NSW Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Camden, New South Wales, Australia.
Vet Parasitol. 2013 Sep 1;196(1-2):96-105. doi: 10.1016/j.vetpar.2012.12.059. Epub 2013 Jan 9.
Cattle within seven NSW herds with a history or risk of clinical Theileria orientalis disease associated with introductions of cattle were examined clinically and by haematological and PCR testing at sequential bleeds or at single sampling of different risk subgroups. The T. orientalis Ikeda type was detected in all herds and Chitose type was detected in six. Pale and jaundiced mucosal surfaces were associated with clinically affected groups of cattle, and herds containing cattle with ≥ 1% theilerias in erythrocytes were associated with high prevalence of Ikeda type, with or without Chitose type. In clinically normal cattle within these Ikeda-affected herds, over half of the smear negative animals were detected as infected with Ikeda type, while 90% of smear positive cases were positive for Ikeda type. Infection with Ikeda and Chitose organisms was detected in calves as young as 1-2 weeks, rapidly increased in prevalence within one month and was maintained until 4.5 months of age. In these calves Ikeda prevalence increased at a faster rate than the other MPSP types, particularly Buffeli which is generally considered to be avirulent, and suggests either an increased growth rate or rate of transmission of the Ikeda type or failure of the host immune system to clear this type. Particularly high T. orientalis prevalence rates were detected (in blood samples from a single time point) in adults that had been in direct contact with weaner cattle introduced from coastal areas; however, the lack of direct contact with affected cattle did not prevent infection with Ikeda type in some cases. Spread within previously naïve herds was variable, and results also depended on the sampling time point. In contrast, groups in which infection was already established gave repeatedly similar results at multiple samplings taken at one month intervals. Our results confirm that a large reservoir of infected but clinically normal animals exists within T. orientalis-affected cattle herds and PCR testing of EDTA bloods is more sensitive for detecting subclinical infection than blood smear examination. Direct contact with weaner cattle introduced from coastal areas appears to be a major risk factor for T. orientalis infection in adult cattle. Frequent sampling may be used to monitor spread of T. orientalis within newly affected herds, but may be unrewarding once a high prevalence is established.
在新南威尔士州的七个牛群中，有七群牛曾有临床东方泰勒虫病的病史或风险，这些牛群通过临床检查、血液学检查和 PCR 检测在连续采血或不同风险亚群的单次采样中进行了检查。在所有牛群中都检测到了 Ikeda 型东方泰勒虫，在六个牛群中检测到了 Chitose 型。苍白和黄疸的黏膜表面与临床受影响的牛群有关，而红细胞中含有 ≥ 1%的东方泰勒虫的牛群与 Ikeda 型的高流行率有关，无论是否存在 Chitose 型。在这些受 Ikeda 影响的牛群中，临床正常的牛中，超过一半的涂片阴性动物被检测为 Ikeda 型感染，而 90%的涂片阳性病例为 Ikeda 型阳性。在 1-2 周龄的小牛中检测到 Ikeda 和 Chitose 生物的感染，在一个月内流行率迅速增加，并持续到 4.5 月龄。在这些小牛中，Ikeda 的流行率增加速度比其他 MPSP 型更快，特别是通常认为没有毒力的 Buffeli，这表明 Ikeda 型的生长速度或传播速度加快，或者宿主免疫系统未能清除这种类型。在与来自沿海地区的断奶牛直接接触的成年牛中，检测到特别高的东方泰勒虫流行率（在单次采血样本中）；然而，在某些情况下，与受感染牛没有直接接触并不能阻止 Ikeda 型的感染。在以前无感染的牛群中，传播情况各不相同，结果也取决于采样时间点。相比之下，在已经建立感染的群体中，在相隔一个月进行多次采样时，结果会重复出现。我们的研究结果证实，在受东方泰勒虫感染的牛群中，存在大量感染但临床正常的动物作为传染源，EDTA 血液的 PCR 检测比血涂片检查更能检测亚临床感染。与来自沿海地区的断奶牛的直接接触似乎是成年牛感染东方泰勒虫的一个主要危险因素。频繁采样可用于监测新感染牛群中东方泰勒虫的传播，但一旦流行率较高，采样可能就没有意义了。
