Wilkinson Laura C, Handel Colleen M, Van Hemert Caroline, Loiseau Claire, Sehgal Ravinder N M
Department of Biology, San Francisco State University, 1600 Holloway Avenue, San Francisco, CA 94132, USA.
U.S. Geological Survey, Alaska Science Center, 4210 University Drive, Anchorage, AK 99508, USA.
Int J Parasitol. 2016 Apr;46(4):281-90. doi: 10.1016/j.ijpara.2015.12.008. Epub 2016 Jan 29.
The prevalence of vector-borne parasitic diseases is widely influenced by biological and ecological factors. Environmental conditions such as temperature and precipitation can have a marked effect on haemosporidian parasites (Plasmodium spp.) that cause malaria and those that cause other malaria-like diseases in birds. However, there have been few long-term studies monitoring haemosporidian infections in birds in northern latitudes, where weather conditions can be highly variable and the effects of climate change are becoming more pronounced. We used molecular methods to screen more than 2,000 blood samples collected from black-capped chickadees (Poecile atricapillus), a resident passerine bird. Samples were collected over a 10 year period, mostly during the non-breeding season, at seven sites in Alaska, USA. We tested for associations between Plasmodium prevalence and local environmental conditions including temperature, precipitation, site, year and season. We also evaluated the relationship between parasite prevalence and individual host factors of age, sex and presence or absence of avian keratin disorder. This disease, which causes accelerated keratin growth in the beak, provided a natural study system in which to test the interaction between disease state and malaria prevalence. Prevalence of Plasmodium infection varied by year, site, age and individual disease status but there was no support for an effect of sex or seasonal period. Significantly, birds with avian keratin disorder were 2.6 times more likely to be infected by Plasmodium than birds without the disorder. Interannual variation in the prevalence of Plasmodium infection at different sites was positively correlated with summer temperatures at the local but not statewide scale. Sequence analysis of the parasite cytochrome b gene revealed a single Plasmodium spp. lineage, P43. Our results demonstrate associations between prevalence of avian malaria and a variety of biological and ecological factors. These results also provide important baseline data that will be informative for predicting future changes in Plasmodium prevalence in the subarctic.
媒介传播寄生虫病的流行受到生物和生态因素的广泛影响。温度和降水等环境条件对引起疟疾的血孢子虫寄生虫（疟原虫属）以及导致鸟类其他类似疟疾疾病的寄生虫有显著影响。然而，在北纬地区，天气条件变化很大且气候变化的影响日益明显，对鸟类血孢子虫感染进行长期监测的研究却很少。我们使用分子方法对从黑顶山雀（Poecile atricapillus）采集的2000多个血样进行了筛查，黑顶山雀是一种留居的雀形目鸟类。样本在10年期间收集，主要在非繁殖季节，地点位于美国阿拉斯加的7个地方。我们测试了疟原虫流行率与当地环境条件之间的关联，包括温度、降水、地点、年份和季节。我们还评估了寄生虫流行率与宿主个体因素（年龄、性别以及是否存在禽角蛋白紊乱）之间的关系。这种疾病会导致喙部角蛋白加速生长，为测试疾病状态与疟疾流行率之间的相互作用提供了一个自然研究系统。疟原虫感染率因年份、地点、年龄和个体疾病状态而异，但没有证据支持性别或季节因素的影响。值得注意的是，患有禽角蛋白紊乱的鸟类感染疟原虫的可能性是未患该疾病鸟类的2.6倍。不同地点疟原虫感染率的年际变化与当地而非全州范围内的夏季温度呈正相关。对寄生虫细胞色素b基因的序列分析揭示了一个单一的疟原虫属谱系，即P43。我们的结果表明了禽疟疾流行率与多种生物和生态因素之间的关联。这些结果还提供了重要的基线数据，有助于预测亚北极地区疟原虫流行率的未来变化。
