Woodbine Kerry A, Medley Graham F, Moore Stephen J, Ramirez-Villaescusa Ana, Mason Sam, Green Laura E
Department of Biological Science, University of Warwick, Coventry, CV4 7AL, UK .
BMC Vet Res. 2008 Sep 15;4:35. doi: 10.1186/1746-6148-4-35.
Neosporosis caused by the protozoan parasite Neospora caninum, is an economically important cause of abortion, stillbirth, low milk yield, reduced weight gain and premature culling in cattle. Consequently, a seroepidemiological study of N. caninum antibodies was conducted in England with 29,782 samples of blood taken from 15,736 cattle from 114 herds visited on three occasions at yearly intervals. Herds were categorised into lower (< 10%) and higher (> or = 10%) median herd seroprevalence. Hierarchical models were run to investigate associations between the sample to positive (S/P) ratio and herd and cattle factors.
Ninety-four percent of herds had at least one seropositive cow; 12.9% of adult cattle had at least one seropositive test. Approximately 90% of herds were seropositive at all visits; 9 herds (8%) changed serological status between visits. The median N. caninum seroprevalence in positive herds was 10% (range 0.4% to 58.8%). There was a positive association between the serostatus of offspring and dams that were ever seropositive. In the hierarchical model of low seroprevalence herds there was no significant association between S/P ratio and cattle age. There was a significantly lower S/P ratio in cattle in herds that were totally restocked after the foot-and-mouth epidemic of 2001 compared with those from continuously stocked herds and cattle purchased into these herds had a higher S/P ratio than homebred cattle. In the model of high seroprevalence herds the S/P ratio increased with cattle age, but was not associated with restocking or cattle origin.
There were no strong temporal changes in herd seroprevalence of N. caninum but 90% of herds had some seropositive cattle over this time period. Vertical transmission from seropositive dams appeared to occur in all herds. In herds with a high seroprevalence the increasing S/P ratio in 2-4 year old cattle is suggestive of exposure to N. caninum: horizontal transmission between adult cattle, infection from a local source or recrudescence and abortions. Between-herd movements of infected cattle enhance the spread of N. caninum, particularly into low seroprevalence herds. Some restocked herds had little exposure to N. caninum, while in others infection had spread in the time since restocking.
由原生动物寄生虫犬新孢子虫引起的新孢子虫病，是导致牛流产、死产、产奶量低、体重增加减少和过早淘汰的一个重要经济因素。因此，在英国对犬新孢子虫抗体进行了血清流行病学研究，从114个牛群的15736头牛中采集了29782份血样，每年采集一次，共采集三次。牛群被分为中位牛群血清阳性率较低（<10%）和较高（≥10%）的两类。运行分层模型以研究样本与阳性（S/P）比值与牛群和牛的因素之间的关联。
94%的牛群至少有一头血清阳性牛；12.9%的成年牛至少有一次血清阳性检测结果。约90%的牛群在所有检测中均为血清阳性；9个牛群（8%）在两次检测之间血清学状态发生了变化。阳性牛群中犬新孢子虫的中位血清阳性率为10%（范围为0.4%至58.8%）。曾为血清阳性的后代与母畜的血清状态之间存在正相关。在低血清阳性率牛群的分层模型中，S/P比值与牛的年龄之间无显著关联。与持续存栏的牛群相比，2001年口蹄疫疫情后全部重新补栏的牛群中的牛的S/P比值显著较低，且购入这些牛群的牛的S/P比值高于本地牛。在高血清阳性率牛群的模型中，S/P比值随牛的年龄增加而升高，但与重新补栏或牛的来源无关。
犬新孢子虫的牛群血清阳性率没有明显的时间变化，但在此期间90%的牛群有一些血清阳性牛。血清阳性母畜的垂直传播似乎在所有牛群中都有发生。在血清阳性率高的牛群中，2至4岁牛的S/P比值增加表明接触了犬新孢子虫：成年牛之间的水平传播、来自本地源的感染或复发及流产。感染牛在牛群间的移动会促进犬新孢子虫的传播，尤其是传播到血清阳性率低的牛群中。一些重新补栏的牛群很少接触犬新孢子虫，而在其他牛群中，感染在重新补栏后的一段时间内已经传播开来。
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