奶牛群中噬吞噬细胞无形体自然感染的流行病学、遗传变异和临床过程。
Epidemiology, genetic variants and clinical course of natural infections with Anaplasma phagocytophilum in a dairy cattle herd.
机构信息
Comparative Tropical Medicine and Parasitology, Faculty of Veterinary Medicine, Ludwig-Maximilians-University Munich, Munich, Germany.
Present Address: Federal Research Institute for Animal Health, Institute of Infectology, Friedrich-Loeffler-Institute, Riems, Germany.
出版信息
Parasit Vectors. 2018 Jan 8;11(1):20. doi: 10.1186/s13071-017-2570-1.
BACKGROUND
Anaplasma phagocytophilum is an obligate intracellular, tick-transmitted bacterium that causes granulocytic anaplasmosis in humans and several mammalian species including domestic ruminants where it is called tick-borne fever (TBF). Different genetic variants exist but their impact with regard to putative differences in host associations and pathogenicity are not yet completely understood.
METHODS
Natural infections with A. phagocytophilum in a dairy cattle herd in Germany were investigated over one pasture season by using serology, haematology, blood chemistry and polymerase chain reaction (PCR). Sequence analysis of partial 16S rRNA, groEL, msp2 and msp4 genes of A. phagocytophilum was carried out in order to trace possible genetic variants and their relations between cattle, roe deer (Capreolus capreolus) and ticks (Ixodes ricinus) in this area.
RESULTS
In total 533 samples from 58 cattle, 310 ticks, three roe deer and one wild boar were examined. Our results show (i) typical clinical symptoms of TBF in first-time infected heifers, such as high fever, reduced milk yield, lower limb oedema and typical haematological and biochemical findings such as severe leukopenia, erythropenia, neutropenia, lymphocytopenia, monocytopenia, a significant increase in creatinine and bilirubin and a significant decrease in serum albumin, γ-GT, GLDH, magnesium and calcium; (ii) a high overall prevalence of A. phagocytophilum infections in this herd as 78.9% (15/19) of the naïve heifers were real-time PCR-positive and 75.9% (44/58) of the entire herd seroconverted; and (iii) a high level of sequence variation in the analysed genes with five variants of the 16S rRNA gene, two variants of the groEL gene, three variants of the msp2 gene and four variants in the msp4 gene with certain combinations of these variants.
CONCLUSIONS
In cattle particular combinations of the genetic variants of A. phagocytophilum occurred, whereas three roe deer showed different variants altogether. This is indicative for a sympatric circulation of variants in this small geographical region (< 1 km). Both re- and superinfections with A. phagocytophilum were observed in five cattle showing that infection does not result in sterile immunity. For prevention of clinical cases we suggest pasturing of young, not pregnant heifers to reduce economical losses.
背景
嗜吞噬细胞无形体（Anaplasma phagocytophilum）是一种专性细胞内、蜱传播的细菌，可引起人类和包括家养反刍动物在内的多种哺乳动物的粒细胞无形体病，在这些动物中该病被称为蜱传发热（Tick-borne fever，TBF）。存在不同的遗传变异体，但它们对宿主关联和致病性方面的潜在差异的影响尚不完全清楚。
方法
通过血清学、血液学、血液化学和聚合酶链反应（PCR），对德国一个奶牛场一个牧场季节内的自然感染情况进行了研究。对嗜吞噬细胞无形体的部分 16S rRNA、groEL、msp2 和 msp4 基因进行序列分析，以追踪该地区牛、狍（Capreolus capreolus）和蜱（Ixodes ricinus）中可能存在的遗传变异体及其关系。
结果
共检查了 58 头牛、310 只蜱、3 只狍和 1 只野猪的 533 份样本。结果表明：（i）首次感染的小母牛出现典型的 TBF 临床症状，如高热、产奶量下降、下肢水肿和典型的血液学和生化发现，如严重白细胞减少症、红细胞减少症、中性粒细胞减少症、淋巴细胞减少症、单核细胞减少症、肌酐和胆红素显著增加，以及血清白蛋白、γ-GT、GLDH、镁和钙显著降低；（ii）该牛群中 A. phagocytophilum 感染的总体患病率很高，19 只小母牛中有 78.9%（15 只）实时 PCR 阳性，整个牛群中有 75.9%（44 只）血清学转换；（iii）分析基因中的序列变异水平很高，16S rRNA 基因有 5 个变异体，groEL 基因有 2 个变异体，msp2 基因有 3 个变异体，msp4 基因有 4 个变异体，这些变异体之间存在特定的组合。
结论
在牛中，A. phagocytophilum 的遗传变异体存在特定的组合，而 3 只狍则显示出完全不同的变异体。这表明在这个小地理区域（<1km）中，变异体存在共生循环。5 只牛出现了 A. phagocytophilum 的再感染和超感染，这表明感染不会导致无菌免疫。为了预防临床病例，我们建议放牧未怀孕的小母牛以减少经济损失。
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