Abstract: Objective　To investigate the development and dynamic changes of cysts in the brain of mice following infection with different forms of Toxoplasma gondii, so as to provide insights into for toxoplasmosis prevention and control. Methods　ICR mice at ages of 6 to 8 weeks, each weighing 20 to 25 g, were intraperitoneally injected with tachyzoites of the T. gondii PRU strain at a dose of 1 × 105 tachyzoites per mouse, orally administered with cysts at a dose of 20 oocysts per mouse or oocysts at a dose of 200 oocysts per mouse for modeling chronic T. gondii infection in mice, and the clinical symptoms and survival of mice were observed post⁃infection. Mice were orally infected with T. gondii cysts at doses of 10 (low⁃dose group), 20 (medium⁃dose group), 40 cysts per mouse (high⁃dose group), and the effect of different doses of T. gondii infections on the number of cysts was examined in the mouse brain. Mice were orally administered with T. gondii cysts at a dose of 20 cysts per mouse, and grouped according to gender (female and male) and time points of infections (20, 30, 60, 90, 120, 150, 180 days post⁃infection), and the effects of gender and time points of infections on the number of cysts was examined in the mouse brain. In addition, mice were divided into the tachyzoite group (Group T), the first⁃generation cyst group (Group C1), the second⁃generation cyst group (Group C2), the third⁃generation cyst (Group C3) and the fourth⁃generation cyst group (Group C4). Mice in the Group T were intraperitoneally injected with T. gondii tachyzoites at a dose of 1 × 105 tachyzoites per mouse, and the cysts were collected from the mouse brain tissues 30 days post⁃infection, while mice in the Group C1 were orally infected with the collected cysts at a dose of 30 cysts per mouse. Continuous passage was performed by oral administration with cysts produced by the previous generation in mice, and the effect of continuous passage on the number of cysts was examined in the mouse brain. Results　Following infection with T. gondii tachyzoites, cysts and oocysts in mice, obvious clinical symptoms were observed on days 6 to 113 and mice frequently died on days 7 to 12. The survival rates of mice were 67.0%, 87.0% and 53.0%, and the mean numbers of cysts were (516.0 ± 257.2), (1 203.0 ± 502.0) and (581.0 ± 183.1) in the mouse brain (F = 11.94, P < 0.01) on day 30 post⁃infection with T. gondii tachyzoites, cysts and oocysts, respectively, and the numbers of cysts in the brain tissues were significantly lower in mice infected with T. gondii tachyzoites and oocysts than in those infected with cysts (all P values < 0.01). The survival rates of mice were 87.0%, 87.0% and 60.0%, and the mean numbers of cysts were (953.0 ± 355.5), (1 084.0 ± 474.3) and (1 113.0 ± 546.0) in the mouse brain in the low⁃, medium⁃ and high⁃dose groups on day 30 post⁃infection, respectively (F = 0.42, P > 0.05). The survival rates of male and female mice were 73.0% and 80.0%, and the mean numbers of cysts were (946.4 ± 411.4) and (932.1 ± 322.4) in the brain tissues of male and female mice, respectively (F = 1.63, P > 0.05). Following continuous passage, the mean numbers of cysts were (516.0 ± 257.2), (1 203.0 ± 502.0), (896.8 ± 332.3), (782.5 ± 423.9) and (829.2 ± 306.0) in the brain tissues of mice in the T, C1, C2, C3 and C4 groups, respectively (F = 4.82, P < 0.01), and the number of cysts was higher in the mouse brain in Group 1 than in Group T (P < 0.01). Following oral administration of 20 T. gondii cysts in mice, cysts were found in the moues brain for the first time on day 20 post⁃infection, and the number of cysts gradually increased over time, peaked on days 30 and 90 post⁃infection and then gradually decreased; however, the cysts were still found in the mouse brain on day 180 post⁃infection. Conclusions　There is a higher possibility of developing chronic T. gondii infection in mice following infection with cysts than with oocysts or tachyzoites and the most severe chronic infection is seen following infection with cysts. The number of cysts does not correlate with the severity of chronic T. gondii infection, and the number of cysts peaks in the mouse brain on days 30 and 90 post⁃infection.

Key words: Toxoplasma gondii, Chronic toxoplasmosis, Cyst, Oocyst, Tachyzoite, Brain tissue, Mouse

摘要： 目的　观察不同形态刚地弓形虫感染后小鼠脑内包囊形成及其动态变化，为弓形虫病防控提供依据。方法　取6～8周龄ICR小鼠（20～25 g）建立慢性弓形虫感染模型，其中弓形虫PRU株速殖子按1 × 105个/只剂量腹腔注射感染小鼠，包囊和卵囊分别按20、200个/只剂量通过灌胃针口服感染小鼠，观察感染后小鼠临床症状和存活情况。分别以10（低剂量组）、20（中剂量组）、40个包囊/只（高剂量组）剂量感染小鼠，观察弓形虫不同感染剂量对小鼠脑内包囊数量的影响。将小鼠按性别（雌、雄性）、感染时间（感染后20、30、60、90、120、150、180 d）分组，按20个/只剂量口服弓形虫包囊后，分别观察性别和感染时间对小鼠脑内包囊数量的影响。将小鼠分成速殖子组（T组）、包囊1代组（C1组）、包囊2代组（C2组）、包囊3代组（C3组）、包囊4代组（C4组）；T组小鼠按1 × 105个/只剂量腹腔注射弓形虫速殖子，感染后第30天处死小鼠并收集其脑组织内包囊，再按20个/只感染C1组小鼠。此后每一代小鼠均采用上一代所产生包囊进行口服连续传代，观察连续传代对小鼠脑内弓形虫包囊数量的影响。结果　以弓形虫速殖子、包囊、卵囊分别感染小鼠，感染第6～13天小鼠出现明显临床症状、感染第7～12 天小鼠出现集中死亡。感染第30天时，感染速殖子、包囊、卵囊的小鼠存活率分别为67.0%、87.0%、53.0%，平均脑内包囊数量分别为（516.0 ± 257.2）、（1 203.0 ± 502.0）、（581.0 ± 183.1）个，差异有统计学意义（F = 11.94，P < 0.01），感染速殖子、卵囊的小鼠脑内包囊数低于感染包囊的小鼠（P均< 0.01）。感染后第30天，低、中、高剂量组小鼠存活率分别为87.0%、87.0%、60.0%，平均脑内包囊数量分别为（953.0 ± 355.5）、（1 084.0 ± 474.3）、（1 113.0 ± 546.0）个，差异无统计学意义（F = 0.42，P > 0.05）；雄、雌性组小鼠存活率分别为73.0%和80.0%，平均脑内包囊数量分别为（946.4 ± 411.4）、（932.1 ± 322.4）个，差异无统计学意义（F = 1.63，P > 0.05）。通过连续传代感染后， T、C1、C2、C3、C4组小鼠平均脑内包囊数量分别为（516.0 ± 257.2）、（1 203.0 ± 502.0）、（896.8 ± 332.3）、（782.5 ± 423.9）、（829.2 ± 306.0）个，差异有统计学意义（F = 4.82，P < 0.01）；C1组小鼠脑内包囊数高于速殖子组，差异有统计学意义（P < 0.01）。小鼠口服20个包囊后，感染第20天首次查见脑内弓形虫包囊，随感染时间延长脑内包囊数量逐渐增加；至感染第30、90天时，脑内包囊数量分别达峰值，此后逐步下降，至感染第180天时仍能查见脑内包囊。结论　刚地弓形虫包囊较速殖子、卵囊感染后形成慢性感染的可能性更高，且慢性感染程度亦最严重；感染弓形虫包囊数量与慢性感染严重程度无关；脑内包囊形成数量于感染第30天和90天时达高峰。 　

关键词: 刚地弓形虫, 慢性弓形虫病, 包囊, 卵囊, 速殖子, 脑组织, 小鼠