Ali Syed A, Hill David R
Division of Infectious Diseases, University of Connecticut School of Medicine, Farmington, Connecticut, USA.
Curr Opin Infect Dis. 2003 Oct;16(5):453-60. doi: 10.1097/00001432-200310000-00012.
Giardia intestinalis (syn. duodenalis or lamblia) is one of the most common intestinal parasites in the world, with an estimated 2.8 x 10(6) infections per year in humans, and it contributes to diarrhea and nutritional deficiencies in children in developing regions. The wide prevalence of Giardia and its unique place in evolutionary biology have led to ongoing research.
Research into the basic biology of Giardia has highlighted some of its unique properties as an 'early-branching' eukaryote. Although Giardia do not contain mitochondria, they have developed pathways to perform some mitochondrial functions. Investigations into encystation and excystation have identified new gene products that are important in cyst wall formation, and signal transduction events that occur during excystation. The ability to transfect Giardia stably will lead to an improved understanding of its development and metabolism. Molecular typing of G. intestinalis isolates indicates that most animal parasites are not associated with human infection. Insights into immunology have helped define the role of IL-6 in the early control of murine giardiasis, and the contributions of IgA in controlling infection. Further studies of giardiasis in poorly nourished children in developing regions supports an important contributing role of Giardia in stunting and cognitive impairment. Finally, new diagnostic assays using antigen detection are being evaluated and a new agent, nitazoxanide, has been approved in the USA for the treatment of giardiasis and cryptosporidiosis in children.
Research into the biology of Giardia should increase knowledge about protist differentiation and will complement studies in other biological systems. Continued study of the role of Giardia in chronic diarrhea and malnutrition in developing regions will help focus strategies to improve childhood growth and nutrition.
肠贾第虫（同义词：十二指肠贾第虫或兰氏贾第虫）是世界上最常见的肠道寄生虫之一，估计每年在人类中引起280万例感染，它导致发展中地区儿童腹泻和营养缺乏。贾第虫的广泛流行及其在进化生物学中的独特地位引发了持续的研究。
对贾第虫基础生物学的研究突出了其作为“早期分支”真核生物的一些独特特性。尽管贾第虫不含有线粒体，但它们已发展出执行某些线粒体功能的途径。对包囊形成和脱囊过程的研究确定了在囊壁形成中起重要作用的新基因产物，以及脱囊过程中发生的信号转导事件。稳定转染贾第虫的能力将有助于更好地理解其发育和代谢。对肠贾第虫分离株的分子分型表明，大多数动物寄生虫与人类感染无关。免疫学方面的见解有助于确定白细胞介素-6在小鼠贾第虫病早期控制中的作用，以及免疫球蛋白A在控制感染中的作用。对发展中地区营养不良儿童贾第虫病的进一步研究支持了贾第虫在发育迟缓及认知障碍中起重要作用。最后，正在评估使用抗原检测的新诊断方法，一种新药硝唑尼特已在美国被批准用于治疗儿童贾第虫病和隐孢子虫病。
对贾第虫生物学的研究应增加对原生生物分化的认识，并将补充其他生物系统的研究。继续研究贾第虫在发展中地区慢性腹泻和营养不良中的作用，将有助于集中精力制定改善儿童生长和营养的策略。
