About Blastocystis

Blastocystis is a highly prevalent single-celled parasite that infects the gastrointestinal tract of humans and animals.  It has become the most prevalent gastrointestinal parasitic infection in developed and many developing countries, and it will produce long-term diarrhea, abdominal pain, and other symptoms in healthy individuals.

BRF’s web site has written and audio descriptions from patients, information on the newest research in diagnosis and treatment of Blastocystis ’hominis’ infection, and information on BRF”s advocacy program.

Blastocystis Acquisition and Loss Can be Highly Dynamic

Travel associated Blastocystis has been reported as a possible cause of traveler’s diarrhea, however there are few studies comparing travelers pre- and post travel.  In one of the few such studies, researchers report that although Blastocystis can be acquired in travel, infection with Blastocystis presents a much more dynamic picture in many individuals.  In this study, researchers report that “stool samples of 479 travelers were analysed. Before travel, 174 of them (36.3%) carried Blastocystis and in most of these, the same subtype was persistently carried. However, in 48/174 of those travellers (27.6%; CI95 20.8-36.6%) no Blastocystis or a different subtype was detected in the post-travel sample, indicating loss of Blastocystis during travel. Only 26 (5.4%; CI95 3.7%-8.0%) of all travellers acquired Blastocystis, including two individuals that were already positive for Blastocystis before travel but acquired a different subtype during travel.”  The study was reported in Travel Medicine and Infectious Diseases.

Blastocystis Infection More Closely Associated with Diarrhea than E. Histolytica or Giardia

Although there are many “single agent” studies that have examined correlation of infection with specific microbes, there are few studies that have compared the presence of gastrointestinal symptoms with multiple potential etiological agents.  The lack of such comparative studies makes it difficult to disentangle methodology from results.  In a report from Pakistan, researchers found that Blastocystis infection was more highly associated with gastrointestinal symptoms than E. histolytica or Giardia.  One hundred and sixty-one patients with diarrhoea were compared to 114 age and sex matched controls. The researchers report that, “There was a marked difference in the presence of parasites between patients and controls: no parasite 42/75%, one parasite 42/15%, two or more parasites 16/10%, respectively (p < 0.001). Patients with diarrhoea were more likely to be infected with Blastocystis sp (p < 0.001), E. histolytica (p = 0.027) and E moshkovskii (p = 0.003). There was no difference in the frequency of H. pylori (p = 0.528), G duodenalis (p = 0.697) or E dispar (p = 0.425). Thirty-three patients and 27 controls had H. pylori infection. Of these, 22 patients and 6 controls were infected with Blastocystis sp (p = 0.001), 6 patients and no controls were infected with E. histolytica (p = 0.02), whilst 7 patents and 9 controls were infected with E dispar (p = 0.292)”  The study was published in the British Journal of Biomedical Sciences.

Rats and Gerbils Can Be Used for Long-Term Models of Blastocystis Infection

A multi-disciplinary team of researchers working in the Czech Republic, Denmark, and Canada report that long-term Blastocystis infection can be modeled in both rats and gerbils.  The researchers report that, “Blastocystis ST1 established in 100% of the outbred rats (Rattus norvegicus) and gerbils (Meriones unguiculatus) challenged. Rats were colonized asymptomatically for more than one year, but Blastocystis ST1 was not transmitted between rats. Mus musculus strain CD1 and Mastomys coucha were not susceptible to Blastocystis ST1. Thus, rats appear to be a suitable in vivo model for studies of Blastocystis ST1, as do gerbils though testing was less extensive.”  The paper was published in the journal Experimental Parasitology.

Blastocystis Shifts Microbiome in Asymptomatic Human Infections

In the first study of its kind, researchers in Mexico report that Blastocystis infection is associated with significant changes in the human microbiome in asymptomatic  adults.  In this study, 156 asymptomatic adult subjects from a rural population in Xoxocotla, Mexico. Colonization with Blastocystis was strongly associated with an increase in bacterial alpha diversity and broad changes in beta diversity and with more discrete changes to the microbial eukaryome. More than 230 operational taxonomic units (OTUs), including those of dominant species Prevotella copri and Ruminococcus bromii, were differentially abundant in Blastocystis-colonized individuals. Large functional changes accompanied these observations, with differential abundances of 202 (out of 266) predicted metabolic pathways (PICRUSt), as well as lower fecal concentrations of acetate, butyrate, and propionate in colonized individuals. Fecal calprotectin was markedly decreased in association with Blastocystis colonization, suggesting that this ecological shift induces subclinical immune consequences to the asymptomatic host.  The open access paper was published in M-Systems, an American Society of Microbiology journal.

High Prevalence of Blastocystis Infection (54%) In Chicken Farm Workers

In a study of farmed chickens and their human farm workers in Lebanon, researchers report that 54% of the farm workers, and 32% of the chickens were found to be infected with Blastocystis sp.  The primary subtypes found in chickens were Blastocystis sp. subtype 6 and 7.  Blastocystis sp. subtype 6 was found at a high prevalence in the human workers, in comparison with the more commonly found Blastocystis sp. subtype 3 in other populations, demonstrating the zoonotic potential of Blastocystis transmission to agricultural workers.  The study was published in BMC Parasites and Vectors.

Extra-Intestinal Blastocystis Infection in Duck

Veterinary researchers from Cambridgeshire, UK have reported a case of extra-intestinal Blastocystis infection observed in a duck.  Although Blastocystis is often thought to occur exclusively in the gastrointestinal tract, samples taken from a facial swelling of the duck in question were found ro bear a morphological similarity to Blastocystis.  Subsequent PCR testing showed that the subtype was consistent with Blastocystis sp. subtype 7.    The full study was published in the Journal of Veterinary Diagnostic Investigation.

In a study of 220 water samples from rivers and the Black Sea, researchers from Turkey report that, “Blastocystis sp. were found in 3 out of the 75 (4%) river water samples that were collected from the Samsun Province. Six of the 120 (5%) river water samples and 1 out of the 48 (2%) seawater samples were positive for Blastocystis in the Amasya and Sinop Provinces. There were two different subtypes (ST; 1 and 3) found from sequencing all of the samples from the investigated sites.”  The study was published in Acta Tropica.

Blastocystosis Mis-Diagnosed as Gluten Intolerance

Italian researchers report on a case of Blastocystis infection, mis-diagnosed as gluten intolerance, which subsequently resolved, possibly due to treatment with Saccharomyces.  The researchers report that, ” 41-year-old Italian man came to the clinician’s observation reporting cramps, bloating and watery diarrhoea a few days after drinking water indicated as unpotable from a fountain in a farm area. The medical suspicion was directed at both gluten intolerance and enteric infection, eventually of waterborne origin. Gluten intolerance was investigated by intestinal biopsy and excluded, while stool analyses ruled out infective bacteriological or viral agents and parasites. Subsequently, a persistent eosinophilia was revealed and a parasitological analysis was again suggested, planning for a more sensitive molecular method.”  The study was published in New Microbiologica.

Anti-Statin Drug Shows Promise Against Blastocystis in Mouse Model

Using a murine model of Blastocystis infection, an Egyptian research team has reported that the anti-cholesterol statin drug Atorvastatin  increases the efficacy of metronidazole in treatment of Blastocystis infection in a murine model.  The researchers report that, “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. ”  The study was published in the Korean Journal of Parasitology.

Blastocystis has Low Prevalence in Infants in Ireland

Although Blastocystis prevalence is frequently reported in adults, there are few studies of Blastocystis infection in infants.  In a study published from Ireland, researchers “surveyed the prevalence and diversity of Blastocystis in an infant population (n = 59) from an industrialized country (Ireland) using Blastocystis-specific primers at three or more time-points up to 24 months old. Only three infants were positive for Blastocystis (prevalence = 5%) and this was only noted for samples collected at month 24. This rate is comparatively low relative to previously reported prevalence rates in the contemporaneous adult population.”  The work was reported in the journal Parasitology.