Department of Basic Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS 39762, United States of America.
Department of Basic Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS 39762, United States of America.
Vet Parasitol Reg Stud Reports. 2020 Jul;21:100421. doi: 10.1016/j.vprsr.2020.100421. Epub 2020 Jun 21.
American canine hepatozoonosis (ACH) is a debilitating tick-borne disease characterized by pyrexia, body wasting, myopathy, mucopurulent ocular discharge, and periosteal proliferation. The causative agent, Hepatozoon americanum, is an apicomplexan that utilizes the Gulf Coast tick, Amblyomma maculatum, as its definitive host and vector. Unlike most tick-borne disease agents, H. americanum is not transmitted via a tick bite, but is transmitted when canids ingest a tick vector that contains sporulated oocysts within the tick hemocoel or paratenic hosts with cystozoites. Our understanding of H. americanum prevalence is based on its detection in the intermediate host, wild or domestic canids, with domestic canids often showing clinical signs at the time of diagnosis. The frequency of H. americanum in A. maculatum, on the other hand, is unknown; this gap in our knowledge hinders our understanding of transmission risk. Furthermore, current diagnostic assays are limited in efficacy, and serologic assays are not widely available. To begin to address gaps in our knowledge, we developed a TaqMan® multiplex qPCR assay for H. americanum detection in A. maculatum tick extracts and evaluated infection rates in questing adult A. maculatum. Additionally, we used a co-culture system to expose H. americanum stages to host cells for in vitro development. Results from qPCR analysis of over 500 tick extracts revealed no positive samples; this suggests both low transmission risk by adult Gulf Coast tick ingestion in the sampled areas, and that surveillance should be focused in areas where ACH has been diagnosed at higher frequencies. Hepatozoon americanum was detectable by qPCR in co-culture of an infected canine buffy coat with ISE6 (Ixodes scapularis embryonic) tick cells, and microscopic examination of samples from those days revealed some structures that were suspicious for developing stages. These data are a starting point for future work to advance our understanding of H. americanum transmission and mechanisms of disease in canids with ACH.
犬种美国血巴尔通体病（ACH）是一种衰弱性蜱传疾病，其特征为发热、消瘦、肌病、黏液脓性眼分泌物和骨膜增生。病原体犬种美国血巴尔通体是一种顶复门原虫，以海湾硬蜱（Amblyomma maculatum）为终末宿主和传播媒介。与大多数蜱传疾病病原体不同，犬种美国血巴尔通体并非通过蜱叮咬传播，而是当犬类摄入含有蜱血腔或中间宿主中的孢子化卵囊或囊合子的感染蜱时传播。我们对犬种美国血巴尔通体流行率的了解是基于其在中间宿主（野生或家养犬类）中的检测，而家养犬类在诊断时通常表现出临床症状。另一方面，海湾硬蜱中的犬种美国血巴尔通体频率尚不清楚；我们知识中的这一空白阻碍了我们对传播风险的理解。此外，目前的诊断检测方法在功效上存在局限性，且血清学检测方法并不广泛可用。为了开始解决我们知识中的空白，我们开发了一种用于检测海湾硬蜱中犬种美国血巴尔通体的 TaqMan®多重 qPCR 检测方法，并评估了在求偶成年海湾硬蜱中的感染率。此外，我们使用共培养系统将犬种美国血巴尔通体各阶段暴露于宿主细胞中进行体外发育。对超过 500 个蜱提取物的 qPCR 分析结果显示没有阳性样本；这表明在所采样区域内，成年海湾硬蜱摄入的传播风险较低，并且监测应集中在 ACH 诊断频率较高的地区。在感染犬类白细胞的共培养中，犬种美国血巴尔通体可通过 qPCR 检测到，并且对来自这些天的样本的显微镜检查显示出一些可疑的发育阶段结构。这些数据是未来工作的起点，旨在推进我们对犬类ACH 中犬种美国血巴尔通体传播和疾病机制的理解。
