蓝氏贾第虫核纤层蛋白基因的初步研究

贾第虫一度被认为是迄今已知的最原始的真核细胞, 但近来争议日盛。利用PCR 和测序等技术, 对 蓝氏贾第虫( Giardia lamblia) 的核纤层蛋白(lamin) 基因进行了研究。结果表明: 蓝氏贾第虫基因组中存在 一个编码具有明显lamin 特征的基因序列。如该基因序列的3′- 端具有编码与核内膜亲和的特征性模体(motif ) CaaX 的序列; 具有B 型lamin 基因所特有的高度保守的27 bp 片段, 该片段编码高度保守的位于α螺旋杆状区 的9 氨基酸片段等。同时, 这些序列特征又与多细胞的后生动物存在一定差异。这些事实说明在贾第虫中已经 进化产生了典型真核细胞的B 型lamin (基因) 或至少是类似B 型的lamin (基因) , 该生物的进化地位可能并 非过去所认为的那么原始。

Nuclear matrix of the most primitive eukaryote Archezoa

Accumulating evidence suggests that unicellular Archezoa are the most primitive eukaryotes and their nuclei are of significance to the study of evolution of the eukaryotic nucleus. Nuclear matrix is an ubiquitous important structure of eukaryotic nucleus; its evolution is certainly one of the most important parts of the evolution of nucleus. To study the evolution of nuclear matrix, nuclear matrices of Archezoa are investigated. Giardia lamblia cells are extracted sequentially. Both embedment-free section EM and whole mount cell EM of the extracted cells show that, like higher eukaryotes, this species has a residual nuclear matrix in its nucleus and rich intermediate filaments in its cytoplasm, and the two networks connect with each other to form a united network. But its nuclear matrix does not have nucleolar matrix and its lamina is not as typical as that of higher eukaryotes; Western blotting shows that lamina of Giardia and two other Archezoa Entamoeba invadens and Trichomonas vaginali all contain only one polypeptide each which reacts with a mammalia anti-lamin polyclonal serum and is similar to lamin B (67 ku) of mammlia in molecular weight. According to the results and references, it is suggested that nuclear matrix is an early acquisition of the eukaryotic nucleus, and it and the "eukaryotic chromatin" as a whole must have originated very early in the process of evolution of eukaryotic cell, and their origin should be an important prerequisite of the origin of eukaryotic nucleus; in the iamin (gene) family, B-type lamins (gene) should be the ancestral type and that A-type lamins (gene) might derive therefrom.

Phylogenetic positions of several amitochondriate protozoa - Evidence from phylogenetic analysis of DNA topoisomerase II

Several groups of parasitic protozoa, as represented by Giardia, Trichomonas, Entamoeba and Microsporida, were once widely considered to be the most primitive extant eukaryotic group - Archezoa. The main evidence for this is their 'lacking mitochondria' and possessing some other primitive features between prokaryotes and eukaryotes, and being basal to all eukaryotes with mitochondria in phylogenies inferred from many molecules. Some authors even proposed that these organisms diverged before the endosymbiotic origin of mitochondria within eukaryotes. This view was once considered to be very significant to the study of origin and evolution of eukaryotic cells (eukaryotes). However, in recent years this has been challenged by accumulating evidence from new studies. Here the sequences of DNA topoisomerase 11 in G lamblia, T vaginalis and E histolytica were identified first by PCR and sequencing, then combining with the sequence data of the microsporidia Encephalitozoon cunicul and other eukaryotic groups of different evolutionary positions from GenBank, phylogenetic trees were constructed by various methods to investigate the evolutionary positions of these amitochondriate protozoa. Our results showed that since the characteristics of DNA topoisomerase 11 make it avoid the defect of 'long-branch attraction' appearing in the previous phylogenetic analyses, our trees can not only reflect effectively the relationship of different major eukaryotic groups, which is widely accepted, but also reveal phylogenetic positions for these amitochondriate protozoa, which is different from the previous phylogenetic trees. They are not the earliest-branching eukaryotes, but diverged after some mitochondriate organisms such as kinetoplastids and mycetozoan; they are not a united group but occupy different phylogenetic positions. Combining with the recent cytological findings of mitochondria-like organelles in them, we think that though some of them (e.g. diplomonads, as represented by Giardia) may occupy a very low evolutionary position, generally these organisms are not as extremely primitive as was thought before; they should be polyphyletic groups diverging after the endosymbiotic origin of mitochondrion to adapt themselves to anaerobic parasitic life.

源真核生物贾第虫与原细菌着丝粒/动粒蛋白的免疫印迹检查

报道了以蓝氏贾第虫(Giardia lamblia)作为源真核生物的代表进行检查, 并与三大枝原细菌(archaebacteria)的代表进行了比较, 贾第虫的着丝粒/动粒蛋白是最接近于原细菌的有关蛋白的。

生物的分界与前源真核生物界的提出

通过对贾第虫(Giardia)细胞的研究、观察, 发现双滴虫类的细胞核有两个极原始的特征: (1)还没有进化出核仁; (2)核被膜尚不完整。它们在核分裂方面也是极原始的。据此提出可把源真核生物(Archezoa)超界中的源真核生物界划分为两个界, 即以双滴虫门为代表的前源真核生物(Proarchezoa)界和包含目前所知的其他源真核生物的后源真核生物(Metarchezoa)界。

涡鞭毛虫(甲藻)着丝粒/动粒蛋白的检索

用ACA血清作荧光观察, 隐沟虫细胞动粒蛋白表明, 隐沟虫的这些蛋白虽结合在核骨架上, 但在间期时并不形成点状的前着丝粒。免疫印迹检查表明隐沟虫和尖尾虫的着丝粒蛋白B彼此一致, 而且与四膜虫和眼虫也高度一致。但用ACA血清作免疫印迹检查时, 尖尾虫的蛋白虽与四膜虫和眼虫的相近, 与隐沟虫的却有极大的差异。以抗动粒蛋白的单抗作此种检查时, 尖尾虫与眼虫的反应带相同, 而隐沟虫则与源真核生物(Archezoa)贾第虫(Giardia lamblia)的相同; 而且隐沟虫和贾第虫都与几种原细菌有两条相同的反应带。

无核仁原生动物蓝氏贾第虫rDNA的分布

过去的工作已表明,源真核生物(Archezoa)中的双滴虫类极其原始,核中尚无核仁发生,以蓝氏贾第虫(Giardia lamblia)作为双滴虫类的代表,用高度特异的核仁组织区银染法(改良的Ag-Ⅰ法,李靖炎,1985)在电镜下检视其rDNA在核中的分布。结果发现,代表rDNA之所在的银粒并不集中形成任何类似核仁组织区或核仁纤维区的结构;在作为对照的小眼虫(Euglena gracilis)体内,银粒则完全集中在核仁纤维区中,因此,作者以为贾第虫rDNA的这种分布代表着核仁组织区进化形成以前的一种原始状态。

贾第虫的“双等核”及其保持等同机制的研究

贾第虫是一类寄生于肠道的单细胞原生动物，也被认为是目前已知的最原始的真核细胞。它的一个十分奇特和令人感兴趣的特点是：具有在形态和大小上都很相似的左右对称的两个细胞核。已有一些证据表明贾第虫的这样的两个核在其它一些方面也都很相似甚至完全相同，如两核的DNA含量相等，两核都含有rDNA和至少一套染色体，并且在DNA复制、转录和核分裂等功能活动方面也基本都是同步的。但是，这两个核在基因的组成方面是否完全一致，甚至两核之间的对应基因（等位基因）的序列是否完全相同呢？若是，贾第虫为什么需要这样两个完全“等价”的细胞核（“双等核”）？这两个核又是如何长期保持一致而不会因两个核内发生不同的基因变异而产生差异呢？此外，目前普遍认为贾第虫至少是四倍体，即每个核至少为二倍体。那么同一个核内的等位基因是否序列也一致？保持其一致的机制又是什么？这些问题不仅饶有趣味，而且对于揭示贾第虫特殊的遗传机制乃至真核细胞基因组倍性的起源进化等问题具有重要意义。 本文首先对其两个核内是否有相同的基因组成进行了检验。我们选择了三个执行不同功能蛋白的基因为代表以检验贾第虫的两个细胞核是否都含有这些基因。这三个基因分别是：DNA拓扑异构酶II基因（topII）, 核仁蛋白KRR1基因（krr1）和目前贾第虫中报道的极少数含有内含子的基因之一的铁硫蛋白基因（fes）。利用荧光原位杂交(FISH)技术在两个核中进行了定位分析。结果表明这几个代表性的基因在贾第虫的两个细胞核中都同时存在。这提示着贾第虫的两核中具有相同的基因组成，也表明贾第虫的这两个核可能在功能方面也是“等价”的。 其次，我们对其两个核中的等位基因是否具有一致的序列进行了检验，并对其两核之间以及同一核内的等位基因保持一致的机制进行了研究。选择前人文献报道的存在多态位点（即这些位点可能是易变位点）的两个基因：fen1和pdi为研究对象，在自己建立的一个贾第虫克隆培养系上进行单细胞PCR和测序的跟踪分析。跟踪分析了18个月（约分裂1600代）后，检测到如下结果：尽管在fen1基因上尚未发现位点变异的规律，但在pdi基因上发现存在几个位点会间歇出现套峰。据此我们推测套峰的出现可能是由于其中一个等位基因发生了突变，而后套峰消失则可能是突变被恢复。这种等位基因的修复机制很可能是基因转换（gene conversion）。进而我们在贾第虫基因组中找到了参与基因转换的很多酶基因的同源基因，RT-PCR的结果也表明这些基因在贾第虫中是活跃转录的。这进一步提示了贾第虫中发生基因转换的可能性。因此以上结果不仅表明贾第虫的两核之间和同一核内的等位基因的序列都是一致的，同时还说明基因转换可能是同一核内等位基因保持一致的机制。至于两个核之间保持等位基因序列一致的机制，我们采用了两种染核的方法对大量的贾第虫细胞进行了观察，以期能从中找到两核保持等同的证据。结果发现在大量细胞群体中存在一定比例的单核细胞和一侧含有两个核的细胞。据此我们推测：贾第虫可能通过发生一侧细胞核的丢失或萎缩，然后由另外一侧的核进行复制，经过核的重排恢复正常的左右核的状态。这可能就是贾第虫消除两核基因出现的差异，保持两核之间等位基因一致乃至两个核完全等同的机制。

贾第虫的核仁基因组与真核细胞核仁的起源进化

核仁是真核细胞核中最明显的结构，是rRNA转录、加工和核糖体亚基组装的场所。核仁的起源进化无疑是真核细胞起源进化问题的一个极为重要的方面。但迄今为止，这方面的研究很少。本文首先对"不具核仁"的低等单细胞真核生物贾第虫的"核仁"基因及核糖体合成系统的基因群进行了研究，进而对已知的核仁蛋白质组的生物进行了比较基因组研究，从而从基因和基因组的角度对核仁的起源进化问题进行了较为深入的研究。获得了如下结，和结论：1）在"不具核仁"的贾第虫中分离鉴定出了典型真核细胞参与pre-rRNA加工的krr］基因；表明贾第虫中的pre-rRNA加工机制与典型真核细胞的是一致的。在具有核仁结构的典型真核细胞中，krr1基因所编码的KRRIP蛋白是参与Pre一rRNA加工的核仁定位蛋白之一。我们在一度被认为是极为原始的"不具核仁结构"的真核生物－贾弟虫的基因组中分离鉴定出了该基因，并证明该基因在贾第虫中是活跃转录的。同时，还调查发现与KRRIP形成蛋白复合体从而发挥功能的众场，其基因在贾第虫中也是存在的，这提示贾第虫的pre寸RNA加工机制与具有核仁结构的典型真核细胞是一致的。2）对贾第虫核糖体合成系统的基因群／亚基因组进行了全面调查，发现在典型真核生物中所共有的参与核搪体合成的129条保守蛋白基因中有89条在贾第虫基因组具有相应的直系同源基因，包括编码参与rRNA申基化和假尿嗜陡化的蛋白复合体成员以及存在于905、405和605复合体中的蛋白等诸多重要基因。这表明贾第虫的核糖体合成系统与典型的真核生物相似，只是参与的成分相对简单些。以上1）、2）的结果表明贾第虫虽然没有核仁结构，但其核糖体合成机制却与具核仁结构的典型真核细胞一致。这可能意味着真核细胞核仁的核糖体合成功能的起源形成是在核仁结构形成之前，那么核仁结构的形成可能是在此功能之外另有"新意"；另外也可能是由于贾第虫因适应寄生生活而导致核仁"退化"之故，虽然这种可能性偏少，但若果真如此也是生物适应性进化中的一个重要现象，值得深入研究。3）对已知核仁蛋白质组的人、酵母和拟南芥进行了比较基因组学研究。通过搜索KOG直系同源蛋白簇数据库，发现约74％的人的核仁蛋白，约75％的酵母的核仁蛋白以及约84％的拟南芥的核仁蛋白在动物、真菌和植物中都保守。这表明这些高等真核生物的核仁蛋白大都在它们分化之前就已起源形成。进一步的调查发现：共同定位于人和酵母核仁中的同源蛋白中，人有154条蛋白对应于酵母的134条蛋白，其中人的核仁蛋白相对于酵母的有10条蛋白发生了基因重复；同样的分析发现，人的核仁蛋自相对于拟南芥的有21条蛋白发生了基因重复。这些事实表明：随着真核生物的进化，至少在高等真核生物中基因重复是核仁成分复杂化和核仁进化的重要途径。4）用人的442条核仁蛋白（它们在植物和真菌中也都存在同源蛋白，但不一定是核仁蛋白）对原核生物基因组进行了搜索。结果表明，在真细菌和原（古）细菌中都能找到好多同源物，但发现下列重要现象：只在原（古）细菌有同源物的核仁蛋白要比只在真细菌中有同源物的核仁蛋白多得多，包括了RNA修饰蛋白、核糖体蛋自以及参与翻译的相关蛋白等；而只在真细菌中有同源物的核仁蛋白只是RNA螺旋酶和WD重复蛋白。因此，我们认为核仁可能是由真细菌和原细菌复合起源的，但其主体起源于原细菌。

贾第虫microRNA 及其靶基因的预测与验证

MicroRNAs (miRNAs)是一类长约21-25nt 的非编码小分子RNAs，通过与靶基因的互补结合在转录水平及转录后水平来负调控基因表达。人们已在众多高等多细胞生物中如人、果蝇、线虫、拟南芥等鉴定出众多microRNAs 分子。近来报道单细胞原生生物衣藻中也存在大量microRNAs。然而到目前为止，在被很多证据证实是最原始的单细胞真核生物贾第虫中却仍未有microRNAs 的报道。那么到底贾第虫这种具有特殊进化地位的单细胞原生动物是否存在有microRNAs 呢？如果存在的话，其microRNAs 的特点是什么？与高等多细胞生物及单细胞衣藻的 microRNA 相比又有何异同点呢？贾第虫的microRNAs 是否与其致病性相关呢？已有研究表明，贾第虫基因组中存在与RNAi 相关的Argonaute（AGO）家族蛋白和Dicer 酶。有意思的是，这些与siRNA 引起RNAi 作用关键的蛋白AGO 和Dicer 同样也是miRNA 系统的关键成份，这就提示我们在贾第虫中很有可能也存在有miRNA 并发挥功能。有研究发现在贾第虫基因组中存在大量的非编码转录物，这些大量的非编码转录物中，是否都是后来所认为的为双向启动子转录有用基因时的副产物，还是也存在一些起调控作用的RNA 分子（如miRNAs 等），需要进一步的研究。本文利用生物信息学的手段，依据miRNAs 的生物学特征，结合多种计算机预测的方法，在贾第虫基因组中筛选可能的microRNAs 分子，结果共鉴定出50 个miRNAs 候选分子，这50 个可能的贾第虫miRNAs 不具有保守性，在已知的其他物种的miRNAs 中找不到同源物。用这50 个microRNAs BLASTN 贾第虫的蛋白质编码序列及其相邻5’端和3’端各200bp 的序列，来寻找这些microRNAs 所调控的靶基因。结果表明，寻找到的贾第虫miRNA 的靶基因除很大一部分未知功能的蛋白外，还包括了很多涉及不同功能的蛋白，如VSP 蛋白（various surface proteins）这样一类表面抗原蛋白，提示我们贾第虫miRNA 可能与其致病性相关。接下来我们对其中14 个预测的贾第虫microRNAs 进行了RT-PCR 检测并克隆测序，结果表明gla-mir-6, gla-mir-35 在贾第虫滋养体细胞中稳定表达。我们的研究第一次用生物信息学结合实验的方法在贾第虫寻找到了microRNAs，为下一步深入研究这些microRNAs 在贾第虫中的功能提供了可能。

贾第虫rDNA的研究

典型的真核生物有四种rRNA（18S、5.8S、28S和5SrRNA）。一般18S、5.8S和28S的基因分别由转录间隔区（ITS）隔开而位于同一个转录单位上构成一个rRNA基因拷贝，多个rRNA基因拷贝串联形成rDNA。rDNA聚集在一起构成核仁组织区（NOR），成为核仁发生的位置。5SrRNA基因除在少数真核生物（如：酵母）中是和18S、28S rRNA基因位于同一个转录单位上外，一般是处在核仁以外的区域。贾第虫一度被认为是现存最原始的真核生物。支持这一观点的一个重要证据之一就是它还不具核仁结构。那么它的rDNA与典型真核生物的相比会有怎样的特点呢？本文在基因组的水平上对贾第虫的rDNA进行了全面调查分析，并对5S rRNA及其相关蛋白进行重点研究，得到如下结果和结论： 1）贾第虫的18S rRNA（1448bp）基因和28S rRNA（2300bp）基因比其他一些真核生物的（一般为1800bp和3400bp）要小的多，甚至比一些原核生物的相应的rRNA基因还要小。不仅如此，其5.8S rRNA基因和28SrRNA基因之间的转录间隔区（ITS2）比典型真核生物的对应区域也要短得多（只有54bp），且GC含量较高。结构预测表明该间隔区不能形成在许多真核生物中所能形成的保守的二级结构。更特别的是，贾第虫基因组中的rRNA基因序列大部分都是不完整的，并且不按照18S-5.8S-28S rRNA基因顺序排列，也没有多个完整拷贝顺序排列的区域。这提示贾第虫rRNA基因可能是以一种不同于典型真核生物的方式聚集的。因此本文认为以上这些特点可能与贾第虫不能形成典型核仁结构有关。 2）本文从贾第虫基因组中鉴定出了5S rRNA基因，并实验验证了其表达及其完整基因序列所编码的5S rRNA具有典型真核生物的T型二级结构，且具有绝大多数保守位点。RT-PCR表明该基因具有转录活性。该结果否定了前人的贾第虫没有5S rRNA的实验结果。并表明贾第虫尽管很原始，但其5S rRNA基因仍然是独立存在的和单独转录的。贾第虫基因组中总共有8个5S rRNA基因拷贝（且其中还有一个拷贝具有15个bp的异常插入）这大大低于一般真核生物的拷贝数。这些5S rRNA基因也不形成串联排列的区域。 我们还在贾第虫中鉴定出在真核生物中唯一与5S rRNA接触的核糖体蛋白L5蛋白并验证了其表达，该序列与其他真核生物的L5蛋白相似性很高，这提示贾第虫在5S rRNA基因转录出核后与L5蛋白结合形成5S RNP的过程可能与典型的真核生物是一致的。此外，我们从贾第虫中鉴定不出符合典型真核生物TFIIIA因子特征的蛋白，这提示贾第虫5S rRNA的转录起始以及转录后出核的机制可能与典型真核生物不同。过去对贾第虫的研究表明高等真核生物里RNA聚合酶III所独有的四个亚基在贾第虫中找不到同源物，而这样不完整的RNA聚合酶III已经可以在贾第虫中完成5S rRNA的转录了，这表明RNA聚合酶III所独有的这些亚基可能是为了完成其他功能而进化出来的。

贾第虫中的基因转换研究

蓝氏贾第鞭毛虫（简称贾第虫）是一种低等的单细胞原生动物，因在全世界引起肠道疾病，并被认为是目前已知的最原始的真核细胞而备受关注。它具有两个左右对称的细胞核，在形态和大小上都很相似，至少都为二倍体。长期以来一直都未有其进行减数分裂或有性生殖的报道，因此被认为是无性繁殖的。目前仅发现其存在有丝分裂过程，而且滋养体的两个细胞核在复制分离等遗传活动方面保持各自独立的状态，分别将子代核传递到子代细胞中。综合以上情形，随着长期传代培养，贾第虫两个细胞核之间及单个核内等位基因之间应该会逐渐积累较大的差异（allelic sequence heterozygosity，ASH）。但事实是贾第虫具有极低的等位基因差异，是什么原因和机制所导致的呢？本文对此进行了如下两方面的研究。其一，采用单细胞PCR技术对fenI和pdi两个基因进行了长期的跟踪观察。研究结果表明，除了极少数的位点突变（在测序结果中表现为“套峰”）外，每次的测序结果几乎完全一致，这说明贾第虫两核间和一核内的等位基因是高度一致的，其等位基因差异性非常低。对套峰位置进行统计后我们发现，pdi基因中数个位点间歇性的出现套峰，暗示了突变发生而后又被修复的过程，这提示贾第虫中肯定存在一种生物学机制，能够修复等位基因的突变，我们推测这种机制很可能是基因转换（gene conversion）。其二，本文对基因转换的基本情况进行了系统的调查。根据已有的理论模型，总结出基因转换过程的主要步骤，以及与各步骤相关的基因；之后，利用同源搜索的方法，在贾第虫基因组中搜索上述基因的同源物。调查结果表明，基因转换过程的主要步骤对应的基因在贾第虫中都存在同源物，这提示在贾第虫中确实存在发生基因转换的可能性。然后，对上述在贾第虫基因组中找到的同源基因进行了荧光原位杂交（FISH）实验和RT-PCR实验。FISH定位实验结果显示，这些基因在两个细胞核中都有杂交信号，表明这些基因在两个细胞核中都存在。 RT-PCR实验结果进一步表明，这些基因在贾第虫中都是活跃转录的。根据以上结果，本文认为贾第虫中确实存在一个维持其极低的等位基因差异的机制，该机制极可能是基因转换。

An estimate of divergence time of parazoa and eumetazoa and that of cephalochordata and vertebrata by aldolase and triose phosphate isomerase clocks

Previously we suggested that four proteins including aldolase and triose phosphate isomerase (TPI) evolved with approximately constant rates over long periods covering the whole animal phyla. The constant rates of aldolase and TPI evolution were reexamined based on three different models for estimating evolutionary distances, It was shown that the evolutionary rates remain essentially unchanged in comparisons not only between different classes of vertebrates but also between vertebrates and arthropods and even between animals and plants, irrespective of the models used, Thus these enzymes might be useful molecular clocks for inferring divergence times of animal phyla, To know the divergence time of Parazoa and Eumetazoa and that of Cephalochordata and Vertebrata, the aldolase cDNAs from Ephydatia fluviatilis, a freshwater sponge, and the TPI cDNAs from Ephydatia fluviatilis and Branchiostoma belcheri an amphioxus, have been cloned and sequenced, Comparisons of the deduced amino acid sequences of aldolase and TPI from the freshwater sponge with known sequences revealed that the Parazoa-Eumetazoa split occurred about 940 million years ago (Ma) as determined by the average of two proteins and three models, Similarly, the aldolase and TPI clocks suggest that vertebrates and amphioxus last shared a common ancestor around 700 Ma and they possibly diverged shortly after the divergence of deuterostomes and protostomes.

Detection of pathogen based on the catalytic growth of gold nanocrystals

A homogenous detection of pathogen (Giardia lamblia cysts) based on the catalytic growth of gold nanoparticles (AuNPs) has been studied. In this study, centrifugal filters were employed as tools to concentrate and separate the pathogen cells, and moreover amplify the detection signal. The catalytic growth of gold nanoparticles was verified to be positively related to gold seeds concentration. On this basis, homogenous detection of the pathogenic bacteria in liquid phase was established by means of conjugating antibody to gold seeds. Under the given experimental condition, detection limit of G. lamblia cysts was determined as low as 1.088 × 103 cells ml-1. The additional nonspecific binding tests were also conducted to verify the detection specificity. This sensing platform has been proved to be a sensitive, reliable and simple method for large-scale pathogen detection, and provide valuable insight for the development of gold nanocrystals based colorimetric biosensors.

Prevalência de parasitoses intestinais nas crianças e conhecimentos, atitudes e práticas dos encarregados de educação - Estratégias de Intervenção (Ilha do Fogo, Cabo Verde)

As doenças tropicais negligenciadas persistem exclusivamente em populações de baixa renda e marginalizadas, sendo esquecidos os progressos necessários para a sua prevenção, eliminação e erradicação. A lista destas doenças é extensa, na qual está incluída a doença parasitária intestinal com origem em agentes infecciosos como os protozários e os helmintas. De distribuição mundial, estas infecções ocorrem frequentemente em regiões quentes, húmidas e desprovidas de saneamento básico, afectando particularmente crianças e adultos jovens, devido à sua susceptibilidade e exposição. As infecções causadas por parasitas intestinais são muitas vezes assintomáticas ou com predomínio de sintomas inespecíficos, e dependendo da carga parasitária e do estado nutricional das crianças podem contribuir para o atraso de crescimento, défice ponderal e dificuldade de aprendizagem. Neste contexto, foi realizado um estudo para determinar a prevelência de parasitoses intestinais nas crianças em idade escolar e os conhecimentos, atitudes e práticas dos seus encarregados de educação, na Ilha do Fogo, Cabo Verde. A amostra abrangeu 200 crianças em idade escolar, sendo 41,7% do sexo masculino e 58,3% do sexo feminino, com idades compreendidas entre os 6 e os 16 anos. Foi observada uma amostra de fezes por cada indivíduo, tendo sido utilizadas as técnicas de laboratório de observação directa e a técnica de concentração de Ritchie, ambas com coloração de lugol. Às crianças do estudo foram também avaliadas as variáveis antropométricas, idade, estatura e peso. Aos encarregados de educação das crianças foi aplicado um questionário para identificação dos conhecimentos, atitudes e práticas relativamente à infecção por parasitas intestinais. Foram observados parasitas intestinais em 51,8% das crianças. Das sete espécies de parasitas intestinais encontradas as mais frequentes foram a Entamoeba coli e Entamoeba histolytica/dispar, seguindo-se a Giardia intestinalis e Enterobius vermicularis e, por fim Iodomoeba buetschlii, Hymenolepis nana e Ascaris lumbricóides. A associação parasitária mais frequentemente encontrada verificou-se entre as espécies Entamoeba coli e Entamoeba histolytica/dispar. Cinquenta por cento das crianças apresentavam um estado de malnutrição aguda, 14,87% um estado de malnutrição crónica e 28,40% um estado de malnutrição global. Os conhecimentos, atitudes e práticas de prevenção de infecções parasitárias intestinais por parte dos encarregados de educação, revelaram algumas deficiências. A procura de diferenças/associações entre a variável Estar parasitado e outras variáveis em estudo, permitiu concluir que as crianças parasitadas viviam em habitações com menor número de quartos, não tinham o hábito de lavar sempre as mãos depois de defecar, não bebiam água desinfectada na escola, e não tinham casa de banho na habitação. Consideramos três actores locais como indispensáveis na implementação das medidas de controlo das parasitoses intestinais na Ilha do Fogo: as delegacias de saúde, as delegações de educação e as autarquias dos três concelhos (S.Filipe, Santa Catarina e Mosteiros). Como grupos alvo e beneficiários directos da intervenção propomos a comunidade escolar (alunos, encarregados de educação, gestores, professores e cozinheiras) e os profissionais de saúde (médicos, enfermeiros, agentes sanitários e técnicos de laboratório). Como intervenções gerais definimos a formação, a educação para a saúde, a desparasitação regular, os rastreios, o diagnóstico e tratamento precoce, a melhoria do saneamento e da higiene.