Blastocystis hominis--past and future

Recent advances in Blastocystis hominis research: hot spots in terra incognita

Despite being discovered more than 80 years ago, progress in Blastocystis research has been gradual and challenging, due to the small number of laboratories currently working on this protozoan parasite. To date, the morphology of Blastocystis hominis has been extensively studied by light and electron microscopy but all other aspects of its biology remain little explored areas. However, the availability of numerous and varied molecular tools and their application to the study of Blastocystis has brought us closer to understanding its biology. The purpose of this review is to describe and discuss recent advances in B. hominis research, with particular focus on new, and sometimes controversial, information that has shed light on its genetic heterogeneity, taxonomic links, mode of transmission, in vitro culture and pathogenesis. We also discuss recent observations that B. hominis has the capacity to undergo programmed cell death; a phenomenon similarly reported for many other unicellular organisms. There are still many gaps in our knowledge of this parasite. Although there is a growing body of evidence suggesting that B. hominis can be pathogenic under specific conditions, there are also other studies that indicated otherwise. Indeed, more studies are warranted before this controversial issue can be resolved. There is an urgent need for the identification and/or development of an animal model so that questions on its pathogenesis can be better answered. Another area that requires attention is the development of methods for the transfection of foreign/altered genes into B. hominis in order to facilitate genetic experiments.

Phylogenetic position of Blastocystis hominis and of stramenopiles inferred from multiple molecular sequence data

Blastocystis hominis, a parasite of the human intestine, has recently been positioned within stramenopiles by the small subunit rRNA phylogeny. To further confirm its phylogenetic position using multiple molecular sequence data, we determined the nucleotide sequences putatively encoding small subunit ribosomal RNA, cytosolic-type 70-kDa heat shock protein, translation elongation factor 2, and the non-catalytic 'B' subunit of vacuolar ATPase of B. hominis (HE87-1 strain). Moreover, we determined the translation elongation factor 2 sequence of an apicomplexan parasite, Plasmodium falciparum, that belongs to alveolates. The maximum likelihood analyses of small subunit rRNA and cytosolic-type 70-kDa heat shock protein clearly demonstrated that B. hominis (HE87-1 strain) is positioned within stramenopiles, being congruent with the previous small subunit rRNA analysis, including the sequences of B. hominis (Nand strain) and a Blastocystis isolate from guinea pig. Although no clear resolution among major eukaryotic groups was obtained by the individual phylogenies based on the four molecules analyzed here, a combined analysis of various molecules, including these, clearly indicated that Blastocystis/stramenopiles are the closest relatives of alveolates.

Parasitic infections of the gastrointestinal tract

This article updates recent advances in the body of knowledge of diagnosis and treatment of intestinal parasites. The articles focus on the manifestations of disease in the immunocompetent adult host from developed countries. Specific pathogens discussed are Giardia lamblia and Dientamoeba fragilis, Entamoeba histolytica, Entamoeba dipar, Blastocystis hominis, Cyclospora cayetanensis, and Cryptosporidium parvum.

Genomic analysis of Blastocystis hominis strains isolated from two long-term health care facilities

The genotype Blastocystis hominis is highly polymorphic. Therefore, a genetic marker would be a powerful tool for the identification or classification of B. hominis subtypes and could be used as a means to resolve the transmission route or origin of the parasite. To this end, 32 B. hominis isolates were collected from patients and/or staff members of two long-term health care facilities (facilities A and B), and these organisms were subjected to genotype analysis based on diagnostic PCR primers and restriction fragment length polymorphism (RFLP) of small subunit rRNA gene (rDNA). Based on PCR amplification using diagnostic primers which were developed from randomly amplified polymorphic DNA analysis of known strains of B. hominis, the 32 isolates of B. hominis were classified into three different subtypes. Thirty isolates, including twenty-four that were isolated from patients and a staff member, from facility A and all isolates isolated from six patients from facility B showed the same genotype. Two of six patients of facility B had been transferred from facility A, and these two patients also had the same-genotype B. hominis that corresponded to 24 isolates from facility A. This genotype strain may have been transmitted by these two patients from facility A to facility B, suggesting human-to-human transmission. In contrast, 2 of 26 isolates from facility A showed distinct genotypes, suggesting that the colonization by these two isolates is attributable to another infectious route. These different subtypes were subjected to RFLP analysis, and the RFLP profiles were correlated with the results obtained by diagnostic PCR primers. This study presents the first molecular evidence of possible human-to-human B. hominis infection between and/or among two small communities.

Genomic polymorphism among Blastocystis hominis strains and development of subtype-specific diagnostic primers

Genomic polymorphisms among nine strains of Blastocystis hominis were examined by random amplified polymorphic DNA (RAPD) using four different arbitrary polymerase chain reaction (PCR) primers. Based on the RAPD patterns, nine strains were classified into three groups. The specific primers designed from the unique bands yielded a single band from within each same group, but did not amplify between all the groups examined. Specificity of these diagnostic primers was tested against several common intestinal parasites and a yeast, and no amplification was confirmed. Since the current criteria indicates that Blastocystis organisms isolated from humans are designated as B. hominis, the authors propose to classify several subtypes among B. hominis groups based on the difference of genomic DNA using three diagnostic primers.

Diarrhea in returning Austrian tourists: epidemiology, etiology, and cost-analyses

BACKGROUND

Between 1995 and 1997, stool samples of 322 Austrian tourists returning from abroad with diarrhea were examined for bacteria, parasites and viruses.

METHODS

Epidemiologic data were collected from information furnished by physicians and hospitals and from questionnaires. Moreover, testing expenses and additional cost for treated cases were evaluated.

RESULTS

In 97 of 322 patients examined (30%), one or more pathogens were detected in the stool. Bacteria were found in 38 patients (39%), parasites in 33 patients (34%) and viruses in 26 patients (27%). In 6 patients, mixed infections with parasites and viruses were detected and in 5 patients with bacteria and viruses. Among bacteria, Campylobacter jejuni was most frequent; among parasitic infections, Giardia lamblia. Significant correlations were established between the country of destination, age, travel style and length of stay. Forty-four percent of all patients visited Asia (including Turkey), 27% Africa, 18% Latin America, and only 10% southern Europe. The group between 20 and 29 years of age was most frequently affected (p<.001), the group between 0 and 19 years of age least. Fifty-seven percent stayed in a hotel without frequent changes of location; 43% undertook a trekking trip; and of those, 75% belonged to the group aged between 20 and 39. In terms of the correlation between travel style and pathogen, it was found that 74% of patients with bacterial infections stayed in a hotel (avg. 57.9%; p<.05) whereas 64% of all patients with parasitic infections undertook a trekking trip (avg. 42%; p<.001). Thirty-six percent of all patients with parasitic infections spent their vacation in India (avg. 13%; p<.001). The length of stay of patients with bacterial infections was shorter than average (72% spent between 1 and 2 weeks abroad, avg. 49.8%). Patients with parasitic infections spent significantly more time abroad than average (42% more than 2 months; avg. 17.7%; p<.001). Average cost of specific antimicrobial therapy was U.S.$31 whereas the average cost of identifying a patient needing such treatment was almost U.S.$580.

CONCLUSION

Optimal detection rate and cost reduction for the diagnosis require precise history, adequate collection of samples using adequate transport media, and rapid transfer to the laboratory.

[An educational intervention to improve the quality of coproparasitological diagnosis in laboratories of Havana City, Cuba]

The aim of this study was to evaluate the effectiveness of an educational program carried out in 1993. The intervention took place after the first external quality assessment in coproparasitology, conducted in 77 laboratories of Havana City. Centers receiving training were compared with those that did not, and better results were obtained in the municipalities of 10 de Octubre, Plaza, and Cerro, as well as in all laboratories that sent people to training. Better diagnosis was found for the helminths Trichuris trichiura, Taenia sp., and Fasciola hepatica as well for the protozoans Blastocystis hominis and Endolimax nana in the laboratories that received training. The laboratories that received training had significantly higher scores than those which did not. The results point to the effectiveness of the educational intervention. We recommend external quality assessment in coproparasitology as well as ongoing, mandatory technical education, held at regular intervals. Such measures should assure steady improvement in diagnosis of intestinal parasites by the health services network.

Phylogenetic position of symbiotic protist Dinenympha [correction of Dinemympha] exilis in the hindgut of the termite Reticulitermes speratus inferred from the protein phylogeny of elongation factor 1 alpha

The phylogenetic position of the symbiotic oxymonad Dinenympha exilis, found in the hindgut of the lower termite Reticulitermes speratus, was determined by analysis of translation elongation factor 1 alpha (EF-1 alpha). cDNA corresponding to a major part of the amino acid coding region of EF-1 alpha mRNA was amplified by the reverse transcription polymerase chain reaction (RT-PCR) method from total mRNA of termite hindgut microorganisms without cultivation. The product was cloned into a plasmid vector, pGEM-T, and the clones were isolated and sequenced. One of the EF-1 alpha clones isolated was assigned to the protist D. exilis by whole-cell in-situ hybridization using a specific oligonucleotide probe with enzymatic signal amplification. The deduced amino acid sequence was aligned with those of other eukaryotic and archaeabacterial EF-1 alpha s, and the phylogenetic relationships among early branching eukaryotes were inferred by using the distance matrix method and the maximum parsimony method. The phylogenetic analysis indicated that the D. exilis offshoot occurred before mitochondria-containing organisms and D. exilis branched out after the diplomonads clade. These results indicate that the oxymonad D. exilis is one of the early branching organisms and suggest that the oxymonads form a lineage independent of other early branching organisms.

Blastocistosis en pre-escolares de Ciudad Bolívar, Venezuela

Para determinar la prevalencia y relevancia clínica de la blastocistosis en una muestra de niños en edad pre-escolar, fueron evaluados 169 alumnos del pre-escolar "Los Coquitos" de Ciudad Bolívar, Venezuela. Las muestras fecales fueron estudiadas mediante la técnica de examen directo y métodos de concentración de Faust y Willis. Se encontraron 72 niños parasitados, de ellos 32 (29,09%) con Blastocystis hominis. Se determinó una prevalencia de infección por este protozoario de 18,93% ± 5,93%. No hubo predilección por el sexo y la edad de los pre-escolares parasitados (ji² = 1.84 DF = 3; p>0.05). Se diagnosticó mayormente como parásito único (53,13%); Giardia lamblia fue el parásito más frecuentemente identificado (39,13%) junto con B. hominis. En el 94,12% de los casos, se observó en un número mayor de 5 células por campo. El 70,58% de los pre-escolares tenía manifestaciones clínicas, sin embargo, la cantidad de Blastocystis presente no fue determinante en su aparición, pero si en la severidad de ellas. Luego del tratamiento, hubo respuesta clínica y parasitológica favorable en el 80% y 90% de los casos, respectivamente. Se concluye que B. hominis es un patógeno de relativa alta frecuencia en el grupo de niños estudiados.

Mechanism of sodium channel blockade in the cardiotoxic action of emetine dihydrochloride in isolated cardiac preparations and ventricular myocytes of guinea pigs

Emetine is used in the therapy of special forms of amebiasis and is abused as syrup of ipecac by persons with bulimia. Severe cardiac side effects were reported. Thus the intracellular microelectrode technique and the patch-clamp technique in the cell-attached mode were used to study the effects of emetine on the action potential and upstroke velocity (Vmax) in papillary muscles and Purkinje fibers of guinea pigs as well as on macroscopic and (S)-DPI 201-106-modified and unmodified single-sodium-channel current (I(Na)) of guinea-pig ventricular myocytes. Emetine caused a tonic block of Vmax and reduced I(Na) independent of frequency. Hill plots were linear, with slopes ranging from 0.96 to 1.06, suggestive of a first-order reaction. The current-voltage relation was not influenced, indicating a voltage-independent blockade of the sodium channels. The most prominent effects were an increase of sweeps without activity, a decrease of the fast component of the open-time distribution, an increase of the slow component of the closed-time distribution, and a reduction in the number of bursts per record. The amplitude of the unitary current was not changed. From the results, we conclude that I(Na) blockade contributes to the cardiotoxicity of emetine.

Blastocystis hominis in animals: incidence of four serogroups

In toto, 520 faecal samples from mammals, birds, reptiles, amphibians, fish, and snails were investigated (see Table 1). 91 strains of Blastocystis hominis could be isolated by culture. However, only 48 of them were suitable for axenisation. 96 percent of samples belonged to four serogroups detected in humans but two strains, one from a pig and another from a duck, could not be classified, suggesting the existence of one or two further serogroups. While humans showed mainly serogroups I and II, pigs harboured serogroups III and IV. Four serogroups were isolated from monkeys. The question whether the genus Blastocystis consists of one or more species is discussed.

The role of Blastocystis hominis as a possible intestinal pathogen in travellers

The role of Blastocystis hominis as a pathogen for man has been controversially discussed, while travel history has been implicated as a risk factor of infection. Few controlled studies of the association between B. hominis and symptomatic diseases have been performed. Therefore, a case-control study among 795 German tourists returning from tropical countries was conducted. The prevalence of the organism among patients with and without symptoms was assessed. Blastocystis hominis was detected in 69 of 469 (14.7%) patients with diarrhoea and in 21 of 326 (5.7%) controls. However, other organisms causing diarrhoea were detected in 18 of the 69 (26.1%) symptomatic patients with B. hominis. Thus, 51 of 469 (10.8%) symptomatic patients had B. hominis in the absence of other pathogens in their stool, significantly more than in the asymptomatic group (5.2%; P = 0.005). Irrespective of the development of symptoms, the organism was most frequently acquired during journeys to the Indian subcontinent. The results of this study suggest that B. hominis is associated with development of diarrhoea in travellers to tropical destinations and that frequently concurrent infections with other organisms occur.

Enterocytozoon bieneusi in AIDS: symptomatic relief and parasite changes after furazolidone

AIMS

To investigate changes in morphology of the developmental stages of Enterocytozoon bieneusi and symptomatic relief observed in AIDS patients after treatment with furazolidone.

METHODS

Six AIDS patients with symptomatic E bieneusi infection of the small intestine were treated with a course of furazolidone. All patients had a weekly monitoring of parasite shedding in stool by light microscopy during and after treatment. At the end of the treatment, duodenal biopsy specimens obtained from three patients were studied by transmission electron microscopy by two pathologists who were unaware of the patients' treatment.

RESULTS

All patients showed both clinical and parasitological response with transient clearance or decrease of spore shedding in stool. After treatment, alterations in faecal spores were observed in all patients by light microscopy, and ultrastructural changes in E bieneusi at all stages of the life cycle were demonstrated in biopsy specimens of the three patients who underwent post-treatment endoscopy.

CONCLUSIONS

The clinical benefit seen after treatment with furazolidone in six AIDS patients with E bieneusi intestinal infection may be due to damage to the developmental stages causing a partial inhibition to reproduction of the parasite.

Parasites and Diarrhea. I: Protozoans and Diarrhea

Intestinal parasitism is extremely common, with approximately 70% of all people harboring one or more intestinal parasite. Parasitism and diarrhea are both hyperendemic in areas where sanitation is suboptimal. Many clinicians assume that the identification of intestinal parasites in patients with diarrhea implies that the parasites are the cause. This approach is frequently misguided. Some intestinal parasites such as Giardia lamblia and Entamoeba histolytica certainly do cause diarrhea. Others, for example Entamoeba coli and Ascaris lumbricoides, almost certainly do not. In addition, there are a number of other organisms that have been associated with diarrheal illness in some cases, which may or may not be important pathogens. In this article, we will review the role of protozoans as definite and possible causes of diarrhea. In Part II, we review the role of helminths in diarrhea.

Control de la calidad del diagnóstico coproparasitológico en la provincia de Ciudad de La Habana, Cuba

Se realizó un estudio sobre la calidad del diagnóstico coproparasitológico en 77 laboratorios de la red de salud pública de la provincia Ciudad de La Habana, Cuba. El procedimiento se basó en la entrega a cada jefe de laboratorio de un modelo de encuesta, y una bolsa de nylon conteniendo 10 viales plásticos con distintos especímenes parasitarios, preservados en formaldehído al 7%. Recogidos los resultados en las primeras 72 horas después de su entrega, se realizó la evaluación mediante una escala de puntuación establecida. La mayoría de los laboratorios aprobaron (70%); sin embargo aún existen centros, sobre todo policlínicas, con calificaciones deficientes. Los municipios con resultados más desfavorables fueron, Lisa, Marianao y Habana del Este, alcanzándose mejores resultados en los hospitales que en las policlínicas. En el análisis de Protozooarios, el mejor diagnosticado fué Giardia lamblia, con solo un centro que erró al identificarlo. Las mayores dificultades se presentaron en Blastocystis hominis con 61% de fallas, Endolimax nana, con 24,6%, y Entamoeba histolytica, con 22%. Entre los helmintos, la mayor aprobación fué en Trichuris trichiura y los errores diagnósticos predominaron con Fasciola hepatica y Taenia sp., ambos con 66,2% de fallas. Dados los resultados obtenidos, hemos organizado una intervención educativa en la red de laboratorios de la provincia.

In vitro response of Blastocystis hominis against traditional Chinese medicine

This is the first inn vitro study on the activity of 20 kinds of crude extracts of traditional Chinese medicine (TCM) on the intestinal parasite, Blastocystis hominis using the criteria of living cell count (LCC) and living cell rate (LCR). LCC and LCR were applied as observation indicators, the former as a fixed-quantity and the latter as a fixed-quality method. LCR calculated percentage rate of living cells using eosin-brilliant cresyl blue staining which could differentiate between living cells and dying or dead cells. There were five extracts with no inhibitory activity, thirteen with moderate inhibition and two with high inhibition. The crude extracts of Coptis chinensis (CC) and Brucea javanica (BJ) were found to be most active against B. hominis. The active concentration of CC was 100 micrograms/ml. The active concentration of BJ was 500 micrograms/ml. The active concentration of metronidazole (MD) was 10 micrograms/ml and this was taken as an active standard drug for B. hominis.

Blastocystis hominis revisited

Blastocystis hominis is a unicellular organism found commonly in the intestinal tract of humans and many other animals. Very little is known of the basic biology of the organism, and controversy surrounds its taxonomy and pathogenicity. There morphological forms (vacuolar, granular, and ameboid) have been recognized, but recent studies have revealed several additional forms (cyst, avacuolar, and multivacuolar). The biochemistry of the organism has not been studied to any extent, and organelles and structures of unknown function and composition are present in the cells. Several life cycles have been proposed but not experimentally validated. The form used for transmission has not been defined. Infections with the organism are worldwide and appear in both immunocompetent and immunodeficient individuals. Symptoms generally attributed to B. hominis infection are nonspecific, and the need for treatment is debated. If treatment appears warranted, metronidazole is suggested as the drug of choice, although failures of this drug in eradicating the organism have been reported. Infection is diagnosed by light microscopic examination of stained smears or wet mounts of fecal material. Most laboratories identify B. hominis by observing the vacuolar form, although morphological studies indicate that other forms, such as the cyst form and multivacuolar form, also should be sought for diagnosis.

DNA polymorphism revealed by arbitrary primers polymerase chain reaction among Blastocystis strains isolated from humans, a chicken, and a reptile

DNA polymorphisms of different strains of Blastocystis isolated from humans, a chicken, and a reptile were examined by an arbitrary primer PCR method. Two strains of Blastocystis hominis isolated from humans in the USA and Japan yielded nearly identical PCR products. However, one strain of B. hominis (isolated from a human in Singapore) yielded quite different PCR products. Blastocystis sp. isolated from a chicken yielded PCR products similar to those of the former two strains, while Blastocystis lapemi, isolated from a reptile, shared no bands with any of the other isolates. These results indicate the possibility that our isolate from the chicken is a zoonotic strain, and that there is intraspecific variation of Blastocystis hominis.

Detection of Blastocystis sp. in pigs in Aragon (Spain)

Infection by Blastocystis sp. has been detected for the first time in pigs in Spain. Detection was carried out by the ethyl acetate-formalin concentration method and direct microscopy. Vacuolated cells of Blastocystis sp. were found in stool samples from 27 of 360 pigs examined (7.5%). The protozoan was present on nine of 17 pig farms studied (53%). Infected pigs ranged from 1 month old to adults, but the organism was most frequent in 1-2 month old (18.4%) and 2-6 month old pigs (15.4%). No correlation was found between Blastocystis sp. infection and occurrence of diarrhoea in pigs.

Histochemical detection of carbohydrates of Blastocystis hominis

The carbohydrates of Blastocystis hominis were detected by histochemical techniques using light and electron microscopy. B. hominis, fixed with various fixatives, followed by treatment with detergents, were stained with periodic acid-Schiff (PAS) or alcian blue (AB). Intense PAS reactions were observed in cells fixed with glutaraldehyde or 1/2 Karnovsky fixative. The cells fixed with other fixatives showed weak or no reactions with PAS staining. Similar results were seen in the case of AB stain. These results indicated that, depending on the fixative used, B. hominis contained PAS- or AB-reactive carbohydrates. At the electron microscopic level, ultrathin sections of B. hominis were stained with periodic acid methenamine silver (PA-MS) or periodic acid thiocarbohydrazide-silver proteinate (PA-TCH-SP) staining techniques. Intense, positive reactions with PA-MS or PA-TCH-SP were observed on the central vacuole, Golgi apparatus, and cytoplasmic vesicles. The filamentous layer showed moderate reactions with PA-MS, whereas in PA-TCH-SP stain, it was stained more densely. The staining intensity of the central vacuole varied from cell to cell. The presence of membrane fusions of the cytoplasmic vesicles with the central vacuole indicated the accumulation of carbohydrates in the central vacuole.

'The tropics in our bathroom': chronic diarrhoea after return from the tropics

Interest in imported tropical diseases has increased with the rising number of travellers to the tropics. This is especially true in the case of tropical gastroenterologic disorders. The causative organisms of chronic diarrhoea are different from those causing acute diarrhoea. Bacteria are relatively unusual; parasites, e.g. Entamoeba histolytica or Giardia lamblia or an opportunistic parasitic infestation associated with an HIV infection are more likely. Furthermore, non-infectious causes, such as postinfective tropical malabsorption, lactase deficiency or coeliac disease have to be considered. Today, elderly people often undertake a journey to the tropics; in these cases the diarrhoea may be associated not only with an increased susceptibility to tropical bowel infections but also with causes previously present, such as diverticulosis, carcinoma or inflammatory bowel disease. The classification of chronic diarrhoea following a visit to the tropics is essentially the same as that for acute diarrhoea: diarrhoea with and without fever and with and without blood. In addition, malabsorption is an important feature of chronic diarrhoea.

Ultrastructure of Blastocystis hominis cysts

Blastocystis hominis cysts were concentrated from human faeces by repeated washing in distilled water and centrifugation on Ficoll-Paque. This procedure gave a concentrated suspension of cysts without yielding any non-cystic forms. The cysts were examined by both transmission (TEM) and scanning electron microscopy (SEM). Cysts were surrounded by a fibrillar layer that appeared porous in SEM. Many naked cysts without the fibrillar layer were also visible in SEM. They were variable in shape but mostly circular to oval. The diameter of the cyst without the fibrillar layer was 3.5 microns in both TEM and SEM. The nuclear structure was typical of Blastocystis and exhibited multiple mitochondria with poorly developed cristae. Glycogen was present in small to large clumps in the cytoplasm. The cyst wall was 5-100 nm thick and was bounded internally by an electron-dense plasmalemma.

Occurrence of blastocystis sp. in cattle in Aragón, northeastern Spain

The occurrence of Blastocystis sp. in cattle is reported herein for the first time in Spain. Stool samples from 554 bovines ranging from 3 days old to adults collected from 30 cattle farms in Aragón (northeastern Spain) were concentrated by the formalin-ethyl acetate method and examined light microscopically for the presence of gastrointestinal parasites. Vacuolated cells of Blastocystis sp. was detected in fecal specimens from 10 calves (1.8%) aged from 7 weeks to 6 months. Infected calves were detected at 3 of the 30 farms surveyed (10%). Blastocystis sp. cells were rounded or oval, with a diameter ranging from 6.25 to 15 microns. Blastocystis infection in cattle was never correlated with diarrhea, although infection intensities were generally low.

Elucidation of the life cycle of the intestinal protozoan Blastocystis hominis

This paper elucidates the status of the different morphological forms of Blastocystis and reports the existence of thin- and thick-walled cysts in B. hominis on the basis of current experimental evidence. It is suggested that the thin-walled cysts are autoinfectious, leading to multiplication of the organism in the intestinal tract. The thick-walled cysts are responsible for external transmission via the faecal-oral route. A life cycle for B. hominis is postulated on the basis of these findings.

Intestinal colonization of symptomatic and asymptomatic schoolchildren with Blastocystis hominis

A study of single stool specimens was done to determine the prevalence of intestinal parasites among 1,000 primary school children. A questionnaire was completed by each child's parents. Specimens were examined by using wet-mount preparation, formaline-ether concentration, and Sheather's flotation technique. Trichrome and acid-fast stains were done. Blastocystis hominis was observed in 203 (20.3%) of the specimens examined, and 175 specimens contained this organism in the absence of other pathogenic parasites. Older children had fewer B. hominis infections (6 to 7 years old, 50% infection rate; 8 to 9 years, 27.5%; 10 to 12 years, 9.5%). The most common complaints reported by 75 children harboring the parasite were a mild recurrent diarrhea, abdominal pain, nausea, anorexia, and fatigue. Blastocystosis is quite common among schoolchildren. Contaminated drinking water is suspected to be the source of infection.

Blastocystis hominis infection and intestinal injury

Blastocystis hominis is an enteric protozoan associated with clinical illness. To determine the prevalence of intestinal injury in patients with B. hominis infection, the authors prospectively evaluated 18 patients with B. hominis infection by endoscopy and a test of intestinal permeability. Seventeen patients had gastrointestinal symptoms. Colonic mucosa appeared normal by lower endoscopy in 12 of 13 patients, and was friable slightly in 1. Duodenal mucosa was normal by upper endoscopy in nine patients. Pathologic examination of mucosal biopsy specimens did not demonstrate evidence of mucosal invasion. 51Cr-edetic acid (51Cr-EDTA) was given to the 18 patients with stools positive for B. hominis and to 32 healthy control subjects. Approximately 100 uCi of 51Cr-EDTA was given orally after an overnight fast, and urine was collected for the following 24 hours. Mean 24-hour urinary excretion of 51Cr-EDTA, calculated as a percent of the administered dose, was 1.31% (0.34-2.76%) in patients with B. hominis infection and 1.99% (0.59-3.48%) in the control subjects. The intestinal permeability to 51Cr-EDTA in blastocystis-infected individuals was not increased, but was decreased significantly compared with healthy subjects (p < 0.005). Therefore, in a group of symptomatic patients with B. hominis infection, endoscopy typically did not show evidence of significant intestinal inflammation, and results of intestinal permeability testing with 51Cr-EDTA did not suggest impaired barrier function of the intestinal mucosa. The clinical literature on B. hominis infection and intestinal injury is reviewed.

Susceptibility testing of Dientamoeba fragilis ATCC 30948 with iodoquinol, paromomycin, tetracycline, and metronidazole

Susceptibility testing was performed on Dientamoeba fragilis ATCC 30948 in a dixenic culture with Klebsiella pneumoniae and Bacteroides vulgatus. D. fragilis was cocultured with the bacteria in TYGM-9 medium (ATCC medium 1171). The activities of antiparasitic drugs were assessed by counting viable D. fragilis trophozoites with a hemacytometer by trypan blue exclusion. The minimal amebicidal concentrations of the following four drugs were determined: iodoquinol at 128 micrograms/ml, paromomycin at 16 micrograms/ml, tetracycline (questionably) at 32 micrograms/ml, and metronidazole at 32 micrograms/ml.

Lipid biosynthesis by axenic strains of Blastocystis hominis

Axenic strains of Blastocystis hominis incorporated 32P, added to the medium as orthophosphate, into a number of phospholipids, including sphingomyelin, cardiolipin, phosphatidic acid, the phosphoglycerides of choline, ethanolamine, serine, and inositol and some other minor phospholipids. Radioactive palmitate and glycerol provided in the growth medium introduced radiolabel into diacylglycerols, triacylglycerols, and all major phosphoglycerides found in the organism. Palmitate is a major fatty acid of cholesterol esters in B. hominis, but radioactive palmitate did not enter the cholesterol ester pool. Radioactive acetate was not incorporated into any lipids. Cholesterol and cholesterol esters of the organism were not labeled when cells were grown in the presence of radioactive glucose, mevalonic acid, or mevalonolactone. Radioactive cholesterol added to the medium became stably associated with B. hominis cells, but none of the radioactive cholesterol entered the cholesterol ester pool. Cholesterol-[3H]-palmitate added to the medium became stably associated with the organism, and most of the radioactivity associated with the cells remained in the cholesterol ester fraction on extended incubation. These results show that this parasitic protozoan has the capacity to synthesize most cellular lipids de novo, but suggest that it acquires free cholesterol and intact cholesterol esters directly from growth medium.

Incidence of Blastocystis hominis in patients with diarrhoea

We studied the occurrence of the parasite Blastocystis hominis in 1066 stool specimens from patients with diarrhoea, and investigated the relationship between the presence of B. hominis in the faeces and the age of patients. The parasite was recovered from 3.7% samples, but as the sole species of micro-organism in the stool it was recovered from 1% samples. There was no statistically significant difference in the number of B. hominis-positive stools between the younger and the older patients (P < 0.25), yet in the latter, B. hominis was more frequently identified as the only species of micro-organism as compared with the younger group (P < 0.005). The presence of B. hominis in faecal samples of patients with diarrhoea harbouring no other intestinal pathogens suggests an aetiology that should receive more attention in Slovenia.

A multiple fission-like mode of asexual reproduction in Blastocystis hominis

A non-axenic and an axenic isolate of Blastocystis hominis have been induced to form cysts in vitro using an encystation medium. The morphology of the parasite at different time points was observed by scanning electron microscopy. In day-2 cultures the cysts were spherical and had a non-uniform, coarse outer surface around the body. A deep, pore-like opening was seen in some of the parasites. Most of the cysts from day-4 and day-6 cultures ruptured, revealing small, uniformly sized spherical bodies occurring in grape-like clusters. Acridine orange staining confirmed that these bodies were the progeny of Blastocystis hominis. A multiple fission-like reproduction process giving rise to many daughter Blastocystis occurs within the cyst.

Four serologically different groups within the species Blastocystis hominis

61 strains of Blastocystis hominis were isolated from 340 stool specimens coming from 140 patients with intestinal symptoms and from 200 healthy persons. The overall female to male ratio was 1.9 to 1. Classification of the 61 isolates of B. hominis was determined with the aid of the immunodiffusion assay. Four serologically different groups could be identified. Their frequency ratio in the population studied was 39.5%:39.5%:18%:3%. Group 3 was found more often than the other three groups in stool samples of patients. However, within the statistical deviation, none of the four immunological different groups was found to be correlated with the disease or the sex of the hosts.

Morphological diversity of Blastocystis hominis in sodium acetate-acetic acid-formalin-preserved stool samples stained with iron hematoxylin

The objective of this investigation was to study the morphological characteristics of Blastocystis hominis in sodium acetate-acetic acid-Formalin-preserved stool samples. Routinely processed samples were examined for morphological detail, including size, shape, nuclear detail, and central body characteristics. Morphological findings revealing the importance of recognizing B. hominis in the diagnostic laboratory are described.

Evidence of an epidemic of Blastocystis hominis infections in preschool children in northern Jordan

Blastocystis hominis is now gaining acceptance as an agent of human intestinal disease. A case-control study of the cause of gastroenteritis in children less than 6 years old was conducted. A total of 500 stool specimens were examined by wet mount preparation, formalin-ether concentration, Sheather's sugar flotation technique, and permanent stains when necessary. B. hominis was found in 63 (25%) of 250 stool specimens of the cases examined; 38 (15%) of these specimens contained this parasite alone. The appearance of severe symptoms was associated with increased numbers of the parasite in the diarrheic specimens (more than five parasites per field at a magnification of x 400). The most common symptoms were abdominal pain, recurrent diarrhea, cramps, anorexia, and fatigue. Contaminated water was suspected to be the major source of infection, since several cases were associated with Giardia infection. These findings support the concept of B. hominis pathogenicity in children with gastroenteritis.

Application of indirect immunofluorescence to detection of Dientamoeba fragilis trophozoites in fecal specimens

An indirect fluorescent-antibody (IFA) assay was carried out to examine for the presence of Dientamoeba fragilis trophozoites in preserved fecal specimens. Antiserum to D. fragilis trophozoites was raised in a rabbit with a dixenic culture of D. fragilis (ATCC 30948) from the American Type Culture Collection. After absorption with Klebsiella pneumoniae and Bacteroides vulgatus, the immune rabbit serum was used for examination by the IFA assay. A total of 155 clinical samples were tested; 42 with no parasites, 9 with D. fragilis, and 104 with other parasites. The IFA assay identified seven D. fragilis organisms. Two specimens with doubtful IFA assay readings showed very scanty amounts of D. fragilis trophozoites on stained smears. There were no false-positive IFA assay readings. The IFA assay appeared to be a promising method because of its speed in screening. The specificity of the IFA assay indicates that other diagnostic tests such as an enzyme-linked immunosorbent assay could be developed to identify D. fragilis antigens in fecal specimens.

Comparative analysis of lipid composition in axenic strains of Blastocystis hominis

1. Six axenic strains of Blastocystis hominis varied in content of lipids from 12 to 43 pg total lipid/cell. With all strains, phospholipid content was about 39% of total lipids. 2. Neutral lipid fractions of B. hominis were resolved into nine constituents, of which seven were identified tentatively. Sterol esters, principally esters of cholesterol, were the major neutral lipid constituent, accounting for 49-63% of the neutral lipids, and at least 30% of the total lipids. 3. Polar lipids were resolved into eleven constituents, of which nine were identified tentatively. Phosphatidylcholine was the major polar lipid constituent of all strains, accounting for 53-63% of the polar lipids, and about 22% of the total lipids.

Protein and DNA evidence for two demes of Blastocystis hominis from humans

Analysis of 10 stocks of Blastocystis hominis isolated from human stools revealed two discrete groups of organisms. Proteins of the two groups were immunologically distinct and hybridization with random probes generated from the DNA of one stock showed that the DNA content of the two groups was different. Further studies are required to determine whether these should be classified as discrete species or whether these groups are epidemiologically significant.

A survey of Blastocystis in reptiles

A total of 28 species of reptiles were investigated for Blastocystis using light microscopy and in vitro culture in biphasic egg slant medium. Blastocystis species were detected in 8 (28.6%) of these 28 species in 3 tortoises (Geochelone elephantopus, G. elegans and G. carbonaria), 3 snakes (Boiga dendrophilla, Python reticulatus and Elaphe radiata), 1 crocodile (Crocodylus porosus) and 1 iguana lizard (Cyclura cornuta). The reptilian Blastocystis appeared to be morphologically similar to B. hominis.