Biogen Idec, 14 Cambridge Center, Cambridge, MA 02142, USA.
J Med Entomol. 2009 Nov;46(6):1468-73. doi: 10.1603/033.046.0633.
Rates of infection of Amblyomma americanum (L.) by Ehrlichia chaffeensis were compared in 100 ticks collected from sites in each of four states: Indiana, North Carolina, Kentucky, and Mississippi. The overall infection rates were similar among sites, ranging from 1 to 4%. Because pathogenic differences may exist between E. chaffeensis strains, nested polymerase chain reaction (PCR) amplification of the variable-length PCR target (VLPT), and sequencing of the amplicons were performed to differentiate between strains. The most common infecting strains at all sites exhibited a repeat profile of 1,2,3,4 (corresponding to the Arkansas/Jax/Osceola and Liberty strains). To determine whether the minimum infection rates (MIRs) or the most common infecting strain were changing over time in southern Indiana sites, 2765 ticks from six counties in 2000 and 837 ticks from seven counties in 2004 also were examined in pools of five ticks per pool. The MIRs for 2000 and 2004 were 3.5 and 4.2% respectively, suggesting that the overall MIRs remained low. At two sites, in Pike and Harrison counties, however, infection rates more than doubled from 2000 to 2004 (7 to 16% and 0.3 to 2.7% respectively). Across all sites, the most common infecting strains (Arkansas/Jax/Osceola and Liberty) did not significantly change (68% in 2000; 79% in 2004).
在美国四个州（印第安纳州、北卡罗来纳州、肯塔基州和密西西比州）的各个地点采集了 100 只孤星蜱（Amblyomma americanum (L.)），比较了其感染查菲埃立克体（Ehrlichia chaffeensis）的比率。各地点的总体感染率相似，介于 1%至 4%之间。由于查菲埃立克体菌株之间可能存在致病性差异，因此进行了嵌套聚合酶链反应（PCR）扩增可变长度 PCR 靶标（VLPT）和扩增子测序，以区分菌株。所有地点最常见的感染株均表现出重复图谱为 1、2、3、4（对应于阿肯色州/杰克逊/奥塞洛拉和自由株）。为了确定印第安纳州南部各地点的最低感染率（MIR）或最常见的感染株是否随时间发生变化，2000 年从六个县采集了 2765 只蜱，2004 年从七个县采集了 837 只蜱，每 5 只蜱一组进行检测。2000 年和 2004 年的 MIR 分别为 3.5%和 4.2%，表明总体 MIR 仍然较低。然而，在派克县和哈里森县的两个地点，感染率从 2000 年到 2004 年翻了一番以上（分别为 7%至 16%和 0.3%至 2.7%）。在所有地点，最常见的感染株（阿肯色州/杰克逊/奥塞洛拉和自由株）没有明显变化（2000 年为 68%；2004 年为 79%）。
