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.
Although culture studies for Blastocystis have been reported for many years, new ones with modern methods and additional results are always valuable. Researchers from Wroclaw University of Environmental and Life Sciences have published a study comparing different culture media for Blastocystis, reporting that “In this article, we compared eight liquid media for cultivation of Blastocystis spp. Study material included fecal samples from clinically healthy pigs. Significant differences in the growth of Blastocystis on individual media were observed.” The study was reported in the Polish Journal of Veterinary Sciences.
Researchers in Jakarta examining 141 stool samples collected from school children report that PCR testing “revealed 89%, 78%, 80% and 88% sensitivity, specificity and positive and negative predictive values, respectively, in comparison with the culture method (McNemar, p > 0.05). Sixteen PCR samples were successfully sequenced and resulted in three Blastocystis subtypes 1, 3 and 4. In conclusion, PCR was sensitive enough and can be used to exclude Blastocystis infection up to 88% of the cases. Subtypes 3 and 1 were the main subtypes found in apparently healthy school children in Jakarta.” The paper was published in the Journal of Tropical Pediatrics.
Although metronidazole has been recommended as a treatment for symptomatic Blastocystis patients, researchers have questioned the efficacy and evidence for the benefit of this treatment. In a paper describing a case report of two Blastocystis patients, physicians report that “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.” The account was published in Parasitology Research.
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.
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.
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.
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.
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.
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.