刚地弓形虫 Toxoplasma gondii
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Introduction
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| Morphology |
Trophozoite (tachyzoites and bradyzoites) Indirect fluorescent antibody test. Slide shows endozoites exposed to antibody containing serum and then treated with fluorescein conjugated anti-human globulin. There is a zone of light green fluorescence around each organism. The cytoplasm appears reddish as it was counterstained with Evan's blue. × 1000. Enlarged by 5.4. In the centre is a macrophage filled with endozoites. This stage is also known as the pseudocyst. Giemsa stain. × 1000. Enlarged by 9.6. A ruptured macrophage which has liberated endozoites. Many are still lying close to the macrophage nucleus. Giemsa stain. × 1000. Enlarged by 9.6. A ruptured macrophage with the endozoites dispersed in the background. Some parasites are undergoing division. The large dense body is the macrophage nucleus. Giemsa stain. × 1000. Enlarged by 5.4. A macrophage containing endozoites and some free endozoites, stained with acridine orange. The cytoplasm of the endozoites consisting mostly of RNA takes up a red color and the nucleus consisting mainly of DNA takes up a yellowish green color. × 1000. Enlarged by 5.4. |
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Intracellular tachyzoites of Toxoplasma gondii . |
Oocyst Freshly passed Toxoplasma oocysts. Most of the oocysts have a single spororblast. Interference contrast. × 400. Enlarged by 5.4. Toxoplasma oocysts after incubation in vitro for 12 hours. Most of the oocysts have now sporulated. Interference contrast. × 400. Enlarged by 23.4. |
cyst Toxoplasma cyst from mouse brain. The cyst has partly detached from the brain tissue. Phase contrast. × 400. Enlarged by 5.4. Toxoplasma cyst from mouse brain. The cyst has completely detached from the brain tissue. Phase contrast. × 400. Enlarged by 5.4. Toxoplasma cyst from mouse brain. Showing the argyllophilic nature of the cyst wall after silver staining. This is the best method for demonstration the cyst wall. × 1000. Enlarged 5.4. Toxoplasma cyst from mouse brain. Showing the PAS positive cystozoites. The cyst wall is faintly visible. This is the best method for demonstrating the cystozoites. × 1000. Enlarged by 5.4. Toxoplasma cyst from mouse brain after H and e stain. The cyst wall is faintly visible and the nuclei appear as dark bodies inside the cyst. × 1000. Enlarged by 5.4. |
| Life Cycle |
在中间宿主体内的发育 1 Infective stage:
(1) Oocyst in feces of cat 2 感染方式和途径 经口感染。 3 肠内逸出 sporozoites, bradyzoites, tachyzoites 侵入肠壁经血或淋巴到全身各器官组织之单核吞噬细胞内寄生。 4 在中间宿主体内进行无性生殖，被寄生细胞破裂释放 tachyzoites ，再侵入新的细胞内。部分 tachyzoites 可在一些器官如脑、眼和骨骼肌内形成 cyst. 5 cysts 在宿主体内可存活数月、数年甚至终生，在免疫功能低下时可破裂，释出 bradyzoites ，侵入其它细胞内继续繁殖。 |
在终宿主（ felid ）体内的发育 1 Cat or other felines 捕食时食入 cyst 或 pseudocyst, 或者通过污染了 Oocyst 的食物或水而感染。 2 肠上皮细胞内有性生殖： Sporozoites →Schizonts→Gametocytes→Gametes→Zygotes→Oocysts in feces. 3 肠上皮细胞外发育 同中间宿主。 |
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| Pathogenesis |
1 致病因子 （1）虫株毒力 RH 株 （强毒株） Beverley 株 （弱毒株） （2） 机体免疫状态 （属Opportunistic protozoiasis） 2 致病机制 tachyzoites 导致组织急性炎症和坏死 bradyzoites 是慢性感染的主要形式， cyst 挤压器官组织，破裂后刺激机体发生变态反应，形成肉芽肿，纤维化。 3 临床分类 先天性弓形虫病 发生于初孕妇女，经胎盘感染胎儿，可致 流产 、早产、畸胎或死产。怀孕早期感染畸胎发生率高， 主要累及大脑和眼，如脑积水、脑钙化、视网膜脉络膜炎和精神、动物障碍为典型症候。 |
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| 获得性弓形虫病（多为隐性感染，属机会致病原虫，
AIDS
等病时转为急性重症，恶化。） (1) 淋巴结肿大 患者淋巴结肿大，变硬，有橡皮样感，伴有长时间低热，疲倦，肌肉不适等。 (2) 脑炎、脑膜炎、癫痫和精神异常等中枢神经系统病症
(3) 眼病，较先天性弓形虫病少见，有些不先天性感染但到成年后发作所致。 Photograph of fundus. Showing a heavily pigmented central choroidal lesion in a young person due to acquired toxoplasmosis. The whitish patches inside the lesion are areas where the sclera is exposed due to the necrosis of the retina. A sharply demarcated lesion, as seen in this photograph, is typical of both acquired and congenital toxoplasmosis. However, in some cases a more diffused lesion may be observed.(4) 其它，如心肌炎、肺炎等。 |
| Diagnosis |
1 病原学诊断 （ 1 ）涂片染色法 取病人各种体液离心后取沉淀物、或活组织穿刺物涂片，经吉氏染色后镜检、查找滋养体。 （ 2 ）动物实验和 细胞培养 法 小鼠腹腔接种，取腹腔液镜检。 |
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2
血清学试验
主要有
Sabin-Feldman氏染色试验；IFA和IHA
等。 Sabin-Feldman氏染色试验 为经典试验，感染后1-2周滴度即可达1：1024。但需活虫作抗原，操作复杂。 IFA 可检测IgM，故可确定患者是否近期感染。但有抗核抗体的患者（如类风湿关节炎、 红斑狼疮 等）可出现假阳性 IHA 操作方便，多用于大规模流行病学调查。但先天感染者阳性出现时间长，几个月内合肥仍可能为阴性。 |
| Epidemiology |
1 广泛流行的原因 2 流行环节 传染源 ： 猫科动物为主的多种哺乳动物和鸟类。猫粪+ 动物肉类 ：猪肉、羊肉等和蛋、奶制品。 途径 ：经口；胎盘为主，另外输血、器官移植也可感染。 对人来说，更多是由于吃生可半生肉而感染。 苍蝇、蟑螂可作为传播媒介。 人群 ：胎儿、婴幼儿和肿瘤、 AIDS 患者等免疫功能受累者。 |
Prevention and Treatment |
1 加强肉类检疫、改变不科学的食肉习惯：不吃生或半生的肉。 2 孕妇定期检查弓形虫抗体，不接触猫等动物。 3 药物治疗：pyrimethamine(乙胺嘧啶)、sulfa磺胺类(如：sulfadiazine等)。孕妇如在怀孕期4-5月感染则应作人工 流产 ，4-5月后感染者要用acetylspiramycin作全程治疗，不可用有致畸作用的pyrimethamine。 |
