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.
For many first world travelers, a trip to the tropics ends in diarrhea, which can be challenging for physicians to diagnose, due to the large number of organisms that can cause that illness. Researchers in Switzerland report some success with the use of a multiplex nucleic acid test in identifying pathogens in returning travelers, both adults and children. Although the multiplex test did not cover Blastocystis, results suggest that this might be an appropriate addition to the assay. The test was more successful at identifying pathogens in children, with 52% of samples from children showing positives, with rotavirus being the most common at 27%. Adult samples were positive only 11% of the time, but a separate microscopic examination showed Blastocystis infection in 23% of those individuals. The study was published in the journal Infection.
Researchers studying nuclear genes in Blastocystis report that a large number of those genes require a process known as mRNA polyadenylation to create functional termination codons, a process necessary for correct cell functioning. This process is somewhat unique in the animal world, found in Blastocystis and a few other organisms, but rarely in human genes. Although the authors did not note the treatment potential, a number of other researchers have studied mRNA polyadenylation as a treatment target for HIV, and even endometriosis, suggesting that this might one day be investigated as a treatment for Blastocystis infection. The study was published in Genome Biology and Evolution.
Researchers studying Blastocystis prevalence and transmission in Calarca’ Columbia report that children in public daycare environments have a high rate of Blastocystis infection, measured at 57.5%. While both Blastocystis-positive and Blastocystis-negative children reported a high rate of diarrhea, children with Blastocystis reported a significantly increased rate (45% vs. 33%, p < 0.05). Blastocystis infection was correlated with the presence of Blastocystis in a sugar cane beverage, drinks other than bottled milk, and foods. The study was published in Biomedia.
Although some infections occur with a consistently higher prevalence in less industrialized areas, Blastocystis sometimes breaks that rule. Researchers comparing Blastocystis infection in pig farmers in Southeast Queensland Australia to Cambodia report an infection rate of 83.3% in SEQ, vs. 55.2% in Cambodian villagers. Pigs in SEQ were more likely to be infected with Blastocystis, with 76.7% of the Austrian pigs infected vs. 45.2% of Cambodian pigs. Even more interesting, although both groups of pigs were infected predominantly with Blastocystis sp. subtype 5, that subtype was not found in Cambodians, but was found in the Austrians, suggesting that transmission from pigs to humans occurs in SEQ but not Cambodia. The study was published in Veterinary Parasitology.
An Austrial study of pigs reports that 81.5% of animals studies showed fecal IgA response to Blastocystis antigens. Immunosuppressed pigs were significantly more likely to show a response to Blastocystis antigens than immunocompetent pigs. Fecal IgA response has previously been studied in humans, but this may be one of the first studies on animal response. The researchers noted that since pigs infected with Blastocystis do not show intestinal pathology, a trait shared with many humans infected with Blastocystis, those animals may provide a good model for some human infections. The study was published in Parasite Immunology.
Since Blastocystis occurs in individuals with and without symptoms, the clinical community has a strong interest in differences that exist between those two types of infections. Researchers comparing Blastocystis isolates from symptomatic and asymptomatic individuals report that isolates from symptomatic individuals exhibited a higher degree of production of a Capase-like proteases, chemicals which cleave other proteins and are involved in the process of programmed cell death. Most interestingly, three different genetically distinct subtypes of Blastocystis exhibited this behavior, with subtypes 1, 3, and 5 from symptomatic individuals showing different behavior from subtypes 1, 3, and 5 from asymptomatic individuals. The full study has been published in BMC Parasites and Vectors.
Researchers studying patients from several large University hospitals in Iran report that Blastocystis infection is found more frequently in individuals with higher serum iron counts, and is also associated with higher levels of C-reactive protein, occult blood, and erythrocyte sedimentation levels. Overall, 97600 stool examinations were done in 4 university hospitals. Parasites were observed in 46,200 specimens. Of these cases, 6851 cases had complete blood work information along with only B. hominis infection. In the control group, 3615 subjects without parasite infestation were included. Erythrocyte sedimentation rate level was significantly higher in cases with B. hominis infection (p < 0.05). C-reactive protein level was positive in 1.46% of cases and 0.5% of controls, which was statistically significant (p < 0.05). Frequency of serum iron < 120 was significantly higher in cases with B. hominis infection compared to controls. Occult blood was positive in 0.93% of cases and in none of the controls (p < 0.05). For more information, refer to the paper from Pzgelad Gastroenterology.
Researchers from Sydney and New South Wales Australia have published a summary of existing research on Blastocystis pathogenicity along with a summary of treatment options. For more information, refer to the paper published in Gut Pathogens.
Researchers from the University of Singapore, working with several strains of Blastocystis sp. subtype 7, report that differences exist between the ability of strains to adhere to intestinal colonic cells. These differences appear to relate to the ability of the cells to increase intestinal permeability, one of the mechanisms that can produce diarrhea in symptomatic individuals. The study suggested that metronidazole resistance was associated with a fitness cost, since cells made resistant to Blastocystis exhibited a lower degree of adhesion. For more information, refer to the paper in PLOS Neglected Pathogens.
Researchers working with human enterocytes, columnal cells found in the intestine, report that exposure to Blastocystis sp. subtype 7 significantly reduces intestinal permeability, a property common to many intestinal pathogens, and one cause of the symptom of diarrhea. Exposure to Blastocystis sp. subtype 7 also produced a statistically significant increase in programmed cell death in enterocytes. Similar exposure to Blastocystis sp. subype 4 did not produce these effects, suggesting the existence of a strain-dependent effect. For additional information, please refer to the paper from Biomed Research International.