Department of Medical Microbiology and Hygiene, University of Mainz, Obere Zahlbacherstrasse 67, 55131, Mainz, Germany.
Institute of Infectology, Friedrich-Loeffler-Institut, Südufer 10, 17493, Greifswald-Insel Riems, Germany.
Parasit Vectors. 2020 Mar 30;13(1):157. doi: 10.1186/s13071-020-04032-2.
Anaplasma phagocytophilum is a Gram-negative obligate intracellular bacterium that replicates in neutrophil granulocytes. It is transmitted by ticks of the Ixodes ricinus complex and causes febrile illness in humans and animals. We used multilocus sequence typing (MLST) and ankA gene-based typing to study the molecular epidemiology of the A. phagocytophilum strains circulating in a German cattle herd over one pasture season. The aim was to investigate whether co-infection with two distinct variants, reinfection with the same and/or superinfection by a different strain occurred during one pasture season. Eight genetic loci were sequenced in 47 PCR-positive samples from 15 animals.
Five different sequence types (ST) and four ankA alleles were detected in the cattle herd. Three different ST caused clinically overt tick-borne fever in primary infected animals. The concordance between ST and ankA allele was 100%. Therefore, the housekeeping genes used for MLST and the highly variable ankA gene were concatenated to increase resolution. Co-infection could be proven because samples of chronologically close collection dates were included. Co-infecting A. phagocytophilum strains differed by 14 to 18 single nucleotide polymorphisms (SNPs). Most superinfecting variants varied by 14 SNPs from the previous strain and appeared in median after a free interval of 31 days. Thus, it is unlikely that superinfecting strains arose by in-animal evolution. Immunity against re- or superinfection was assumed because the cattle developed clinical signs only during primary infection.
The tick-pathogen-vertebrate host interaction is probably much more complex than previously thought taking into account the frequently occurring events of co-infection, reinfection and superinfection. This complex situation could not be easily simulated in an experimental infection and underlines the value of field studies.
嗜吞噬细胞无形体（Anaplasma phagocytophilum）是一种革兰氏阴性专性细胞内细菌，在中性粒细胞中繁殖。它通过硬蜱属（Ixodes ricinus）复合物传播，引起人类和动物的发热疾病。我们使用多位点序列分型（MLST）和 ankA 基因分型来研究德国一个牛群在一个牧场季节中循环的 A. phagocytophilum 菌株的分子流行病学。目的是研究在一个牧场季节中是否发生了两种不同变体的合并感染、同一菌株的再感染和/或不同菌株的超感染。从 15 只动物的 47 个 PCR 阳性样本中对 8 个遗传位点进行了测序。
在牛群中检测到 5 种不同的序列类型（ST）和 4 种 ankA 等位基因。3 种不同的 ST 在原发性感染动物中引起了明显的临床蜱传发热。ST 和 ankA 等位基因的一致性为 100%。因此，用于 MLST 的管家基因和高度可变的 ankA 基因被串联起来以提高分辨率。由于包含了时间上接近的采集日期的样本，因此可以证明合并感染。合并感染的 A. phagocytophilum 菌株之间存在 14 至 18 个单核苷酸多态性（SNP）差异。大多数超感染变体与前一菌株的差异为 14 SNP，并在 31 天的自由间隔后出现中位数。因此，超感染菌株不太可能通过动物体内进化产生。由于牛只仅在原发性感染期间出现临床症状，因此假定对再感染或超感染具有免疫力。
考虑到合并感染、再感染和超感染的频繁发生，蜱-病原体-脊椎动物宿主的相互作用可能比以前想象的要复杂得多。这种复杂情况在实验感染和野外研究中都很难模拟，突出了野外研究的价值。
