Medical Entomology Section, Laboratory of Zoonotic Pathogens, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, USA.
Infect Immun. 2013 Aug;81(8):2899-908. doi: 10.1128/IAI.00542-13. Epub 2013 May 28.
Multilocus sequence typing of Borrelia hermsii isolates reveals its divergence into two major genomic groups (GG), but no differences in transmission efficiency or host pathogenicity are associated with these genotypes. To compare GGI and GGII in the tick-host infection cycle, we first determined if spirochetes from the two groups could superinfect the tick vector Ornithodoros hermsi. We infected mice with isolates from each group and fed ticks sequentially on these mice. We then fed the infected ticks on naive mice and measured GGI and GGII spirochete densities in vector and host, using quantitative PCR of genotype-specific chromosomal DNA sequences. Sequential feedings resulted in dual tick infections, showing that GGI or GGII primary acquisition did not block superinfection by a secondary agent. On transmission to naive mice at short intervals after acquisition, ticks with primary GGI and secondary GGII spirochete infections caused mixed GGI and GGII infections in mice. However, ticks with primary GGII and secondary GGI spirochete infections caused only GGII infections with all isolate pairs examined. At longer intervals after acquisition, the exclusion of GGI by GGII spirochetes declined and cotransmission predominated. We then examined GGI and GGII spirochetemia in mice following single inoculation and coinoculation by needle and found that GGI spirochete densities were reduced on multiple days when coinoculated with GGII. These findings indicate that dual GGI-GGII spirochete infections can persist in ticks and that transmission to a vertebrate host is dependent on the order of tick acquisition and the interval between acquisition and transmission events.
伯氏疏螺旋体分离株的多位点序列分型显示其分为两个主要基因组群（GG），但这些基因型与传播效率或宿主致病性没有差异。为了比较 GGⅠ和 GGⅡ在蜱-宿主感染周期中的作用，我们首先确定这两组螺旋体是否能够感染蜱的向量钝缘蜱。我们用每组的分离株感染小鼠，然后让这些蜱顺序叮咬这些小鼠。然后，我们将感染的蜱叮咬未感染的小鼠，并使用针对基因型特异性染色体 DNA 序列的定量 PCR 来测量载体和宿主中的 GGⅠ和 GGⅡ螺旋体密度。顺序喂养导致双重蜱感染，表明 GGⅠ或 GGⅡ的初次感染不会阻止二次病原体的超感染。在获得后短时间内向未感染的小鼠传播时，带有原发性 GGⅠ和继发性 GGⅡ螺旋体感染的蜱在小鼠中引起 GGⅠ和 GGⅡ的混合感染。然而，带有原发性 GGⅡ和继发性 GGⅠ螺旋体感染的蜱在所有检查的分离株对中仅引起 GGⅡ感染。在获得后较长的时间间隔内，GGⅡ螺旋体对 GGⅠ的排斥作用下降，共同传播占主导地位。然后，我们在通过针单一接种和共同接种后检查了小鼠中的 GGⅠ和 GGⅡ螺旋体血症，并发现当与 GGⅡ共同接种时，GGⅠ螺旋体密度在多日减少。这些发现表明，双 GGⅠ-GGⅡ螺旋体感染可以在蜱中持续存在，并且向脊椎动物宿主的传播取决于蜱的获得顺序和获得与传播事件之间的间隔。
