Bowie M V, Reddy G R, Semu S M, Mahan S M, Barbet A F
Department of Pathobiology, College of Veterinary Medicine, University of Florida, Gainesville, Florida 32610, USA.
Clin Diagn Lab Immunol. 1999 Mar;6(2):209-15. doi: 10.1128/CDLI.6.2.209-215.1999.
Cowdria ruminantium is the etiologic agent of heartwater, a disease causing major economic loss in ruminants in sub-Saharan Africa and the Caribbean. Development of a serodiagnostic test is essential for determining the carrier status of animals from regions where heartwater is endemic, but most available tests give false-positive reactions with sera against related Erhlichia species. Current approaches rely on molecular methods to define proteins and epitopes that may allow specific diagnosis. Two major antigenic proteins (MAPs), MAP1 and MAP2, have been examined for their use as antigens in the serodiagnosis of heartwater. The objectives of this study were (i) to determine if MAP2 is conserved among five geographically divergent strains of C. ruminantium and (ii) to determine if MAP2 homologs are present in Ehrlichia canis, the causative agent of canine ehrlichiosis, and Ehrlichia chaffeensis, the organism responsible for human monocytic ehrlichiosis. These two agents are closely related to C. ruminantium. The map2 gene from four strains of C. ruminantium was cloned, sequenced, and compared with the previously reported map2 gene from the Crystal Springs strain. Only 10 nucleic acid differences between the strains were identified, and they translate to only 3 amino acid changes, indicating that MAP2 is highly conserved. Genes encoding MAP2 homologs from E. canis and E. chaffeensis also were cloned and sequenced. Amino acid analysis of MAP2 homologs of E. chaffeensis and E. canis with MAP2 of C. ruminantium revealed 83.4 and 84.4% identities, respectively. Further analysis of MAP2 and its homologs revealed that the whole protein lacks specificity for heartwater diagnosis. The development of epitope-specific assays using this sequence information may produce diagnostic tests suitable for C. ruminantium and also other related rickettsiae.
反刍兽考德里氏体是心水病的病原体，心水病在撒哈拉以南非洲和加勒比地区的反刍动物中造成重大经济损失。开发一种血清学诊断检测方法对于确定心水病流行地区动物的带菌状态至关重要，但大多数现有检测方法对针对相关埃立克体属物种的血清会产生假阳性反应。目前的方法依赖分子方法来确定可能允许进行特异性诊断的蛋白质和表位。已经研究了两种主要抗原蛋白（MAPs），即MAP1和MAP2，作为心水病血清学诊断中的抗原的用途。本研究的目的是：（i）确定MAP2在五个地理上不同的反刍兽考德里氏体菌株中是否保守；（ii）确定犬埃立克体（犬埃立克体病的病原体）和恰菲埃立克体（人类单核细胞埃立克体病的病原体）中是否存在MAP2同源物。这两种病原体与反刍兽考德里氏体密切相关。克隆、测序了来自四个反刍兽考德里氏体菌株的map2基因，并与先前报道的来自水晶泉菌株的map2基因进行了比较。在这些菌株之间仅鉴定出10个核酸差异，并且它们仅转化为3个氨基酸变化，表明MAP2高度保守。还克隆并测序了来自犬埃立克体和恰菲埃立克体的编码MAP2同源物的基因。对恰菲埃立克体和犬埃立克体的MAP2同源物与反刍兽考德里氏体的MAP2进行氨基酸分析，分别显示出83.4%和84.4%的同一性。对MAP2及其同源物的进一步分析表明，整个蛋白质缺乏用于心水病诊断的特异性。利用该序列信息开发表位特异性检测方法可能会产生适用于反刍兽考德里氏体以及其他相关立克次氏体的诊断检测方法。
