Nested PCR for detection and genotyping of Ehrlichia ruminantium: use in genetic diversity analysis

Molecular screening and genetic diversity of tick-borne pathogens associated with dogs and livestock ticks in Egypt

BACKGROUND

The Middle East and North Africa (MENA) offer optimal climatic conditions for tick reproduction and dispersal. Research on tick-borne pathogens in this region is scarce. Despite recent advances in the characterization and taxonomic explanation of various tick-borne illnesses affecting animals in Egypt, no comprehensive examination of TBP (tick-borne pathogen) statuses has been performed. Therefore, the present study aims to detect the prevalence of pathogens harbored by ticks in Egypt.

METHODOLOGY/PRINCIPAL FINDINGS

A four-year PCR-based study was conducted to detect a wide range of tick-borne pathogens (TBPs) harbored by three economically important tick species in Egypt. Approximately 86.7% (902/1,040) of the investigated Hyalomma dromedarii ticks from camels were found positive with Candidatus Anaplasma camelii (18.8%), Ehrlichia ruminantium (16.5%), Rickettsia africae (12.6%), Theileria annulata (11.9%), Mycoplasma arginini (9.9%), Borrelia burgdorferi (7.7%), Spiroplasma-like endosymbiont (4.0%), Hepatozoon canis (2.4%), Coxiella burnetii (1.6%) and Leishmania infantum (1.3%). Double co-infections were recorded in 3.0% (27/902) of Hy. dromedarii ticks, triple co-infections (simultaneous infection of the tick by three pathogen species) were found in 9.6% (87/902) of Hy. dromedarii ticks, whereas multiple co-infections (simultaneous infection of the tick by ≥ four pathogen species) comprised 12% (108/902). Out of 1,435 investigated Rhipicephalus rutilus ticks collected from dogs and sheep, 816 (56.9%) ticks harbored Babesia canis vogeli (17.1%), Rickettsia conorii (16.2%), Ehrlichia canis (15.4%), H. canis (13.6%), Bo. burgdorferi (9.7%), L. infantum (8.4%), C. burnetii (7.3%) and Trypanosoma evansi (6.6%) in dogs, and 242 (16.9%) ticks harbored Theileria lestoquardi (21.6%), Theileria ovis (20.0%) and Eh. ruminantium (0.3%) in sheep. Double, triple, and multiple co-infections represented 11% (90/816), 7.6% (62/816), and 10.3% (84/816), respectively in Rh. rutilus from dogs, whereas double and triple co-infections represented 30.2% (73/242) and 2.1% (5/242), respectively in Rh. rutilus from sheep. Approximately 92.5% (1,355/1,465) of Rhipicephalus annulatus ticks of cattle carried a burden of Anaplasma marginale (21.3%), Babesia bigemina (18.2%), Babesia bovis (14.0%), Borrelia theleri (12.8%), R. africae (12.4%), Th. annulata (8.7%), Bo. burgdorferi (2.7%), and Eh. ruminantium (2.5%). Double, triple, and multiple co-infections represented 1.8% (25/1,355), 11.5% (156/1,355), and 12.9% (175/1,355), respectively. The detected pathogens' sequences had 98.76-100% similarity to the available database with genetic divergence ranged between 0.0001 to 0.0009% to closest sequences from other African, Asian, and European countries. Phylogenetic analysis revealed close similarities between the detected pathogens and other isolates mostly from African and Asian countries.

CONCLUSIONS/SIGNIFICANCE

Continuous PCR-detection of pathogens transmitted by ticks is necessary to overcome the consequences of these infection to the hosts. More restrictions should be applied from the Egyptian authorities on animal importations to limit the emergence and re-emergence of tick-borne pathogens in the country. This is the first in-depth investigation of TBPs in Egypt.

Molecular diagnosis and characterization of Anaplasma marginale and Ehrlichia ruminantium infecting beef cattle of Maputo Province, Mozambique

BACKGROUND

Members of the Anaplasmataceae family, such as the Anaplasma and Ehrlichia species, cause economic losses and public health risks. However, the exact economic impact has not been comprehensively assessed in Mozambique due to limited data available on its basic epidemiology. Therefore, we investigated the molecular occurrence and identity of Anaplasma and Ehrlichia spp. infecting beef cattle in Maputo province, Mozambique.

METHODS

A total of 200 whole blood samples were collected from apparently healthy beef cattle. Whole blood DNA was extracted and tested for presence of Anaplasma spp. and Ehrlichia ruminantium DNA through amplification of the 16S rRNA and map1 genes. Positive samples to Anaplasma spp. were subject to PCR assay targeting the A. marginale-msp5 gene. Amplicons obtained were purified, sequenced and subject to phylogenetic analyses.

RESULTS

Anaplasma spp., A. marginale and E. ruminantium were detected in 153 (76.5%), 142 (71%) and 19 (9.5%) of all the samples analyzed, respectively. On this same sample group, 19 (9.5%) were co-infected with A. marginale and E. ruminantium. The 16S rRNA sequences of Anaplasma spp. obtained were phylogenetically related to A. marginale, A. centrale and A. platys. Phylogenetic analysis revealed that A. marginale-msp5 nucleotide sequences were grouped with sequences from Asia, Africa and Latin America, whereas E. ruminantium-map1 DNA nucleotide sequences were positioned in multiple clusters.

CONCLUSION

Cattle in Maputo Province are reservoirs for multiple Anaplasma species. A high positivity rate of infection by A. marginale was observed, as well as high genetic diversity of E. ruminantium. Furthermore, five new genotypes of E. ruminantium-map1 were identified.

The potential of Rhipicephalus microplus as a vector of Ehrlichia ruminantium in West Africa

Heartwater, or cowdriosis, is a virulent tick-borne rickettsial disease of ruminants caused by Ehrlichia ruminantium, biologically transmitted by Amblyomma species (A. variegatum in West Africa). In West Africa, this bacterium was recently reported to naturally infect the invasive cattle tick, Rhipicephalus microplus (Rm) through trans-ovarian transmission from replete adult females to offspring. A 'sheep-tick-sheep' cycle was set up to determine whether feeding the progeny of these ticks on naïve sheep could lead to infection, and to compare clinical outcomes resulting from this transmission with those observed following infection by the natural A. variegatum (Av) vector. Using local strains of ticks (KIMINI-Rm and KIMINI-Av) and of E. ruminantium (BK242), we recorded, using the PCR technique, the presence of bacterial DNA in ticks (larvae for Av and females for Rm) engorged on sheep inoculated by BK242-infected blood. The bacterial DNA was also detected in the next stages of the lifecycle of R. microplus (eggs and larvae), and in sheep infested either by those R. microplus larvae or by A. variegatum nymphs moulted from larvae engorged on blood-inoculated sheep. Bacterial infection in these sheep was demonstrated by detecting antibodies to E. ruminantium using the MAP1-B ELISA and by isolation of the bacterium on cell culture from blood. The sequences of PCS20 gene detected in ticks and sheep were identical to that of the BK242 strain. Our results confirm that R. microplus can acquire and transmit E. ruminantium to the next stage. However, this transmission resulted in a mild subclinical disease whereas severe clinical disease was observed in sheep infested by A. variegatum infected nymphs, suggesting differences in the tick/bacteria relationship. Future studies will focus on replicating these findings with ticks of different isolates and life stages to determine if R. microplus is playing a role in the epidemiology of heartwater in West Africa. Additionally, studies will investigate whether sheep that are seropositive due to infestation by E. ruminantium-infected R. microplus are subsequently protected against heartwater. Such data will add to our understanding of the possible impact of R. microplus in areas where it has become recently established.

Molecular Detection and Genetic Characterization of Ehrlichia ruminantium Harbored by Amblyomma hebraeum Ticks of Domestic Ruminants in North West Province, South Africa

Ehrlichia ruminantium (E. ruminantium) is the causative agent of heartwater disease and it is mainly transmitted to livestock by Amblyomma hebraeum (A. hebraeum) tick in South Africa. This study investigated the occurrence of E. ruminantium and its genetic diversity in ticks within Ngaka Modiri Molema district of North West Province in South Africa. Genomic DNA was extracted from whole A. hebraeum ticks totaling 876 and resulted in a total of 292 pooled DNA samples. Firstly, conventional PCR was used to detect Ehrlichia spp. targeting the dsbA gene, followed by nested PCR targeting the Map1 gene performed on DNA pool samples that were positive from the first PCR. One hundred and six tick DNA pool samples were positive by dsbA gene PCR for the presence of Ehrlichia spp. with minimum infection rate (MIR) of 121, while 13/106 were positive by Map1 PCR with MIR of 15. Different E. ruminantium Map1 genotypes (NWUe1, NWUe2, NWUe3, NWUe5, and NWUe6) were detected from tick samples and were closely related to more than 13 gene sequences of E. ruminantium from the NCBI GenBank database. These findings suggest that there is a significant diversity of E. ruminantium infecting ticks in the study area.

Genetic diversity of Ehrlichia ruminantium field strains from selected farms in South Africa

Heartwater is a tick-borne disease caused by the intracellular rickettsial parasite Ehrlichia ruminantium and transmitted by Amblyomma hebraeum ticks. Heartwater is problematic in endemic areas because it causes high mortality in ruminants and leads to economic losses that threaten productivity and food security. This may indicate that there is augmented genetic diversity in the field, which may result in isolates that are more virulent than the Ball3 and Welgevonden isolates. The genetic diversity of E. ruminantium was investigated in this study, focussing on the pCS20 gene region and four polymorphic open reading frames (ORFs) identified by subtractive hybridisation. The 16S ribosomal ribonucleic acid gene confirmed E. ruminantium in brain, blood and tick genomic deoxyribonucleic acid samples (n = 3792) collected from 122 farms that were randomly selected from seven provinces of South Africa where heartwater is endemic. The conserved E. ruminantium pCS20 quantitative polymerase chain reaction (qPCR) assay was used to scan all collected field samples. A total of 433 samples tested positive with the qPCR using the pCS20 gene region, of which 167 were sequenced. The known stocks and field samples were analysed, and phylogenetic trees were generated from consensus sequences. A total of 25 new clades were identified; of these, nine isolates from infected blood could be propagated in cell cultures. These clades were not geographically confined to a certain area but were distributed amongst heartwater-endemic areas in South Africa. Thus, the knowledge of strain diversity of E. ruminantium is essential for control of heartwater and provides a basis for further vaccine development.

Molecular detection of Ehrlichia ruminantium in engorged ablyomma variegatum and cattle in Ogun State, Nigeria

Early diagnosis of Ehrlichia ruminantium in cattle is a recipe for effective control of heartwater in ruminants. Hence, we assessed the presence of E. ruminantium in the blood of cattle and the engorged Amblyomma variegatum by nested PCR. The electrophoresed PCR products obtained after primary and secondary amplifications revealed amplicon sizes of about350 bp and 280 bp respectively, which corresponded with the partial region of pSC20 gene amplified. Sequences obtained had 95-99% homology with those sequences available in GenBank. The prevalence of the E. ruminantium in ticks (50%; 126/252) was significantly (p < 0.05) higher than that in cattle blood 23.55% (61/259). The prevalence was significantly (p < 0.05) higher in ticks from adult cattle 51.47% (133/259) than those from the young cattle 44.86% (116/259) and in tick from females 54.55% (141/259) than in ticks from the males 41.38% (107/259). Alignment of autochthonous sequences revealed that the three sequences were polymorphic with two sequences showing similar nucleotides deletion at points 87-91 and 107-108. The phylogenetic trees inferred by ML showed topologies with two autochthonous sequences, one each from cattle blood and tick, clustering together in one clade and the other clustering within those sequences from South Africa and Zimbabwe in another clade. In conclusion, this study revealed a higher prevalence of E. ruminantium in engorged A. variegatum than in the blood of infected cattle. Hence, it is suggested that the amplification that targets the pCS20 gene in engorged ticks may be more suitable to determine the E. ruminantium carrier status of cattle.

Molecular detection and characterization of Ehrlichia ruminantium from cattle in Mozambique

Heartwater caused by Ehrlichia ruminantiumis a disease of domestic and wild ruminants and one of the most economically important tick-borne diseases in Africa. The present study aimed to investigate the occurrence and genetic diversity of E. ruminantium in blood samples from 210 cattle sampled in five districts of Maputo Province, Mozambique. DNA blood samples were initially submitted to PCR assays targeting E. ruminantium pCS20 gene fragments. Additionally, in order to assess the genetic diversity of E. ruminantium, the positive samples were submitted to a PCR assay targeting the E. ruminantium map1 gene. Finally, the amplicons were sequenced and phylogenetic position was inferred using the Maximum Likelihood method. PCR results revealed that the overall prevalence in Maputo Province was 15% of the animals sampled. E. ruminantium map1 sequences showed not to be conserved. In the phylogenetic analysis, E. ruminantium map1 genotypes were positioned into multiple-clades. This study provides information on the prevalence and genetic diversity of E. ruminantium in five localities of Maputo Province. The future immune control strategies against local E. ruminantium must be designed in the light of the genetic diversity of this parasite.

Detection of Ehrlichia ruminantium infection in cattle in Cameroon

OBJECTIVES

Ehrlichia ruminantium infection (heartwater) is a major constraint that impacts negatively on the cattle industry development in sub-Saharan Africa and so far, little is known of the presence of heartwater in cattle in Cameroon. This study sought to investigate the prevalence of E. ruminantium infection in cattle in Cameroon and to determine the predictors of infection.

RESULTS

A species-specific semi-nested pCS20 polymerase chain reaction was used to screen the buffy coats from 182 cattle (comprising 82 cattle that received intensive tick control regimen and 100 cattle on strategic tick control) from two study sites in Cameroon for E. ruminantium DNA in a cross-sectional study. E. ruminantium infection was confirmed in 12 (6.6%) of the 182 cattle comprising 11 that received intensive tick control and one on strategic tick control. Of the 12 cattle detected, 11 were apparently healthy and one was clinically diagnosed of heartwater. All DNA sequences of pCS20 amplicons were identical to each other (a representative sequence deposited in GenBank under accession number JQ039939). These findings which have veterinary and epidemiological significance, suggest the need for further investigation to determine the extent and role of heartwater in cattle in Cameroon.

Comparative Transcriptome Profiling of Virulent and Attenuated Ehrlichia ruminantium Strains Highlighted Strong Regulation of map1- and Metabolism Related Genes

The obligate intracellular pathogenic bacterium, Ehrlichia ruminantium, is the causal agent of heartwater, a fatal disease in ruminants transmitted by Amblyomma ticks. So far, three strains have been attenuated by successive passages in mammalian cells. The attenuated strains have improved capacity for growth in vitro, whereas they induced limited clinical signs in vivo and conferred strong protection against homologous challenge. However, the mechanisms of pathogenesis and attenuation remain unknown. In order to improve knowledge of E. ruminantium pathogenesis, we performed a comparative transcriptomic analysis of two distant strains of E. ruminantium, Gardel and Senegal, and their corresponding attenuated strains. Overall, our results showed an upregulation of gene expression encoding for the metabolism pathway in the attenuated strains compared to the virulent strains, which can probably be associated with higher in vitro replicative activity and a better fitness to the host cells. We also observed a significant differential expression of membrane protein-encoding genes between the virulent and attenuated strains. A major downregulation of map1-related genes was observed for the two attenuated strains, whereas upregulation of genes encoding for hypothetical membrane proteins was observed for the four strains. Moreover, CDS_05140, which encodes for a putative porin, displays the highest gene expression in both attenuated strains. For the attenuated strains, the significant downregulation of map1-related gene expression and upregulation of genes encoding other membrane proteins could be important in the implementation of efficient immune responses after vaccination with attenuated vaccines. Moreover, this study revealed an upregulation of gene expression for 8 genes encoding components of Type IV secretion system and 3 potential effectors, mainly in the virulent Gardel strain. Our transcriptomic study, supported by previous proteomic studies, provides and also confirms new information regarding the characterization of genes involved in E. ruminantium virulence and attenuation mechanisms.

Survey of Anaplasma phagocytophilum and Anaplasma sp. 'Omatjenne' infection in cattle in Africa with special reference to Ethiopia

Background

As evidence of the infection of domestic animals by Anaplasma phagocytophilum and Anaplasma sp. ‘Omatjenne’ is presently becoming available, understanding the epidemiological and ecological significance of infection is important to quantify the clinical and socio-economic impact of the diseases they cause.

Methods

The first aim of this study was to analyse the occurrence of A. phagocytophilum and Anaplasma sp. ‘Omatjenne’ in cattle samples collected from selected African countries using a polymerase chain reaction and restriction enzyme fragment length polymorphism. Secondly, this study was aimed at the molecular identification of Ehrlichia spp. and Anaplasma spp. infection in ruminants raised under different production systems in selected sites in central Ethiopia.

Results

In total, 695 samples from cattle in six African countries were analysed. Overall, 45 positive results were obtained for Anaplasma sp. ‘Omatjenne’ (6.47%) and 19 for A. phagocytophilum (2.73%). Anaplasma sp. ‘Omatjenne’ was detected in all countries except Tanzania while A. phagocytophilum was detected only in samples from Ethiopia. The proportion of samples tested positive for Anaplasma sp. ‘Omatjenne’ ranged from 1.2% in Morocco to 16% in Rwanda. The occurrence of both agents is now confirmed in African cattle. For the survey in Ethiopia a semi-nested 16S rDNA polymerase chain reaction followed by restriction fragment length polymorphism was used for the identification of Ehrlichia spp. and Anaplasma spp. in blood samples. Randomly selected samples were also analysed by pCS20 polymerase chain reaction for the detection of E. ruminantium. Positive results were obtained for E. ruminantium and five species of Anaplasma including a zoonotic species. To our knowledge, this is the first report of infection of domestic ruminants with A. phagocytophilum, A. ovis and Anaplasma sp. ‘Omatjenne’ in Ethiopia.

Conclusion

The present study showed widespread occurrence of Anaplasma sp. 'Omatijenne' in African cattle and five Anaplasma species in Ethiopia.

Efficient high-throughput molecular method to detect Ehrlichia ruminantium in ticks

BACKGROUND

Ehrlichia ruminantium is the causal agent of heartwater, a fatal tropical disease affecting ruminants with important economic impacts. This bacterium is transmitted by Amblyomma ticks and is present in sub-Saharan Africa, islands in the Indian Ocean and the Caribbean, where it represents a threat to the American mainland.

METHODS

An automated DNA extraction method was adapted for Amblyomma ticks and a new qPCR targeting the pCS20 region was developed to improve E. ruminantium screening capacity and diagnosis. The first step in the preparation of tick samples, before extraction, was not automated but was considerably improved by using a Tissue Lyser. The new pCS20 Sol1 qPCR and a previously published pCS20 Cow qPCR were evaluated with the OIE standard pCS20 nested PCR.

RESULTS

pCS20 Sol1 qPCR was found to be more specific than the nested PCR, with a 5-fold increase in sensitivity (3 copies/reaction vs 15 copies/reaction), was less prone to contamination and less time-consuming. As pCS20 Sol1 qPCR did not detect Rickettsia, Anasplasma and Babesia species or closely related species such as Panola Mountain Ehrlichia, E. chaffeensis and E. canis, its specificity was also better than Cow qPCR. In parallel, a tick 16S qPCR was developed for the quality control of DNA extraction that confirmed the good reproducibility of the automated extraction. The whole method, including the automated DNA extraction and pCS20 Sol1 qPCR, was shown to be sensitive, specific and highly reproducible with the same limit of detection as the combined manual DNA extraction and nested PCR, i.e. 6 copies/reaction. Finally, 96 samples can be tested in one day compared to the four days required for manual DNA extraction and nested PCR.

CONCLUSIONS

The adaptation of an automated DNA extraction using a DNA/RNA viral extraction kit for tick samples and the development of a new qPCR increased the accuracy of E. ruminantium epidemiological studies, as well as the diagnostic capabilities and turn-over time for surveillance of heartwater. This new method paves the way for large-scale screening of other bacteria and viruses in ticks as well as genetic characterization of ticks and tick-pathogen coevolution studies.

Ehrlichia ruminantium infects Rhipicephalus microplus in West Africa

Background

The invasion of West Africa by Rhipicephalus microplus during the past decade has changed the ecological situation of the agent of heartwater Ehrlichia ruminantium in this area. Before, its local vector, Amblyomma variegatum, was the most abundant tick species found on livestock. Today, the abundance of the R. microplus is one magnitude higher than that of A. variegatum in many west-African localities. We investigated the potential of this new ecological situation to impact the circulation of E. ruminantium in West Africa.

Methods

Ehrlichia ruminantium infections were assessed with the specific PCR-diagnosis targeting the PCS20 region. This screening was applied on field samples of 24 R. microplus adults, on four females from a laboratory strain that had been blood-fed since larvae on one E. ruminantium-infected steer as well as on the offspring of these females at egg and larval stages.

Results

The PCR detected E. ruminantium in 29 % of the field-collected R. microplus, i.e. twice as much as reported for A. variegatum with the same protocol. Regarding the laboratory strain, the PCR-diagnosis performed showed that all females were infected and passed the rickettsia to their progeny. Sequencing of the PCR product confirmed that the maternally inherited rickettsia was E. ruminantium.

Conclusion

According to the present findings, the invasive dynamic of R. microplus in West Africa is currently impacting the local evolutionary conditions of E. ruminantium since it offers new transmission roads such as maternal transmission in R. microplus.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1651-x) contains supplementary material, which is available to authorized users.

Comparative Proteomic Profiling of Ehrlichia ruminantium Pathogenic Strain and Its High-Passaged Attenuated Strain Reveals Virulence and Attenuation-Associated Proteins

The obligate intracellular bacterium Ehrlichia ruminantium (ER) causes heartwater, a fatal tick-borne disease in livestock. In the field, ER strains present different levels of virulence, limiting vaccine efficacy, for which the molecular basis remains unknown. Moreover, there are no genetic tools currently available for ER manipulation, thus limiting the knowledge of the genes/proteins that are essential for ER pathogenesis and biology. As such, to identify proteins and/or mechanisms involved in ER virulence, we performed the first exhaustive comparative proteomic analysis between a virulent strain (ERGvir) and its high-passaged attenuated strain (ERGatt). Despite their different behaviors in vivo and in vitro, our results from 1DE-nanoLC-MS/MS showed that ERGvir and ERGatt share 80% of their proteins; this core proteome includes chaperones, proteins involved in metabolism, protein-DNA-RNA biosynthesis and processing, and bacterial effectors. Conventional 2DE revealed that 85% of the identified proteins are proteoforms, suggesting that post-translational modifications (namely glycosylation) are important in ER biology. Strain-specific proteins were also identified: while ERGatt has an increased number and overexpression of proteins involved in cell division, metabolism, transport and protein processing, ERGvir shows an overexpression of proteins and proteoforms (DIGE experiments) involved in pathogenesis such as Lpd, AnkA, VirB9 and B10, providing molecular evidence for its increased virulence in vivo and in vitro. Overall, our work reveals that ERGvir and ERGatt proteomes are streamlined to fulfill their biological function (maximum virulence for ERGvir and replicative capacity for ERGatt), and we provide both pioneering data and novel insights into the pathogenesis of this obligate intracellular bacterium.

Development of Loop-Mediated Isothermal Amplification (LAMP) assay for rapid detection of Fusarium oxysporum f. sp. ciceris - wilt pathogen of chickpea

Background

Fusarium oxysporum f. sp. ciceris (Foc), the causal agent of Fusarium wilt is a devastating pathogen of chickpea. In chickpea, various soil borne pathogens produce (s) similar symptoms, therefore cannot be distinguished easily at field level. There is real need for a rapid, inexpensive, and easy to operate and maintain genotyping tool to facilitate accurate disease diagnosis and surveillance for better management of Fusarium wilt outbreaks.

Results

In this study, we developed a loop-mediated isothermal amplification (LAMP) assay targeting the elongation factor 1 alpha gene sequence for visual detection of Foc. The LAMP reaction was optimal at 63°C for 60 min. When hydroxynaphthol blue (HNB) was added before amplification, samples with Foc DNA developed a characteristic sky blue colour but those without DNA or with the DNA of six other plant pathogenic fungi did not. Results obtained with LAMP and HNB were confirmed when LAMP products were subjected to gel electrophoresis. The detection limit of this LAMP assay for Foc was 10 fg of genomic DNA per reaction, while that of conventional PCR was 100 pg.

Conclusions

In conclusion, it was found that a LAMP assay combined with HNB is simple, rapid, sensitive, and specific. The LAMP assay does not require specialized equipment, hence can be used in the field for the rapid detection of Foc. This is the first report of the use of LAMP assay for the detection of Foc. The presented LAMP method provides a specific, sensitive and rapid diagnostic tool for the distinction of Foc, with the potential to be standardized as a detection method for Foc in endemic areas and will be very useful for monitoring the disease complex in the field further suggesting the management strategies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-015-0997-z) contains supplementary material, which is available to authorized users.

Genetic diversity of <i>Ehrlichia ruminantium</i> strains in Cameroon

In order to investigate the extent of genetic diversity among Ehrlichia ruminantium strains in Cameroon, a partial fragment (800 bp) of the E. ruminantium map1 gene was amplified by nested polymerase chain reaction in 121 of 156 E. ruminantium pCS20-positive DNA samples extracted from ticks and cattle collected from two ranches. Deoxyribonucleic acid sequencing of the map1 gene products indicated the presence of at least 21 genotypes at the nucleotide level and 16 genotypes at the amino acid level circulating within the study sites. Some of the genotypes were identical to Antigua (U50830), Blaaukrans (AF368000) or UmBanein (U50835), whilst the others were new genotypes. Twenty-four representative sequences were deposited in GenBank and given accession numbers JX477663 - JX477674 (for sequences of tick origin) and JX486788 - JX486799 (for sequences of cattle origin). Knowledge of E. ruminantium strain diversity could be important in understanding the epidemiology of heartwater.

Improved molecular detection of Ehrlichia and Anaplasma species applied to Amblyomma ticks collected from cattle and sheep in Ethiopia

Detection of Ehrlichia and Anaplasma species in animals and tick vectors is crucial for an understanding of the epidemiology of diseases caused by these pathogens. In this study, a pair of primers designated EBR2 and EBR3 was designed from the Anaplasma 16S rDNA sequence and was used along with a previously described primer EHR 16SD for the simultaneous detection of Ehrlichia and Anaplasma species by nested PCR. The primers were used to amplify 925bp of DNA from known species of Ehrlichia and Anaplasma. Restriction with MboII and MspI enzymes allowed Ehrlichia and Anaplasma speciation. Restriction with MboII differentiated between An. marginale, Anaplasma (formerly Ehrlichia) sp. Omatjenne, and An. centrale with An. marginale and Anaplasma (formerly Ehrlichia) sp. Omatjenne yielding 2 distinct fragments each while An. centrale produced 3 distinct bands. Ehrlichia ruminantium and An. phagocytophylum remained undigested. Subsequent restriction with MspI differentiated E. ruminantium from An. phagocytophylum with 2 and 4 fragments, respectively. When used on tick samples from the field, 63 ticks (16.4%) out of 384 collected from cattle and sheep were positive for one or more species of Ehrlichia and Anaplasma. The positivity ranged from 6.3% at Andasa to 36.7% at Habernosa. Higher overall infection rates were found in Amblyomma lepidum than in Amblyomma variegatum ticks (p=0.009). Amblyomma lepidum from Habernosa were more often infected with all detected species of Anaplasma and Ehrlichia than Am. variegatum. At Bako, however, Anaplasma (formerly Ehrlichia) sp. Omatjenne was detected only in Am. variegatum. A significantly higher proportion of ticks collected from cattle (20.6%) was found positive than in those collected from sheep (3.3%) (p=0.003). Simultaneous detection of Ehrlichia and Anaplasma species and correct identification of mixed infections was possible. Since the ticks were collected from animals, the occurrence of the major species of Ehrlichia and Anaplasma in ruminants in the area is confirmed.

Prevalence of Ehrlichia ruminantium in adult Amblyomma variegatum collected from cattle in Cameroon

Ehrlichia ruminantium, the etiologic agent of the economically important disease heartwater, is an obligate intracellular bacterium transmitted by ticks of the genus Amblyomma, particularly A. hebraeum and A. variegatum. Although serologic and microscopic evidence of the presence of heartwater have been reported in ruminants in Cameroon, knowledge of E. ruminantium infection in the tick vector, A. variegatum, is lacking. In order to determine the infectivity of A. variegatum ticks by E. ruminantium, we analysed 500 un-engorged A. variegatum ticks collected by hand-picking from predilection sites from 182 cattle [115 ticks from 82 cattle at Société de Développement et d'Exploitation des Productions Animales (SODEPA) Dumbo ranch (SDR) and 385 ticks from 100 cattle at the Upper Farms ranch (UFR)] by amplification of the open reading frame (ORF) 2 of the pCS20 region of E. ruminantium. PCR amplification of the 279 bp fragment of the pCS20 region detected E. ruminantium DNA in 142 (28.4 %) of the 500 ticks with a higher infection rate (47/115; 40.9 %) observed in ticks from SDR and 24.7 % (95/385) of ticks collected from cattle at UFR. Twenty five randomly selected PCR products were sequenced and results indicated that some of the isolates shared homology with one another and to sequences of E. ruminantium in the GenBank. This report represents the first molecular evidence of E. ruminantium infection in A. variegatum ticks in Cameroon and suggests possible exposure of cattle to this pathogen in our environment.

A new typing technique for the Rickettsiales Ehrlichia ruminantium: multiple-locus variable number tandem repeat analysis

Ehrlichia ruminantium (ER) is a member of the order Rickettsiales transmitted by Amblyomma ticks. This obligatory intracellular bacterium is the causative agent of a fatal disease in ruminants, named heartwater. It represents a constraint on breeding development in sub-Saharan Africa and in the Caribbean. The genetic diversity of the strains of ER, which could be a limiting factor to obtain effective vaccines, needs to be better characterized. For this purpose, we developed a molecular typing technique based on the polymorphism of variable number tandem repeat (VNTR) sequences, MLVA (multiple locus VNTR analysis). Eight (out of 21) VNTR candidates were validated using 17 samples representing a panel of ER strains from different geographical origins from West, South Africa, and Caribbean areas and in ER infected ticks and goat tissues. This result demonstrated the ability of these VNTRs to type a wide range of strains. The stability of the selected VNTR markers was very good, at the time scale needed for epidemiological purposes: in particular, no difference in the VNTR profiles was observed between virulent and attenuated strains (for Gardel and Senegal strains) and between strains (Gardel and Blonde strains) isolated in the same area 19years apart. We validated the strong discriminatory power of MLVA for ER and found a high level of polymorphism between the available strains, with 10 different profiles out of 13 ER strains. The MLVA scheme described in this study is a rapid and efficient molecular typing tool for ER, which allows rapid and direct typing of this intracellular pathogen without preliminary culture and gives reliable results that can be used for further epidemiological studies.

Development of multiple-locus variable-number tandem-repeat analysis for rapid genotyping ofEhrlichia ruminantiumand its application to infectedAmblyomma variegatumcollected in heartwater endemic areas in Uganda

The rickettsial bacteriumEhrlichia ruminantiumis the causative agent of heartwater, a serious tick-borne disease in ruminants. The genetic diversity of organisms in the field will have implications for cross-protective capacities of any vaccine developed, and for an effective vaccine design strategy proper genotyping and understanding of existing genetic diversity in the field is necessary. We searched for variable-number tandem-repeat (VNTR) loci for use in a multi-locus VNTR analysis (MLVA). Sequencing analysis of 30 potential VNTRs using a panel of 17 reference strains from geographically diverse origins identified 12 VNTRs with allelic profiles differing between strains. Application of MLVA to 38E. ruminantium-infectedAmblyomma variegatumcollected from indigenous cattle in 6 different districts of Uganda identified 21 MLVA types. The discriminatory power of MLVA was greater than that ofmap1PCR-restriction fragment length polymorphism analysis, with which only 6 genotypes were obtained. The high discriminatory power as well as cost- effective performance of MLVA provide the potential for this technique to be applied in the future with respect to optimizing vaccine trials by identifying local strain diversity, and also raise the possibility of exploring the association betweenE. ruminantiumgenotypes and phenotypes such as pathological outcome in the ruminant host.

Multi-locus sequence typing of Ehrlichia ruminantium strains from geographically diverse origins and collected in Amblyomma variegatum from Uganda

Background

The rickettsial bacterium Ehrlichia ruminantium is the causative agent of heartwater in ruminants. A better understanding of the population genetics of its different strains is, however, needed for the development of novel diagnostic tools, therapeutics and prevention strategies. Specifically, the development of effective vaccination policies relies on the proper genotyping and characterisation of field isolates. Although multi-locus sequence typing (MLST) has been recently developed, only strains from geographically restricted collections have been analysed so far. The expansion of the MLST database to include global strains with different geographic origins is therefore essential. In this study, we used a panel of reference strains from geographically diverse origins and field samples of E. ruminantium detected from its vector, Amblyomma variegatum, in heartwater-endemic areas in Uganda.

Results

A total of 31 novel alleles (six, four, six, three, two, five, three, and two for gltA, groEL, lepA, lipA, lipB, secY, sodB, and sucA loci, respectively) and 19 novel sequence types (STs) were identified. Both neighbour-joining and minimum spanning tree analyses indicated a high degree of genetic heterogeneity among these strains. No association was observed between genotypes and geographic origins, except for four STs from West African countries. When we performed six different tests for recombination (GeneConv, Bootscan, MaxChi, Chimaera, SiScan, and 3Seq) on concatenated sequences, four possible recombination events were identified in six different STs. All the recombination breakpoints were located near gene borders, indicating the occurrence of intergenic recombination. All four STs that localized to a distinct group in clustering analysis showed evidence of identical recombination events, suggesting that recombination may play a significant role in the diversification of E. ruminantium.

Conclusions

The compilation of MLST data set across the African continent will be particularly valuable for the understanding of the existing genetic diversity of field isolates in African countries. Comprehensive information on the degree of cross-protection between strains and further understanding of possible relationships between genotypes and phenotypes such as vaccine efficacy are expected to lead to the development of region-specific vaccination strategies.

Ehrlichia ruminantium in Amblyomma variegatum and domestic ruminants in the Caribbean

The highly sensitive nested pCS20 polymerase chain reaction assay for Ehrlichia ruminantium was negative on 506 Amblyomma variegatum from Caribbean islands where clinical heartwater has not been reported, mainly the United States Virgin Islands (18), Dominica (170), Montserrat (5), Nevis (34), St. Kitts (262), and St. Lucia (17). Positive results were obtained with positive controls (Crystal Springs strain) and A. variegatum from countries in Africa where infections are endemic, mainly Tanzania (1/37) and Burkino Faso (2/29). Positive major antigenic protein-1 enzyme-linked immunosorbent assays for E. ruminantium were obtained on convenience samples of sera from apparently healthy cattle, sheep, and goats on Dominica (0/95, 0%; 3/135, 2%; 2/57, 4%), Grenada (0/4, 0%; 1/98, 1%; 1/86, 1%), Montserrat (0/12, 0%; 0/28, 2%; 5/139, 4%), Nevis (0/45, 0%; 0/157, 0%; 0/90, 0%), Puerto Rico (0/422, 0%; 0, 0%), St. Kitts (3/86, 4%; 1/25, 0%; 0/26, 0%), and St. Lucia (0/184, 0%; 0/15, 0%; 0, 0%), respectively. The pCS20 polymerase chain reaction results indicate E. ruminantium is not present on islands where clinical heartwater does not occur. The occasional positive major antigenic protein-1B enzyme-linked immunosorbent assay results appear, then, to be false-positive reactions, and serology appears to be of limited use in testing for E. ruminantium in the Caribbean, as is the case in Africa.

Ehrlichia species, probable emerging human pathogens in sub-Saharan Africa: environmental exacerbation

Ehrlichiae are obligate intracellular Gram-negative tick-borne bacteria that are responsible for life-threatening emerging human zoonoses and diseases of veterinary importance worldwide, collectively called ehrlichioses. The genus Ehrlichia consists of five recognized species, including E. canis, E. chaffeensis, E. ewingii, E. muris, and E. ruminantium. The recent discoveries of Ehrlichia species in new areas and of tick species that were previously thought to be uninfected by these agents have suggested that these agents may have wider distribution than originally thought. Environmental factors like temperature, migration, control failure, and host population have been known to exacerbate the spread of Ehrlichia species. Human cases of moderate to severe disease caused by E. chaffeensis have been reported mainly in North America. In this article, we present an overview of ehrlichiae as emerging pathogens in sub-Saharan Africa, where E. ruminantium, the causative agent of heartwater, a disease of domestic and wild ruminants, is most established. Molecular evidence indicates that E. ruminantium may be an emerging pathogen of a life-threatening human disease. Ehrlichia ruminantium is considered an agricultural biothreat, with several strains reported throughout sub-Saharan Africa, where the infection is considered endemic. Understanding the diversity of E. ruminantium and other Ehrlichia species from all geographically distinct areas of sub-Saharan Africa may enhance our knowledge of the pathogenesis and epidemiology of these pathogens.

Development of loop-mediated isothermal amplification (LAMP) assays for rapid detection of Ehrlichia ruminantium

Background

The rickettsial bacterium Ehrlichia ruminantium is the causative agent of heartwater, a potential zoonotic disease of ruminants transmitted by ticks of the genus Amblyomma. The disease is distributed in nearly all of sub-Saharan Africa and some islands of the Caribbean, from where it threatens the American mainland. This report describes the development of two different loop-mediated isothermal amplification (LAMP) assays for sensitive and specific detection of E. ruminantium.

Results

Two sets of LAMP primers were designed from the pCS20 and sodB genes. The detection limits for each assay were 10 copies for pCS20 and 5 copies for sodB, which is at least 10 times higher than that of the conventional pCS20 PCR assay. DNA amplification was completed within 60 min. The assays detected 16 different isolates of E. ruminantium from geographically distinct countries as well as two attenuated vaccine isolates. No cross-reaction was observed with genetically related Rickettsiales, including zoonotic Ehrlichia species from the USA. LAMP detected more positive samples than conventional PCR but less than real-time PCR, when tested with field samples collected in sub-Saharan countries.

Conclusions

Due to its simplicity and specificity, LAMP has the potential for use in resource-poor settings and also for active screening of E. ruminantium in both heartwater-endemic areas and regions that are at risk of contracting the disease.

Innovative approach for transcriptomic analysis of obligate intracellular pathogen: selective capture of transcribed sequences of Ehrlichia ruminantium

Background

Whole genome transcriptomic analysis is a powerful approach to elucidate the molecular mechanisms controlling the pathogenesis of obligate intracellular bacteria. However, the major hurdle resides in the low quantity of prokaryotic mRNAs extracted from host cells. Our model Ehrlichia ruminantium (ER), the causative agent of heartwater, is transmitted by tick Amblyomma variegatum. This bacterium affects wild and domestic ruminants and is present in Sub-Saharan Africa and the Caribbean islands. Because of its strictly intracellular location, which constitutes a limitation for its extensive study, the molecular mechanisms involved in its pathogenicity are still poorly understood.

Results

We successfully adapted the SCOTS method (Selective Capture of Transcribed Sequences) on the model Rickettsiales ER to capture mRNAs. Southern Blots and RT-PCR revealed an enrichment of ER's cDNAs and a diminution of ribosomal contaminants after three rounds of capture. qRT-PCR and whole-genome ER microarrays hybridizations demonstrated that SCOTS method introduced only a limited bias on gene expression. Indeed, we confirmed the differential gene expression between poorly and highly expressed genes before and after SCOTS captures. The comparative gene expression obtained from ER microarrays data, on samples before and after SCOTS at 96 hpi was significantly correlated (R² = 0.7). Moreover, SCOTS method is crucial for microarrays analysis of ER, especially for early time points post-infection. There was low detection of transcripts for untreated samples whereas 24% and 70.7% were revealed for SCOTS samples at 24 and 96 hpi respectively.

Conclusions

We conclude that this SCOTS method has a key importance for the transcriptomic analysis of ER and can be potentially used for other Rickettsiales. This study constitutes the first step for further gene expression analyses that will lead to a better understanding of both ER pathogenicity and the adaptation of obligate intracellular bacteria to their environment.

Diversity of Ehrlichia ruminantium major antigenic protein 1-2 in field isolates and infected sheep

Proteins expressed from the map1 multigene family of Ehrlichia ruminantium are strongly recognized by immune T and B cells from infected animals or from animals that were infected and have recovered from heartwater disease (although still remaining infected carriers). Analogous multigene clusters also encode the immunodominant outer membrane proteins (OMPs) in other ehrlichial species. Recombinant protein analogs of the expressed genes and DNA vaccines based on the multigene clusters have been shown to induce protective immunity, although this was less effective in heterologous challenge situations, where the challenge strain major antigenic protein 1 (MAP1) sequence differed from the vaccine strain MAP1. Recent data for several ehrlichial species show differential expression of the OMPs in mammalian versus tick cell cultures and dominant expression of individual family members in each type of culture system. However, many genes in the clusters appear to be complete and functional and to generate mRNA transcripts. Recent data also suggest that there may be a low level of protein expression from many members of the multigene family, despite primary high-level expression from an individual member. A continuing puzzle, therefore, is the biological roles of the different members of these OMP multigene families. Complete genome sequences are now available for two geographically divergent strains of E. ruminantium (Caribbean and South Africa strains). Comparison of these sequences revealed amino acid sequence diversity in MAP1 (89% identity), which is known to confer protection in a mouse model and to be the multigene family member primarily expressed in mammalian cells. Surprisingly, however, the greatest sequence diversity (79% identity) was in the less-studied map1-2 gene. We investigated here whether this map1-2 diversity was a general feature of E. ruminantium in different cultured African strains and in organisms from infected sheep. Comparison of MAP1-2s revealed amino acid identities of 75 to 100% (mean of 86%), compared to 84 to 100% (mean of 89%) for MAP1s. Interestingly, MAP1-2s varied independently of MAP1s such that E. ruminantium strains with similar MAP1s had diverse MAP1-2s and vice versa. Different MAP1-2s were found in individual infected sheep. Different regions of a protein may be subjected to different evolutionary forces because of recombination and/or selection, which results in those regions not agreeing with a phylogeny deduced from the whole molecule. This appears to be true for both MAP1 and MAP1-2, where statistical likelihood methods detect heterogeneous evolutionary rates for segments of both molecules. Sera from infected cattle recognized a MAP1-2 variable-region peptide in enzyme-linked immunosorbent assay, but less strongly and consistently than a MAP1 peptide (MAP1B). Heterologous protective immunity may depend on recognition of a complex set of varying OMP epitopes.

Amblyomma variegatum ticks and heartwater on three Caribbean Islands

Amblyomma variegatum tick infestation, tick infection by Ehrlichia ruminantium (ER), and ER genetic diversity were studied in the Caribbean Islands of Guadeloupe, Marie-Galante, and Antigua between 2003 and 2005. Nested PCR for pCS20 was used to detect ER, while ER strains were characterized by sequencing or by restriction fragment length polymorphism (RFLP) profiles of map-1 PCR products. In 2003 in Guadeloupe, the prevalence of tick-infested herds was 35.6%. In Marie-Galante 79.1% of herds in 2003 and 73.8% in 2005 were infested, while only an average of 2.2% of the herds were infected in Antigua between this same period. In Marie-Galante, 19.1% of ticks were ER positive, and ER-infected ticks were found in 33.3% of the herds. In Antigua only 5.8% of the ticks were ER positive. High ER tick infection rate combined with a very high level of tick infestation highlight the risk of heartwater in Marie-Galante and Guadeloupe more than in Antigua. The three islands still represent a reservoir for tick and heartwater in the Caribbean. Nine different African and Caribbean map-1 ER genotypes were identified. This diversity was observed even in restricted areas, and identical map-1 genotypes were observed on all three islands. This high genetic diversity of ER strains suggests that there was a simultaneous introduction of several strains from African countries into the Caribbean region.

Viral association with the elusive rickettsia of viper plague from Ghana, West Africa

We previously reported a rickettsial heartwater-like disease in vipers from Ghana that resembled heartwater in its gross lesions, was apparently transmitted by ticks (Aponomma and Amblyomma), and responded clinically favorably to early treatment with tetracycline. Cell culture showed consistent cytopathic effects in bovine endothelial cells, viper cells, and mouse cells, and inhibition of cytopathic effect by tetracycline in vitro. A type D retrovirus was observed in vacuoles in all infected cells. The virus and rickettsia infection was associated with transfer of cytopathic effect, regardless of cell species. Close association of virus and rickettsia may indicate a dual infection etiology of viper plague.

Differential strain-specific diagnosis of the heartwater agent: Ehrlichia ruminantium

Ehrlichia ruminantium is the causative agent of heartwater, a major tick-borne disease of livestock in Africa introduced in the Caribbean and threatening to emerge and spread in the American mainland. Complete genome sequencing was done for two isolates of E. ruminantium of differing phenotype, isolates Gardel (Erga) from Guadeloupe Island and Welgevonden (Erwe) originating from South Africa and maintained in Guadeloupe. The type strain of E. ruminantium (Erwo), previously isolated and sequenced in South Africa; is identical to Erwe with respect to target genes. They make the Erwe/Erwo complex. Comparative analysis of the genomes shows the presence of 49 unique CDS and 28 truncated CDS differentiating Erga from Erwe/Erwo. Three regions of accumulated differences (RAD) acting as mutational hot spots were identified in E. ruminantium. Ten CDS, six unique CDS and four truncated CDS corresponding to major genomic changes (deletions or extensive mutations) were considered as targets for differential diagnosis on four isolates of E. ruminantium: Erga, Erwe/Erwo, Senegal and Umpala. Pairs of PCR primers were developed for each target gene. PCR analysis of the target genes generated strain-specific patterns on Erga and Erwe/Erwo as predicted by comparative genomics, but also for isolates Senegal and Umpala. The target genes identified by bacterial comparative genomics are shown to be highly efficient for strain-specific PCR diagnosis of E. ruminantium and further vaccine management tools.

Amblyomma variegatum in cattle in Marie Galante, French Antilles: prevalence, control measures, and infection by Ehrlichia ruminantium

We report Marie Galante as one of the Caribbean islands most heavily infested by the tropical bont tick (TBT) Amblyomma variegatum which is associated with two major diseases of ruminants: heartwater and dermatophilosis. In 2005, a survey was undertaken to assess the prevalence of TBT infestation in cattle, the prevalence of Ehrlichia ruminantium infection in TBTs, and the tick control measures implemented by livestock owners. A random sample of 195 cattle herds out of 1885 recorded on the island was investigated by thoroughly counting adult ticks on each animal and filling a questionnaire. A randomly collected sample of 136 TBTs was tested for infection by E. ruminantium by pCS20 nested PCR. Cattle herd prevalence (hp) was 73.8% for infestation by at least one TBT, 17.9% for infestation by at least one engorged female TBT, and 8.2% for clinical dermatophilosis. Cattle individual prevalence was 42.3% for infestation by at least one TBT, 6.6% for infestation by at least one engorged female TBT, and 2.2% for clinical dermatophilosis. The minimum, maximum and average numbers of TBTs per infested animal were, respectively 1, 108 and 11.5. Prevalence of TBT infection by E. ruminantium was 19.1%. No significant difference in herd prevalence was found among parishes or among ecological zones. For cattle owners treating against ticks (97.9% of all owners), all used aspersion of amitraz and herd prevalence was significantly different among those treating every 1-2-week (hp=69.6%, n=148), and less often than every 2-week (hp=88.6%, n=35) (P=0.031). Of the 42 herd subunits treated less than 4 days before the survey, 27 (64%) were infested with at least one TBT, and 6 (14%) with at least one engorged female TBT. These results indicate a high level of TBT infestation in Marie Galante, the inefficacy of tick treatments currently performed, and the need for an improved tick control strategy. Persisting high levels of infestation in Marie Galante threaten the success of on-going TBT eradication programs in the Caribbean because TBT can spread through migrating birds and trade of animals or of animal hides to other islands and potentially the American continent.

Genetic diversity of Ehrlichia ruminantium in Amblyomma variegatum ticks and small ruminants in The Gambia determined by restriction fragment profile analysis

Understanding genetic diversity of Ehrlichia ruminantium in host and vector populations is an important prerequisite to controlling heartwater by vaccination in traditional livestock systems in sub-Saharan Africa. We carried out a study in two phases: (i) evaluating the usefulness of the PCR-RFLP assay based on the map1 coding sequence of E. ruminantium as a discriminatory tool to characterise genetic diversity, (ii) applying the technique to field samples from Amblyomma variegatum ticks and small ruminants to characterise genotypic diversity of the organism in three main agroecological zones of The Gambia, Sudano-Guinean (SG), Western Sudano-Sahelian (WSS) and Eastern Sudano-Sahelian (ESS). Restriction fragment length polymorphisms were observed among different strains of E. ruminantium supporting the usefulness of the PCR-RFLP technique for studying genetic diversity of the organism. Restriction enzyme map1 profile analysis indicated the presence in The Gambia of multiple genotypes (at least 11) of E. ruminantium with sites in the WSS and SG zones showing comparatively high number of diverse genotypes. Profiles similar to the Kerr Seringe genotype (DQ333230) showed the highest distribution frequency, being present at sites in all three agroecological zones, thereby making the strain a suitable candidate for further characterisation in cross-protection studies. An additional three genotypes showed relatively high distribution frequency and were present in all three zones making them equally important for isolation and subsequent characterisation. The study demonstrated the occurrence of mixed infections with E. ruminantium genotypes in ruminants and ticks.

Immunisation of sheep against heartwater in The Gambia using inactivated and attenuated Ehrlichia ruminantium vaccines

Heartwater (cowdriosis) is a disease of ruminants caused by a rickettsial pathogen Ehrlichia ruminantium and transmitted by ticks of the genus Amblyomma. The purpose of this work was to evaluate the protective efficacies of inactivated and attenuated vaccines to protect sheep against heartwater in The Gambia. An inactivated vaccine, prepared from E. ruminantium (Gardel stock), and a live attenuated vaccine from E. ruminantium (Senegal stock), were evaluated in two independent on-station trials. A local stock of E. ruminantium (Kerr Seringe) was used as challenge material. Inactivated and live attenuated vaccines provided 43% and 100% protection, respectively, against virulent needle challenge. In a subsequent field trial, the attenuated vaccine protected 75% of sheep against virulent tick challenge, which was fatal for all control sheep. Quantification by real-time PCR showed that an immunising dose of approximately 23,000 attenuated E. ruminantium organisms was sufficient. Moreover, restriction fragment length polymorphism (RFLP) analysis indicated that the local Kerr Seringe genotype caused mortality amongst control sheep, whereas fatalities in the vaccinated group could be attributed to a different genotype.

Effect of the purification process and the storage conditions on the efficacy of an inactivated vaccine against heartwater

This work evaluates the effect of purification process and storage conditions (buffer formulation and temperature) on the efficacy of Ehrlichia ruminantium (ER) elementary bodies to be used as an inactivated vaccine candidate against heartwater. In vitro assays revealed that, to avoid major losses in ER integrity and corresponding antigenic properties, a buffer with pH between 5.6 and 8 and an osmolality above 100 mOsmol/kg H(2)O is recommended. Amongst the tested formulations, both PBS and NaCl have shown to stabilize ER antigens at -20 degrees C. To assess the protective properties of the different vaccine formulations, in vivo experiments were performed using a goat model. The results obtained showed that the preparation of ER antigens using a novel membrane-based purification strategy and a simple vaccine formulation (NaCl, -20 degrees C) induced equivalent protection to the conventional vaccine based on ER antigens prepared by a multistep centrifugation methodology and stored at -20 degrees C in PBS buffer.

Comparative genomics of three strains of Ehrlichia ruminantium: a review

The tick-borne Rickettsiale Ehrlichia ruminantium (E. ruminantium) is the causative agent of heartwater in Africa and the Caribbean. Heartwater, responsible for major losses on livestock in Africa represents also a threat for the American mainland. Three complete genomes corresponding to two different groups of differing phenotypes, Gardel and Welgevonden, have been recently described. One genome (Erga) represents the Gardel group from Guadeloupe Island and two genomes (Erwo and Erwe) belong to the Welgevonden group. Erwo, isolated in South Africa, is the parental strain of Erwe, which was maintained for 18 years in Guadeloupe under different culture conditions than Erwo. The three strains display genomes of differing sizes with 1,499,920 bp, 1,512,977 bp, and 1,516,355 bp for Erga, Erwe, and Erwo, respectively. Gene sequences and order are highly conserved between the three strains, although several gene truncations could be pinpointed, most of them occurring within three regions of accumulated differences (RAD). E. ruminantium displays a strong leading/lagging compositional bias inducing a strand-specific codon usage. Finally, a striking feature of E. ruminantium is the presence of long intergenic regions containing tandem repeats. These repeats are at the origin of an active process, specific to E. ruminantium, of genome expansion/contraction based on the addition or removal of tandem units.

Understanding the mechanisms of transmission of Ehrlichia ruminantium and its influence on the structure of pathogen populations in the field

The understanding of the structure of Ehrlichia ruminantium stock population in the field was highlighted by experiments done in controlled conditions on the goat model. The mixture of strains observed in ticks seemed to be due to simultaneous infections rather than successive infections of the carrier. During a dual infection, the timing of Ehrlichia ruminantium circulation of the two stocks in hosts influenced their selection by ticks.

Comparative genomic analysis of three strains of Ehrlichia ruminantium reveals an active process of genome size plasticity

Ehrlichia ruminantium is the causative agent of heartwater, a major tick-borne disease of livestock in Africa that has been introduced in the Caribbean and is threatening to emerge and spread on the American mainland. We sequenced the complete genomes of two strains of E. ruminantium of differing phenotypes, strains Gardel (Erga; 1,499,920 bp), from the island of Guadeloupe, and Welgevonden (Erwe; 1,512,977 bp), originating in South Africa and maintained in Guadeloupe in a different cell environment. Comparative genomic analysis of these two strains was performed with the recently published parent strain of Erwe (Erwo) and other Rickettsiales (Anaplasma, Wolbachia, and Rickettsia spp.). Gene order is highly conserved between the E. ruminantium strains and with A. marginale. In contrast, there is very little conservation of gene order with members of the Rickettsiaceae. However, gene order may be locally conserved, as illustrated by the tuf operons. Eighteen truncated protein-encoding sequences (CDSs) differentiate Erga from Erwe/Erwo, whereas four other truncated CDSs differentiate Erwe from Erwo. Moreover, E. ruminantium displays the lowest coding ratio observed among bacteria due to unusually long intergenic regions. This is related to an active process of genome expansion/contraction targeted at tandem repeats in noncoding regions and based on the addition or removal of ca. 150-bp tandem units. This process seems to be specific to E. ruminantium and is not observed in the other Rickettsiales.