我国犬埃立克体病研究现状

犬埃立克体病是由严格细胞内寄生的埃立克体所致的疾病。目前,我国已经发现的犬埃立克体病原有犬埃立克体(Ehrlichia)和扁平埃立克体(E.platy)两种。我国已发现的犬埃立克体病均为E.canis和E.platy的混合感染。临床症状包括发热、体重严重减轻、流鼻血和腹泻带血等;白细胞和血小板计数同时下降是我国犬埃立克体病的特点;严重的病犬常因广泛性出血或继发感染而死亡。犬埃立克体病的病原学诊断主要依靠镜检、血清学试验和PCR等。犬血清埃立克体抗体的调查结果表明,我国犬埃立克体病的流行与蜱活动密切相关。四环素类抗生素是治疗犬埃立克体病的有效药物。     

比格犬埃立克体病实验模型研究Ⅲ病原观察

为了观察犬埃立克体病病犬血细胞中病原的感染情况,对6只人工感染埃立克体的比格犬血细胞进行了光镜和透射电镜观察.结果发现,单核细胞的细胞质和血小板中均存在埃立克体包涵体,其中单核细胞的包涵体内病原多达8个,血小板的包涵体内也发现数个病原.这一结果进一步证实我们成功地建立了比格犬埃立克体病实验模型,也为临床上诊断犬埃立克体病提供了形态学依据.     

我国犬埃立克体病病原的分离与鉴定——Ⅰ.病原16SrRNA基因序列测定与分析

用实验动物接种法,分离保存我国某养犬基地犬埃立克体病病原。以此病原对易感犬接毒,接毒犬发病后采集急性期全血提取基因组,对病原 １６ Ｓｒ Ｒ Ｎ Ａ 基因进行扩增、克隆测序。结果,病原被保存在病犬血细胞内,并能成功地使健康犬感染发病;检测到的 ２ 种致犬埃立克体病病原 １６ Ｓ ｒ Ｒ Ｎ Ａ 基因序列与国外已发现的相应病原基因序列有一定差异,显示其为不同菌株,分别命名为埃立克体 Ｇｚｈ ９８１ 株和 Ｇｚｈ９８２ 株。进一步分析表明,导致我国某养犬基地犬埃立克体病的病原为扁平埃立克体和犬埃立克体。     

我国犬埃立克体病病原分离与鉴定Ⅲ.病原的电镜观察

对埃立克体感染犬的单核细胞和血小板进行了透射电镜观察，结果表明，单核细胞的细胞质和血小板中均存在埃立克体包涵体，其中单核细胞的包涵体内病原多达８个，血小板的包涵体内至少有３个病原。这一结果从形态学角度进一步证实了引起了广州市郊栽养犬基地流行犬埃立克体病的病原为２处，即感染单核细胞的犬埃立克体（Ｅｈｒｌｉｃｈｉａ ｃａｎｉｓ）和感染血小板的扁平埃立克体（Ｅ．ｐｌａｔｙｓ）。     

比格犬埃立克体病实验模型的建立

为犬埃立克体病的病理学、临床学、病原学的深入研究，我们用Beagle(比格犬）复制犬埃立克体病以建立犬埃立克体病实验模型。比格犬静脉接种E.platy和E.canis后，利用PCR和电镜技术确证感染成功。进一步的观察发现，接种后比格犬与最最感的德国牧羊犬自然感染埃立克体病的临床症关放病理学变化基本吻合。结果说明通过静脉接种病原成功建立了比格犬埃立克体病实验模型。     

比格犬埃立克体病实验模型研究Ⅰ.血常规及血生化检测

为观察犬埃立克体病急性期血液学变化,对6只人工感染埃立克体的比格犬进行了血常规及血生化检测.采集比格犬感染前后的血液样本,测定血常规及各项血生化指标,并对测定结果作统计学处理.血常规检测发现感染后RBC、WBC、HGB、HCT、PLT、MPV、LYM和MONO值极显著降低(P＜0.01),RDW显著降低(P＜0.05);血生化检测发现感染后ALT和AST极显著升高(P＜0.01),ALB极显著降低(P＜0.01).结果表明,我国犬埃立克体病急性期血液学变化较国外报道的更为明显,这可能与埃立克体中国病原株的致病性不同有关.     

犬埃立克体实验模型初步研究

将犬埃立克体标准毒株（Florida株）体外细胞纯培养物和我国犬埃立克体病病犬血白细胞分别接种于C3H小鼠，接毒后d，经PCR检测证实均感染成功。本试验为犬埃立克体病小动物模型的建立打下了基础。     

应用PCR检测犬埃立克体病的研究

用已确证为扁平埃立克体（Ehrlichia platys)和犬埃立克体（E.canis）混合感染的犬全血对6只格犬进行人工感染，通过对其临床症状，血流学变化，血涂片包涵体观察，并将其PCR结果与后来确诊为犬埃立克体病的18只病犬血的PCR结果比较，表明PCR方法能够对早期犬埃立克体病做出准确诊断。     

比格犬埃立克体病实验模型研究及治疗试验

犬埃立克体病是由严格细胞内（白细胞或血小板）寄生的革兰氏阴性球杆菌一埃立克体引起的犬的急（慢）性传染病，也是一种人兽共患自然疫源性疾病。由于埃立克体主要对白细胞和脾脏等造成损伤，病犬表现为免疫力低下、极度消瘦，犬埃立克体病也被称为犬的艾滋病。犬埃立克体病是全球分布性疾病，蜱为其主要传播媒介。到目前为止，已从自然感染病犬体内分离到4种埃立克体，即犬埃立克体、尤因埃立克体、血小板埃立克体和立氏埃立克体。犬埃立克体和血小板埃立克体已被证实是引起我国犬埃立克体病的病原体。     

比格犬埃立克体病试验观察及盐酸强力霉素治疗研究

作者研究了比格犬埃立克体病试验模型及盐酸强力霉素对犬埃立克体病的疗效。 结果表明，临床症状表现为急性发热、皮肤表面出现瘀血斑点，个别犬出现血便和血尿；姬姆萨染色血液涂片可见白细胞数稀少，单核细胞内有病原包涵体；血常规检查可见发病急性期血红蛋白含量和白细胞数较接种前相比显著减少；血液生化检测发现谷草转氨酶和谷丙转氨酶较接种前明显升高，而白蛋白明显降低；病理组织学观察发现淋巴结、脾脏、肝脏病变最为显著；试验再次证实强力霉素对犬埃立克体病的疗效是确定的。     

Tick- and flea-borne rickettsial emerging zoonoses

Between 1984 and 2004, nine more species or subspecies of spotted fever rickettsiae were identified as emerging agents of tick-borne rickettsioses throughout the world. Six of these species had first been isolated from ticks and later found to be pathogenic to humans. The most recent example is Rickettsia parkeri, recognized as a human pathogen more than 60 years after its initial isolation from ticks. A new spotted fever rickettsia, R. felis was also found to be associated with fleas and to be a human pathogen. Similarly, bacteria within the family Anaplasmataceae have been considered to be of veterinary importance only, yet three species have been implicated in human diseases in recent years, including Ehrlichia chaffeensis, the agent of human monocytic ehrlichiosis, Anaplasma phagocytophilum, the agent of human anaplasmosis (formerly known as "human granulocytic ehrlichiosis agent", E. equi and E. phagocytophila), and finally Ehrlichia ewingii, which causes granulocytic ehrlichiosis in humans. We present here an overview of the various tick- and flea-borne rickettsial zoonoses described in the last 20 years, focusing on the ecological, epidemiological and clinical aspects.     

Ehrlichial infection in Cameroonian canines by Ehrlichia canis and Ehrlichia ewingii

Ehrlichia chaffeensis and Ehrlichia ewingii are agents of emerging human ehrlichioses in North America and are transmitted primarily by Amblyomma americanum ticks, while Ehrlichia canis is the globally distributed cause of canine monocytic ehrlichiosis (CME) and is transmitted by the brown dog tick, Rhipicephalus sanguineus. Although E. canis and Ehrlichia ruminantium are endemic in Africa, the presence of ehrlichial agents in dogs and ticks in Cameroon has not been investigated. The objective of this study was to determine the prevalence of ehrlichial infections in Cameronian dogs using a combination of serologic and molecular methods. Peripheral blood was collected, clinical signs and the presence or absence of ticks on dogs (n=104) presenting for various reasons at local veterinary clinics around the Mount Cameroon region were noted. IFA identified 33 dogs (32%) with antibodies reactive with E. canis, and reactivity of these sera with all major E. canis antigens (200, 140, 95, 75, 47, 36, 28, and 19-kDa) was confirmed by immunoblotting. Multicolor real-time PCR detected ehrlichial DNA (E. canis (15) and E. ewingii (2)) in 17 dogs (16.3%), all of which had attached ticks at time of presentation. The dsb amplicons (378 bp) from E. canis and E. ewingii were identical to gene sequences from North American isolates. This study identifies canine ehrlichiosis as a prevalent unrecognized cause of disease in Cameroonian canines.     

Host surveys, ixodid tick biology and transmission scenarios as related to the tick-borne pathogen, Ehrlichia canis

The ehrlichioses have been subject to increasing interest from veterinary and public health perspectives, but experimental studies of these diseases and their etiologic agents can be challenging. Ehrlichia canis, the primary etiologic agent of canine monocytic ehrlichiosis, is relatively well characterized and offers unique advantages and opportunities to study interactions between a monocytotropic pathogen and both its vertebrate and invertebrate hosts. Historically, advances in tick-borne disease control strategies have typically followed explication of tick-pathogen-vertebrate interactions, thus it is reasonable to expect novel, more sustainable approaches to control of these diseases as the transmission of their associated infections are investigated at the molecular through ecological levels. Better understanding of the interactions between E. canis and its canine and tick hosts would also elucidate similar interactions for other Ehrlichia species as well as the potential roles of canine sentinels, reservoirs and models of tick-borne zoonoses. This article summarizes natural exposure studies and experimental investigations of E. canis in the context of what is understood about biological vectors of tick-borne Anaplasmataceae.     

A preliminary study to evaluate the immune responses induced by immunization of dogs with inactivated Ehrlichia canis organisms

Ehrlichia canis is an intracellular pathogen that causes canine monocytic ehrlichiosis. Although the role of antibody responses cannot be discounted, control of this intracellular pathogen is expected to be by cell mediated immune responses. The immune responses in dogs immunized with inactivated E. canis organisms in combination with Quil A were evaluated. Immunization provoked strong humoral and cellular immune responses, which were demonstrable by Western blotting and lymphocyte proliferation assays. By Western blotting antibodies to several immunodominant E. canis proteins were detected in serum from immunized dogs and antibody titres increased after each immunization. The complement of immunogenic proteins recognized by the antisera were similar to those recognized in serum from infected dogs. Upon challenge with live E. canis, rapid anamnestic humoral responses were detected in the serum of immunized dogs and primary antibody responses were detected in the serum from control dogs. Following immunization, a lymphocyte proliferative response (cellular immunity) was detected in peripheral blood mononuclear cells (PBMNs) of immunized dogs upon stimulation with E. canis antigens. These responses were absent from non-immunized control dogs until after infection with live E. canis, when antigen specific-lymphocyte proliferation responses were also detected in the PBMNs of the control dogs. It can be thus concluded that immunization against canine monocytic ehrlichiosis may be feasible. However, the immunization regimen needs to be optimized and a detailed investigation needs to be done to determine if this regimen can prevent development of acute and chronic disease.     

Consensus statement on ehrlichial disease of small animals from the infectious disease study group of the ACVIM. American College of Veterinary Internal Medicine

Within the past several decades, the number of Ehrlichia spp. recognized to infect cats, dogs, and human beings has expanded substantially. The recent application of advanced techniques in molecular biology has changed how ehrlichiosis is diagnosed and has provided new tools for the assessment of treatment. As these techniques are applied, the numerous questions that relate to the management of dogs and cats with ehrlichiosis ultimately will be answered. We hope this consensus statement will assist veterinarians in the management of their patients.     

Ehrlichiosis and polyarthritis in three dogs

Three dogs admitted for evaluation of lameness were determined to be infected with a neutrophilic strain of Ehrlichia. Ehrlichia morulae were detected in low numbers in both synovial fluid and blood neutrophils. The dogs had rapid clinical improvement after appropriate antibiotic therapy. A diagnosis of canine ehrlichiosis easily could have been missed if morulae had not been identified. Ehrlichiosis should be considered in acutely lame dogs residing in areas enzootic for ehrlichiosis. A careful search for Ehrlichia morulae within synovial fluid and blood neutrophils should be performed. An E canis titer determination also may be helpful.     

New molecular biology detection methods for tick-borne infectious agents

Tick-borne zoonotic pathogens are well known in many areas all over the world. Among the tick-borne transmitted diseases in Switzerland, Lyme disease caused by Borrelia burgdorferi, ehrlichiosis caused by various species of Ehrlichia and tick-borne encephalitis caused by the tick-borne encephalitis virus (TBEV) are the most important zoonotic diseases. Early diagnosis and treatment is necessary to prevent fatal infections and chronic damage to various tissues. Due to the variety of uncharacteristic clinical signs, tick-borne diseases are not easily recognized. Diagnosis is based on clinical findings, a record of tick exposure, and direct or indirect detection of the pathogen. Here we discuss briefly the most important tick-borne infections and their diagnosis with emphasis on a new molecular diagnostic tool--the real-time TaqMan PCR--and its importance for the diagnosis of tick-borne pathogens.     

Detection of platelet-bound antibodies in beagle dogs after artificial infection with Ehrlichia canis

Six dogs were infected with Ehrlichia canis by intravenous injection of heavily infected DH82 cells. All dogs developed typical signs of canine monocytic ehrlichiosis. Using flow cytometric technology, platelet-bound IgG (PBIgG) were detected in 5 of the 6 dogs after experimental infection with E. canis over a period of 3-10 days post infection (PI). The first detection of PBIgG was made as early as day 3 PI in 2 out of 6 dogs, and on day 5 PI in 1 dog. On day 7 PI, PBIgG was detected in 2 dogs, and on day 10 PI in 3 out of 6 dogs. This is the first report documenting the presence of PBIgG following E. canis infection in dogs. This finding further supports the theory that the thrombocytopenia seen in canine monocytic ehrlichiosis has an immunological component and that exposure to an infectious agent, in this case the rickettsia E. canis, can trigger autoimmune mechanisms. Due to the heterogeneous appearance of PBIgG among the infected dogs it was concluded that other non-immunological mechanisms are probably also involved in the pathogenesis of the thrombocytopenia seen in canine monocytic ehrlichiosis.     

Ectoparasites of dogs belonging to people in resource-poor communities in North West Province, South Africa

A total of 344 dogs belonging to people in resource-poor communities in North West Province, South Africa, was examined for ectoparasites, and all visible arthropods were collected from the left side of each dog. By doubling these numbers it was estimated that the dogs harboured 14,724 ixodid ticks, belonging to 6 species, 1,028 fleas, belonging to 2 species, and 26 lice. Haemaphysalis leachi accounted for 420 and Rhipicephalus sanguineus for 14,226 of the ticks. Pure infestations of H. leachi were present on 14 dogs and of R. sanguineus on 172 dogs. Small numbers of Amblyomma hebraeum, R. appendiciulatus, R. evertsi evertsi and R. simus were also collected. The predominance of R. sanguitneus accounts for the high prevalence of canine ehrlichiosis (Ehrlichia canis) within the survey region, compared to canine babesiosis (Babesia canis), which is transmitted by H. leachi, and is a much rarer disease.