Comparative Medicine and Integrative Biology Program, Michigan State University, East Lansing, MI, 48824, United States.
Vector-borne Disease Laboratory, Maine Medical Center Research Institute, Scarborough, ME, 04074, United States.
Ticks Tick Borne Dis. 2019 Apr;10(3):682-689. doi: 10.1016/j.ttbdis.2019.02.014. Epub 2019 Feb 26.
Borrelia miyamotoi is a relapsing fever spirochete transmitted by ticks in the Ixodes ricinus complex. In the eastern United States, B. miyamotoi is transmitted by I. scapularis, which also vectors several other pathogens including B. burgdorferi sensu stricto. In contrast to Lyme borreliae, B. miyamotoi can be transmitted vertically from infected female ticks to their progeny. Therefore, in addition to nymphs and adults, larvae can vector B. miyamotoi to wildlife and human hosts. Two widely varying filial infection prevalence (FIP) estimates - 6% and 73% - have been reported previously from two vertically infected larval clutches; to our knowledge, no other estimates of FIP or transovarial transmission (TOT) rates for B. miyamotoi have been described in the literature. Thus, we investigated TOT and FIP of larval clutches derived from engorged females collected from hunter-harvested white-tailed deer in 2015 (n = 664) and 2016 (n = 599) from Maine, New Hampshire, Tennessee, and Wisconsin. After engorged females oviposited in the lab, they (n = 492) were tested for B. miyamotoi infection by PCR. Subsequently, from each clutch produced by an infected female, larval pools, as well as 100 individual eggs or larvae, were tested. The TOT rate of the 11 infected females was 90.9% (95% CI; 57.1-99.5%) and the mean FIP of the resulting larval clutches was 84.4% (95% CI; 68.1-100%). Even though the overall observed vertical transmission rate (the product of TOT and FIP; 76.7%, 95% CI; 44.6-93.3%) was high, additional horizontal transmission may be required for enzootic maintenance of B. miyamotoi based on the results of a previously published deterministic model. Further investigation of TOT and FIP variability and the underlying mechanisms, both in nature and the laboratory, will be needed to resolve this question. Meanwhile, studies quantifying the acarological risk of Borrelia miyamotoi disease need to consider not only nymphs and adults, but larval I. scapularis as well.
伯氏疏螺旋体是一种通过革螨属（Ixodes ricinus complex）传播的回归热螺旋体。在美国东部，伯氏疏螺旋体通过伊蚊（Ixodes scapularis）传播，后者还传播几种其他病原体，包括伯氏疏螺旋体。与莱姆病螺旋体不同，感染的雌性革螨可以将伯氏疏螺旋体垂直传播给后代。因此，除了若虫和成虫外，幼虫也可以将伯氏疏螺旋体传播给野生动物和人类宿主。此前，从两个垂直感染的幼虫卵囊中报告了两个差异很大的亲代感染流行率（FIP）估计值 - 6%和 73%；据我们所知，文献中尚未描述伯氏疏螺旋体的任何其他 FIP 或经卵传递（TOT）率的估计值。因此，我们调查了 2015 年（n = 664）和 2016 年（n = 599）从缅因州、新罕布什尔州、田纳西州和威斯康星州采集的猎捕白尾鹿的已饱血雌蜱中衍生的幼虫卵囊的 TOT 和 FIP。在已饱血的雌蜱产卵后，（n = 492）对其进行了 PCR 检测以确定伯氏疏螺旋体感染情况。随后，从每个感染雌蜱产生的幼虫卵囊中，以及 100 个单独的卵或幼虫中，进行了幼虫池检测。11 只感染雌蜱的 TOT 率为 90.9%（95%置信区间；57.1-99.5%），由此产生的幼虫卵囊的平均 FIP 为 84.4%（95%置信区间；68.1-100%）。尽管总体观察到的垂直传播率（TOT 和 FIP 的乘积；76.7%，95%置信区间；44.6-93.3%）较高，但根据之前发表的确定性模型的结果，可能需要额外的水平传播才能维持伯氏疏螺旋体的地方流行。需要进一步研究 TOT 和 FIP 的变异性及其内在机制，包括在自然界和实验室中，以解决这个问题。同时，量化伯氏疏螺旋体病的蜱传风险的研究不仅需要考虑若虫和成虫，还需要考虑幼虫伊蚊。
