刚地弓形虫 Toxoplasma gondii

互联网2013-09-06

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<big> <big>Introduction</big> </big>

Toxoplasma gondii 是猫科动物的肠道球虫，因其滋养体形似弓形而得名。
其分类地位是： Kingdom Protista>Subkingdom Protozoa>Phylum Apicomplexa>Class Sporozoa>Order ?>Family Toxoplasmatidae> Toxoplasma gondii
该虫呈世界性分布，可感染鸟类、鱼类、哺乳动物和人，引起 Toxoplasmosis.
人群平均感染率33%，有5亿人抗体阳性。我室血清学检查数据显示重庆地区孕妇抗体阳性率20%以上。

<big> <big>Morphology</big> </big>

Trophozoite (tachyzoites and bradyzoites)

弓滋.jpg (8679 字节)

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.

toxo_tachyzoites.gif (8282 字节)

Intracellular tachyzoites of Toxoplasma gondii .

Oocyst

弓卵囊.jpg (7293 字节)

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

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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.

<big> <big>Life Cycle</big> </big>

在中间宿主体内的发育

1 Infective stage:

(1) Oocyst in feces of cat
(2) cyst or pseudocyst in muscle of animals.

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。

<big> <big> Pathogenesis </big> </big>

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。

Hydrozephalus.jpg (17739 字节)
Hydrocephalitis

Intracranial calcification.gif (225377 字节)
intracraninal calcification

<big> Chorioretinitis </big>

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

gxcbb.jpg (65786 字节)

(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。

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。

<big> <big> Epidemiology </big> </big>

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。

<big> <big>Prevention and Treatment</big> </big>

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。