LUNAM Université, Oniris, UMR 1300 Bio-Agression, Epidémiologie et Analyse de Risque, Nantes, F-44307, France.
Vet Parasitol. 2012 Apr 30;185(2-4):101-9. doi: 10.1016/j.vetpar.2011.10.022. Epub 2011 Oct 21.
Babesia divergens, transmitted by the tick Ixodes ricinus, is the main agent of bovine piroplasmosis in France. This Apicomplexa often is present in asymptomatic carriers; however, clinical cases are rare. While numerous factors are known to influence tick density, no risk factor of contact with B. divergens has been identified for cattle. Our study aimed to explore whether a Vegetation Index could serve as an indirect indicator of within-herd B. divergens seroprevalence. In February 2007, blood samples were taken from all of the cows in 19 dairy cattle herds in Western France and IFAT serology was performed individually to measure B. divergens seroprevalence. The following spring, I. ricinus nymphs were collected by drag sampling along transects on the vegetation of each farm's pasture perimeters. Tick density was related significantly to a Vegetation Index (V.I., ranging from 1 to 5) that took into account the abundance of trees and bushes on the edge of pastures: most ticks (57%) were found in transects with the highest V.I. (covering 15% of the explored surface in the study area). At the farm level, the proportion of transects presenting I. ricinus nymphs was significantly related to B. divergens seroprevalence: the farms with more than 15% of transects with I. ricinus had a significantly higher risk of high seroprevalence. The proportion of pasture perimeters where the V.I.=5 also was significantly related to B. divergens seroprevalence: the farms where more than 20% of transects had a V.I.=5 had a significantly higher risk of high seroprevalence. Given that the Vegetation Index is a steady indicator of the potential I. ricinus density in the biotope, we recommend that the risk of high B. divergens seroprevalence in cows be evaluated using this tool rather than drag samplings.
分歧巴贝斯虫，由硬蜱传播伊莱克斯ricinus，是法国牛梨形虫病的主要病原体。这种顶复门寄生虫通常存在于无症状携带者中;然而，临床病例很少见。虽然有许多因素被认为会影响蜱的密度，但尚未确定牛与分歧巴贝斯虫接触的风险因素。我们的研究旨在探讨植被指数是否可以作为牛群内分歧巴贝斯虫血清阳性率的间接指标。2007 年 2 月，从法国西部 19 个奶牛场的所有奶牛身上采集血样，并进行间接荧光抗体试验（IFAT）血清学检测，以单独测量分歧巴贝斯虫血清阳性率。次年春天，在每个农场的牧场周边植被上，通过拖曳采样收集硬蜱若虫。蜱密度与植被指数（V.I.）显著相关，V.I. 考虑到牧场边缘树木和灌木的丰度：在研究区域内，V.I. 最高的样带中发现了 57%的蜱（V.I. 范围为 1 到 5）。在农场水平上，存在硬蜱若虫的样带比例与分歧巴贝斯虫血清阳性率显著相关：有超过 15%的样带出现硬蜱的农场，其血清阳性率较高的风险显著增加。V.I.=5 的牧场周边比例也与分歧巴贝斯虫血清阳性率显著相关：V.I.=5 的样带比例超过 20%的农场，其血清阳性率较高的风险显著增加。由于植被指数是生物群落中硬蜱潜在密度的稳定指标，我们建议使用该工具而不是拖曳采样来评估奶牛中高分歧巴贝斯虫血清阳性率的风险。
