Blastocystis hominis and travelers

B. hominis is a unicellular protozoan commonly identified in stool specimens of travelers who have returned from tropical countries. It has a world-wide distribution, and infection is more common in developing countries compared to industrialized nations. Clinical features of illness which have been attributed to Blastocystis include nausea, anorexia, abdominal pain, flatulence and acute or chronic diarrhea. The preferred method of diagnosis is a permanently stained smear of an unconcentrated stool specimen. The presence of B. hominis in stool specimens of symptomatic travelers should prompt clinicians to search for other unrecognized co-pathogens. Due to controversy regarding the pathogenicity of B. hominis in humans, clinicians are often faced with the dilemma of whether or not they should offer treatment for B. hominis infection in returned travelers. The most commonly used drugs for treatment include metronidazole and trimethoprim-sulfamethoxazole (TMP-SMX), when treatment is deemed necessary. Prevention in travelers should focus on food and water precautions as the organism is transmitted by the fecal-oral route.     

Blastocystis hominis in Hospital Employees

Several reports have appeared that either support or deny the importance of the protozoan Blastocystis hominis as an intestinal pathogen in humans. In this report, we describe the clinical characteristics of B. hominis and its response to therapy in hospital employees found to have the parasite on routine screening of stools. During the study, 49 patients with B. hominis were identified, and 413 stools were examined from these patients. Twenty-nine patients were asymptomatic (59%), and 20 had symptoms of bloating, flatulence, soft/loose stools, or constipation. Of these 20 patients, 10 had symptoms that correlated with the presence or absence of B. hominis, four had symptoms that were independent of B. homonis, and six had other intestinal parasites that could account for their symptoms. Nineteen percent of patients without treatment had eradication of B. hominis from stool on follow-up examination. Metronidazole did not increase this rate. Iodoquinol treatment eradicated the organism in 41% of patients (p less than 0.05), and resulted in the reduction or eradication of the parasite in 62%, as determined by follow-up examination.     

人芽囊原虫标本染色方法的改进

人芽囊原虫标本经肖氏液固定后,用改良的哈氏苏木素染色。结果表明,标本内部结构清晰,中心体明显,与传统的铁苏木素染色方法相比,染色效果好,制片时间短,操作步骤简单。     

人芽囊原虫的研究进展

人芽囊原虫是一种常见的人和哺乳动物肠道寄生原虫。因在有症状与无症状个体均可发现,故人芽囊原虫的致病性一直存在争议。该文从生物学、流行病学、分子生物学、免疫学、临床表现与治疗、及实验室检查等几方面简要概述近年来国内外对其研究的进展。     

Effect of trimethoprim-sulfamethaxazole in Blastocystis hominis infection

OBJECTIVE: Blastocystis hominis (B. hominis) is a common intestinal parasite that has long been considered nonpathogenic. Recently there have been many reports supporting a role for the organism as a potential pathogen. We performed a study to examine the pathogenicity of B. hominis and the effect of trimethoprim-sulfamethaxazole (TMP-SMX) on this organism. METHODS: Stool samples of patients, who came to the Department of Parasitology, Faculty of Medicine, Celal Bayar University, were examined by direct wet-mount, trichrome staining, formalin-ethyl acetate concentration, and Kinyoun acid fast techniques for intestinal parasites, and bacteriological stool cultures were performed. Fifty-three symptomatic patients (38 children and 15 adults) with two consequent stool samples positive for abundant B. hominis (five or more organisms per x400 field) and negative for other parasitic and bacterial pathogens were treated with TMP-SMX for 7 days, children 6 mg/kg TMP, 30 mg/kg SMX, and adults 320 mg TMP, 1600 mg SMX, daily. On the seventh day, at the end of treatment, stool samples of all patients were examined by same methods, and clinical symptoms were again evaluated. RESULTS: B. hominis was eradicated in 36 of 38 (94.7%) children, and 14 of 15 (93.3%) adults. Clinical symptoms disappeared in 39 (73.6%), decreased in 10 (18.9%), and no change was observed in one (1.9%) patient, whereas symptoms persisted in all three (5.7%) patients in whom B. hominis could not be eradicated. Mean number of stools per day was significantly decreased from 4.3 to 1.2 in the 33 children (p < 0.001), and decreased from 3.5 to 1.0 in the four adults (p = 0.06) with diarrhea. CONCLUSIONS: These results suggested that B. hominis may be pathogenic, especially when it is present in large numbers, and TMP-SMX is highly effective against this organism. Although there are some anecdotal reports, to our knowledge this is the first study examining the effect of TMP-SMX on B. hominis in humans.     

Questionable clinical significance of Blastocystis hominis infection

In the period from January 1986 to July 1988, Blastocystic hominis was found in moderate and numerous quantities in 103 (1.6%) of 6,262 stool specimens examined in our laboratory. There was no significant association of the detection of B. hominis with travel history or symptoms. Indeed, 20 patients (36%) with moderate to heavy infections had no gastrointestinal symptoms, and three symptomatic patients did not show clinical improvement after elimination of the parasite. Reexamination of stool samples revealed that eight untreated patients had spontaneous disappearance of B. hominis. We conclude that B. hominis probably is not responsible for clinical symptoms when detected, and additional investigations should be pursued for other etiologies of the patient's symptoms.     

人芽囊原虫的形态与超微结构

目的　观察人芽囊原虫的形态与超微结构。　方法　对人芽囊原虫培养 4～ 5 d的培养物进行多种染色后置光镜下观察形态结构 ,同时经过 4%的戊二醛固定处理后在透射电镜下观察超微结构。　结果　人芽囊原虫形态有空泡型、颗粒型、阿米巴型、复分裂型及包囊型等。分裂方式有二分裂方式及孢子分裂方式。透射电镜下可见虫体内含有细胞核、线粒体、粗面内质网、脂滴和溶酶体等细胞器 ,泡状结构内含有糖原颗粒。　结论　人芽囊原虫空泡型的泡状结构可能与储留排泄物有关 ,阿米巴型可能系该虫的致病类型。     

人芽囊原虫感染小鼠试验

目的 通过感染不同免疫状态ICR小鼠寻求人芽囊原虫(Blastocystis hominis, B.h)对小鼠的易感途径及有效感染数量。 方法 ①将104、105、106个培养３代的B.h分别经口及直肠感染ICR小鼠。② 106个B.h经直肠感染免疫功能低下该种小鼠，观察感染后不同时间小鼠胃肠道B.h繁殖情况及消化道组织病理改变。 结果 B.h经口及直肠两种途径均可使小鼠感染，免疫功能低下小鼠感染后出现行动迟缓、精神萎靡、嗜睡、体重下降等，部分小鼠出现腹泻，排粘液便等症状，个别小鼠死亡。经解剖肉眼观察见空回肠、回盲部、结肠的肠壁组织严重水肿、充血、淤血等。在小鼠胃肠道内容物中均发现B.h。病理切片显示，小肠及结肠黏膜上皮脱落，黏膜下层不同程度的炎性细胞浸润，腺体结构不完整。 结论 B.h经直肠比经口更易感染小鼠，B.h可寄生于小鼠整个胃肠道。小鼠免疫功能降低时，B.h可迅速繁殖、致病性增强，并引起严重的肠黏膜病理改变。     

Resistance of Blastocystis hominis cysts to metronidazole

Blastocystis hominis cysts concentrated from faeces were resistant to metronidazole up to a concentration of 5 mg/ml. A cysticidal drug is therefore needed for radical treatment, to avoid relapse and to prevent transmission.     

Isolate resistance of Blastocystis hominis to metronidazole

Isolates of Blastocystis hominis from infected immigrant workers from Indonesia, Bangladesh and infected individuals from Singapore and Malaysia were assessed for growth pattern and degree of resistance to different concentrations of metronidazole. Viability of the cells was assessed using eosin-brillian cresyl blue which stained viable cells green and nonviable cells red. The Bangladeshi and Singaporean isolates were nonviable even at the lowest concentration of 0.01 mg/ml, whereas 40% of the initial inoculum of parasites from the Indonesian isolate at day one were still viable in cultures with 1.0 mg/ml metronidazole. The study shows that isolates of B. hominis of different geographical origin have different levels of resistance to metronidazole. The search for more effective drugs to eliminate th parasite appears inevitable, especially since surviving parasites from metronidazole cultures show greater ability to multiply in subcultures than controls.     

Terminal Ileitis Associated with Blastocystis hominis Infection

We report on the previously unobserved clinical presentation of terminal ileitis secondary to Blastocystis hominis in a 37-yr-old white male. When the patient was treated with metronidazole, the symptoms improved and the radiographic abnormalities resolved. We believe that this is the first well-documented instance of terminal ileitis secondary to B. hominis.     

Infective arthritis due to Blastocystis hominis.

A patient with rheumatoid arthritis taking prednisone developed Blastocystis hominis acute diarrhoea, which was associated with increased inflammation and effusion of the left knee. B hominis organisms were found in synovial fluid from the left knee. The patient responded dramatically to metronidazole treatment. B hominis may become disseminated in immunosuppressed patients with diarrhoea and may cause infective arthritis.     

Blastocystis hominis: epidemiology and natural history

To study the demographic profile of Blastocystis hominis carriers from Hamilton, Canada, the Regional Parasitology Laboratory records for 1988 were reviewed, and a prospective study on carriers was conducted to clarify the natural history of the infection and ascertain the role of B. hominis as an intestinal pathogen. Retrospective analysis revealed that 8% of stool samples harbored B. hominis. The median age of the carriers was 37 years; 55% were female. Prospective analysis of 139 patients showed that most (76%) of 86 in whom B. hominis was the sole organism found (and for whom data were complete) continued to harbor the parasite in stool samples submitted a median of 57 days after the first sample. There was no correlation between the presence of B. hominis and symptoms. Thus, B. hominis, though commonly seen in stool samples submitted to this laboratory, is thought to be a commensal organism.     

婴儿感染人芽囊原虫1例报告

患儿,女性,4月龄,湖南省常德市临澧城关镇人。因无明显诱因血样便,于2006年5月8日来广西医科大学一附院儿科就诊。大便3次/d,有腥臭味,较稀烂,伴少许黏液,无浓性物,量中等,同时伴呕吐(非喷射状),无咖啡样物,进食即吐,无明显烦躁和哭闹。患儿为顺产第1胎,新法接生,出生时体重3.1