Raghavan Ram K, Almes Kelli, Goodin Doug G, Harrington John A, Stackhouse Paul W
1 Kansas State Veterinary Diagnostic Laboratory, Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University , Manhattan, Kansas.
Vector Borne Zoonotic Dis. 2014 Jul;14(7):486-95. doi: 10.1089/vbz.2013.1496. Epub 2014 Jun 30.
Feline cytauxzoonosis is a highly fatal tick-borne disease caused by a hemoparasitic protozoan, Cytauxzoon felis. This disease is a leading cause of mortality for cats in the Midwestern United States, and no vaccine or effective treatment options exist. Prevention based on knowledge of risk factors is therefore vital. Associations of different environmental factors, including recent climate were evaluated as potential risk factors for cytauxzoonosis using Geographic Information Systems (GIS).
There were 69 cases determined to be positive for cytauxzoonosis based upon positive identification of C. felis within blood film examinations, tissue impression smears, or histopathologic examination of tissues. Negative controls totaling 123 were selected from feline cases that had a history of fever, malaise, icterus, and anorexia but lack of C. felis within blood films, impression smears, or histopathologic examination of tissues. Additional criteria to rule out C. felis among controls were the presence of regenerative anemia, cytologic examination of blood marrow or lymph node aspirate, other causative agent diagnosed, or survival of 25 days or greater after testing. Potential environmental determinants were derived from publicly available sources, viz., US Department of Agriculture (soil attributes), US Geological Survey (land-cover/landscape, landscape metrics), and NASA (climate). Candidate variables were screened using univariate logistic models with a liberal p value (0.2), and associations with cytauxzoonosis were modeled using a global multivariate logistic model (p<0.05). Spatial heterogeneity among significant variables in the study region was modeled using a geographically weighted regression (GWR) approach.
Total Edge Contrast Index (TECI), grassland-coverage, humidity conditions recorded during the 9(th) week prior to case arrival, and an interaction variable, "diurnal temperature range × percent mixed forest area" were significant risk factors for cytauxzoonosis in the study region. TECI and grassland areas exhibited significant regional differences in their effects on cytauxzoonosis outcome, whereas others were uniform.
Land-cover areas favorable for tick habitats and climatic conditions that favor the tick life cycle are strong risk factors for feline cytauxzoonosis. Spatial heterogeneity and interaction effects between land-cover and climatic variables may reveal new information when evaluating risk factors for vector-borne diseases.
猫胞虫病是一种由血液寄生原生动物——猫胞虫引起的高度致命的蜱传疾病。该疾病是美国中西部地区猫死亡的主要原因，目前尚无疫苗或有效的治疗方法。因此，基于风险因素知识的预防至关重要。利用地理信息系统（GIS）评估了包括近期气候在内的不同环境因素与猫胞虫病潜在风险因素之间的关联。
根据血片检查、组织印片或组织病理检查中猫胞虫的阳性鉴定，确定69例猫胞虫病阳性病例。从有发热、不适、黄疸和厌食病史但血片、印片或组织病理检查中未发现猫胞虫的猫病例中选择了123例阴性对照。排除对照中猫胞虫的其他标准包括再生性贫血的存在、骨髓或淋巴结穿刺液的细胞学检查、诊断出的其他病原体或检测后存活25天或更长时间。潜在的环境决定因素来自公开可用的数据源，即美国农业部（土壤属性）、美国地质调查局（土地覆盖/景观、景观指标）和美国国家航空航天局（气候）。使用具有宽松p值（0.2）的单变量逻辑模型筛选候选变量，并使用全局多变量逻辑模型（p<0.05）对与猫胞虫病的关联进行建模。使用地理加权回归（GWR）方法对研究区域内显著变量之间的空间异质性进行建模。
总边缘对比度指数（TECI）、草地覆盖率、病例出现前第9周记录的湿度条件以及一个交互变量“日温度范围×混交林面积百分比”是研究区域内猫胞虫病的显著风险因素。TECI和草地面积对猫胞虫病结果的影响存在显著的区域差异，而其他因素则较为一致。
有利于蜱虫栖息地的土地覆盖区域和有利于蜱虫生命周期的气候条件是猫胞虫病的重要风险因素。在评估媒介传播疾病的风险因素时，土地覆盖和气候变量之间的空间异质性和交互作用可能会揭示新的信息。
