Laboratory of Histology and Embriology, Institute of Biomedical Sciences, Federal University of Uberlândia, 38405-320 Uberlândia, MG, Brazil.
Placenta. 2011 Feb;32(2):116-20. doi: 10.1016/j.placenta.2010.11.012. Epub 2010 Dec 10.
Toxoplasma gondii is an obligate intracellular protozoan parasite that causes a variety of clinical syndromes, but the infection is severe in immunocompromised individuals and during pregnancy due to the possibility of transplacental transmission of the parasite causing congenital toxoplasmosis. Vertical transmission of the parasite usually occurs when females are primarily infected during pregnancy. Calomys callosus is resistant to T. gondii ME49 strain, which presents a moderate virulence and congenital disease occurs only during the acute phase of infection. The aim of this study was to determine whether vertical transmission occurs when females of C. callosus chronically infected with ME49 strain of T. gondii are reinfected with a highly virulent strain (RH, type I). Females were infected with cysts of the ME49 strain. On the 1st day of pregnancy, animals were reinfected with tachyzoites of the RH strain. In the 19th day of pregnancy, placentas and embryos were processed for morphological analysis, immunohistochemistry and for detection of the parasite by PCR and mouse bioassay. Morphological and immunohistochemical analyses revealed the presence of parasites only in placental tissues. Mouse bioassay results showed seroconversion only in mice that were inoculated with placental tissues. Also, T. gondii DNA was detected only in placental samples. Congenital toxoplasmosis does not occur in C. callosus females chronically infected with the moderately virulent ME49 strain of T. gondii and reinfected with the highly virulent RH strain, thus indicating that primary T. gondii infection before pregnancy leads to an effective long-term immunity preventing transplacental transmission to the fetus.
刚地弓形虫是一种专性细胞内寄生的原虫，可引起多种临床综合征，但在免疫功能低下者和妊娠期间，由于寄生虫有可能经胎盘传播导致先天性弓形虫病，感染较为严重。寄生虫的垂直传播通常发生在妊娠期间女性初次感染时。Callomys callosus 对 T. gondii ME49 株具有抗性，该株具有中等毒力，先天性疾病仅在感染的急性期发生。本研究旨在确定慢性感染 ME49 株 T. gondii 的 Calomys callosus 雌性动物在再次感染高毒力株（RH，I 型）时是否会发生垂直传播。雌性动物感染 ME49 株的包囊。在妊娠第 1 天，动物用 RH 株的速殖子再次感染。在妊娠第 19 天，处理胎盘和胚胎进行形态分析、免疫组织化学以及通过 PCR 和小鼠生物测定检测寄生虫。形态学和免疫组织化学分析显示仅在胎盘组织中存在寄生虫。小鼠生物测定结果仅显示在接种胎盘组织的小鼠中发生血清转化。此外，仅在胎盘样本中检测到 T. gondii DNA。慢性感染中等毒力 ME49 株 T. gondii 并再次感染高毒力 RH 株的 Calomys callosus 雌性动物不会发生先天性弓形虫病，这表明妊娠前的初次 T. gondii 感染会导致有效的长期免疫，防止向胎儿的胎盘传播。
