Davidar P, Wilson M, Ribeiro J M
Department of Tropical Public Health, Harvard School of Public Health, Boston, Massachusetts 02115.
J Parasitol. 1989 Dec;75(6):898-904.
Ectoparasites such as ixodid ticks that remain attached to hosts for several days while feeding on blood are able to overcome the inflammatory and immune responses of some hosts and not others. The immature stages of the deer tick Ixodes dammini are found more frequently on the white-footed mouse, Peromyscus leucopus, than on other rodents. We propose that P. leucopus is more tolerant to I. dammini than is a less common host, the meadow vole, Microtus pennsylvanicus. To test this hypothesis, the distribution patterns and engorgement indices were determined for larval and nymphal I. dammini collected from wild-caught P. leucopus and M. pennsylvanicus. There were more immature ticks, which were more fully engorged, on P. leucopus than on M. pennsylvanicus. There were more and better engorged ticks on male than on female hosts. Laboratory studies on the number and weights of larval I. dammini collected off naive and previously exposed P. leucopus and M. pennsylvanicus support the results of the field study. Fewer larval ticks were recovered from previously exposed M. pennsylvanicus than P. leucopus, and the ticks weighed less. Larval and nymphal ticks aggregated among hosts in the study grid, and higher densities per male P. leucopus were correlated with higher engorgement indices, suggesting that immature I. dammini feed better at higher densities. The feeding success of I. dammini on its preferred host species might be due to its adaptation to the immune and inflammatory reactions of the host.
诸如硬蜱之类的体外寄生虫在吸食血液时会在宿主身上附着数天，它们能够克服某些宿主而非其他宿主的炎症和免疫反应。白足鼠（Peromyscus leucopus）身上比其他啮齿动物更频繁地发现鹿蜱（Ixodes dammini）的未成熟阶段。我们推测，相较于不太常见的宿主草原田鼠（Microtus pennsylvanicus），白足鼠对鹿蜱的耐受性更强。为了验证这一假设，我们确定了从野生捕获的白足鼠和草原田鼠身上采集的鹿蜱幼虫和若虫的分布模式及饱血指数。白足鼠身上的未成熟蜱更多，且饱血程度更高，相比之下草原田鼠身上的则较少。雄性宿主身上的蜱比雌性宿主身上的更多且饱血情况更好。对从未接触过和先前接触过的白足鼠及草原田鼠身上采集的鹿蜱幼虫数量和重量进行的实验室研究支持了野外研究的结果。从先前接触过的草原田鼠身上回收的幼虫蜱比白足鼠身上的少，且蜱的重量也更轻。在研究网格中，幼虫和若虫蜱在宿主之间聚集，每只雄性白足鼠身上更高的密度与更高的饱血指数相关，这表明未成熟的鹿蜱在更高密度时进食情况更好。鹿蜱在其偏好宿主物种上的进食成功率可能归因于它对宿主免疫和炎症反应的适应。
