Transmission of Ehrlichia chaffeensis by Adult Ticks

描述（由申请人提供）：控制人类单核细胞埃利希体病（HME）的方法，是迄今为止在美国报道的最普遍的人畜共患埃利希体疾病，依赖于更好地了解病原体沙菲埃利希体及其蜱宿主之间的相互作用。已经证明，一些硬蚊属，包括弱视虫、革螨和硬蚊，可以自然感染沙非伊蚊。虽然在自然暴露的蜱中检测到沙非伊虫表明这些蜱对感染易感性，但并不能证明它们有能力将这种病原体传播给易感的脊椎动物宿主。被怀疑的病媒反复实验传播节肢动物传播的病原体，是判定有能力的病媒有罪之前必须满足的主要标准之一。这一特殊应用的目的是鉴定导致该病原体有效实验传播的蜱种和病原体获取情景，这是确定沙非伊蚊传播机制的重要一步。本研究的中心假设是，相对于成年雌蜱或跨栏感染的成年雄蜱，经栏内感染的成年雄蜱是更有效的沙非伊蚊实验载体。这一中心假设将通过以下具体目标的实现来验证：(1)开发一种针对沙非伊虫的PCR检测方法，该方法足够敏感，可以在实验感染的蜱虫个体中检测出病原体；(2)沙非伊虫的体表内和体表间蜱虫传播；(3)沙非伊虫通过成年雄性蜱虫传播给多个宿主。本研究的基本原理是为了更好地了解不同蜱种在自然条件下沙非伊蚊传播中的潜在重要性和获取情况。此外，一旦确定了有效的传播周期，将有一个实验传播模型，使我们能够研究沙非伊蚊与其蜱宿主之间的相互作用。这项工作具有创新性，因为它质疑了这种蜱传病原体仅经体腔传播的教条，但这一范式将在体腔内和跨体腔传播两种情况下进行客观检验。除了建立传播模型外，还将确定几个潜在媒介的能力，这对于确定狗是否可能是人类感染沙非埃希菌的来源以及准确诊断和预防HME非常重要。总的来说，这些结果预计将对人类（和动物）健康产生重大的积极影响，因为它们将有助于了解沙菲伊布绦虫和其他密切相关的病原体在人类和家养宿主之间传播的机制。

DESCRIPTION (provided by the applicant): Approaches to the control of human monocytic ehrlichiosis (HME), the most prevalent zoonotic ehrlichial disease reported in the USA to date, rely on better understanding of interactions between Ehrlichia chaffeensis, the etiologic agent, and its tick host. It has been demonstrated that several ixodid genera, including Amblyomma, Dermacentor and Ixodes, can be naturally infected with E. chaffeensis. Although detection of E. chaffeensis in naturally exposed ticks indicates susceptibility of these ticks to infection, it does not demonstrate their ability to transmit this pathogen to a susceptible vertebrate host. Repeated experimental transmission of an arthropod-borne pathogen by the suspected vector(s) is chief among the criteria that must be fulfilled before the competent vector(s) is (are) incriminated. The objective of this particular application, which is an essential step in determining the mechanisms behind tick transmission of E. chaffeensis, is to identify tick species and pathogen-acquisition scenarios that lead to effective experimental transmission of this pathogen. The central hypothesis of this project is that intrastadially infected adult male ixodid ticks are more effective experimental vectors of E. chaffeensis than adult female or trans-stadially infected adult male ticks. This central hypothesis will be tested through fulfillment of specific aims focused on (1) development of a PCR assay for E. chaffeensis that is sensitive enough to detect the pathogen within individual experimentally infected ticks, (2) intrastadial and transstadial tick-transmission of E. chaffeensis and (3) transmission of E. chaffeensis to multiple hosts by adult male ticks. The rationale for the proposed research is that it will lead to better understanding of the potential importance of different tick species and acquisition scenarios in the transmission of E. chaffeensis under natural conditions. Furthermore, once effective transmission cycles are identified, an experimental transmission model will be available to enable us to investigate interactions between E. chaffeensis and its tick host(s). This work is innovative because it questions the dogma that this tick borne pathogen is only transmitted transstadially, but this paradigm will be tested objectively with both intrastadial and transstadial transmission scenarios. In addition to development of a transmission model, the competence of several potential vectors will be determined, which is important for determining whether dogs could be a source of human infection with E. chaffeensis and for accurate diagnosis and prevention of HME. Collectively, these outcomes are expected to have significant positive effects on human (and animal) health, because they will lead to understanding the mechanisms responsible for transmission of E. chaffeensis and perhaps other closely related pathogens among human and domestic hosts.