Parameters such as pathogen dose and inoculation route are paramount in animal models when studying disease pathogenesis. Here, clinical findings, including foetal mortality, parasite transmission rates and lesion severity, and immune responses were evaluated in Asturiana pregnant heifers at day 110 of gestation challenged with a virulent (Nc-Spain7) Neospora caninum isolate. Four different doses of parasite tachyzoites were inoculated intravenously (IV1, 107 parasites, n = 6; IV2, 105, n = 6; IV3, 103, n = 6; and IV4, 102, n = 5), and the subcutaneous (SC) inoculation route was also assessed for the dose of 105 tachyzoites (SC, n = 6). In addition, a control group (n = 4 pregnant heifers) was evaluated. Foetal death was observed in all infected groups from 25 to 62 days post-infection, varying with the dose (IV1:4/6, IV2:3/6; IV4:2/5, IV3:1/6), and was three times less frequently associated with the SC route than IV inoculation (1/6 vs. 3/6). A dose-dependent effect for parasite loads in placental and foetal brain tissues was also detected. After SC challenge, a reduced number of tachyzoites were able to reach foetal brain tissues, and no lesions were observed. In calves, specific IgG responses in precolostral sera were mainly associated with high-dose groups (IV1 [100.0%] and IV2 [66.7%]), and cerebral parasite DNA detection was scarce (3/18). In dams, IFN-γ production and the dynamics of anti-N. caninum IgG antibodies varied with the dose, and the cell-mediated immune response was also found to be route-dependent. Our results confirm the influence of parasite dose and inoculation route on the outcome and dynamics of bovine neosporosis at mid-gestation.

中文翻译：

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妊娠中期强毒新孢子虫Nc-Spain7分离株的激发剂量和接种途径的影响。

在研究疾病发病机理时，诸如病原体剂量和接种途径之类的参数在动物模型中至关重要。在这里，在妊娠第110天接受强毒（Nc-Spain7）新孢子虫分离株攻击的Asturiana怀孕小母牛中，评估了包括胎儿死亡率，寄生虫传播率和病变严重程度以及免疫反应在内的临床发现。静脉内接种了四种不同剂量的寄生虫速殖子（IV1，107寄生虫，n = 6; IV2，105，n = 6; IV3，103，n = 6; IV4，102，n = 5）和皮下注射（SC ）还评估了105种速殖子（SC，n = 6）的接种途径。此外，评估了一个对照组（n = 4个怀孕的小母牛）。感染后25至62天，所有感染组均观察到胎儿死亡，随剂量的不同而不同（IV1：4/6，IV2：3/6； IV4：2/5，IV3：1/6），与SC路径相关的频率比静脉接种的频率低三倍（1/6比3/6）。还检测到胎盘和胎儿脑组织中寄生虫负荷的剂量依赖性效应。SC攻击后，能够到达胎儿脑组织的速殖子数量减少，并且未观察到病变。在犊牛中，初大肠前血清中的特异性IgG反应主要与高剂量组有关（IV1 [100.0％]和IV2 [66.7％]），并且脑寄生虫DNA检测很少（3/18）。在大坝中，IFN-γ的产生和抗N的动力学。犬IgG抗体随剂量的变化而变化，并且还发现细胞介导的免疫反应是途径依赖性的。我们的结果证实了寄生虫剂量和接种途径对妊娠中期牛新孢子虫病的结局和动力学的影响。