U.S. Geological Survey, Alaska Science Center, 4210 University Dr., Anchorage, AK, 99508, USA.
Parasit Vectors. 2019 Jun 10;12(1):292. doi: 10.1186/s13071-019-3545-1.
Climate-related changes are expected to influence the prevalence and distribution of vector-borne haemosporidian parasites at northern latitudes, although baseline information about resident birds is still lacking. In this study, we investigated prevalence and genetic diversity of Plasmodium, Haemoproteus, and Leucocytozoon parasites infecting the northwestern crow (Corvus caurinus), a non-migratory passerine with unique life-history characteristics. This species occupies both intertidal and forested habitats and is subject to high prevalence of avian keratin disorder (AKD), a disease that causes gross beak deformities. Investigation of avian blood parasites in northwestern crows at sites broadly distributed across coastal Alaska provided an opportunity to evaluate specific host factors related to parasite infection status and assess geographical patterns of prevalence.
We used molecular methods to screen for haemosporidian parasites in northwestern crows and estimated genus-specific parasite prevalence with occupancy modeling that accounts for imperfect detection of parasite infection. We observed considerable geographical and annual variation in prevalence of Plasmodium, Haemoproteus, and Leucocytozoon, but these patterns were not correlated with indices of local climatic conditions. Our models also did not provide support for relationships between the probability of parasite infection and body condition or the occurrence of co-infections with other parasite genera or clinical signs of AKD. In our phylogenetic analyses, we identified multiple lineages of each parasite genus, with Leucocytozoon showing greater diversity than Plasmodium or Haemoproteus.
Results from this study expand our knowledge about the prevalence and diversity of avian blood parasites in northern resident birds as well as corvids worldwide. We detected all three genera of avian haemosporidians in northwestern crows in Alaska, although only Leucocytozoon occurred at all sites in both years. Given the strong geographical and annual variation in parasite prevalence and apparent lack of correlation with climatic variables, it appears that there are other key factors responsible for driving transmission dynamics in this region. Thus, caution is warranted when using standard climatic or geographical attributes in a predictive framework. Our phylogenetic results demonstrate lower host specificity for some lineages of Leucocytozoon than is typically reported and provide insights about genetic diversity of local haemosporidian parasites in Alaska.
预计与气候相关的变化将影响北方纬度地区媒介传播的血孢子虫寄生虫的流行和分布，但有关当地鸟类的基线信息仍然缺乏。在这项研究中，我们调查了感染西北乌鸦（Corvus caurinus）的疟原虫、血孢子虫和白细胞虫寄生虫的流行率和遗传多样性，西北乌鸦是一种具有独特生活史特征的非迁徙雀形目鸟类。该物种栖息于潮间带和森林栖息地，且易患鸟类角蛋白紊乱（AKD），这是一种导致严重喙畸形的疾病。在阿拉斯加沿海广泛分布的地点对西北乌鸦中的鸟类血液寄生虫进行调查，为评估与寄生虫感染状况相关的特定宿主因素和评估流行率的地理模式提供了机会。
我们使用分子方法筛查西北乌鸦中的血孢子虫寄生虫，并使用占寄生虫感染检测不完全的占有模型估计属特异性寄生虫流行率。我们观察到疟原虫、血孢子虫和白细胞虫的流行率存在相当大的地理和年度变化，但这些模式与当地气候条件指数没有相关性。我们的模型也没有为寄生虫感染的可能性与身体状况之间的关系提供支持，也没有为与其他寄生虫属的共同感染或 AKD 临床症状的关系提供支持。在我们的系统发育分析中，我们确定了每个寄生虫属的多个谱系，白细胞虫的多样性大于疟原虫或血孢子虫。
这项研究的结果扩展了我们对北方候鸟以及全球鸦科鸟类中鸟类血液寄生虫的流行率和多样性的认识。我们在阿拉斯加的西北乌鸦中检测到了所有三种属的鸟类血孢子虫，但只有白细胞虫在两年中的所有地点都有发生。鉴于寄生虫流行率的强烈地理和年度变化以及与气候变量明显缺乏相关性，似乎还有其他关键因素影响该地区的传播动态。因此，在预测框架中使用标准气候或地理属性时需要谨慎。我们的系统发育结果表明，一些白细胞虫谱系的宿主特异性低于通常报道的水平，并提供了关于阿拉斯加当地血孢子虫寄生虫遗传多样性的见解。
