Rickettsial Zoonoses Branch, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA.
Rickettsial Zoonoses Branch, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA.
Ticks Tick Borne Dis. 2021 Nov;12(6):101819. doi: 10.1016/j.ttbdis.2021.101819. Epub 2021 Sep 4.
This study assessed the duration of tick attachment necessary for a successful transmission of Anaplasma phagocytophilum by an infected I. scapularis nymph. Individual nymphs were placed upon BALB/c mice and allowed to feed for predetermined time intervals of 4 to 72 h. Ticks removed from mice at predetermined intervals were tested by PCR for verification of infection and evaluation of the bacterial load. The success of pathogen transmission to mice was assessed by blood-PCR at 7, 14 and 21 days postinfestation, and IFA at 21 days postinfestation. Anaplasma phagocytophilum infection was documented in 10-30 % of mice, from which ticks were removed within the first 20 h of feeding. However, transmission success was ≥70% if ticks remained attached for 36 h or longer. Notably, none of the PCR-positive mice that were exposed to infected ticks for 4 to 8 h and only half of PCR-positive mice exposed for 24 h developed antibodies within 3 weeks postinfestation. On the other hand, all mice with detectable bacteremia after being infested for 36 h seroconverted. This suggests that although some of the ticks removed prior to 24 h of attachment succeed in injecting a small amount of A. phagocytophilum, this amount is insufficient for stimulating humoral immunity and perhaps for establishing disseminated infection in BALB/c mice. Although A. phagocytophilum may be present in salivary glands of unfed I. scapularis nymphs, the amount of A. phagocytophilum initially contained in saliva appears insufficient to cause sustainable infection in a host. Replication and, maybe, reactivation of the agent for 12-24 h in a feeding tick is required before a mouse can be consistently infected.
本研究评估了感染性 I. scapularis 若虫附着足够长的时间以成功传播嗜吞噬细胞无形体。将单个若虫置于 BALB/c 小鼠身上，并允许其以预定的 4 至 72 小时的时间间隔进食。在预定的时间间隔内从老鼠身上取下的蜱虫通过 PCR 进行测试，以验证感染情况并评估细菌负荷。通过血液-PCR 在感染后 7、14 和 21 天，以及 IFA 在感染后 21 天评估病原体向小鼠传播的成功率。在最初 20 小时进食的蜱虫中，有 10-30%的小鼠记录到嗜吞噬细胞无形体感染。然而，如果蜱虫附着 36 小时或更长时间，则传播成功率≥70%。值得注意的是，在感染蜱虫 4 至 8 小时的所有 PCR 阳性小鼠中，只有一半的 PCR 阳性小鼠在 24 小时内接触到感染性蜱虫后产生了抗体。另一方面，所有在感染 36 小时后检测到菌血症的小鼠都发生了血清转化。这表明，尽管在附着 24 小时之前取下的一些蜱虫成功地注入了少量的嗜吞噬细胞无形体，但这一数量不足以刺激体液免疫，也不足以在 BALB/c 小鼠中建立弥散性感染。尽管未进食的 I. scapularis 若虫的唾液腺中可能存在嗜吞噬细胞无形体，但最初存在于唾液中的嗜吞噬细胞无形体数量似乎不足以导致宿主持续感染。在能够持续感染小鼠之前，需要在进食的蜱虫中复制（也许是重新激活）12-24 小时的病原体。
