Blastocystis, urticaria, and skin disorders: review of the current evidences.

Blastocystis is one of the most common intestinal protozoan parasites worldwide, which is linked to cutaneous lesions and urticaria. In a setting of systematic review, the data on the association of Blastocystis infection with cutaneous lesions were searched in order to summarize the main clinical symptoms, diagnostic methods, treatment, and outcome of the patients. The search identified 28 eligible articles, including 12 cross-sectional studies and 16 case reports/case series (including 23 cases). A diverse spectrum of skin symptoms, mainly urticaria, rash, and itching, was reported from the studies. Of the 23 infected cases with the skin symptoms, gastrointestinal symptoms were reported from the 16 cases, whereas 7 cases with urticaria had asymptomatic infection. The most frequent subtypes were ST1, ST2, and ST3, respectively. Metronidazole, paromomycin, and tinidazole were the most prescribed drugs in patients with single Blastocystis infection. Notably, urticaria and other cutaneous symptoms of all treated patients were resolved after treatment. In conclusion, this study indicates that Blastocystis infection can be a neglected cause of urticaria and skin disorders. Since the treatment of Blastocystis infection is simple, screening and treatment of this infection should be considered in patients with urticaria and other skin disorders.

Saccharomyces boulardii inhibits the expression of pro-inflammatory cytokines and inducible nitric oxide synthase genes in the colonic mucosa of rats experimentally-infected with Blastocystis subtype-3 cysts.

Blastocystis spp. is the most frequent infectious unicellular, luminal parasite in all species of animals and humans. It has been linked to diarrhoea and irritable bowel syndrome. Saccharomyces boulardii (Sb) is a widely used probiotic that previously showed efficacy against several intestinal pathogens. The aim of this study was to investigate the therapeutic role of Sb on Blastocystis spp. Methods: Five groups of Blastocystis subtype-3 infected rats were treated with either live Sb alone, metronidazole (MTZ) alone, Sb extract, both Sb and MTZ, or placebo-treated besides the noninfected control group. Assessment of treatment effectiveness was done by study of parasitological cure rate, histopathological effect and analysis of the colonic mucosal level of mRNAs expressions for the proinflammatory cytokines interleukin-6 (IL-6), IL-8, tumour necrosis factor alpha (TNF-α) and Inducible nitric oxide synthase (iNOS) by real-time reverse transcription-polymerase chain reaction (real-time RT-PCR). Results showed that live Sb significantly improved the histological characteristics and decreased the cytokines and iNOS in the colonic mucosa. Co-administration of live Sb together with MTZ gave a better effect than other treatments and had early efficacy and revealed a 100% reduction of the parasite stages from both the stool and intestinal wash fluid.

Exacerbated symptoms in Blastocystis sp.-infected patients treated with metronidazole: two case studies.

Blastocystis sp. is a gastrointestinal (GI) protozoan parasite reported to cause non-specific GI symptoms including diarrhea, flatulence, abdominal pain, and nausea. Complete eradication of Blastocystis sp. is rather challenging even with the drug of choice, i.e., metronidazole. Here, we report on two Blastocystis sp.-infected individuals, who presented increased parasite load and exacerbated symptoms upon treatment with the usual recommended dosage and regime of metronidazole. The two studies uniquely demonstrate for the first time a cyst count as high as fivefold more than the original cyst count before treatment and show an exacerbation of GI symptoms despite treatment. The study provides additional support in recognizing metronidazole resistance in Blastocystis sp. and its consequences towards the pathogenicity of the parasite.

Blastocystis Hominis and Chronic Abdominal Pain in Children: Is there an Association between Them?

Chronic abdominal pain has many etiologies, one of them being parasites. The aim of this study was to find an association between chronic abdominal pain in children and Blastocystis hominis (Bh). Clinical files of patients with Bh and functional abdominal pain were reviewed. A comparison was made between patients who showed an improvement of their symptoms and those who did not. Out of the 138 patients who had functional abdominal pain and Bh, 37 patients did not receive any treatment (26.8%), while 101 received it and were treated with different antimicrobial agents (73.2%); regarding the improvement of symptoms, a statistically significant difference (p < 0.001) was observed. Chronic abdominal pain in children has different etiologies; however, we have documented through this work that it is appropriate to provide antimicrobial treatment for patients with Bh and chronic abdominal pain.

Atorvastatin: In-Vivo Synergy with Metronidazole as Anti-Blastocystis Therapy.

Blastocystis is an enteric Straminopile in tropical, subtropical and developing countries. Metronidazole has been a chemotheraputic for blastocystosis. Failures in its regimens were reported and necessitate new studies searching for alternative therapeutic agents. Aim of current study is to investigate potential effects of Atorvastatin (AVA) compared to the conventional chemotherapeutic MTZ in experimentally Blastocystis-infected mice. Anti-Blastocystis efficacy of AVA was evaluated parasitologically, histopathologically and by transmission electron microscopy using MTZ (10 mg/kg) as a control. Therapeutic efficacy of AVA was apparently dose-dependent. Regimens of AVA (20 and 40 mg/kg) proved effective against Blastocystis infections with high reduction in Blastocystis shedding (93.4-97.9%) compared to MTZ (79.3%). The highest reductions (98.1% and 99.4%) were recorded in groups of combination treatments AVA 20-40 mg/kg and MTZ 10 mg/kg. Blastocystis was nearly eradicated by the 20th day post infection. Genotype analysis revealed that genotype I was most susceptible, genotype III was less. Histopathologic and ultrastructural studies revealed apoptotic changes in Blastocystis and significant improvement of intestinal histopathological changes more remarkable in combinational therapy groups. Thus, the present study offers AVA as a potential candidate for Blastocystis therapy combined with MTZ.

Blastocystis: how do specific diets and human gut microbiota affect its development and pathogenicity?

Blastocystis is an enteric parasite that inhabits the gastrointestinal tract of humans and many animals. This emerging parasite has a worldwide distribution. It is often identified as the most common eukaryotic organism reported in human fecal samples. This parasite is recognized and diagnosed more often than ever before. Furthermore, some strains develop resistance against currently recommended drugs, such as metronidazole; therefore, the use of natural remedies or special diets has many positive aspects that may address this problem. The goal of this review is to compare natural treatments and various diets against the efficacy of drugs, and describe their influence on the composition of the gut microbiota, which affects Blastocystis growth and the occurrence of symptoms. This article reviews important work in the literature, including the classification, life cycle, epidemiology, pathogenesis, pathogenicity, genetics, biology, and treatment of Blastocystis. It also includes a review of the current knowledge about human gut microbiota and various diets proposed for Blastocystis eradication. The literature has revealed that garlic, ginger, some medical plants, and many spices contain the most effective organic compounds for parasite eradication. They work by inhibiting parasitic enzymes and nucleic acids, as well as by inhibiting protein synthesis. The efficacy of any specific organic compound depends on the Blastocystis subtype, and, consequently, on its immunity to treatment. In conclusion, the article discusses the findings that human gut microbiota composition triggers important mechanisms at the molecular level, and, thus, has a crucial influence on the parasitic pathogenicity.

Low efficacy of metronidazole in the eradication of Blastocystis hominis in symptomatic patients: Case series and systematic literature review. / Escasa eficacia de metronidazol en la erradicación de Blastocystis hominis en pacientes sintomáticos: serie de casos y revisión sistemática de la literatura.

INTRODUCTION: Blastocystis hominis (B. hominis) is a protozoan commonly found in the gastrointestinal tract. There are doubts about its clinical significance. Metronidazole (MTZ) is the recommended first-line treatment. MATERIALS AND METHODS: A retrospective review was carried out between 2011 and 2012. A total of 151 samples were randomly selected from 383 samples positive for B. hominis. Inclusion criteria were: suggestive symptoms, treatment indication and microbiological follow-up. A systematic review was performed of all studies that evaluated the effect of MTZ on B. hominis infection. RESULTS: Forty-six patients met the inclusion criteria (64% women; age, 44.2±2 years). MTZ was used in 39 patients, 31 of whom obtained a clinical response (79.5%) but only 15 a microbiological response (48.4%). No dose-effect relationship was observed. Twenty patients with no initial microbiological response received a second round of treatment (MTZ, cotrimoxazole, paramomycin, others), with a microbiological response in 70%. Overall, B. hominis was cured in 72% (95% CI: 57%-83%). Of 54 treatments associated with a clinical response, a microbiological response occurred in 31 (57%), while in the remaining 12 with no clinical response, microbiological cure was observed in only 2 (17%) (P=.022). The eradication rate in the systematic review varied between 0% and 100%. CONCLUSIONS: There seems to be a relationship between the clinical and microbiological response to B. hominis treatment. The microbiological response to MTZ treatment is insufficient in our geographical setting. The systematic review shows that the response to MTZ is very variable.

Increase number of mitochondrion-like organelle in symptomatic Blastocystis subtype 3 due to metronidazole treatment.

Blastocystis sp., an intestinal organism is known to cause diarrhea with metronidazole regarded as the first line of treatment despite reports of its resistance. The conflicting reports of variation in drug treatment have been ascribed to subtype differences. The present study evaluated in vitro responses due to metronidazole on ST3 isolated from three symptomatic and asymptomatic patients, respectively. Symptomatic isolates were obtained from clinical patients who showed symptoms such as diarrhea and abdominal bloating. Asymptomatic isolates from a stool survey carried out in a rural area. These patients had no other pathogens other than Blastocystis. Ultrastructural studies using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) revealed drug-treated ST3 from symptomatic patients were irregular and amoebic with surface showing high-convoluted folding when treated with metronidazole. These organisms had higher number of mitochondrion-like organelle (MLO) with prominent cristae. However, the drug-treated ST3 from asymptomatic persons remained spherical in shape. Asymptomatic ST3 showed increase in the size of its central body with the MLO located at the periphery.

BLASTOCYSTIS SP. AND BLASTOCYSTIS RATTI IN A BRAZILIAN PORCUPINE (COENDOU PREHENSILIS) WITH DIARRHEA.

A hand-raised, 5-mo-old, intact male Brazilian porcupine (Coendou prehensilis) was evaluated for chronic diarrhea, failure to thrive, and anorexia. On presentation the porcupette was dull, dehydrated, and passing yellow, malodourous, watery diarrhea. Cytologic examination of feces revealed a large number of organisms, morphologically consistent with Blastocystis. Blastocystis polymerase chain reaction (PCR) performed on feces was positive. Direct sequencing on two sequential samples confirmed the presence of Blastocystis ratti and a novel Blastocystis sequence. The porcupette was treated supportively, which included a 4-wk metronidazole course. Diarrhea resolved within 2 wk of treatment, and the animal's growth rate dramatically improved. Recheck PCR was negative for Blastocystis. Although an important and controversial cause of diarrhea in immunocompromised humans, this organism is not well recognized as a potential pathogen and zoonosis in zoo animals. Clinicians should be aware of the potential for disease associated with this organism, especially in immunocompromised animals.

[Frequency and in vitro susceptibility antiparasitic of Blastocystis hominis from patients admitted to the Hospital Regional Lambayeque, Peru]. / Frecuencia y susceptibilidad antiparasitaria in vitro de Blastocystis hominis en pacientes admitidos en el HospitalRegional Lambayeque, Perú.

OBJECTIVE: To describe the frequency and antiparasitic in vitro susceptibility of Blastocystis hominis in patients admitted to theHospital Regional Lambayeque, Peru. MATERIAL AND METHODS: A cross-sectional study was conducted from January to August 2015 at 313 patients of all ages. B. hominis detection was performed on serial fecal samples by direct microscopic examination and microculture in modified Locke solution. The in vitro susceptibility testing against the drug metronidazole, nitazoxanide, trimethoprim-sulfamethoxazole and erythromycin was performed in 24 strains of B. hominis, which grew up (microculture method) in 10 double concentrations of each antimicrobial (from 256 ug/ml to 0.5 ug/mL) plus a control. RESULTS: 46.3% (145/313) of the sample had B. hominis, also the age between 12 to 17 years and 60 years was associated with higher frequency of parasites (OR: 2.93 and 2.62). The minimum inhibitory concentration (MIC) 90 of metronidazole and nitazoxanide was 3.19 ug/mL and 11.19 ug/ml, respectively, whereas the MIC 90 of trimethoprim-sulfamethoxazole and erythromycin were above 256 ug/mL. CONCLUSIONS: B. hominis occurs in high frequency in patients admitted to the Hospital Regional in Lambayeque, proving to be an important problem of public health in the region. Also B. hominis isolated from these patients were shown to be susceptible in vitro to low concentrations of metronidazole and nitazoxanide so they could be chosen for treatment of this parasite.

In Vitro Antimicrobial Susceptibility Patterns of Blastocystis.

Blastocystis is the most common human enteric protist with controversial clinical significance. Metronidazole is considered a first-line treatment for Blastocystis infection; however, there has been increasing evidence for the lack of efficacy of this treatment. Treatment failure has been reported in several clinical cases, and recent in vitro studies have suggested the occurrence of metronidazole-resistant strains. In this study, we tested 12 Blastocystis isolates from 4 common Blastocystis subtypes (ST1, ST3, ST4, and ST8) against 12 commonly used antimicrobials (metronidazole, paromomycin, ornidazole, albendazole, ivermectin, trimethoprim-sulfamethoxazole [TMP-SMX], furazolidone, nitazoxanide, secnidazole, fluconazole, nystatin, and itraconazole) at 10 different concentrations in vitro. It was found that each subtype showed little sensitivity to the commonly used metronidazole, paromomycin, and triple therapy (furazolidone, nitazoxanide, and secnidazole). This study highlights the efficacy of other potential drug treatments, including trimethoprim-sulfamethoxazole and ivermectin, and suggests that current treatment regimens be revised.

In vivo antiprotozoan effects of garlic (Allium sativum) and ginger (Zingiber officinale) extracts on experimentally infected mice with Blastocystis spp.

Controversy surrounding the pathogenic role of Blastocystis spp. in humans and lack of well-established diagnostic criteria led to debates concerning the treatment for that organism. Furthermore, some strains develop resistance against the recommended drugs. Thus, using natural medicine has many positive aspects to address these points. In an earlier study, we addressed in vitro effect of garlic and ginger on Blastocystis spp. isolates as an alternative treatment. Accordingly, this study was conducted to evaluate in vivo activities of these two herbs on mice infected with Blastocystis spp. Antiprotozoan activities were determined by monitoring Blastocystis shedding in stools and histopathological changes of the intestine of infected mice. Additionally, assessment of the antioxidant effect (via measuring the level of malondialdehyde (MDA) production) of these herbs on the treated groups of mice was done. Also, their effects on nitric oxide (NO) production were assessed. In this work, treatment of infected mice with garlic, ginger, and nitazoxanide (NTZ) reduced the shedding of cysts significantly compared to the infected untreated group, P value ≤0.001, 0.0001, and 0.0003, respectively. As well, histopathological examination revealed that Blastocystis was frequently observed within the lumen, at the tip of the epithelium, and/ or infiltrated in an enterocyte in the infected group without treatment compared to that of the infected treated ones. Furthermore, mice infected with Blastocystis exhibited increased levels of NO (440.09 ± 3.7 vs. 276.66 ± 0.8, P ≤ 0.001) and MDA production (106.19 ± 0.43 vs. 63.06 ± 0.45, P ≤ 0.0004) compared to that of the uninfected controls. Treatment of infected mice with garlic, ginger, and NTZ reduced NO levels to 54.41 ± 1.2, 47.70 ± 1.2, and 37.43 ± 0.98 and MDA levels to 22.38 ± 0.17, 63.34 ± 3.89, and 66.76 ± 9.1, respectively. We conclude that using ginger and garlic for treatment of blastocystosis is beneficial.

Blastocystis hominis -associated Acute Appendicular Peritonitis in a 9-Year-old Boy: A Case Report and a Comprehensive Review of the Literature.

Although Blastocystis sp. has been classically considered a commensal parasite with limited pathogenicity, recent studies suggest that its pathogenic potential is high. We report the case of a 9-year-old Spanish male who presented with peritonitis secondary to acute appendicitis with abundant intra-abdominal turbid-free fluid. A standard appendectomy was performed, and a sample of the fluid was taken for microbiological culture. Multimicrobial flora was isolated in peritoneal fluid culture. The antibiotic resistance study showed that all the microorganisms were sensitive to meropenem. On the 5th postoperative day, a control blood test showed relative eosinophilia and a persistently elevated C-reactive protein. A stool parasitological study showed abundant cysts morphologically compatible with Blastocystis hominis . The hematoxylin & eosin and Giemsa study identified abundant parasitic cysts in the appendix. The patient evolved favorably and is currently asymptomatic and under follow-up. Regarding acute appendicitis, there is only one report in the literature of peritonitis of appendiceal origin associated with Blastocystis sp. In conclusion, although infrequent, parasitosis should be considered as a potential etiological agent of acute appendicitis, even in nonendemic areas. Relative eosinophilia or persistently elevated acute phase reactants despite adequate antibiotic coverage should help to establish diagnostic suspicion.

Is paromomycin the drug of choice for eradication of Blastocystis in adults?

Blastocystis is a protozoan parasite of controversial clinical significance that is often detected in stools of patients with gastrointestinal complaints. Patients infected with Blastocystis and persistent, unexplained gastrointestinal complaints are often treated with the intention to eradicate Blastocystis. However, there is no consensus on the most effective drug. We performed a retrospective follow-up study with a large cohort of patients in which the natural disease course and efficacy of treatment with either paromomycin, clioquinol, or metronidazole were evaluated. With an eradication rate of 77 %, treatment with paromomycin appeared significantly more effective than treatment with clioquinol (38 %), metronidazole (38 %), or no treatment (22 %). This study showed that (1) Blastocystis was frequently observed in the stools of our patient group (34 %), (2) spontaneous clearance of Blastocystis infections occurred only in a small proportion of patients (22 %), and therefore (3) drug treatment is required for more efficient eradication of Blastocystis. Paromomycin exhibited superior performance in comparison to both metronidazole and clioquinol.

[Evaluation of the efficacy of antiparasitic drugs in the treatment of concurrent parasitic diseases in patients with HIV infection and in those with pulmonary tuberculosis].

The efficacy of albendazole (400 mg taken once), mebendazole (100 mg taken once), and metronidazole (0.5 g thrice daily for 7 days) was evaluated when treating ascariasis, enterobiosis, and blastocystosis, respectively, in patients with HIV infection and in those with pulmonary tuberculosis. Metronidazole-resistant lambliasis was treated with exdisten (5 mg four times for 10 days) in 30.4% of the patients with HIV infection and in 43.3% of those with tuberculosis. Most HIV infected patients received antiretroviral therapy (ARVT). All the tuberculosis patients took isoniazid, ethambutol, pyrazinamide, rifampicin, and streptomycin. Efficiency was monitored by triple coproscopy at an interval of 5-7 days and by additional examinations using the method of Ritchii et al. There was parasitological cure (decreased infection rate for blastocystosis) and clinical improvement as positive changes in symptoms, such as nausea, weakness, headache, weight loss, and others, in all the patients with concomitant ascariasis, enterobiosis, and lambliasis. ARVT and antituberculosis drugs were observed to be better tolerated in all cases.

Medicinal Plants as Natural Anti-Parasitic Agents Against Blastocystis Species.

BACKGROUND: Blastocystis species (sp.) are enteric parasites that live in both humans' and animals' gastrointestinal tracts. Blastocystis hominis (B. hominis) is the recognizable human isolates in clinical and diagnostic specimens. Human infection occurs via the oro-fecal route, particularly in developing areas due to the lack of sanitation and hygienic facilities. B. hominis can exist in the large intestine for weeks to years until treated appropriately. Metronidazole is the drug of choice for the treatment of Blastocystis infection. However, it induces intolerable side effects and has been shown to have teratogenic and carcinogenic potential. Several medicinal plant extracts have been experimentally tested against Blastocystis infection in comparison to currently available treatments. OBJECTIVE: Based on in vitro and in vivo studies, this article reviewed anti-Blastocystis activity of some medicinal plants. METHODS: To conduct the research for this review, Google Scholar and PubMed were the primary search engines used to find relevant literature. A total of 19 published in vitro and in vivo studies were evaluated to identify the anti-Blastocystis effects of various medicinal plants. RESULTS: Multiplication of Blastocystis parasites as well as nucleic acids and protein synthesis, all be inhibited by extracts from different medicinal plants. These natural agents have been shown to be both safe and effective when compared to the existing treatment options. CONCLUSION: Different medicinal plants can combat Blastocystis infection and could be a good substitute for metronidazole and other synthetic treatments.

Should we treat Blastocystis sp.? A double-blind placebo-controlled randomized pilot trial.

BACKGROUND: Blastocystis sp. is a worldwide-distributed protist colonizing the guts of humans and a great variety of animals. It is unclear whether it is just a commensal or an infectious parasite that prompts eradication.The main objective of this study was to evaluate the usefulness of metronidazole in patients with gastrointestinal symptoms harbouring only Blastocystis sp. In addition, we explored whether Blastocystis subtype or concomitant parasitic infection detected by polymerase chain reaction (PCR) may influence treatment outcome. METHODS: We included adults with persistent gastrointestinal symptoms (>14 days) visiting a primary care physician and in whom stool microscopy revealed only Blastocystis sp. Eligible patients were randomized to receive 10 days of metronidazole or placebo, followed by a crossover if still symptomatic. The primary outcome was normal stool consistency. Secondary outcomes were the changes in other abdominal symptoms (bloating, flatulence, abdominal pain, number of daily bowel movements) and general wellbeing. After the clinical phase of the study, Blastocystis subtypes were determined by PCR sequencing and stool samples were tested for 11 other protozoa with an in-house PCR. RESULTS: We screened 581 outpatients for inclusion, of which 50 met the eligibility criteria. There was no difference in the primary outcome, nor any of the secondary outcomes between the subjects treated with metronidazole and placebo.The most frequent Blastocystis subtypes were ST4 (11/36) and ST2 (10/36). The in-house PCR was positive for other protozoa in 25% (10/40) of the patients. We identified Dientamoeba fragilis in 5, Entamoeba dispar in 3 and Cyclospora cayetanensis in 2 patients. Stratified analysis according to Blastocystis subtype or the presence of other protozoa showed no significant difference in treatment outcome with metronidazole or placebo. CONCLUSIONS: Among patients infected with Blastocystis sp., metronidazole, compared with placebo, was not better in improving gastrointestinal symptoms, irrespective of subtype or microscopically undetected coinfection with other protozoa.

Blastocystis: to treat or not to treat...

Parasites in the genus Blastocystis comprise several subtypes (genotypes) and have a worldwide distribution. In some surveys, these are the most common parasites found in human stool specimens. An emerging literature suggests that the pathogenicity of Blastocystis is related to specific subtypes and parasite burden, although even individuals with small numbers of cysts may be symptomatic. Some data suggest an association between infection with Blastocystis and irritable bowel syndrome. However, there are few clinical studies demonstrating a direct relationship between the presence of this parasite and disease, few animal models to explore this relationship, and no consensus as to appropriate treatment. We recommend that asymptomatic individuals with few cysts not be treated. However, those who have gastrointestinal or dermatologic signs and symptoms and many cysts in stool specimens may require treatment. Metronidazole is the drug of choice. Additional studies are required to determine pathogenicity and appropriate therapy.

No advantage for antibiotic treatment over placebo in Blastocystis hominis-positive children with recurrent abdominal pain.

OBJECTIVE: The aim of the study was to investigate whether recurrent abdominal pain (RAP) in Blastocystis hominis-positive children can be treated successfully with trimethoprim-sulfamethoxazole (TMP/SMX). METHODS: From October 2004 to December 2008, all of the patients referred to the Division of Gastroenterology and Nutrition of the University Children's Hospital Zurich because of RAP and detection of B hominis in stool samples as the only pathological finding after a standard workup were offered to participate in the study. Patients were randomly assigned into 2 groups. TMP/SMX or placebo was given for 7 days in a double-blind, placebo-controlled manner. Pain index (PI) was measured with a visual analogue scale. Two weeks after completion of treatment, 3 stool samples were collected and patients were followed clinically. If B hominis was still present, metronidazole was given for 7 days. RESULTS: Forty patients were included; 37 finished the study (TMP/SMX n = 20, placebo n = 17). Mean PI declined from 7.1 to 3.6 for all of the patients, with a decrease from 6.9 to 4.1 in the TMP/SMX and 7.4 to 3.0 in the placebo group, irrespective of detection of B hominis after treatment. There was no statistically significant difference in PI reduction between the 2 groups. Metronidazole treatment led to a further PI decline from 3.7 to 1.9. Eradication rates were 35% (TMP/SMX) and 44% (metronidazole), compared with spontaneous clearance of 29% in the placebo group. CONCLUSIONS: There is no advantage for TPM/SMX over placebo in the treatment of RAP in B hominis-positive children.

Blastocystis subtypes in symptomatic and asymptomatic family members and pets and response to therapy.

BACKGROUND: Blastocystis is a common, enteric parasite. The pathogenicity of the organism is uncertain, but subtypes (ST) 1 and 3 have been reported more likely to cause irritable bowel-like symptoms. AIMS: We treated symptomatic patients positive for Blastocystis with conventional therapy and analysed 16 small-subunit (SSU) rDNA to assess clearance and carriage rates and ST prevalence of the parasite in the asymptomatic household members. METHODS: In a longitudinal, prospective case study, 11 symptomatic patients positive for Blastocystis underwent outpatient clinical assessment to exclude other diagnoses before 14 days of either metronidazole 400 mg three times daily or trimethoprim/sulfamethoxazole 160/800 mg twice-daily therapy. Faecal specimens were collected from patients at baseline, day 15, 28 and 56 after therapy and from 17 family members and eight pets at day 15. Specimens were analysed using faecal smear, culture and polymerase chain reaction analysis of 16SSU rDNA. RESULTS: No patient cleared the organism following therapy. ST 1 (45%), 3 (36%), 4 (36%) and 6 (9%) were found in the symptomatic Blastocystis patients, and ST identified before and after therapy were identical in each individual. All household contacts were positive for Blastocystis and 16/17 (94%) contacts showed identical Blastocystis ST to the symptomatic family member. All pets were positive for Blastocystis with polymerase chain reaction testing, 7/8 (88%) demonstrating ST concordance with the symptomatic Blastocystis patients. CONCLUSIONS: Conventional therapy is ineffective for symptomatic Blastocystis infection. The high prevalence of Blastocystis infection within households suggested transmission between humans and their pets. Subtyping analysis of SSU rDNA alone in Blastocystis does not appear to predict pathogenicity.