National Reference Laboratory for Toxoplasmosis, Centre for Parasitic Zoonoses, Centre of Excellence in Biomedicine, Institute for Medical Research, University of Belgrade, Belgrade, Serbia.
Exp Parasitol. 2012 Jul;131(3):372-6. doi: 10.1016/j.exppara.2012.05.006. Epub 2012 May 18.
A sensitive real-time PCR technique was used to examine the distribution of Toxoplasma gondii in the blood and tissues of mice during acute and chronic infection. Groups of Swiss Albino mice, inoculated i.p. with 10(2) or 10(6) tachyzoites of the RH strain as a typical type-1 strain, or fed 10 cysts of the Me49 strain as a typical type-2 strain, were killed at different time points post-infection (p.i.), and blood and organs including the lungs, brain and liver were harvested for DNA extraction. Toxoplasma DNA was quantified by a real-time PCR targeted at the 529bp gene fragment, with a detection limit of a single parasite per g/ml of tissue. The results showed a strain- and dose-dependent spread of Toxoplasma. In infection with type-1 parasites, in case of a high infective dose, Toxoplasma DNA was detected within 24h p.i. in all analyzed tissues including the brain. Conversely, in case of a low infective dose, parasitaemia was undetectable early p.i., at a time when Toxoplasma DNA was detected in the tissues, but reached very high levels as infection progressed. With both infective doses, pre-death parasite burdens were higher in the blood than in the tissues, whereas the same loads in the lungs suggest that reaching these Toxoplasma burdens may be critical for survival. In infection with Me49 parasites, steady high parasite burdens were noted up to the end of the experiment at d42 only in the brain, parasitaemia was low but detectable throughout, and Toxoplasma DNA was completely cleared only from the liver. These data are important to better understand the pathogenesis of toxoplasmosis, and also as baseline data for the experimental evaluation of novel chemotherapeutics.
采用灵敏的实时 PCR 技术，研究了急性和慢性感染期间弓形虫在小鼠血液和组织中的分布。用 RH 株（典型的 1 型株）的 10(2)或 10(6)速殖子或 Me49 株（典型的 2 型株）的 10 个包囊经腹腔接种感染瑞士白化鼠，在感染后不同时间点（p.i.）处死，采集血液和肺、脑、肝等器官，用于 DNA 提取。通过针对 529bp 基因片段的实时 PCR 定量 Toxoplasma DNA，检测限为组织中每克/ml 寄生虫。结果表明，Toxoplasma 的传播与株系和剂量有关。感染 1 型寄生虫时，高感染剂量下，所有分析组织（包括脑）中均在感染后 24 小时内检测到 Toxoplasma DNA。相反，低感染剂量下，早期 p.i.时无法检测到寄生虫血症，此时组织中可检测到 Toxoplasma DNA，但随着感染的进展，寄生虫血症迅速升高。两种感染剂量下，死亡前的寄生虫负荷在血液中均高于组织，而肺部的相同负荷表明达到这些 Toxoplasma 负荷可能对生存至关重要。感染 Me49 寄生虫时，仅在脑内可检测到直到实验结束时（第 42 天）持续高寄生虫负荷，血液中寄生虫血症较低但可检测到，仅肝脏中可完全清除 Toxoplasma DNA。这些数据对于更好地了解弓形体病的发病机制非常重要，也是评估新型化疗药物的实验的基线数据。
