Center for Infectious Disease Dynamics and Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA.
Int J Parasitol. 2012 Jun;42(7):647-55. doi: 10.1016/j.ijpara.2012.04.011. Epub 2012 May 11.
Co-infections can alter the host immune responses and modify the intensity and dynamics of concurrent parasitic species. The extent of this effect depends on the properties of the system and the mechanisms of host-parasite and parasite-parasite interactions. We examined the immuno-epidemiology of a chronic co-infection to reveal the immune mediated relationships between two parasites colonising independent organs, and the within-host molecular processes influencing the dynamics of infection at the host population level. The respiratory bacterium, Bordetella bronchiseptica, and the gastrointestinal helminth, Graphidium strigosum, were studied in the European rabbit (Oryctolagus cuniculus), using long-term field data and a laboratory experiment. We found that 65% of the rabbit population was co-infected with the two parasites; prevalence and intensity of co-infection increased with rabbit age and exhibited a strong seasonal pattern with the lowest values recorded during host breeding (from April to July) and the highest in the winter months. Laboratory infections showed no significant immune-mediated effects of the helminth on bacterial intensity in the lower respiratory tract but a higher abundance was observed in the nasal cavity during the chronic phase of the infection, compared with single bacterial infections. In contrast, B. bronchiseptica enhanced helminth intensity and this was consistent throughout the 4-month trial. These patterns were associated with changes in the immune profiles between singly and co-infected individuals for both parasites. This study confirmed the general observation that co-infections alter the host immune responses but also highlighted the often ignored role of bacterial infection in helminth dynamics. Additionally, we showed that G. strigosum had contrasting effects on B. bronchiseptica colonising different parts of the respiratory tract. At the host population level our findings suggest that B. bronchiseptica facilitates G. strigosum infection, and re-infection with G. strigosum assists in maintaining bacterial infection in the upper respiratory tract and thus long-term persistence.
合并感染会改变宿主的免疫反应，并改变同时存在的寄生虫物种的强度和动态。这种影响的程度取决于系统的特性以及宿主-寄生虫和寄生虫-寄生虫相互作用的机制。我们研究了一种慢性合并感染的免疫流行病学，以揭示两种寄生在独立器官中的寄生虫之间的免疫介导关系，以及影响宿主群体水平感染动态的宿主内分子过程。我们在欧洲兔（Oryctolagus cuniculus）中研究了呼吸道细菌博德特氏菌（Bordetella bronchiseptica）和胃肠道蠕虫 Graphidium strigosum，使用了长期的现场数据和实验室实验。我们发现，65%的兔群同时感染了这两种寄生虫；合并感染的患病率和强度随兔子年龄的增长而增加，并且表现出强烈的季节性模式，即在宿主繁殖期间（从 4 月到 7 月）记录到的最低值和冬季的最高值。实验室感染表明，蠕虫对下呼吸道细菌强度没有明显的免疫介导作用，但在感染的慢性阶段，鼻腔中的细菌丰度较高，与单一细菌感染相比。相比之下，B. bronchiseptica 增强了蠕虫的强度，这种情况在整个 4 个月的试验中都很一致。这些模式与两种寄生虫的单独和合并感染个体之间的免疫特征变化有关。这项研究证实了一般观察结果，即合并感染会改变宿主的免疫反应，但也强调了细菌感染在寄生虫动态中的经常被忽视的作用。此外，我们还表明，Graphidium strigosum 对博德特氏菌在呼吸道不同部位的定植有相反的影响。在宿主群体水平上，我们的研究结果表明，博德特氏菌促进了 Graphidium strigosum 的感染，而 Graphidium strigosum 的再次感染有助于维持上呼吸道的细菌感染，从而实现长期持续存在。
