Swilks Emma, Fell Shayne A, Hammer Jade F, Sales Narelle, Krebs Gaye L, Jenkins Cheryl
School of Animal and Veterinary Sciences, Charles Sturt University, Locked Bag 588, Wagga Wagga, NSW, 2678, Australia.
NSW Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Woodbridge Rd, Menangle, NSW, 2568, Australia.
Parasit Vectors. 2017 May 8;10(1):227. doi: 10.1186/s13071-017-2166-9.
Bovine theileriosis, caused by the haemoprotozoan Theileria orientalis, is an emerging disease in East Asia and Australasia. Previous studies have demonstrated transplacental transmission of various Theileria spp. but molecular confirmation of transplacental transmission of T. orientalis has never been confirmed in the field. In this study, cow-calf (< 48 h old) pairs were sampled across 3 herds; opportunistic samples from aborted foetuses or stillborn calves were also examined. Molecular (multiplex qPCR) and serological (ELISA) methods were used to determine infection prevalence and the presence of anti-Theileria antibodies in each herd. In addition, pregnant heifers and foetal calves were sampled at abattoir and tested for the presence of T. orientalis by qPCR.
The qPCR results indicated that, even though there was a high prevalence of T. orientalis infection in cows, the rate of transplacental transmission to their calves was low, with only one newborn calf from one herd and one foetus from the abattoir testing positive for T. orientalis DNA. Five aborted foetuses and stillborn calves, 3 of which were derived from a herd experiencing a high number of clinical theileriosis cases at the time of sampling, all tested negative for T. orientalis by qPCR. This suggests that in utero infection of calves with T. orientalis may not be a major driver of abortions during theileriosis outbreaks. Temporal monitoring of 20 calves born to T. orientalis-positive mothers indicated that T. orientalis was detectable in most calves between 10 and 27 days post-partum, consistent with prior field studies on adult cattle introduced to Theileria-affected herds. There was a positive correlation between the ELISA ratio of newborn calves and their mothers within 48 h of calving; however, maternal antibodies were only detectable in some calves and only for 4-4.5 weeks post-partum. All calves displayed high parasite loads peaking at 4-8 weeks post-partum, with only some calves subsequently mounting a detectable adaptive antibody response.
These findings indicate transplacental transmission of T. orientalis appears to play only a minor role in persistence of T. orientalis infection in the field; however calves are highly susceptible to developing high level T. orientalis infections at 4-8 weeks of age regardless of whether maternal antibodies are present post-partum.
由血液原虫东方泰勒虫引起的牛泰勒虫病是东亚和澳大拉西亚地区一种新出现的疾病。先前的研究已证明各种泰勒虫属可经胎盘传播，但在野外尚未通过分子手段证实东方泰勒虫的经胎盘传播。在本研究中，对来自3个牛群的母牛 - 犊牛（<48小时龄）对进行了采样；还检查了流产胎儿或死产犊牛的机会性样本。采用分子方法（多重定量聚合酶链反应）和血清学方法（酶联免疫吸附测定）来确定每个牛群中的感染率以及抗泰勒虫抗体的存在情况。此外，在屠宰场对怀孕的小母牛和胎儿小牛进行采样，并通过定量聚合酶链反应检测东方泰勒虫的存在。
定量聚合酶链反应结果表明，尽管母牛中东方泰勒虫感染率很高，但其向犊牛的经胎盘传播率很低，只有一个牛群中的一头新生犊牛和屠宰场的一个胎儿检测出东方泰勒虫DNA呈阳性。5头流产胎儿和死产犊牛，其中3头来自采样时临床泰勒虫病病例数较多的牛群，通过定量聚合酶链反应检测东方泰勒虫均为阴性。这表明在泰勒虫病暴发期间，子宫内犊牛感染东方泰勒虫可能不是流产的主要原因。对20头东方泰勒虫阳性母牛所生犊牛的时间监测表明，大多数犊牛在产后10至27天可检测到东方泰勒虫，这与先前对引入受泰勒虫感染牛群的成年牛的野外研究结果一致。产犊后48小时内，新生犊牛与其母亲的酶联免疫吸附测定比值呈正相关；然而，仅在一些犊牛中可检测到母源抗体，且仅在产后4 - 4.5周内可检测到。所有犊牛在产后4 - 8周寄生虫载量达到峰值，只有一些犊牛随后产生可检测到的适应性抗体反应。
这些发现表明，东方泰勒虫的经胎盘传播在野外东方泰勒虫感染的持续存在中似乎仅起次要作用；然而，无论产后母源抗体是否存在，犊牛在4 - 8周龄时极易感染高水平的东方泰勒虫。
