Instituto de Investigación de la Cadena Láctea (IDICAL, INTA-CONICET), Instituto Nacional de Tecnología Agropecuaria, Estación Experimental Agropecuaria Rafaela (INTA E.E.A. Rafaela), Ruta 34 km 227, Rafaela, Santa Fe CP 2300, Argentina.
Zoologische Staatssammlung München, München, Germany.
Vet Parasitol. 2024 Oct;331:110283. doi: 10.1016/j.vetpar.2024.110283. Epub 2024 Aug 6.
The aim of this study was to identify factors that play a key role in the epidemiology of bovine anaplasmosis by adapting a model primarily developed for cattle babesiosis. A cross-sectional observational study was conducted to study the proportion of calf herds in endemic stability/instability for A. marginale in a semi-arid area of Argentina. The A. marginale inoculation rate (h) was calculated from age-specific seroprevalence using double-antigen sandwich ELISA in 58 herds of 4.5-8.5-month-old calves. Herds were considered to be in endemic instability (EI) at h < 0.005 and, therefore, at risk of anaplasmosis outbreaks. A generalized linear model was performed to explore husbandry practices associated with differences in A. marginale transmission. Additionally, spatial clustering of herds with the same immunological status was analyzed using spatial scan statistics (SatScan, Bernoulli model). Spearman's correlation was used to explore a possible association between A. marginale h and Babesia bovis and B. bigemina h (data obtained in previous works). Almost half (43 %) of the herds were in the EI zone for A. marginale. Calves raised under forage combinations had a greater risk of being in EI (OR = 5.41, CI95 %OR = 1.43-20.41) than those reared exclusively on permanent pastures, where cattle density is higher (P = 0.01). Moreover, calves from herds treated only with pyrethroids to control ticks had more chances of being in EI (OR = 4.16, CI95 %OR = 1.12-15.38) than calves from herds receiving different acaricide combinations (P = 0.03). Calves from herds subjected to more than two treatments against Haematobia irritans had higher odds for EI (OR = 5.69, CI95 %OR = 1.24-26.11) than those from herds using fewer than two treatments (P = 0.02). The spatial analysis revealed no spatial clustering of the immune status of the herds (P = 0.67 and P = 0.74 for low and high incidence rates, respectively). A significant variation between farms was observed in A. marginale h (CV = 90.38 %). The correlation analysis revealed a strong epidemiological link of A. marginale h with B. bovis h (Rho=0.794, P<0.001) and B. bigemina h (Rho=0.839, P<0.001). Given that R. microplus is the only vector of B. bovis and B. bigemina in the region, the results of this work strongly suggest an active and significant role of R. microplus in the transmission of A. marginale.
本研究的目的是通过适应主要针对牛巴贝斯虫病开发的模型，确定在牛环形泰勒虫病流行病学中起关键作用的因素。在阿根廷半干旱地区进行了一项横断面观察性研究，以研究处于边缘性稳定性/不稳定性的小牛群中 A. marginale 的比例。使用双抗原夹心 ELISA 从 58 个 4.5-8.5 月龄小牛的年龄特异性血清阳性率计算 A. marginale 接种率 (h)。如果 h < 0.005，则认为牛群处于地方性不稳定 (EI)，因此有发生环形泰勒虫病暴发的风险。使用广义线性模型探索与 A. marginale 传播差异相关的畜牧业实践。此外，使用空间扫描统计 (SatScan，Bernoulli 模型) 分析具有相同免疫状态的牛群的空间聚类。使用 Spearman 相关性探索 A. marginale h 与 B. bovis 和 B. bigemina h 之间可能存在的关联（之前的研究中获得的数据）。近一半（43%）的牛群处于 A. marginale 的 EI 区。与仅在永久性牧场上饲养的牛群（牛密度较高，P = 0.01）相比，采用草料组合饲养的小牛更有可能处于 EI 区（OR = 5.41，95%CI OR = 1.43-20.41）。此外，仅用拟除虫菊酯类药物控制蜱虫的牛群中，小牛更有可能处于 EI 区（OR = 4.16，95%CI OR = 1.12-15.38），而接受不同杀螨剂组合治疗的牛群中的小牛则较少（P = 0.03）。与使用少于两种治疗方法的牛群相比，接受超过两种针对 Haematobia irritans 的治疗方法的牛群中 EI 的可能性更高（OR = 5.69，95%CI OR = 1.24-26.11）（P = 0.02）。空间分析显示牛群免疫状态没有空间聚类（低发生率和高发生率时分别为 P = 0.67 和 P = 0.74）。A. marginale h 观察到农场之间存在显著差异（CV = 90.38%）。相关性分析显示 A. marginale h 与 B. bovis h（Rho = 0.794，P<0.001）和 B. bigemina h（Rho = 0.839，P<0.001）之间存在很强的流行病学联系。鉴于 R. microplus 是该地区 B. bovis 和 B. bigemina 的唯一媒介，因此这项工作的结果强烈表明 R. microplus 在 A. marginale 的传播中起着积极和重要的作用。
