Swai E S, French N P, Beauchamp G, Fitzpatrick J L, Bryant M J, Kambarage D, Ogden N H
Tanga Dairy Development Programme, Tanga, Tanzania.
Vet Parasitol. 2005 Jul 15;131(1-2):129-37. doi: 10.1016/j.vetpar.2005.04.027.
A longitudinal study of sero-conversion of youngstock to the tick-borne pathogens Theileria parva, T. mutans, Anaplasma marginale, Babesia bigemina and B. bovis was conducted over two years on smallholder dairy farms in Tanga region, Tanzania. There was evidence of maternal antibodies to all tick-borne pathogens in animals less than 18 weeks of age. Seroprevalence increased as expected with age in animals older than this but seroprevalence profiles underestimated the force of infection due to waning antibody levels between samplings. By the end of the 2-year study, less than 50% of study animals had seroconverted to each of the tick-borne pathogens investigated, consistent with the low levels of tick attachment observed on the study animals. Some associations between seroconversion to tick-borne pathogens, and counts of their known tick vectors on the animals, were identified as expected. However, some were not, suggesting that counts of some tick species may act as an index of rates of attachment of other vector species. Variation in acaricide treatment frequencies was not associated with variations in tick-borne pathogen seroprevalence suggesting that acaricides may be used more frequently than necessary on many farms. Most animals were zero-grazed, a management system associated with a significantly lower likelihood that animals seroconverted to any tick-borne pathogen except A. marginale. Seroprevalence varied locally with farm location (particularly for Babesia spp.) but was not well predicted by indices of ecological conditions. Our findings suggest that attempts to achieve a state of 'endemic stability' for tick-borne pathogens may be unreasonable on the smallholder dairy farms studied but reductions in the frequency of use of acaricides may be possible following prospective studies of effects on mortality and morbidity due to tick-borne pathogens.
在坦桑尼亚坦噶地区的小农户奶牛场，对幼畜针对蜱传播病原体小泰勒虫、变形泰勒虫、边缘无形体、双芽巴贝斯虫和牛巴贝斯虫的血清转化情况进行了为期两年的纵向研究。有证据表明，18周龄以下的动物体内存在针对所有蜱传播病原体的母源抗体。在此年龄以上的动物中，血清阳性率随年龄增长而如预期那样上升，但由于两次采样之间抗体水平下降，血清阳性率曲线低估了感染强度。到两年研究结束时，不到50%的研究动物针对所调查的每种蜱传播病原体发生了血清转化，这与在研究动物身上观察到的蜱附着水平较低相一致。正如预期的那样，确定了针对蜱传播病原体的血清转化与动物身上已知蜱传播媒介数量之间的一些关联。然而，有些关联并未确定，这表明某些蜱种的数量可能作为其他媒介种类附着率的指标。杀螨剂处理频率的变化与蜱传播病原体血清阳性率的变化无关，这表明在许多农场，杀螨剂的使用频率可能高于必要水平。大多数动物采用零放牧方式，这种管理系统与动物针对除边缘无形体之外的任何蜱传播病原体发生血清转化的可能性显著较低有关。血清阳性率因农场位置而在当地有所不同（特别是对于巴贝斯虫属），但未被生态条件指数很好地预测。我们的研究结果表明，在所研究的小农户奶牛场，试图实现蜱传播病原体的“地方流行稳定状态”可能不合理，但在对蜱传播病原体导致的死亡率和发病率影响进行前瞻性研究之后，有可能降低杀螨剂的使用频率。
