Data from: Co-infections and environmental conditions drive the distributions of blood parasites in wild birds

Experimental work increasingly suggests that non-random pathogen associations can affect the spread or severity of disease. Yet due to difficulties distinguishing and interpreting co-infections, evidence for the presence and directionality of pathogen co-occurrences in wildlife is rudimentary. We provide empirical evidence for pathogen co-occurrences by analysing infection matrices for avian malaria (Haemoproteus and Plasmodium spp.) and parasitic filarial nematodes (microfilariae) in wild birds (New Caledonian Zosterops spp.). Using visual and genus-specific molecular parasite screening, we identified high levels of co-infections that would have been missed using PCR alone. Avian malaria lineages were assigned to species level using morphological descriptions. We estimated parasite co-occurrence probabilities, while accounting for environmental predictors, in a hierarchical multivariate logistic regression. Co-infections occurred in 36% of infected birds. We identified both positively and negatively correlated parasite co-occurrence probabilities when accounting for host, habitat and island effects. Two of three pairwise avian malaria co-occurrences were strongly negative, despite each malaria parasite occurring across all islands and habitats. Birds with microfilariae had elevated heterophil to lymphocyte ratios and were all co-infected with avian malaria, consistent with evidence that host immune modulation by parasitic nematodes facilitates malaria co-infections. Importantly, co-occurrence patterns with microfilariae varied in direction among avian malaria species; two malaria parasites correlated positively but a third correlated negatively with microfilariae. We show that wildlife co-infections are frequent, possibly affecting infection rates through competition or facilitation. We argue that combining multiple diagnostic screening methods with multivariate logistic regression offers a platform to disentangle impacts of environmental factors and parasite co-occurrences on wildlife disease.越来越多的实验研究表明，非随机的病原体关联会影响疾病的传播与严重程度。然而，由于难以区分并阐释共感染现象，目前关于野生动物体内病原体共存现象的存在性与方向性的相关证据仍十分有限。本研究通过分析野生鸟类（新喀里多尼亚绣眼鸟属（New Caledonian Zosterops spp.））的感染矩阵，为病原体共存现象提供了实证依据，所涉病原体包括禽疟（avian malaria）原虫（血变原虫属（Haemoproteus）与疟原虫属（Plasmodium）各物种）以及寄生丝虫线虫（微丝蚴（microfilariae））。本研究采用镜检与属特异性分子寄生虫筛查相结合的方法，检出了大量仅通过聚合酶链式反应（PCR）无法发现的共感染病例。本研究通过形态学描述将禽疟原虫谱系划分至物种水平。本研究采用分层多变量逻辑回归模型，在纳入环境预测因子的前提下，估算了寄生虫共存概率。受感染鸟类中共有36%存在共感染现象。在控制宿主、栖息地与岛屿效应的前提下，本研究发现了呈正相关与负相关的寄生虫共存概率模式。尽管每种疟原虫均分布于所有岛屿与栖息地中，三组禽疟原虫的两两共存关系中有两组呈现显著负相关。携带微丝蚴的鸟类其嗜异粒细胞与淋巴细胞比值升高，且均合并感染禽疟原虫，这与寄生线虫通过调控宿主免疫促进疟疾共感染的相关研究结论一致。值得注意的是，微丝蚴与禽疟原虫的共存模式在不同疟原虫物种间存在方向差异：两种疟原虫与微丝蚴呈正相关，而第三种疟原虫则与之呈负相关。本研究表明，野生动物共感染现象十分普遍，可能通过竞争或易化作用影响感染率。本研究认为，将多种诊断筛查方法与多变量逻辑回归相结合，可为解析环境因子与寄生虫共存对野生动物疾病的影响提供研究框架。