Levin M L, Fish D
Department of Epidemiology, Yale School of Medicine, New Haven, Connecticut 06520-8034, USA.
Infect Immun. 2000 Mar;68(3):1514-8. doi: 10.1128/IAI.68.3.1514-1518.2000.
Infection with Ehrlichia phagocytophila in white-footed mice is transient and followed by a strong immune response. We investigated whether the presence of acquired immunity against E. phagocytophila precludes white-footed mice from further maintenance of this agent in nature. Mice were infected with E. phagocytophila via tick bite and challenged either 12 or 16 weeks later by Ixodes scapularis nymphs infected with the same agent. Xenodiagnostic larvae fed upon each mouse simultaneously with challenging nymphs and 1 week thereafter. Ticks were tested for the agent by PCR, and the prevalence of infection was compared to that in ticks that fed upon nonimmune control mice. Only 30% of immunized mice sustained cofeeding transmission of E. phagocytophila between simultaneously feeding infected and uninfected ticks, compared to 100% of control mice. An average of 6.3% of xenodiagnostic ticks acquired Ehrlichia from previously immunized mice when fed 1 week after the challenge, compared to 82.5% infection in the control group. Although an immune response to a single infection with E. phagocytophila in white-footed mice provided only partial protection against reinfection with the same agent, the majority of mice were rendered reservoir incompetent for at least 12 to 16 weeks. Immunity acquired by mice during I. scapularis nymphal activity in early summer may exclude a large proportion of the mouse population from maintaining E. phagocytophila during the period of larval activity later in the season.
白足鼠感染嗜吞噬细胞埃立克体是短暂的,随后会产生强烈的免疫反应。我们研究了对白足鼠而言,获得性抗嗜吞噬细胞埃立克体免疫的存在是否会阻止其在自然界中进一步维持这种病原体。通过蜱叮咬使小鼠感染嗜吞噬细胞埃立克体,在12周或16周后,用感染相同病原体的肩突硬蜱若虫对小鼠进行攻击。在对小鼠进行攻击的同时,用异源诊断幼虫叮咬每只小鼠,并在1周后再次叮咬。通过聚合酶链反应(PCR)检测蜱是否携带病原体,并将感染率与叮咬非免疫对照小鼠的蜱的感染率进行比较。与100%的对照小鼠相比,只有30%的免疫小鼠在同时叮咬的感染和未感染蜱之间维持嗜吞噬细胞埃立克体的共同进食传播。在攻击后1周喂食时,平均有6.3%的异源诊断蜱从先前免疫的小鼠身上获得埃立克体,而对照组的感染率为82.5%。虽然白足鼠对单一嗜吞噬细胞埃立克体感染的免疫反应仅提供了部分针对同一病原体再次感染的保护,但大多数小鼠至少在12至16周内不再具有储存宿主能力。小鼠在初夏肩突硬蜱若虫活动期间获得的免疫力,可能会使很大一部分小鼠群体在该季节后期幼虫活动期间无法维持嗜吞噬细胞埃立克体。