First European case of ehrlichiosis

Tick-Borne Bacterial Diseases in Europe: Threats to public health

BACKGROUND

Tick-borne diseases, caused by bacterial pathogens, pose a growing threat to public health in Europe. This paper provides an overview of the historical context of the discovery of the most impactful pathogens transmitted by ticks, including Borrelia burgdorferi sensu lato, Rickettsia spp., Anaplasma spp., Francisella spp., Ehrlichia spp., and Neoehrlichia mikurensis. Understanding the historical context of their discovery provides insight into the evolution of our understanding of these pathogens.

METHODS AND RESULTS

Systematic investigation of the prevalence and transmission dynamics of these bacterial pathogens is provided, highlighting the intricate relationships among ticks, host organisms, and the environment. Epidemiology is explored, providing an in-depth analysis of clinical features associated with infections. Diagnostic methodologies undergo critical examination, with a spotlight on technological advancements that enhance detection capabilities. Additionally, the paper discusses available treatment options, addressing existing therapeutic strategies and considering future aspects.

CONCLUSIONS

By integrating various pieces of information on these bacterial species, the paper aims to provide a comprehensive resource for researchers and healthcare professionals addressing the impact of bacterial tick-borne diseases in Europe. This review underscores the importance of understanding the complex details influencing bacterial prevalence and transmission dynamics to better combat these emerging public health threats.

Ticks and Tick-Borne Pathogens Circulating in Peri-Domestic Areas in Mainland Portugal

Over the years, tick-borne pathogens (TBPs) have garnered significant interest due to their medical, veterinary and economic importance. Additionally, TBPs have drawn attention to how these microorganisms interact with their own vectors, increasing the risk to human and animal infection of emerging and reemerging zoonoses. In this sense, ticks, which are obligate hematophagous ectoparasites, have a key role in maintaining and transmitting TBPs among humans and animals. The aim of this study was to assess the prevalence of neglected TBPs in mainland Portugal, namely Anaplasma spp., Babesia spp., Ehrlichia spp. and Neoehrlichia mikurensis. DNA fragments were detected in questing ticks collected from five different ecological areas under investigation. To the best of the authors' knowledge, this study reports new worldwide findings, including B. bigemina infecting Ixodes frontalis, Ixodes ricinus and Rhipicephalus sanguineus sensu lato. Additionally, it presents new findings in Portugal of N. mikurensis infecting I. ricinus and of presumably Wolbachia endosymbionts being detected in I. ricinus. Overall, there were 208 tick samples that were negative for all screened TBPs. The results herein obtained raise concerns about the circulation of neglected TBPs in mainland Portugal, especially in anthropophilic ticks, highlighting the importance of adopting a One Health perspective.

Molecular survey of Anaplasma and Ehrlichia species in livestock ticks from Kassena-Nankana, Ghana; with a first report of Anaplasma capra and Ehrlichia minasensis

Tick-borne pathogens harm livestock production and pose a significant risk to public health. To combat these effects, it is necessary to identify the circulating pathogens to create effective control measures. This study identified Anaplasma and Ehrlichia species in ticks collected from livestock in the Kassena-Nankana Districts between February 2020 and December 2020. A total of 1550 ticks were collected from cattle, sheep and goats. The ticks were morphologically identified, pooled and screened for pathogens using primers that amplify a 345 bp fragment of the 16SrRNA gene and Sanger sequencing. The predominant tick species collected was Amblyomma variegatum (62.98%). From the 491 tick pools screened, 34 (6.92%) were positive for Ehrlichia and Anaplasma. The pathogens identified were Ehrlichia canis (4.28%), Ehrlichia minasensis (1.63%), Anaplasma capra (0.81%) and Anaplasma marginale (0.20%). This study reports the first molecular identification of the above-mentioned Ehrlichia and Anaplasma species in ticks from Ghana. With the association of human infections with the zoonotic pathogen A. capra, livestock owners are at risk of infections, calling for the development of effective control measures.

Emerging Tick-Borne Diseases

Increases in tick-borne disease prevalence and transmission are important public health issues. Efforts to control these emerging diseases are frustrated by the struggle to control tick populations and to detect and treat infections caused by the pathogens that they transmit. This review covers tick-borne infectious diseases of nonrickettsial bacterial, parasitic, and viral origins. While tick surveillance and tracking inform our understanding of the importance of the spread and ecology of ticks and help identify areas of risk for disease transmission, the vectors are not the focus of this document. Here, we emphasize the most significant pathogens that infect humans as well as the epidemiology, clinical features, diagnosis, and treatment of diseases that they cause. Although detection via molecular or immunological methods has improved, tick-borne diseases continue to remain underdiagnosed, making the scope of the problem difficult to assess. Our current understanding of the incidence of tick-borne diseases is discussed in this review. An awareness of the diseases that can be transmitted by ticks in specific locations is key to detection and selection of appropriate treatment. As tick-transmitted pathogens are discovered and emerge in new geographic regions, our ability to detect, describe, and understand the growing public health threat must also grow to meet the challenge.

Emerging and threatening vector-borne zoonoses in the world and in Europe: a brief update

Climatic changes, landscape management, massive human, animal and commodity transportation represent important factors which are contributing to the spread of zoonotic diseases. The environmental and socioeconomic factors affecting the incidence of vector-borne zoonoses and possibilities for the reduction of disease impacts are discussed in the article. The most important zoonoses with expanding area of incidence and/or increasing occurrence are summarized, with special emphasis on the European region. While some diseases and their respective pathogens are indigenous to Europe (e.g. Lyme disease), others have been introduced to Europe from tropical areas (e.g. chikungunya or dengue fever). These emerging diseases may represent a serious threat in near future and better understanding of their spreading mechanisms, pathogenesis and consequent treatment is very important.

Human Granulocytic Anaplasmosis as a Cause of Febrile Illness in Korea Since at Least 2006

AbstractHuman granulocytic anaplasmosis (HGA) is a tick-borne rickettsial zoonosis with fever, thrombocytopenia, and leukopenia. HGA has been reported in Korea in 2013 but it is uncertain how long it has existed. A retrospective study was conducted on patients who underwent bone marrow examination due to fever and cytopenia, with no clear hematologic or microbiologic causes, from 2003 through 2012. Laboratory diagnosis was made by detecting 16S rRNA genes of Anaplasma phagocytophilum from the stored blood samples. Among the 70 patients, five (7.1%) HGA cases were found, and the earliest case dated back to 2006. Two cases met the diagnostic criteria of hemophagocytic lymphohistiocytosis (HLH) and were fatal. Although HGA has been prevalent in Korea since at least 2006, it is not always diagnosed and has posed a possible lethal health risk to the people in Korea. HGA should be considered as a cause of fever with cytopenia or HLH.

Ticks in the External Auditory Canal

Ticks attack a wide range of vertebrates including humans, and are important vectors of numerous pathogens, e.g. virus, rickettsia, and protozoa. We present a case of ticks found in the external auditory canal. A 12-year-old girl presented to the emergency service with one-day history of right-sided earache. Otological examination found a tick blocking the external auditory canal. The tick was removed under local anaesthesia with a light microscope. After the tick was removed, another tick was detected in the external auditory canal. The second tick was not adhered to the ear canal skin and was mobile. It was also removed completely. The patient's post-procedure course was uneventful. A broad spectrum antibiotic, an analgesic, and an antihistamine were prescribed. Both ticks were sent to the infectious disease laboratory for investigation of Crimean-Congo haemorrhagic fever. They turned out to be Hyalomma species.

Natural history of Ehrlichia chaffeensis: vertebrate hosts and tick vectors from the United States and evidence for endemic transmission in other countries

Ehrlichia chaffeensis, an intracellular gram-negative zoonotic bacterium, is the causative agent of human monocytotropic ehrlichiosis (HME). In humans, the disease can range from a mild, non-specific illness with few to no clinical signs to a moderately severe to fatal disease, especially those with compromised immune systems. E. chaffeensis is maintained in a complex cycle involving white-tailed deer (WTD; Odocoileus virginianus) as a primary reservoir and the lone star tick (LST; Amblyomma americanum) as a primary vector. Numerous other species are naturally exposed to E. chaffeensis and disease has been documented in some domestic animals and wildlife including domestic dogs and ring-tailed lemurs. The organism has been found throughout the natural range of the LST and as the tick continues to expand its range, the geographic range of risk for E. chaffeensis infections will likely continue to expand. Recent data have indicated that E. chaffeensis, or a closely related organism, has been found in many species of ticks and vertebrate hosts in numerous countries.

Tick bites in the external auditory canal

We report a case of Ixodes ovatus tick in the external auditory canal. Chief complaints of earfullness and pruritus appeared after the contact with dog. Using a removal method consisting of excising the abdomen of the tick and suctioning its body fluids, followed by removal of the tick body 3 days later, the patient was successfully treated without the development of complications.

[Human ehrlichiosis]

BACKGROUND

Human ehrlichiosis is a newly recognized disease. It is a tick-borne disease caused by several bacterial species of the genhus Erlichia. These are small gram-negative pleomorphic cocci, that are obligatory intracellular bacteria. Tick Ixodes is the principle vector in Europe, and Amblyomma amenicanum in the United States. Bacterial organisms replicate in a tick, and are transmited from infected cells in a vector to the blood cells of animals or humans. Human ehrlichiosis is a name for a group of diseases caused by different species of Ehrlichia. One of them is the disease named human monocytic ehrlichiosis, caused by Ehrlichia chaffeensis, and the other is a human granulocytic ehrlichiosis caused by Anaplasma phagocytophilia.

CASE REPORT

We reported a 23-year-old patient admitted for the clinical treatment with the symptoms of high febrility (above 40 degrees C), headache, vomiting, general weakness and exhaustion, but without data on a tick bite. The patient was treated with trimetoprim-sulfamethoxazole for a week when Ehrlichia chaffeensis was confirmed by the immunofluoroscence test, and the therapy contimed with doxacyclin.

CONCLUSION

Human ehrlichiosis is also present in our country, so this disease should be considered everyday, especially in infectology practice.

Human granulocytic anaplasmosis in Austria: epidemiological, clinical, and laboratory findings in five consecutive patients from Tyrol, Austria

We report five consecutive cases of Anaplasma (A.) phagocytophilum infection (the causative agent of human granulocytic anaplasmosis (HGA)) from western Austria. All infections were acquired between June and August in 2003 and 2004 in the Inn valley (Tyrol, Austria). Four patients required hospitalisation, one patient was treated as an outpatient. During the acute stage of illness, laboratory findings included thrombocytopenia (5/5), elevated C-reactive protein (5/5), elevated neopterin (5/5), elevated lactate dehydrogenase (4/5), and elevation of liver enzymes (4/5). Leukopenia (3/5) and elevated procalcitonin (2/5) were less frequently observed. All patients were treated with tetracyclines, which led to prompt improvement of the clinical conditions. Anti-platelet antibodies were observed in one of four patients, but remained unchanged after complete covalescence.

Emerging tick-borne infections: rediscovered and better characterized, or truly ‘new’?

The emergence of Lyme borreliosis as a public health burden within the last two decades has stimulated renewed interest in tick-borne infections. This attention towards ticks, coupled with advances in detection technologies, has promoted the recognition of diverse emergent or potentially emerging infections, such as monocytic and granulocytic ehrlichiosis, local variants of spotted fever group rickettsioses, WA-1 babesiosis, or a Lyme disease mimic (Masters' Disease). The distribution of pathogens associated with well-described tick-borne zoonoses such as human babesiosis due toBabesia microtiorB.divergensseems wider than previously thought. Bartonellae, previously known to be maintained by fleas, lice or sandflies, have been detected within ticks. Purported ‘new’ agents, mainly identified by sequencing of PCR products and comparison with those sequences present in GenBank, are being increasingly reported from ticks. We briefly review the diversity of these infectious agents, identify aetiological enigmas that remain to be solved, and provide a reminder about ‘old friends’ that should not be forgotten in our pursuit of novelty. We suggest that newly recognised agents or tick/pathogen associations receive careful scrutiny before being declared as potential public health burdens.

Detection and identification of Ehrlichia spp. in ticks collected in Tunisia and Morocco

A broad-range 16S rRNA gene PCR assay followed by partial sequencing of the 16S rRNA gene was used for the detection of members of the family Anaplasmataceae in ticks in North Africa. A total of 418 questing Ixodes ricinus ticks collected in Tunisia and Morocco, as well as 188 Rhipicephalus ticks from dogs and 52 Hyalomma ticks from bovines in Tunisia, were included in this study. Of 324 adult I. ricinus ticks, 16.3% were positive for Ehrlichia spp., whereas only 3.4 and 2.8% of nymphs and larvae, respectively, were positive. A large heterogeneity was observed in the nucleotide sequences. Partial sequences identical to that of the agent of human granulocytic ehrlichiosis (HGE) were detected in I. ricinus and Hyalomma detritum, whereas partial sequences identical to that of Anaplasma platys were detected in Rhipicephalus sanguineus. However, variants of Anaplasma, provisionally designated Anaplasma-like, were predominant in the I. ricinus tick population in Maghreb. Otherwise, two variants of the genus Ehrlichia were detected in I. ricinus and H. detritum. Surprisingly, a variant of Wolbachia pipientis was evidenced from I. ricinus in Morocco. These results emphasized the potential risk of tick bites for human and animal populations in North Africa.

Characterization of Ehrlichia species from Ixodes ovatus ticks at the foot of Mt. Fuji, Japan

A total of 390 adult ticks (288 Ixodes ovatus and 102 I. persulcatus ) collected at the foot of Mt. Fuji and two near cities in Shizuoka prefecture, Japan, were examined for Ehrlichia infection by isolation with laboratory mice from whole tick tissues. Ehrlichial DNAs were detected from the spleens of mice inoculated with tissues from I. ovatus, but not I. persulcatus. The prevalence of ehrlichiae in the ticks was estimated to be ca. 3%. The 16S rDNA analysis revealed that the sequences of 8 ehrlichial isolates (termed "Shizuoka" isolates) obtained were identical, and they were very similar, but not identical, to those of two Ehrlichia species strain variants recently isolated in Japan, followed by Ehrlichia chaffeensis in the US. Analysis of parts of the omp-1 multigene family specific for monocytic ehrlichiosis agents showed that the Shizuoka isolates were distinct from other ehrlichial organisms. The Shizuoka isolates caused death in immunocompetent laboratory mice, suggesting that they are highly pathogenic in mice. The data show that the Shizuoka isolates are likely to be a new strain variant of Ehrlichia species in Japan. Further characterization and surveillance will be required in Japan due to the presence of these human ehrlichiosis agent-like organisms.

Identification of Ehrlichia chaffeensis, Anaplasma phagocytophilum, and A. bovis in Haemaphysalis longicornis and Ixodes persulcatus ticks from Korea

A total of 1,467 tick (1,463 of Haemaphysalis longicornis, three of Ixodes persulcatus and one of I. turdus) collected from nine provinces of Korea were examined by TaqMan real-time PCR for the presence of Ehrlichia and Anaplasma species. One set of primers and a probe were designed for detection of all of the Ehrlichia and Anaplasma species. Template DNAs (total 803) were prepared either from pools of larvae, nymphs, adult males and females, or from the salivary gland and midgut of adult ticks. Only DNAs positive in TaqMan PCR were examined for A. phagocytophilum with nested PCR and for E. chaffeensis with PCR. Four A. phagocytophilum 16S rRNA gene PCR products were sequenced for comparison with sequences previously reported. Amplification of a 16S rRNA gene fragment of Ehrlichia and Anaplasma species was observed in 364 tick DNAs (45.3% of the total). Of these 364 positive ticks, species-specific PCRs confirmed that 35 H. longicornis and one I. persulcatus were positive for A. phagocytophilum and one I. persulcatus was positive in E. chaffeensis. Except for one (AB-GGHL, GenBank accession number [GAN] AF470698), three of the four 16S rRNA gene fragment sequences of the A. phagocytophilum-positive samples were similar or identical to the sequences of variants of A. phagocytophilum deposited in GenBank. The 16S rRNA gene fragment sequence of AB-GGHL was similar to that of Anaplasma (Ehrlichia) bovis 16S rRNA (GAN U03775). The identities of the Anaplasmataceae genus and species DNA in the 327 ticks that could not be confirmed infected with either E. chaffeensis, A. phagocytophilum, or A. bovis are not known. This study is the first to demonstrate the presence of E. chaffeensis, A. phagocytophilum and A. bovis in Korean ticks.

Candidatus Ehrlichia walkerii: a new Ehrlichia detected in Ixodes ricinus tick collected from asymptomatic humans in Northern Italy

Ixodes ricinus harbors many infectious agents pathogenic for humans. A cause of fever is found in less than 50% of patients exposed to ticks. Investigations on 359 Ixodes ticks removed from asymptomatic patients in Northern Italy revealed the presence of a new ehrlichial agent in 10 ticks. Comparison of the 16S rRNA and the gltA gene sequences showed the organism is most closely related to Ehrlichia ruminantium. We propose this new Ehrlichia be named "candidatus Ehrlichia walkerii."

Ehrlichia chaffeensis: a prototypical emerging pathogen

Ehrlichia chaffeensis is an obligately intracellular, tick-transmitted bacterium that is maintained in nature in a cycle involving at least one and perhaps several vertebrate reservoir hosts. The moderate to severe disease caused by E. chaffeensis in humans, first identified in 1986 and reported for more than 1,000 patients through 2000, represents a prototypical "emerging infection." Knowledge of the biology and natural history of E. chaffeensis, and of the epidemiology, clinical features, and laboratory diagnosis of the zoonotic disease it causes (commonly referred to as human monocytic ehrlichiosis [HME]) has expanded considerably in the period since its discovery. In this review, we summarize briefly the current understanding of the microbiology, pathogenesis, and clinical manifestations associated with this pathogen but focus primarily on discussing various ecological factors responsible for the recent recognition of this important and potentially life-threatening tick-borne disease. Perhaps the most pivotal element in the emergence of HME has been the staggering increases in white-tailed deer populations in the eastern United States during the 20th century. This animal serves as a keystone host for all life stages of the principal tick vector (Amblyomma americanum) and is perhaps the most important vertebrate reservoir host for E. chaffeensis. The contributions of other components, including expansion of susceptible human populations, growth and broadening geographical distributions of other potential reservoir species and A. americanum, and improvements in confirmatory diagnostic methods, are also explored.

Prevalence of IgG antibodies against Borrelia Burgdorferi s.l. and Ehrlichia Phagocytophila in sera of patients presenting symptoms of Lyme disease in a central region of Italy

The aim of this study was to evaluate the prevalence (seroprevalence) of antibodies against Borrelia burgdorferi and Ehrlichia phagocytophila among patients resident in Lazio, a region of central Italy. Of a sample of 1,050 patients, which presented clinical manifestations related to Lyme disease, 34 (3.2%) were Borrelia-seropositive (Lyme index value >/= 1.2). The sera of 25 out of the 34 patients that were Borrelia-positive were also analysed for the presence of antibodies against E. phagocytophila and 3 (12%) were found Ehrlichia-positive (titres >1:64). No Ehrlichia positive samples were found among sera of 250 Borrelia-negative patients. Since both B. burgdorferi s.l. and Ehrlichia species share the same tick vector (Ixodes ricinus), our results indicate that concurrent transmission of these microbial pathogens might have been occurred among the patients included in this study.

Serologic and molecular detection of Ehrlichia chaffeensis and Anaplasma phagocytophila (human granulocytic ehrlichiosis agent) in Korean patients

Sera from 491 Korean patients with acute febrile diseases were tested for Ehrlichia chaffeensis and Anaplasma phagocytophila antibodies by indirect immunofluorescence assay (IFA), Western blotting, and TaqMan real-time PCR. Overall, 0.4% of sera reacted with E. chaffeensis, and 1.8% reacted with A. phagocytophila in IFAs. This is the first report of detection of antibodies to A. phagocytophila and E. chaffeensis in Korea and suggests the presence of A. phagocytophila and E. chaffeensis or antigenically similar species.

Identification of Ehrlichia chaffeensis by nested PCR in ticks from Southern China

A total of 717 ticks collected from southern China were examined by nested PCR for the presence of Ehrlichia chaffeensis. Sixteen (55. 2%) of 29 adult Amblyomma testudinarium ticks and 28 (11.7%) of 240 adult and at least 4.2% of 215 nymphal (pooled specimens) Haemaphysalis yeni ticks tested positive. Four other species of ticks were negative. Selected positive amplicons were confirmed by DNA sequencing.

New Ehrlichia species closely related to Ehrlichia chaffeensis isolated from Ixodes ovatus ticks in Japan

Seven Ehrlichia strains (six HF strains and one Anan strain) that were obtained from laboratory mice by intraperitoneally inoculating homogenates of adult Ixodes ovatus collected in Japan were characterized. 16S rRNA sequences of all six HF strains were identical, and the sequences were 99.7, 98.2, and 97.7% identical to those of Anan strain, Ehrlichia chaffeensis (human monocytic ehrlichiosis agent), and E. muris, respectively. Partial GroEL amino acid sequencing also revealed that the six HF strains had identical sequences, which were 99.0, 98.5, and 97.3% identical to those of E. chaffeensis, the Anan strain, and E. canis, respectively. All HF strains were lethal to mice at higher dosages and intraperitoneal inoculation, whereas the Anan or E. muris strain induced only mild clinical signs. Light and electron microscopy of moribund mice inoculated with one of the HF strains revealed severe liver necrosis and the presence of numerous ehrlichial inclusions (morulae) in various organs. The study revealed that members of E. canis genogroup are naturally present in Ixodes ticks. HF strains that can cause severe illness in immunocompetent laboratory mice would be valuable in studying the pathogenesis and the roles of both cellular and humoral immune responses in ehrlichiosis caused by E. canis genogroup.

Western and dot blotting analyses of Ehrlichia chaffeensis indirect fluorescent-antibody assay-positive and -negative human sera by using native and recombinant E. chaffeensis and E. canis antigens

Human monocytic ehrlichiosis is an emerging infectious disease caused by Ehrlichia chaffeensis, a gram-negative obligatory intracellular bacterium closely related to E. canis. The immunoreactive recombinant fusion proteins rP28 and rP30 have become available after cloning and expressing of the 28- and 30-kDa major outer membrane protein genes of E. chaffeensis and E. canis, respectively. Western immunoblotting was performed to analyze the antibody responses of the 37 E. chaffeensis indirect fluorescent-antibody assay (IFA)-positive and 20 IFA-negative serum specimens with purified whole organisms, rP28, and rP30. All IFA-negative sera were negative with purified whole organisms, rP28, or rP30 by Western immunoblot analysis (100% relative diagnostic specificity). Of 37 IFA-positive sera, 34 sera reacted with any native proteins of E. chaffeensis ranging from 44 to 110 kDa, and 30 sera reacted with 44- to 110-kDa native E. canis antigens. The 28-kDa E. chaffeensis and 30-kDa E. canis native proteins were recognized by 25 IFA-positive sera. Fifteen IFA-positive sera reacted with rP28 by Western blot analysis, whereas 34 IFA-positive sera reacted with rP30 (92% relative diagnostic specificity), indicating that rP30 is more sensitive than rP28 for detecting the antibodies in IFA-positive sera. These 34 IFA-positive sera were positive by the dot blot assay with rP30, distinguishing them from IFA-negative sera. Except for three rP30-negative but IFA-positive specimens that instead showed an E. ewingii infection-like profile by Western immunoblotting, the results of Western and dot blot assays with rP30 matched 100% with the IFA test results. Densitometric analysis of dot blot reactions showed a positive correlation between the dot density and the IFA titer. These results suggest that rP30 antigen would provide a simple, consistent, and rapid serodiagnosis for human monocytic ehrlichiosis.

Detection and identification of Ehrlichia, Borrelia burgdorferi sensu lato, and Bartonella species in Dutch Ixodes ricinus ticks

A sensitive and specific PCR hybridization assay was developed for the simultaneous detection and identification of Ehrlichia and Borrelia burgdorferi sensu lato. In separate assays the 16S rRNA gene of Ehrlichia species and the 23S-5S rRNA spacer region of B. burgdorferi sensu lato were amplified and labeled by PCR. These PCR products were used in a reverse line blot hybridization assay in which oligonucleotide probes are covalently linked to a membrane in parallel lines. Hybridization of the samples with the oligonucleotide probes on this membrane enabled the simultaneous detection and identification of Ehrlichia, B. burgdorferi, and Bartonella species in 40 different samples. The application of the assay to DNA extracts from 121 Ixodes ricinus ticks collected from roe deer demonstrated that 45% of these ticks carried Ehrlichia DNA. More than half of these positive ticks carried species with 16S rRNA gene sequences closely related to those of E. phagocytophila and the human granulocytic ehrlichiosis agent. The majority of the other positive ticks were infected with a newly identified Ehrlichia-like species. In addition, 13% of the ticks were infected with one or more B. burgdorferi genospecies. In more than 70% of the ticks 16S rRNA gene sequences for Bartonella species or other species closely related to Bartonella were found. In five of the ticks both Ehrlichia and B. burgdorferi species were detected.

Ehrlichia chaffeensis and E. sennetsu, but not the human granulocytic ehrlichiosis agent, colocalize with transferrin receptor and up-regulate transferrin receptor mRNA by activating iron-responsive protein 1

Ehrlichia chaffeensis and E. sennetsu are genetically divergent obligatory intracellular bacteria of human monocytes and macrophages, and the human granulocytic ehrlichiosis (HGE) agent is an obligatory intracellular bacterium of granulocytes. Infection with both E. chaffeensis and E. sennetsu, but not HGE agent, in the acute monocytic leukemia cell line THP-1 almost completely inhibited by treatment with deferoxamine, a cell-permeable iron chelator. Transferrin receptors (TfRs) accumulated on both E. chaffeensis and E. sennetsu, but not HGE agent, inclusions in THP-1 cells or the cells of the promyelocytic leukemia cell line HL-60. Reverse transcription-PCR showed an increase in the level of TfR mRNA 6 h postinfection which peaked at 24 h postinfection with both E. chaffeensis and E. sennetsu infection in THP-1 or HL-60 cells. In contrast, HGE agent in THP-1 or HL-60 cells induced no increase in TfR mRNA levels. Heat treatment of E. chaffeensis or the addition of monodansylcadaverine, a transglutaminase inhibitor, 3 h prior to infection inhibited the up-regulation of TfR mRNA. The addition of oxytetracycline 6 h after E. chaffeensis infection caused a decrease in TfR mRNA which returned to the basal level by 24 h postinfection. These results indicate that both internalization and continuous proliferation of ehrlichial organisms or the production of ehrlichial proteins are required for the up-regulation of TfR mRNA. Results of electrophoretic mobility shift assays showed that both E. chaffeensis and E. sennetsu infection increased the binding activity of iron-responsive protein 1 (IRP-1) to the iron-responsive element at 6 h postinfection and remained elevated at 24 h postinfection. However, HGE agent infection had no effect on IRP-1 binding activity. This result suggests that activation of IRP-1 and subsequent stabilization of TfR mRNA comprise the mechanism of TfR mRNA up-regulation by E. chaffeensis and E. sennetsu infection.

Serologic evidence of human monocytic and granulocytic ehrlichiosis in Israel

We conducted a retrospective serosurvey of 1,000 persons in Israel who had fever of undetermined cause to look for Ehrlichia chaffeensis antibodies. Four of five cases with antibodies reactive to E. chaffeensis were diagnosed in the summer, when ticks are more active. All patients had influenzalike symptoms with high fever. None of the cases was fatal. Three serum samples were also seroreactive for antibodies to E. canis, and one was also reactive to the human granulocytic ehrlichiosis (HGE) agent. The titer to the HGE agent in this patient was higher than the serum titer to E. chaffeensis, and the Western blot analysis also indicated that the HGE agent was the primary cause of infection. We present the first serologic evidence that the agents of human monocytic ehrlichiosis (HME) and HGE are present in Israel. Therefore, human ehrlichiosis should be included in the differential diagnoses for persons in Israel who have been exposed to ticks and have influenzalike symptoms.

Emerging and resurging vector-borne diseases

Over the last four decades, a number of arthropod-borne infections have been recognized for the first time. Some have become of considerable public health importance, such as dengue hemorrhagic fever (DHF), and others are spreading geographically and their incidence is increasing. There has been an important recrudescence of several long-known vector-borne diseases. Malaria, leishmaniasis, dengue, and plague have resurged in numerous foci, in some cases where they were thought to be under effective control. In most instances, the appearance of new diseases and syndromes and the resurgence of old can be associated with ecological changes that have favored increased vector densities. Dam construction, irrigation and other development projects, urbanization, and deforestation have all resulted in changes in vector population densities that appear to have enabled the emergence of new diseases and the resurgence of old diseases. Greatly increased human travel has spread infectious agents, introducing them into areas in which they had been hitherto absent. It is essential to understand the factors that caused increased vector densities and hence the transmission of disease to prevent the emergence and resurgence of more diseases, as well as to serve as a basis for effective control.

Immunoserologic evidence of Human Granulocytic Ehrlichiosis in Danish patients with Lyme neuroborreliosis

Human Granulocytic Ehrlichiosis (HGE) is a recently described human illness in the US which manifests as fever, myalgia and headache combined with pancytopenia and elevated concentrations of hepatic transaminases. Genetic analyses indicate that the agent of HGE appears to be an Ehrlichia species that is closely related to E. equi and E. phagocytophila. Ixodes dammini and I. scapularis were identified as potential vectors of HGE. Ixodes ticks are also the vector of Borrelia burgdorferi, the agent of Lyme borreliosis. The presence of antibodies against Ehrlichia in 132 sera from Danish patients with definite Lyme neuroborreliosis were examined in order to provide immunoserologic evidence of this infection in Denmark. Patients with Lyme neuroborreliosis were chosen as a test cohort, as these patients had been infested by a tick sufficient for transmission of B. burgdorferi. All had cerebrospinal fluid lymphocytic pleocytosis. As controls, serum samples from 50 healthy Danish blood donors were included. Of the 132 patients with Lyme neuroborreliosis, 5 (3.8%) reacted with the E. equi antigen substrate at titres 1:128. None of the blood donors were found seropositive for E. equi. At least 2 of the patients found seropositive for HGE constituted probable cases of HGE with E. equi antibody titres of at least 80 combined with fever, headache and myalgias. However, in no cases were we able to detect the presence of the HGE agent in the serum by PCR. We conclude that human exposure to granulocytic Ehrlichiae species may also occur in Europe, although further studies will be necessary to document active infection with these potential pathogens.

Borrelia burgdorferi s.l. and Ehrlichia chaffeensis in the National Park of Abruzzo

The aims of the present study were (a) to determine the presence of Ixodes ricinus in three different areas of the National Park of Abruzzo; (b) to search for the presence of Borrelia burgdorferi in the collected sample of Ixodes; (c) to determine the seroprevalence of B. burgdorferi antibodies and E. chaffeensis antibodies in inhabitants of the park and in park workers. The presence of B. burgdorferi in Ixodes was checked by PCR. For the detection of antibodies to B. burgdorferi all sera were assayed by ELISA as screening test and by Western blot as confirmatory test. For the detection of antibodies to E. chaffeensis all sera were assayed by IFA. Antibodies to B. burgdorferi were present in 9.1% of the park workers, 4.5% were confirmed positive by the IgG Western blot test. None of the inhabitants of the park was positive. Antibodies against E. chaffeensis were found in 4.5% of the park workers and 8% of the inhabitants of the park. The results obtained in the collecting of the ticks seem to show that the presence of I. ricinus in the park territory is rather discontinuous and small in number, therefore it is not epidemiologically significant for the transmission of B. burgdorferi sensu lato. Serological study for Ehrlichia revealed a high frequency of E. chaffeensis antibodies in the park inhabitants and a lower prevalence in the park workers.

Ehrlichiosis

HGE and HME have been recognized as distinct clinical conditions for only 5 and 10 years, respectively, and much information regarding their ecology and epidemiology remains uncertain. The nonspecific character of the illness complicates this incomplete knowledge, as an unknown percentage of infections are likely misdiagnosed. Ehrlichiosis should be considered in any patient presenting with flu-like illness and history of a tick bite. Although expanding, diagnostic support for human ehrlichioses is currently limited to a few regional academic and public health laboratories. Healthcare providers should educate themselves regarding the clinical presentation of ehrlichioses and the availability of diagnostic resources in their area.

Human disease in Europe caused by a granulocytic Ehrlichia species

Human granulocytic ehrlichiosis (HGE) was recently described in North America. It is caused by an Ehrlichia species closely related to Ehrlichia phagocytophila and Ehrlichia equi, recognized to infect mostly ruminants and horses, respectively. The vector in North America is the tick Ixodes scapularis, which is also the vector of the Lyme disease agent, Borrelia burgdorferi. Previous serologic studies in patients with a diagnosis of Lyme borreliosis indicate that HGE may exist in Europe. We report the first documented case of HGE in Europe. The diagnosis was established by seroconversion to E. equi and the HGE agent and by PCR with sequence analysis of the gene encoding the HGE agent 16S rRNA. Interestingly, the patient presented with a self-limited but moderately severe illness. Thus, European physicians need to be aware that HGE exists in Europe and that the diagnosis should be considered in febrile patients with tick bites in areas where Lyme disease is endemic.

Ehrlichia chaffeensis inclusions are early endosomes which selectively accumulate transferrin receptor

Ehrlichia chaffeensis is an obligatory intracellular bacterium which infects macrophages and monocytes. Double immunofluorescence labeling was used to characterize the nature of E. chaffeensis inclusion in the human promyelocytic leukemia cell line THP-1. E. chaffeensis was labeled with dog anti-E. chaffeensis serum and fluorescein isothiocyanate-conjugated anti-dog immunoglobulin G (IgG). Lissamine rhodamine-conjugated anti-mouse IgG was used to label various mouse monoclonal antibodies. Ehrlichial inclusions did not fuse with lysosomes, since they were not labeled with anti-CD63 or anti-LAMP-1. The ehrlichial inclusions were slightly acidic, since they weakly accumulated 3-(2,4-dinitroanilino)-3'-amino-N-methyldipropylamine and stained weakly positive for vacuolar type H+ ATPase. Some ehrlichial inclusions were labeled positive with antibodies against HLA-DR, HLA-ABC, and beta2 microglobulin, while other inclusions in the same cell were labeled negative. The inclusions were labeled strongly positive for transferrin receptors (TfRs) and negative for the clathrin heavy chain. Time course labeling for TfRs showed that up to 3 h postinfection, most of the ehrlichial inclusions were negative for TfRs. After 6 h postinfection, 100% of the ehrlichial inclusions became TfR positive and the intensity of labeling was increased during the subsequent 3 days. Reverse transcription-PCR showed a gradual increase in the level of TfR mRNA postinfection, which reached a peak at 24 h postinfection. These results suggest that ehrlichial inclusions are early endosomes which selectively accumulate TfRs and that the ehrlichiae up-regulate TfR mRNA expression.

Clinical features and serology of 14 dogs affected by granulocytic ehrlichiosis in Sweden

The clinical features and the titres to Ehrlichia equi, E canis, E risticii, Rickettsia rickettsii and Borrelia afzelii in 14 Swedish dogs, in which ehrlichiosis was diagnosed on the basis of the presence of inclusions in granulocytes, are reported. Most of the dogs were moderately ill but made a rapid recovery after treatment with doxycycline. The dogs with inclusions were thrombocytopenic. Analysis of the antibody titres indicates that serology to E equi will remain the most appropriate serological test for granulocytic ehrlichiosis in Swedish dogs, until a specific test is developed for detecting the recently identified subspecies of Ehrlichia.

Cloning and sequencing of the gene for a 120-kDa immunodominant protein of Ehrlichia chaffeensis

Ehrlichia chaffeensis is the tick-borne, obligately intracellular bacterium that causes human monocytic ehrlichiosis. A 120-kDa protein is one of the immunodominant proteins of E. chaffeensis that stimulates production of specific antibodies in infected humans. A genomic library of E. chaffeensis was constructed in a lambda ZAP II phage vector, and a clone expressing the 120-kDa protein of E. chaffeensis was identified using canine anti-E. chaffeensis serum. DNA sequence analysis of the cloned 120-kDa protein gene of E. chaffeensis identified a 1884-bp open reading frame with an ehrlichial promoter. Five identical 240-bp tandem repeat units were identified in the 120-kDa protein gene of E. chaffeensis, comprising 60% of the entire gene. Aside from the first repeat unit, all the other repeat units are identical. In the first repeat unit there are four nucleotides that are different from the other repeats. Hydropathy analysis of the deduced amino-acid sequence demonstrated that the repeat domain contains highly hydrophilic segments. The 120-kDa protein should be evaluated for a role in stimulating protective immunity.

Absence of tumor necrosis factor alpha, interleukin-6 (IL-6), and granulocyte-macrophage colony-stimulating factor expression but presence of IL-1beta, IL-8, and IL-10 expression in human monocytes exposed to viable or killed Ehrlichia chaffeensis

Ehrlichia chaffeensis is a recently isolated minute gram-negative obligatory intracellular bacterium of monocytes/macrophages and is the etiologic agent of human monocytic ehrlichiosis. It is not known how macrophages respond when they encounter ehrlichiae in terms of cytokine production. In this study, we examined cytokine mRNA expression by incubating E. chaffeensis with THP-1 cells and performing competitive reverse transcription-PCR (RT-PCR). At 2 h postinfection, the levels of interleukin-1beta (IL-1beta), IL-8, and IL-10 mRNAs were significant but lower than those following Escherichia coli lipopolysaccharide (LPS) stimulation. Unlike the situation with E. coli LPS stimulation, however, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF), and tumor necrosis factor alpha (TNF-alpha) mRNAs were not induced. Time course and dose-response studies confirmed the absence of IL-6, GM-CSF, and TNF-alpha mRNA induction with E. chaffeensis. Viable E. chaffeensis organisms were not required for IL-1beta IO, IL-8, and IL-10 mRNA induction, since heat-killed E. chaffeensis induced identical time course responses. IL-1beta, IL-8, and IL-10 mRNAs were detected for up to 21, 21, and 24 h postexposure with E. chaffeensis, respectively, which were shut off more rapidly than with LPS stimulation. Although heat treatment of E. chaffeensis had no effect, periodate treatment completely abolished the ability of E. chaffeensis to induce IL-1beta, IL-8, and IL-10 mRNAs. The capture enzyme-linked immunosorbent assay result corresponded with the RT-PCR results, showing that viable and heat-killed E. chaffeensis produced and secreted the same levels of IL-1beta and IL-8. IL-10 production was significantly reduced by heat treatment. Periodate-treated ehrlichiae did not induce production of any of the cytokines tested. Anti-CD14 monoclonal antibody and polymyxin B did not inhibit IL-1beta mRNA expression upon exposure to E. chaffeensis. The absence of TNF-alpha, IL-6, and GM-CSF mRNA induction may delay the development of a protective immune response, thereby allowing E. chaffeensis to set up residence in macrophages.

Emergence of the ehrlichioses as human health problems

Ehrlichiae are small, gram-negative, obligately intracellular bacteria that reside within a phagosome. The first human ehrlichial infection was recognized in the United States in 1987. It was later shown to be caused by a new species, Ehrlichia chaffeensis. In 1994, an ehrlichial pathogen within neutrophils that is closely related to the known veterinary pathogens E. equi and E. phagocytophila was found to infect humans. Molecular methods were required to detect, characterize, and identify these fastidious and uncultivated bacteria. Subsequently, E. chaffeensis infection was documented in more than 400 patients in 30 states, Europe, and Africa. Likewise, approximately 170 cases of human granulocytic ehrlichiosis have been diagnosed, most since 1994, predominantly in the upper midwestern and northeastern states, but also in northern California. The disease caused by ehrlichiae is generally undifferentiated but is often associated with leukopenia, thrombocytopenia, and elevated serum hepatic transaminase levels in tick-exposed patients. Infection ranges from subclinical to fatal; tetracycline appears to be an effective therapy. The emergence of these two newly recognized tickborne infections as threats to human health is probably due to increased clinical cognizance, but as in other emerging tickborne infections, it is likely that the rapid increase in identified cases signals a true emergence of disease associated with a changing vector-host ecology.

Ehrlichiosis mimicking thrombotic thrombocytopenic purpura. Case report and pathological correlation

Human ehrlichiosis is a tick-borne zoonosis caused by the newly described human hematotropic rickettsiae, Ehrlichia chaffeensis. The pathology and pathogenesis of human ehrlichiosis have not been adequately studied. Even with immunoperoxidase, the only previously known method to detect these organisms in tissue, ehrlichae are difficult or impossible to identify. This led many investigators to speculate that the pathogenesis of ehrlichiosis was not caused directly by the organism but could be caused by host-mediated injury. In this case study, a patient presented with rapidly progressive central nervous system symptoms and severe thrombocytopenia, prompting a presumptive diagnosis of thrombotic thrombocytopenic purpura (TTP). Despite corticosteroids, and later, antibiotics, the patient rapidly deteriorated and died. Postmortem examination showed hemorrhages in multiple organs and mononuclear inclusions of infection with a monocytic ehrlichia. Other findings included widespread lymphohistiocytic perivascular infiltrates, focal hepatic necroses, interstitial pneumonitis, interstitial nephritis, mononuclear phagocyte invasion and proliferation in splenic, liver, and bone marrow, and hemophagocytosis. The diagnosis was proven by serology, immunohistology with both polyclonal and monoclonal anti E chaffeensis, and polymerase chain reaction on paraffin-embedded tissues using E chaffeensis-specific oligonucleotide primers. The presence of numerous ehrlichia with notable tissue and cellular injury but without a marked host response indicate that unlike other cases of documented human ehrlichiosis, this patient died after significant direct ehrlichia-mediated injury, and that immune mechanisms initiated after ehrlichiosis played little if any role in the pathogenesis.

Cultivation of Ehrlichia chaffeensis in mouse embryo, Vero, BGM, and L929 cells and study of Ehrlichia-induced cytopathic effect and plaque formation

We successfully propagated Ehrlichia chaffeensis in mouse embryo, Vero, BGM, and L929 cells inoculated with host cell-free ehrlichiae, indicating that E. chaffeensis is capable of entry, survival, and growth in a relatively wide range of cell types derived from different species. We demonstrated rapid adaptation of E. chaffeensis in these cell lines, so that typical morulae could be detected as early as 5 days after inoculation. E. chaffeensis-induced cytopathic effect with different morphological characteristics in mouse embryo, Vero, and L929 cells. The earliest cytopathic effect appeared in untreated and irradiated mouse embryo cells at 4 days postinoculation. As the infected foci gradually expanded, the center of the foci showed necrotic cells with pyknotic nuclei and degraded morulae. E. chaffeensis caused cell lysis in untreated and irradiated L929 cells, with formation of distinct, round macroscopic plaques at 18 days postinoculation. In untreated and irradiated Vero cells, E. chaffeensis produced infected foci composed of loosely interwoven necrotic cells, spaces of detached cells, cells filled with morulae, and uninfected cells, resulting in characteristic reticular foci. Irradiated cells generally contained many large morulae and presented larger cytopathic foci. DH82 and BGM cells did not develop obvious cytopathic foci under the conditions employed. The findings reported herein offer the opportunity to study the pathogenic mechanism of cell injury by E. chaffeensis, the basis for quantification of infectious E. chaffeensis, improved approaches for recovery of ehrlichiae from human patients and tick hosts, and additional methods for cultivation of E. chaffeensis for molecular analysis.

Serologic evidence for human ehrlichiosis in Africa

Human ehrlichiosis is a recently recognized rickettsial disease. It is caused by Ehrlichia chaffeensis, an intraleucocytic Gram-negative, obligate intracellular bacterium, grouped within the genus Ehrlichiae. Most human cases of ehrlichiosis have been diagnosed in the USA. Two cases have been reported outside of the USA, one in Europe and one in Africa. From 1 January to 30 June 1992, 765 sera from blood donors or other asymptomatic subjects in 8 African countries, including Ivory Coast, Burkina Faso, Mali, Central African Republic, Angola, Zimbabwe, Mozambique and Commores Islands, were tested by indirect immunofluorescence for the presence of E. chaffeensis antibodies. Positive sera were confirmed by Western immunoblotting. Only two of 765 sera tested were positive. One serum obtained from Burkina Faso had an IgG titer of 1:200 and one from Mozambique had an IgG titer of 1:80. Human ehrlichiosis seems to occur infrequently in Africa, although many more sera from additional African countries need to be evaluated.

Abrogation of gamma interferon-induced inhibition of Ehrlichia chaffeensis infection in human monocytes with iron-transferrin

Ehrlichia chaffeensis is an obligate intracellular bacterium which infects cells of the macrophage/monocyte lineage. To test whether gamma interferon (IFN-gamma) inhibits infection of monocytes with E. chaffeensis, human peripheral blood monocytes were incubated with recombinant human IFN-gamma for 3 h and then exposed to E. chaffeensis. With 2,000 U of IFN-gamma per ml, maximal inhibition of infection by E. chaffeensis was observed. THP-1 cells, a human monocyte cell line, pretreated with phorbol myristic acetate or not pretreated, were incubated with various concentrations of IFN-gamma. Maximum inhibition was obtained at 1,000 U of IFN-gamma per ml with phorbol myristic acetate-treated THP-1 cells. However, nontreated cells did not achieve a similar level of anti-ehrlichial activity even with 10,000 U of IFN-gamma per ml. IFN-gamma given within 6 h postinfection was effective in inhibiting E. chaffeensis. Nitric oxide production was not demonstrated in the monocyte medium incubated with IFN-gamma and E. chaffeensis. None of the reactive oxygen intermediate scavengers tested blocked the IFN-gamma-induced anti-ehrlichial activity. Deferoxamine, an intracellular iron chelator, at 15 microM completely inhibited the survival of E. chaffeensis. Iron-saturated transferrin at 1.67 mg/ml completely reversed the IFN-gamma-induced ehrlichial killing. These results indicate that (i) E. chaffeensis is sensitive to intracytoplasmic iron depletion, (ii) E. chaffeensis is sensitive to IFN-gamma-induced killing, and (iii) the anti-ehrlichial activity induced in human monocytes by IFN-gamma is mediated by limitation of available cytoplasmic iron and is not due to the generation of reactive oxygen intermediates or nitric oxide.

Detection of Ehrlichia chaffeensis in human tissue by using a species-specific monoclonal antibody

A mouse monoclonal antibody (MAb 1A9) was produced and used in detection of Ehrlichia chaffeensis in human tissues including kidney, liver, and lung by using an indirect immunohistologic stain. MAb 1A9 was specific to E. chaffeensis and did not react with other bacteria, including Ehrlichia canis, which is the organism most closely related to E. chaffeensis. It reacted with an epitope present in two surface proteins of E. chaffeensis with molecular masses of 29 and 27 kDa. E. chaffeensis was easily detected in human tissue by immunohistology with MAb 1A9. This study demonstrates that our MAb can provide a specific and simple method for detection of E. chaffeensis in clinical specimens for establishing an etiologic diagnosis of human ehrlichiosis; it may also provide a tool for the investigation of immunopathologic characteristics in infected patients.

Human ehrlichiosis: hematopathology and immunohistologic detection of Ehrlichia chaffeensis

Human ehrlichiosis is a recently described zoonosis caused by a rickettsia that infects leukocytes. Most patients have fever, headache, chills, and myalgias and develop leukopenia, thrombocytopenia, anemia, and elevations in serum hepatic aminotransferases. The cause of the peripheral leukopenia and thrombocytopenia is not known. We studied peripheral blood smears, bone marrow aspirates, and bone marrow biopsy specimens from patients with serologically proven ehrlichiosis to characterize the pathologic changes associated with leukopenia or thrombocytopenia, to detect the presence of immunohistologically demonstrable ehrlichiae, and to establish the infected host target cell(s). Specimens were obtained from 12 patients, and immunohistology for Ehrlichia chaffeensis was performed on tissue sections, aspirated bone marrow, and peripheral blood smears. Mean leukocyte and platelet counts available for nine patients were white blood cell count 3,300/microL (range, 1,100 to 10,300/microL) and platelets 61,000/microL (range, 40,000 to 82,000/microL). Findings included myeloid hyperplasia (eight cases), megakaryocytosis (seven cases), granulomas (eight cases), marrow histiocytosis (one case), myeloid hypoplasia (one case), pancellular hypoplasia (one case), and normocellular marrow (two cases). Morulae of E chaffeensis were detected in four of 10 cases examined by immunohistology. Most ehrlichiae were detected within histiocytes, although morulae were rarely present within lymphocytes. Leukopenia, thrombocytopenia, or pancytopenia apparently most often results from peripheral sequestration or destruction; however, hypoplasia of marrow elements is present occasionally. Immunohistologic demonstration of E chaffeensis offers a direct means for establishing the etiologic diagnosis. These observations show the relatively frequent occurrence of bone marrow granulomas and suggest that infection of cells of the reticuloendothelial system may participate in the pathogenesis of human ehrlichiosis.

Antigenic characterization of ehrlichiae: protein immunoblotting of Ehrlichia canis, Ehrlichia sennetsu, and Ehrlichia risticii

In recent years a febrile illness apparently associated with tick bite in patients in the United States has been attributed to infection by an Ehrlichia species. This implication is based on serologic responses to E. canis, morphologic demonstration of ehrlichiae in clinical materials, and a single isolate distinct from E. canis which was obtained from a human patient by the Centers for Disease Control. Little is known about the antigens of the ehrlichiae. This report expands the breadth of available knowledge concerning the antigenic components and serologic responses to component antigens of E. canis, E. sennetsu, and E. risticii. Protein immunoblotting after sodium dodecyl sulfate-polyacrylamide gel electrophoresis by using density gradient-purified ehrlichiae and homologous antisera demonstrated reproducible and characteristic antigens within each species (for E. sennetsu, 91, 64, 54, 44, 36, 34, 28, 25, and 24 kDa; for E. risticii, 70, 52, 48, 44, 35, 28, 24, 23, and 20 kDa; for E. canis, 110, 64, 52, 42, 33, 28, 24, 23, and 20 kDa). When antisera were reacted with heterologous antigens, cross-reactivity among these species was virtually restricted to the 70-kDa antigen. Furthermore, when serum samples obtained from 10 patients who were convalescing from ehrlichiosis were tested against each antigen, only three serum samples had any reactivities, and these serum samples reacted with only a few of the antigenic bands. These results documented the molecular sizes of electrophoretically separated antigens of the three Ehrlichia species, confirm their serologic relationships, and support the novel nature of the agent(s) of human ehrlichiosis in the United States.