23S intergenic spacer amplicon (rrf-rrl) and outer surface protein A (ospA) genes of B. burgdorferi sensu lato. Phylogenetic relationships were analyzed by comparing the sequences of rrf-rrl and ospA genes obtained from 27 strains of Borrelia spirochetes representing six genospecies of Borrelia. Seven major clades can be easily distinguished by neighbour-joining analysis and were congruent by maximum-parsimony method. Phylogenetic analysis based on rrf-rrl gene revealed that this detected spirochete (strain IO-TP-TW) was genetically affiliated to the same clade with a high homogeneous sequences (96.7 to 98.1% similarity) within the genospecies of B. garinii and can be discriminated from other genospecies of Borrelia spirochetes. Interspecies analysis based on the genetic distance values indicates a lower level (<0.022) of genetic divergence (GD) within the genospecies of B. garinii, and strain IO-TP-TW was genetically more distant ( >0.113) to the strains identified in I. ovatus collected from Japan and China. Intraspecies analysis also reveals a higher homogeneity (GD<0.005) between tick (strain IO-TP-TW) and human (strain Bg-PP-TW1) isolates of B. garinii in Taiwan. This study provides the first evidence of B. garinii isolated and identified in an I. ovatus tick in Asia, and the higher homogeneity of B. garinii between tick and human strain may imply the risk of human infection by I. ovatus bite.

Expression of heat shock proteins and subolesin affects stress responses, Anaplasma phagocytophilum infection and questing behaviour in the tick, Ixodes scapularis

We characterized the effects of subolesin and heat shock protein (HSP) expression on Ixodes scapularis Say (Acari: Ixodidae) stress responses to heat shock and feeding, questing behaviour and Anaplasma phagocytophilum (Rickettsiales: Anaplasmataceae) infection. Ticks and cultured tick cells were analysed before and after subolesin, hsp20 and hsp70 gene knock-down by RNA interference. The results of these studies confirm that HSPs are involved in the tick cell response to heat stress and that subolesin and HSPs are both involved in the tick response to blood-feeding stress and A. phagocytophilum infection. Subolesin and hsp20 are involved in the tick protective response to A. phagocytophilum infection and hsp70 expression may be manipulated by the pathogen to increase infectivity. Importantly, these results demonstrate that subolesin, hsp20 and hsp70 expression also affect tick questing behaviour. Overall, this research demonstrates a relationship between hsp and subolesin expression and tick stress responses to heat shock and blood feeding, A. phagocytophilum infection and questing behaviour, thereby extending our understanding of the tick-host-pathogen interface.

Confirmation of occurrence of Ixodes (Pholeoixodes) rugicollis Schulze et Schlottke, 1929 (Acari: Ixodidae) in Poland, including the morphological description and diagnostic features of this species

Research on feline and canine ticks was conducted in the years 2004-2005 in the vicinities of Przemyśl, in the village of Torki (Medyka region) and in Przemyśl. Ticks were collected by examining thoroughly the bodies of cats and dogs. Ticks were preserved in 70% ethyl alcohol and their taxonomic identity was determined. It was confirmed that dogs and cats in the study sites carried four species of ticks: Ixodes (Ph.) rugicollis, I. (Ph.) hexagonus, I. (Ph.) crenulatus and I. (I.) ricinus. Ixodes (Ph.) rugicollis was shown to be a common species among the ectoparasites on these hosts and therefore is considered now to be a regular component of the Polish fauna. Morphological characteristics of all the development stages of I. rugicollis are given in the paper.

Isolation and establishment of the raccoon Ehrlichia-like agent in tick cell culture

Feral animals are reservoirs of emerging human pathogens, as well as carriers of closely related wildlife diseases. The latter may interfere with epidemiologic studies by inducing cross-reactive antibodies, or by providing false positive signals in PCR based tests. We cultured a novel intracellular bacterium from the blood of two raccoons (Procyon lotor): RAC413 and RAC414. RAC413 had been experimentally inoculated with blood from a wild-caught raccoon, and provided the material for a blood passage into RAC414. The microbes grew in Ixodes scapularis (black-legged tick) cells, line ISE6, inoculated either with the leukocyte or erythrocyte fraction of anticoagulated blood. Giemsa-stained cells sampled two and three months after initial inoculation of the cultures revealed inclusions similar to those of Ehrlichia sp., except that individual bacteria commonly were elongated and clustered within endosomes. Electronmicroscopy confirmed the presence of irregularly shaped bacteria with evenly granular bacterioplasm bounded by a unit membrane. 16S rDNA sequencing identified the microbes as the raccoon Ehrlichia-like agent previously detected in feral raccoons from Georgia, United States. In conclusion, the availability of a culture isolate of this agent will facilitate future studies to determine its biology, epidemiologic significance, vector association, and host range. The Ehrlichia-like agent infecting raccoons joins a growing list of tick-borne agents cultivable in tick cells.

Targeting the tick/pathogen interface for developing new anaplasmosis vaccine strategies

Bovine anaplasmosis is a tick-borne hemolytic disease of cattle that occurs worldwide caused by the intraerythrocytic rickettsiae Anaplasma marginale. Control measures, including use of acaricides, administration of antibiotics and vaccines, have varied with geographic location. Our research is focused on the tick-pathogen interface for development of new vaccine strategies with the goal of reducing anaplasmosis, tick infestations and the vectorial capacity of ticks. Toward this approach, we have targeted (1) development of an A. marginale cell culture system to provide a non-bovine antigen source, (2) characterization of an A. marginale adhesion protein, and (3) identification of key tick protective antigens for reduction of tick infestations. A cell culture system for propagation of A. marginale was developed and provided a non-bovine source of A. marginale vaccine antigen. The A. marginale adhesion protein, MSP1a, was characterized and use of recombinant MSP1a in vaccine formulations reduced clinical anaplasmosis and infection levels in ticks that acquired infection on immunized cattle. Most recently, we identified a tick-protective antigen, subolesin, that reduced tick infestations, as well as the vectorial capacity of ticks for acquisition and transmission of A marginale. This integrated approach to vaccine development shows promise for developing new strategies for control of bovine anaplasmosis.

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.

Host range specificity of flaviviruses: correlation with in vitro replication

Vector-borne flaviviruses have been traditionally grouped into either mosquito-borne or tick-borne group. However, this vector range specificity has sometimes been questioned because of the puzzling records of occasional isolation of mosquito-borne viruses from ticks and of tick-borne viruses from mosquitoes. In this study, host range of the flaviviruses representing not only the two vector-borne groups but also insect flaviviruses and vertebrate viruses that are not arboviruses was comprehensively reexamined by a serial passage experiment in vitro by using cell cultures derived from mosquitoes, ticks, and vertebrates. The results showed that the host range specificity in the four groups of viruses, based on replication for five consecutive passages as a criterion to evaluate the ability of viruses to replicate in three different cell cultures, agreed with the conventional grouping as well as phylogenetic clustering. Thus, this assay provides useful, supplementary information regarding host range for those flaviviruses when their natural host range is unknown, ambiguous, or questionable.

Phagocytosis of the Lyme disease spirochete, Borrelia burgdorferi, by cells from the ticks, Ixodes scapularis and Dermacentor andersoni, infected with an endosymbiont, Rickettsia peacockii

Tick cell lines were used to model the effects of endosymbiont infection on phagocytic immune responses. The lines tested for their ability to phagocytose the Lyme disease spirochete, Borrelia burgdorferi (Spirochaetales: Spirochaetaceae), were ISE6 and IDE12 from the black-legged tick, Ixodes scapularis Say (Acari: Ixodidae) and DAE15 from the Rocky Mountain wood tick, Dermacentor andersoni Stiles. Rickettsia peacockii (Rickettsiales: Rickettsiaceae), an endosymbiont of D. andersoni, was used as a representative tick endosymbiont. 70-80% of uninfected or R. peacocciz-infected IDE12 and DAE15 cells phagocytosed heat-killed borreliae and 80-90% of IDE12 and DAE15 cells phagocytosed viable spirochetes. ISE6 cells were permissive of spirochetes; less than 1% of these cells phagocytosed borreliae, and spirochetes remained adherent to the cells seven days after inoculation. Cytochalasin B blocked phagocytosis of killed and viable borreliae by IDE12 cells, and prevented phagocytosis of killed spirochetes by DAE15 cells, whereas viable spirochetes successfully invaded cytochalasin-treated DAE15. IDE12 and DAE15 cells degraded borreliae within phagolysosome-like compartments. Time-lapse microscopy showed that DAE15 cells phagocytosed borreliae more rapidly than IDE12 cells. IDE12 and DAE15 cells eliminated most adherent spirochetes within 7 days of inoculation. Thus, endosymbiont infection does not significantly interfere with the phagocytic activity of immunocompetent tick cells.

In vitro cultivation of a south African isolate of an Anaplasma sp. in tick cell cultures

This paper describes the first successful in vitro cultivation of a South African isolate of an Anaplasma sp., initially thought to be Anaplasma marginale, in the continuous tick cell line IDE8. Blood from a bovine naturally infected with A. marginale kept on the farm Kaalplaas (28 degrees 08' E, 25 degrees 38' S) was collected, frozen, thawed and used as inoculum on confluent IDE8 cell cultures. Twenty days after culture initiation small intracellular colonies were detected in a Cytospin smear prepared from culture supernatant. Cultures were passaged on Day 34. Attempts to infect IRE/CTVM18 cell cultures with the Kaalplaas isolate derived from IDE8 cultures failed, whereas a reference stock of A. marginale from Israel infected IRE/CTVM18 tick cell cultures. Attempts to infect various mammalian cell lines (BA 886, SBE 189, Vero, L 929, MDBK) and bovine erythrocytes, kept under various atmospheric conditions, with tick cell-derived Anaplasma sp. or the Israeli strain of A. marginale failed. Molecular characterization revealed that the blood inoculum used to initiate the culture contained both A. marginale and Anaplasma sp. (Omatienne) whereas the organisms from established cultures were only Anaplasma sp. (Omatjenne).

Confirmation of tick bite by detection of antibody to Ixodes calreticulin salivary protein

Ticks introduce a variety of pharmacologically active molecules into their host during attachment and feeding in order to obtain a blood meal. People who are repeatedly exposed to ticks may develop an immune response to tick salivary proteins. Despite this response, people usually are unaware of having been bitten, especially if they are not repeatedly exposed to ticks. In order to develop a laboratory marker of tick exposure that would be useful in understanding the epidemiology of tick-borne infection and the immune response to tick bite, we developed an enzyme-linked immunosorbent assay (ELISA) to detect antibody to a recombinant form of calreticulin protein found in the salivary glands of Ixodes scapularis, a member of a complex of Ixodes ticks that serve as the vectors for Lyme disease, human babesiosis, and human granulocytic anaplasmosis. Using this assay, we tested sera obtained from C3H/HeN and BALB/c mice before and after experimental deer tick infestation. These mice developed antibody to Ixodes calreticulin antigen after infestation. We then used the same assay to test sera obtained from people before and after they experienced deer tick bite(s). People experiencing deer tick bite(s) developed Ixodes calreticulin-specific antibody responses that persisted for up to 17 months. This Ixodes recombinant calreticulin ELISA provides objective evidence of deer tick exposure in people.

A comparison of Chryseobacterium indologenes pathogenicity to the soft tick Ornithodoros moubata and hard tick Ixodes ricinus

A yellow-pigmented Gram-negative bacterium, Chryseobacterium indologenes, was found in the gut contents of about 65% of soft ticks Ornithodoros moubata from a perishing laboratory colony. The isolated putative pathogen, C. indologenes, was susceptible to cotrimoxazol and addition of this antibiotic (Biseptol 480) to the blood meal significantly decreased the tick mortality rate. The artificial infection of healthy O. moubata by membrane feeding on blood contaminated with C. indologenes was lethal to all ticks at concentrations 10(6) bacteria/ml. On the contrary, a similar infection dose applied to the hard tick Ixodes ricinus by capillary feeding did not cause significant mortality. Examination of guts dissected from infected O. moubata and I. ricinus revealed that C. indologenes was exponentially multiplied in the soft tick but were completely cleared from the gut of the hard ticks within 1 day. In both tick species, C. indologenes were found to penetrate from the gut into the hemocoel. The phagocytic activity of hemocytes from both tick species was tested by intrahaemocoelic microinjection of C. indologenes and evaluated by indirect fluorescent microscopy using antibodies raised against whole bacteria. Hemocytes from both tick species displayed significant phagocytic activity against C. indologenes. All O. moubata injected with C. indologenes died within 3 days, whereas the increase of the mortality rate of I. ricinus was insignificant. Our results indicate that hard ticks possess much more efficient defense system against infection with C. indologenes than the soft ticks. Thus, C. indologenes infection has the potential to be a relevant comparative model for the study of tick immune reactions to transmitted pathogens.

Lyme borreliosis: insights into tick-/host-borrelia relations

Lyme borreliosis (LB) is a serious infectious disease of humans and some domestic animals in temperate regions of the Northern Hemisphere. It is caused by certain spirochetes in the Borrelia burgdorferi sensu lato (s.l.) species complex. The complex consists of 11 species (genospecies). Borrelia burgdorferi sensu stricto (s.s.), Borrelia garinii and Borrelia afzelii are the major agents of human disease. Borrelia burgdorferi s.l. species are transmitted mainly by ticks belonging to the Ixodes ricinus species complex plus a few additional species not currently assigned to the complex. B. burgdorferi infections may produce an acute or chronic disease with a wide array of clinical symptoms such as erythema migrans (EM), carditis, arthritis, neuroborreliosis, and acrodermatitis chronica atrophicans (ACA). Differences in LB spirochetes 'genospecies' and strains/isolates determine the occurrence and severity of this multi-system disease. Accurate and reliable identification of the LB spirochetes in ticks as well as knowledge of their prevalence are essential for prevention against the disease and development of an effective vaccine. An overview of the knowledge of molecular factors with emphasis on potential protein-carbohydrate interactions in the tick-borrelia system is the main focus of this review.

A symbiont of the tick Ixodes ricinus invades and consumes mitochondria in a mode similar to that of the parasitic bacterium Bdellovibrio bacteriovorus

We have recently performed molecular characterisation of an intracellular alpha-proteobacterium, named IricES1, which resides in the ovarian tissue of female Ixodes ricinus ticks from Italy. A unique characteristic of this bacterium is its ability to invade the mitochondria of the cells in which it resides. Although some ultrastructural studies have been performed on close relatives of this bacterium from I. ricinus in England and Switzerland, a number of questions remain about its movement within ovarian tissues and mitochondria. We have performed the first detailed ultrastructural examination of IricES1 in engorged female adult I. ricinus. Among our findings was that the bacterium enters mitochondria in a similar way to that employed by the 'predatory' bacterium Bdellovibro bacteriovorus, that is, between the inner and outer membranes. It then appears to multiply, with the new 'colony' consuming the mitochondrial matrix. Despite having many of their mitochondria consumed, oocytes appear to develop normally, and the bacteria are likely to be vertically transferred to all eggs.

Glycosylation of Anaplasma marginale major surface protein 1a and its putative role in adhesion to tick cells

Anaplasma marginale, the causative agent of bovine anaplasmosis, is a tick-borne rickettsial pathogen of cattle that multiplies in erythrocytes and tick cells. Major surface protein 1a (MSP1a) and MSP1b form the MSP1 complex of A. marginale, which is involved in adhesion of the pathogen to host cells. In this study we tested the hypothesis that MSP1a and MSP1b were glycosylated, because the observed molecular weights of both proteins were greater than the deduced molecular masses. We further hypothesized that the glycosylation of MSP1a plays a role in adhesion of A. marginale to tick cells. Native and Escherichia coli-derived recombinant MSP1a and MSP1b proteins were shown by gas chromatography to be glycosylated and to contain neutral sugars. Glycosylation of MSP1a appeared to be mainly O-linked to Ser/Thr residues in the N-terminal repeated peptides. Glycosylation may play a role in adhesion of A. marginale to tick cells because chemical deglycosylation of MSP1a significantly reduced its adhesive properties. Although the MSP1a polypeptide backbone alone was adherent to tick cell extract, the glycans in the N-terminal repeats appeared to enhance binding and may cooperatively interact with one or more surface molecules on host cells. These results demonstrated that MSP1a and MSP1b are glycosylated and suggest that the glycosylation of MSP1a plays a role in the adhesion of A. marginale to tick cells.

Intracellular symbionts and other bacteria associated with deer ticks (Ixodes scapularis) from Nantucket and Wellfleet, Cape Cod, Massachusetts

The diversity of bacteria associated with the deer tick (Ixodes scapularis) was assessed using PCR amplification, cloning, and sequencing of 16S rRNA genes originating from seven ticks collected from Nantucket Island and Wellfleet, Cape Cod, Mass. The majority of sequences obtained originated from gram-negative proteobacteria. Four intracellular bacteria were detected including strains of Ehrlichia, Rickettsia, and Wolbachia and an organism related to intracellular insect symbionts from the Cytophaga-Flavobacterium-Bacteroides group. Several strains of members of the Sphingomonadaceae were also detected in all but one tick. The results provide a view of the diversity of bacteria associated with I. scapularis ticks in the field.

[Indication of Borrelia burgdorferi sensu lato in the taiga tick larvae obtained from spontaneously infected females]

Hungry larvae from 17 clutches by spontaneously infected Ixodes persulcatus females were examined by inoculation of the BSK II medium, by microscopy of fixed smears, and by polymerase chain reaction (PCR) with the primers specific toward the conserved sequences of Borrelia burgdorferi 16S ribosomal RNA gene. A study of 781 larvae individually or as pools could not reveal Borrelia DNA by PCR. Inoculations of the BSK II medium with 600 larvae yielded no positive results either; immobile spiral forms of Bacillus spp. were detected in 16 (26.7 +/- 5.7%) cultures of the larvae obtained from 7 females. Microscopy of 1416 fixed smears showed typical Borrelia in 7 (0.5 +/- 0.4%) specimens of larvae resulting from the same hatch; spirochaete-like cells were present in 13 (0.9 +/- 0.5%) cases. The single female from those of the 17 hatches transmitted Borrelia through eggs to filial-generation larvae. The infection rate of the larvae emerged from the eggs of this hatch was 7% and their individual infection rates were 0.4-0.8 Borrelia per 100 fields of vision. The findings suggest that there may a transovarian transmission of Borrelia in I. persulcatus ticks, but its likelihood is very little.

Tick salivary gland extract-activated transmission of Borrelia afzelii spirochaetes

Saliva-activated transmission of Borrelia afzelii Canica, Nato, du Merle, Mazie, Baranton et Postic, 1993 was demonstrated using salivary gland extract (SGE) from Ixodes ricinus (L., 1758) ticks and C3H mice. Injection of Borrelia spirochaetes together with SGE increased the level of bacteraemia and accelerated the appearance of bacteria in the urinary bladder, compared with the injection of spirochaetes alone. More I. ricinus nymphs became infected when feeding on mice inoculated with B. afzelii plus SGE. Analysis of cytokines produced by cells of draining lymph nodes from SGE-treated mice showed a suppression of proinflammatory cytokines IFN-gamma, IL-6 and GM-CSF following a transient upregulation in comparison with the control mice infected without SGE.

Applications of a cell culture system for studying the interaction of Anaplasma marginale with tick cells

A cell culture system for the tick-borne rickettsia Anaplasma marginale offers new opportunities for research on this economically important pathogen of cattle. A. marginale multiplies in membrane-bound inclusions in host cells. Whereas erythrocytes appear to be the only site of infection in cattle, A. marginale undergoes a complex developmental cycle in ticks and transmission occurs via the salivary glands during feeding. We recently developed a cell culture system for A. marginale using a cell line derived from embryos of Ixodes scapularis. Here we review the use of this cell culture system for studying the interaction of A. marginale with tick cells. Several assays were developed using the A. marginale/tick cell system. An adhesion assay was developed for the identification of proteins required by A. marginale for adhesion to tick cells. The effect of antibodies against selected major surface proteins in inhibiting A. marginale infection was tested in an assay that allowed further confirmation of the role of surface proteins in the infection of tick cells. A drug screening assay for A. marginale was developed and provides a method of initial drug selection without the use of cattle. The culture system was used to test for enhancing effects of tick saliva and saliva components on A. marginale infection. The tick cell culture system has proved to be a good model for studying A. marginale-tick interactions. Information gained from these studies may be applicable to other closely related tick-borne pathogens that have been propagated in the same tick cell line.

Salivary gland extract from Ixodes ricinus tick modulates the host immune response towards the Th2 cytokine profile

In our previous work, the salivary gland extract (SGE) from Ixodes ricinus ticks impaired T-lymphocyte proliferation and clearly modulated the immune response towards the Th2 pattern in human peripheral blood mononuclear cell culture. In the present work, the results obtained on mouse splenocytes are compared with those on human leukocytes. ELISA (protein level) and RNAse protection assay (mRNA level) showed that SGE enhanced interleukin (IL)-1alpha, IL-1beta, IL-1Ra, IL-6, and IL-12p40 cytokines, whereas production of IL-2, IL-5, IL-10, and IL-13 was decreased. The minute levels of IL-9, IL-15 and IL-12p70 were not changed after the addition of tick saliva. IL-4 was upregulated, whereas the production of gamma interferon and migratory inhibition factor was downregulated after the addition of SGE. Tick saliva decreased concanavalin A-stimulated spleen cell proliferation and the percentage of activated T-cells. We conclude that the Th2 polarization did not involve all of the cytokines tested. However, the Th2 subset-augmenting effect of tick saliva was confirmed.

Differential adhesion of major surface proteins 1a and 1b of the ehrlichial cattle pathogen Anaplasma marginale to bovine erythrocytes and tick cells

Anaplasma marginale is a tick-borne ehrlichial pathogen of cattle for which six major surface proteins (MSPs) have been described. The MSP1 complex, a heterodimer composed of MSP1a and MSP1b, was shown to induce a protective immune response in cattle and both proteins have been identified as putative adhesins for bovine erythrocytes. In this study the role of MSP1a and MSP1b as adhesins for bovine erythrocytes and tick cells was defined. msp1alpha and msp1beta1 genes from the Oklahoma isolate of A. marginale were cloned and expressed in Escherichia coli K-12 under the control of endogenous and tac promoters for both low and high level protein expression. Expression of the recombinant polypeptides was confirmed and localised on the surface of transformed E. coli. The adhesion properties of MSP1a and MSP1b were determined by allowing recombinant E. coli expressing these surface polypetides to react with bovine erythrocytes, Dermacentor variabilis gut cells and cultured tick cells derived from embryonic Ixodes scapularis. Adhesion of the recombinant E. coli to the three cell types was determined using recovery adhesion and microtiter haemagglutination assays, and by light and electron microscopy. MSP1a was shown by all methods tested to be an adhesin for bovine erythrocytes and both native and cultured tick cells. In contrast, recombinant E. coli expressing MSP1b adhered only to bovine erythrocytes and not to tick cells. When low expression vectors were used, single E. coli expressing MSP1a was seen adhered to individual tick cells while reaction of tick cells with the E. coli/MSP1a/high expression vector resulted in adhesion of multiple bacteria per cell. With electron microscopy, fusion of E. coli cell membranes expressing MSP1a or MSP1b with erythrocyte membranes was observed, as well as fusion of tick cell membranes with E. coli membranes expressing MSP1a. These studies demonstrated differential adhesion for MSP1a and MSP1b for which MSP1a is an A. marginale adhesin for both bovine erythrocytes and tick cells while MSP1b is an adhesin only for bovine erythrocytes. The role of the MSP1 complex, therefore, appears to vary among vertebrate and invertebrate hosts.

Establishment and characterization of an Oklahoma isolate of Anaplasma marginale in cultured Ixodes scapularis cells

Anaplasma marginale is a tick-borne hemoparasite of cattle worldwide. The Virginia isolate of A. marginale was propagated previously in a cell line derived from embryos of the tick, Ixodes scapularis. The cultured Anaplasma (VA-tc) was passaged continuously for over 4 years and retained its infectivity for cattle and antigenic stability. We report herein the continuous in vitro cultivation of a second isolate of A. marginale derived from a naturally infected cow in Oklahoma (OK-tc). Blood from the infected cow was subinoculated into a splenectomized calf and blood collected at peak parasitemia was frozen, thawed and used as inoculum on confluent tick cell monolayers. Colonies of Anaplasma were apparent in low numbers at 9 days post exposure (PE) and infection in monolayers reached 100% by 4-5 weeks PE. Cultures were passaged by placing supernatant onto fresh tick cell monolayers at a dilution of 1:5 or 1:10. By the third passage development of the OK-tc was similar to that of the VA-tc and a 1:5 dilution resulted in 100% infection in 10-12 days. Inoculation of OK-tc into a splenectomized calf caused clinical anaplasmosis and Dermacentor ticks that fed on this calf transmitted the organism to a second susceptible calf. Major surface proteins (MSPs) 1-5 of the OK-tc were compared with homologous proteins present on VA-tc and the erythrocytic stage of the Oklahoma isolate. The MSPs 1, 2, 4, 5 were conserved on the OK-tc but there was evidence for structural variation in MSP3 between the cultured and erythrocytic stage of Anaplasma. MSP2 and MSP3 were the major proteins recognized by serum from infected cattle. Two-dimensional gels also identified positional differences between VA-tc and OK-tc in MSP2 and MSP3. The OK-tc may have potential to be used as antigen for development of an improved vaccine for anaplasmosis in the South Central United States.

Comparison of surface proteins of Anaplasma marginale grown in tick cell culture, tick salivary glands, and cattle

Anaplasma marginale, a tick-borne rickettsial pathogen of cattle, infects bovine erythrocytes, resulting in mild to severe hemolytic disease that causes economic losses in domestic livestock worldwide. Recently, the Virginia isolate of A. marginale was propagated in a continuous tick cell line, IDE8, derived from embryonic Ixodes scapularis. Development of A. marginale in cell culture was morphologically similar to that described previously in ticks. In order to evaluate the potential of the cell culture-derived organisms for use in future research or as an antigen for serologic tests and vaccines, the extent of structural conservation of the major surface proteins (MSPs) between the cell culture-derived A. marginale and the bovine erythrocytic stage, currently the source of A. marginale antigen, was determined. Structural conservation on the tick salivary-gland stage was also examined. Monoclonal and monospecific antisera against MSPs 1 through 5, initially characterized against erythrocyte stages, also reacted with A. marginale from cell culture and tick salivary glands. MSP1a among geographic A. marginale isolates is variable in size because of different numbers of a tandemly repeated 28- or 29-amino-acid peptide. The cell culture-derived A. marginale maintained the same-size MSP1a as that found on the Virginia isolate of A. marginale in bovine erythrocytes and tick salivary glands. Although differences were observed in the polymorphic MSP2 antigen between culture and salivary-gland stages, MSP2 did not appear to vary, by two-dimensional gel electrophoresis, during continuous passage in culture. These data show that MSPs of erythrocyte-stage A. marginale are present on culture stages and may be structurally conserved during continuous culture. The presence of all current candidate diagnostic and vaccine antigens suggests that in vitro cultures are a valuable source of rickettsiae for basic research and for the development of improved diagnostic reagents and vaccines against anaplasmosis.

Establishment of the tick (Acari:Ixodidae)-borne cattle pathogen Anaplasma marginale (Rickettsiales:Anaplasmataceae) in tick cell culture

Anaplasma marginale is a tick-borne rickettsia that causes bovine anaplasmosis worldwide. Despite its importance, A. marginale has thus far not been established in a continuous culture system. We have propagated A. marginale continuously for the 1st time in a tick cell line derived from the black-legged tick, Ixodes scapularis Say, using infected bovine blood as the inoculum. Erythrocytic stages invaded the tick cells and multiplied in membrane-lined vacuoles to form colonies typical of those observed in naturally infected ticks as demonstrated by light and electron microscopy. The rickettsiae have been passaged serially for 3 yr and have been cryopreserved in liquid nitrogen. Antigens present in A. marginale from tick cell culture were recognized by bovine immune serum against the blood stages of A. marginale. A. marginale grown in this tick cell line was infective for calves, and male ticks fed on the calves transmitted A. marginale to a susceptible calf. The ability to culture A. marginale removes a major impediment to the study of Anaplasma biology in vitro, and will enhance development of vaccines and diagnostic tests.