Prevalence of Blastocystis hominis infection in schoolchildren from Bolivar City, Venezuela

Blastocystis hominis is found in about 25% of feces in normal asymptomatic people. Its pathogenic role is still discussed. A prospective study was performed to determine the prevalence of B. hominis infection in schoolchildren from Bolivar City. We evaluated 446 children, between five and fourteen years old, both sexes, using direct examination of feces and Willis Method. They were also evaluated clinically. Results showed that B. hominis had a prevalence of 16.8%. We did not find a statistically significant association between sex (P > 0.05) or age and infection with B. hominis (x2 = 1.94 g.l = 4). In 39 schoolchildren (52.0%) we identified other parasites along with B. hominis, the most frequent was Trichuris trichiura as helminth and Giardia lamblia as protozoan. We observed B. hominis alone in 36 cases (48.0%). There was a spectrum of clinical symptoms in 41 (54.7%) of all children evaluated. Diarrhea was the most frequently clinical manifestation observed. Other studies are necessary to determine clinical relevance of B. hominis in school population in Bolivar City.     

Scanning electron microscopy of Blastocystis hominis cysts

Scanning electron microscopy of Blastocystis hominis cysts reveals that some cysts have an outer coat, whereas others are naked. If intact, the outer coat forms a fan-like structure around the cyst and its surface is granular. The fragmented outer coat adheres to other cysts and bacteria, forming irregular clumps.     

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.     

In vitro encystment and experimental infections of Blastocystis hominis

Cultures of Blastocystis hominis were induced to encyst using three encystation media: (a) an encystation medium (EM) comprising yeast extract in buffered saline containing 50% horse serum, (b) an encystation medium (CEM) comprising EM conditioned with bacterial soluble products and (c) an encystation medium (TEM) containing 0.5% trypticase in EM. Two isolates of B. hominis were studied, an axenized isolate C and a non-axenized isolate MS. In EM, isolate C did not encyst, whereas 6.1% of isolate MS had encysted by day 1. However, in CEM and TEM, 17.4% and 25.7% of isolate C, respectively, had encysted by day 5. In all three media, isolate MS encysted more readily than isolate C, with as much as 91.7% of the former encysting in TEM. As viewed by phase-contrast microscopy, cyst-like stages appeared highly refractile. Direct stool examination of juvenile Wistar rats infected with 10,000 cyst-like stages of both C and MS isolates showed Blastocystis at day 2 post-infection. At autopsy on day 7, large numbers of Blastocystis were seen in the cecum, with smaller numbers being observed in the large intestine. In contrast, rats fed with various inocula of the vacuolar stages of isolates C and MS did not become infected, indicating the importance of the encysted stages in the transmission of the parasite.     

Epidemiology of Blastocystis hominis infection in Papua New Guinea: age-prevalence and associations with other parasites

A community-based study of Blastocystis and other intestinal parasites in the Asaro Valley, Papua New Guinea showed an extraordinary high prevalence and variety of protozoan infections. Apart from infants, nearly everybody had at least one infection, and the mean number of infections per person was around 2.7. The graph of age-specific prevalence for Blastocystis is similar in shape to those for Entamoeba coli and Endolimax nana, indicating probable similarity in transmission patterns and host response. There was no evidence for pathogenicity of Blastocystis at the community level. Three methods are compared for the measurement of association between infections. Two show strong associations, but these are considered to be the result of parallel age-prevalence curves and environmental factors at the village level. When age- and village-matched pairs were considered, only a weak positive association with E. nana was detectable.     

Cytopathic effect of Blastocystis hominis after intramuscular inoculation into laboratory mice

The present study investigated the pathogenesis of Blastocystis hominis by intramuscular injection of the organism into experimental mice. A total of 27 na?ve BALB/c mice aged 6-8 weeks were injected in the leg muscle with axenic culture isolate B of B. hominis. Histological examination at different times revealed that B. hominis could produce a severe inflammatory reaction and myonecrosis. Most changes were observed at 6 h after injection and for up to 2-3 days. By 2 weeks the muscle had regained normal histology. There was infiltration of polymorphonuclear leukocytes (PML) into the injection site, indicating that B. hominis had a strong chemoattractant activity for PML.     

Survival of Blastocystis hominis clones after exposure to a cytotoxic monoclonal antibody

Our previous studies have shown that monoclonal antibodies (MAbs) to Blastocystis hominis react mainly with carbohydrate epitopes, while 1 MAb (1D5) reacts specifically with a protein of 30.5 kDa. In the present study, 3 monoclonal antibodies (1D5, 1E7 and 4F7) were used in immunogold localization. 1E7 and 4F7 were found to react primarily with the surface coat, while 1D5 was plasma membrane-specific. In the presence of complement, only 1D5 exhibited a cytotoxic effect on B. hominis whereas 1E7 and 4F7 did not, suggesting that the surface coat of B. hominis could serve as an immunological barrier against host antibodies. Using a recently described agar plating method, only 1D5 exhibited significant (P < 0.01) complement-independent cytotoxicity to B. hominis, inhibiting colony growth at low concentrations. Parasites that had been exposed to 1D5 were morphologically smaller than those that were not exposed to this MAb. Colonies that grew in the presence of 1D5 were isolated and grown in liquid medium containing increasing amounts of the cytotoxic MAb. Two clones that grew well in liquid medium containing 1D5 were also able to develop into colonies in soft agar. This study has shown that the 30.5 kDa protein found on the plasma membrane of B. hominis is a functionally important protein and that not all cells within a certain population would be susceptible to the cytotoxic effects of 1D5. These findings suggest that a heterogenous population exists in continuously maintained cultures of B. hominis.     

A survey of Blastocystis in domestic chickens

The prevalence and morphology of Blastocystis in fresh faecal material from 227 domestic chickens was investigated. A very high prevalence of infection (approximately 95%) was found in chickens from four of the five commercial farms studied. Extremely high numbers of Blastocystis were found in the majority of samples. Blastocystis cells showed considerable variation in size, ranging from approx. 3 microm to approx. 120 microm in diameter. This size range is more extreme than those previously recognised for the organism from chickens. All chickens from one farm appeared free of Blastocystis infection. Most Blastocystis cells appeared to be the vacuolar form, although the shape of the cells and the appearance of the central vacuole contents varied considerably within and among faecal samples. Nuclei showed "spots" of electron-opaque material, generally arranged as a band within the nuclei. Multiple individual cysts within a single outer fibrillar layer were found in addition to single cysts without an encompassing fibrillar layer.     

Myiasis caused by Dermatobia hominis

In two patients, a woman of 35 and a man of 62 years old, myiasis caused by the larvae of the fly Dermatobia hominis was diagnosed. Both patients had recently returned from a visit to Central America. This ectoparasitosis is found in Central and South America. Patients present themselves with an insect bite which fails to heal. If the clinical presentation is unknown, the disease may well be mistaken for furunculosis. The condition may be easily treated by applying vaseline to the insect bite, which causes extrusion of the larva.     

Sac-like pouches in Blastocystis from the house lizard Cosymbotus platyurus

We report a 65-year-old male with progressive supranuclear palsy (PSP) who developed bilateral vocal cord abductor paralysis (VCAP). The patient was admitted to our hospital because of impaired gait. He was well until two years earlier, when he began to walk unsteadily. During the next two years, dysarthria and dysphagia developed and his gait worsened gradually. On admission, neurological examination showed impaired vertical and incomplete lateral gaze. His speech was slow and monotonous. Contractures were found in the neck muscles and elbows. The deep tendon reflexes were increased in the upper and decreased in the lower extremities. Babinski sign was negative. Snout and forced grasping reflexes were elicited. He showed marked bradykinesia. Magnetic resonance imaging revealed a midbrain tectum atrophy. Single photon emission tomography showed severe hypoper-fusion in the frontal cortex. No improvement was provided by the administration of levodopa-carbidopa, bromocriptine, droxydopa and amitriptyline. One month after admission, inspiratory stridor developed at night. The laryngofiberscopic examination demonstrated VCAP. An emergency tracheostomy relieved his respiratory distress. Although VCAP rarely occurs in neurodegenerative disorders other than multiple system atrophy, attention to VCAP should be required in PSP patients.     

Sexual risk behaviour in women carriers of Mycoplasma hominis

OBJECTIVE: To study the sexual behaviour of women harbouring Mycoplasma hominis in the vagina. SETTING: Two family planning clinics and a youth clinic for contraceptive advice. METHODS: The vaginal flora of 996 women were investigated microbiologically, including culturing for M. hominis from the posterior vaginal fornix. Cultures and tests were also made to diagnose genital Chlamydia trachomatis infections, gonorrhoea, genital herpes, cervical human papillomavirus infection, trichomoniasis, genital warts and human immunodeficiency virus. The sexual behaviour of these women was investigated by structured in-depth personal interviews. RESULTS: Of the 996 women, 123 (12.3%) harboured M. hominis in the vagina. The remainder (87.7%), who had a negative M. hominis culture, served as a reference group. Those with M. hominis were significantly more likely to have had more than 10 partners during their lifetime, had a greater frequency of more than one sexual partner during the preceding month and the last six months, and reported more frequent experience of "casual sex', including casual "travel sex'. More of them also had experience of group sex and were more likely to have been sexually abused than the women in the reference group. Fewer women with M. hominis had a current steady partner and were less often cohabitors, but more had had sexual intercourse during the previous week than those in the reference group. There was an association between the occurrence of M. hominis and bacterial vaginosis and genital chlamydial infection. Adjustment in multifactorial regression analyses therefore changed the results only marginally. CONCLUSIONS: Women with M. hominis have almost the same sexual risk behaviour as women with classic sexually transmitted diseases.