Lane R S, Quistad G B
Division of Insect Biology, University of California, Berkeley 94720, USA.
J Parasitol. 1998 Feb;84(1):29-34.
In some populations of the western black-legged tick, Ixodes pacificus, the prevalence of infection with Lyme disease spirochetes (Borrelia burgdorferi) in nymphal ticks exceeds those in adult ticks by 3-4-fold. Experiments were conducted to determine if the reduced spirochetal prevalence in adult ticks is due to the presence of anti-borrelial antibodies or to another borreliacidal factor in the blood of the western fence lizard, Sceloporus occidentalis, a primary host of subadult I. pacificus, or to loss of spirochetes as nymphal ticks molt to the adult stage. Ten lizards were each exposed to the feeding activities of 10 nymphs having a 78% prevalence of B. burgdorferi infection. Five of the lizards had been hyperimmunized first with 10(8) heat-killed spirochetes and 5 were seronegative to B. burgdorferi. After repletion and the transstadial molt, none of 62 resultant adult ticks from both groups of lizards was found to contain spirochetes. In contrast, 11 of 20 (55%) infected nymphs that had fed on 4 preimmune rabbits passed spirochetes to adult ticks. Taken together, these findings demonstrate that host immunoglobulins and the transstadial molt by themselves are not necessary for eliminating B. burgdorferi from infected nymphal ticks. A novel in vitro assay revealed that nearly all spirochetes placed in plasma or sera from lizards died in less than 1 hr, whereas many spirochetes injected into mouse plasma or sera survived for 72 hr. When spirochetes were put in lizard sera that had been preheated (100 C for 10 min) and allowed to cool, survival was extended to 72 hr. We conclude that the blood of S. occidentalis contains a thermolabile, borreliacidal factor, probably a protein, that destroys spirochetes in the midgut diverticula of feeding I. pacificus nymphs.
在西部黑腿蜱（太平洋硬蜱）的一些种群中，若蜱感染莱姆病螺旋体（伯氏疏螺旋体）的患病率比成蜱高出3至4倍。开展了实验，以确定成蜱中螺旋体患病率降低是由于西部围栏蜥蜴（西部强棱蜥）血液中存在抗伯氏螺旋体抗体或另一种杀伯氏螺旋体因子（太平洋硬蜱未成熟若虫的主要宿主），还是由于若蜱蜕皮变为成蜱阶段时螺旋体丧失。10只蜥蜴分别暴露于10只感染伯氏疏螺旋体患病率为78%的若蜱的取食活动中。其中5只蜥蜴先用10⁸个热灭活螺旋体进行了超免疫，另外5只对伯氏疏螺旋体血清学阴性。饱血并经变态蜕皮后，两组蜥蜴产生的62只成蜱均未发现含有螺旋体。相比之下，以4只未免疫兔子为宿主取食的20只感染若蜱中有11只（55%）将螺旋体传给了成蜱。综合来看，这些发现表明宿主免疫球蛋白和变态蜕皮本身并非从感染若蜱中清除伯氏疏螺旋体所必需的。一项新的体外试验显示，置于蜥蜴血浆或血清中的几乎所有螺旋体在不到1小时内死亡，而注入小鼠血浆或血清中的许多螺旋体存活了72小时。当将螺旋体置于预热（100℃10分钟）后冷却的蜥蜴血清中时，存活时间延长至72小时。我们得出结论，西部强棱蜥的血液中含有一种热不稳定的杀伯氏螺旋体因子，可能是一种蛋白质，它能破坏取食的太平洋硬蜱若虫中肠憩室中的螺旋体。
