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摘要:在最近的几十年间，由于先进的技术，溶组织阿米巴与和迪斯帕内阿米巴得已区分使阿米巴的病原学重新定义。随着对阿米巴的认识深入，在阿米巴病的流行病学，诊断，治疗和控制方面也取得了更多的知识。
关键词:溶组织阿米巴;流行;诊断;治疗
The epidemiology，diagnosis and treatment of Entamoeba histolytica.
LI Li，ZHANG Zai-xing，ZHOU Sheng.
（Yunnan Institute of Parasitic Diseases，Simao665000，Yunnan，P.R.China）
Abstract:Due to technologic advances，the definition of entamoeba has been changed in last decades by differentiating Entamoeba histolytica from Entamoeba dispar.Entamoeba histolytica is the causative agent of amoebiasis and Entamoeba dispar is not.Along with further deep understanding of the organism，the more information in epidemiology，diagnosis，treatment and control have been achieved.
Key words:Entamoeba histolytica;Epidemiology;Diagnosis;Treatment
1 Epidemiology
Amoebiasis is the third leading cause of death due to parasitic diseases globally following malaria and schistosomiasis ［1］ .The pathogen of amoebiasis was recently defined as E.histolytica which is the only species of Entamoeba causing human disease.The most com-mon manifestation of intestinal amoebiasis is amoebic colitis，and of ex-traintestinal disease is amoebic liver abscess ［2～4］ .E.histolytica has a worldwide distribution and is endemic in most countries with poor socio-economic conditions.Because E.disparwhich is a non pathogenic intestinal parasite is morphologically identical with E.histolytica，overdiagnosis amoebiasis occurs.The data on the prevalence of amoe-biasis available until now relied on the microscopy，so the real preva-lence of E.histolytica is not well understood.Based on the studies with tools that can differentiate E.histolytica and E.dispar，most in-dividuals who did not develop invasive disease were infected by E.dispar ［2，3］ .Even of those genuinely infected by E.histolytica，only about10%will develop invasive disease ［2，3］ .
2 Life cycle
E.histolytica has a simple life cycle which consists of two stages:cyst and trophozoite stage.Cysts are the transmission and in-fective form and contain four nuclei.The trophozoite is the invasive form and has the potential to cause disease.The trophozoite contains a single nucleus with a central karyosome.Cysts are about10～16μm in diameter and trophozoites about20～40μm in diameter ［3］ .Humans is infected by ingestion of food and water contaminated by cysts.After in-gestion，the cysts pass through the host intestine where eight tropho-zoites excyst in the lumen of the small intestine ［5］ .In the colon tropho-zoites multiply and encyst producing cysts which are passed in the fae-ces.In some cases the trophozoites will enter the bloodstream and in-fect other organs，such as the liver，brain and lungs.Cysts can survive in moist environments for several weeks and remain infective whilst trophozoites cannot remain viable outside the body and can not survive the upper gastrointestinal tract ［3］ .
3 Diagnosis
For years，diagnosis of amoebiasis depended upon light mi-croscopy，which can not distinguish E.histolytica from E.dispar ［2，3］ .Another limitation of the technique is the requirement for skilled staff to distinguish E.histolytica/E.dispar from non-pathogenic amoebae and even white blood cells ［8］ .Isoenzyme analysis is considered to be the gold standard for differentiating E.histolytica from E.invadensor E.moshkovskii，but it takes one several weeks and is required trained staff and specific facilities ［3，4］ .To diagnose amoebic liver-abscess，imaging techniques can be used to detect lesions of the liver，such as ultransound，computed tomography or magnetic resonance.The sensi-tivity of imaging techniques is reasonable but not their specificity ［3，4］ .False positive results from imaging techniques can be obtained in pyo-genic abscesses or necrotic tumours ［6］ .Serological tests that detect an-tibodies are still useful in those countries where amoebiasis is not en-demic，but it can not distinguish past infection from current infection in endemic areas due to the antibody persisting for years.Serology is also useful when liver lesions have been detected by imaging as antibody titres are usually very high in these cases.
ELISA based on detected antigen from stool samples have been developed by many researchers and some ELISA kits are commercially available ［1，5］ .The most used kit is TechLab E.histolytica test which can distinguish E.histolytica and E.dispar infection ［1，5］ .The kits have the advantages that there is no need to train staff，and results are available in a short time.In Bangladesh，the sensitivity of the TechLab test to detect antigens in fresh stool specimens of patients was85%and the sensitivity of PCR was87% ［7］ .The study also showed isoenzyme analysis had an excellent performance as well.But only TechLab E.histolytica test is suitable for use in the developing countries where the prevalence of E.histolytica is high ［7］ .With the recently developed molecular techniques，separating E.histolytica from E.dispar is now liable ［8］ .Based on the molecular techniques，we can get more accu-rate maps of the prevalence of E.histolytica globally.A major disad-vantage of molecular techniques for diagnosis of E.histolytica is the very high cost，therefore molecular tools are not suitable for large-scale use in developing countries.However，molecular tools can be used in the mapping of genomic diversity of E.histolyticaworldwide，which can then provide more accurate information in control methods tailored for different areas.
4 Treatment and control
Two kinds of drugs used in treatment of amoebic infections;ni-troimidazole derivatives（metronidazole，tinidazole，ornidazole）and luminal agents（paromomycin，iodoquinol or diloxanide furoate） ［2，4］ .Nitroimidazole derivative are used to treat invasive disease and the lu-minal agent can eradicate cyst passage.Advantages of the more recent nitroimidazole derivatives，such as tinidazole，are longer half-lives，good toleration and shorter periods of treatment ［8］ .Because nitroimida-zole derivatives cannot eradicate intestinal colonisation，nitroimidazole derivatives followed with luminal agent are used to treat ameobic colitis or ameobic liver abscess ［2～4］ .Drainage of ameobic liver abscesses is another useful intervention，but should only used in abscesses which are large or have a high probability of left lobe abscesses rupture，and when medical therapy is failing.For uncomplicated amoebic liver ab-scess，surgical drainage is not recommended ［4］ .
Improvement in sanitation，such as safe drinking water supplies and adequate disposal of faeces，have worked well in ameobiasis con-trol.But applying this tool worldwide is not feasible in the near future.Other methods，including screening of food handlers and health educa-tion，are useful tools in control of E.histolytica infection.As the molecular tools are rapidly developed，a vaccine is another potential tools in prevention of ameobiasis.However，as yet，an effective vac-cine has not been developed for use in humans.
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