الفهرس 
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Abstract
B. hominis is a single-celled organism belonging to a group known as the Stramenopiles (also called Heterokonts) that includes algae, diatoms, and water molds. Blastocystis comprises several species, living in the gastrointestinal tracts of humans, farm animals, birds, rodents, reptiles, amphibians, fish, and cockroaches. Blastocystis infections have a worldwide distribution with prevalence of 30% to 60% in developing countries and 1.5% to 20% in developed countries.
These differences are due to poor hygiene practices and consumption of contaminated food or water. The organism is mainly transmitted through fecal-oral route. A higher risk of infection has been found in humans with close animal contact and several studies provided molecular-based evidence on the zoonotic potential of Blastocystis spp.
Blastocystis is currently classified into 17 small subunit ribosomal RNA (SSU rDNA) subtypes (STs; ST1–17) according to the nomenclature established by Stensvold et al (2007) (138) These subtypes represent genetically diverse Blastocystis species isolated from humans and animals. A majority of human infections with Blastocystis sp. are attributable to ST3, but infections with ST1, ST2 and ST4 are also common. ST5-ST9 have been isolated only sporadically from humans (12) while ST10 –ST17 have not been found in humans to date.
The aim of the present work is to detect B. hominis parasite by routine microscopic examination in comparison with rt-PCR in patients with gastrointestinal manifestations referred for colonoscopy and correlation with pathological findings.
The current study was conducted on 100 patients attending the gastroenterology department in the Medical Research Institute and referred for endoscopy of the colon. The study patients were 56 males and 44 females, varying in age from 18 to 69 years, 52% of them were from urban areas.
All stool samples were collected and subjected to microscopic examination, DNA extraction and rt-PCR analysis for detection of B. hominis infection. Histopathologic study was done in the Pathology department of Medical Research Institute after colonoscopy and findings correlated to microscopy and rt-PCR results.
The total parasitic infections rate was 46%, with 31% B.hominis infection, E.coli showed (5%), E. histolytica (5%), G. lamblia (2%), Enterobius Vermicularis (2%) and D. fragilis (1%).
Among 31 cases positive for B. hominis by microscope, 14 (35.8%) out of 39 were under the age of 40 years and 17 (27.9%) out of 61 were above 40 years. There was no statistically significant association between infection by B.hominis and age. Regarding gender, 14 (25%) out of 56 males were positive for B.hominis and 17 (38.6%) out of 44 females were positive for B.hominis, no statistically significant difference was observed between the two groups. As for residence, 19 out of 52 (36.5%) cases were positive with B.hominis from urban areas while 12 out of 48 (25%) cases were positive with B.hominis from rural areas. No statistically significant difference was seen between both groups.
Among 88 cases diagnosed by rt-PCR, 33 (84.6%) out of 39 were under the age of 40 years and 55 (90%) out of 61 were above 40 years. There was no statistically significant association between infection by B.hominis and age. Regarding gender, 50 out of 56 males (89.2%) were positive for B.hominis and 38 out of 44 females (85.4%) were positive for B.hominis, no statistically significant difference was observed between the two groups. As for residence, 44 out of 52 (84.6%) were positive for B.hominis from urban areas while 44 out of 48 (91%) were positive for B.hominis from rural areas. No statistically significant difference was seen between both groups.
Various gastrointestinal manifestations were found among the 100 patients enrolled in the study. Using microscopy, 31 of them were positive for B. hominis. 29 patients (93.5%) had abdominal pain, 28 (90.3%) had dyspepsia, 10 (32.3%) complained of blood in stool, 7 (22.6%) had diarrhea, and 2 patients (6.5%) had constipation (putting into consideration many patients may have multiple complaints simultaneously). Using rt-PCR, 88 of the 100 patients were positive for B. hominis. 77 patients (87.5%) complained of abdominal pain, 65 (73.9%) had dyspepsia, 38 (43.2%) had blood in stool, 22 (25.0%) had diarrhea, and 5 patients (5.7%) had constipation.
Regarding pathology results correlated to positive microscopic results ,12 (83.7%) were normal, 13(41.9%) colitis, 4(12.9%)colon cancer, 2(6.2%) inflammatory ulcer. No significant association between pathologic diagnosis and microscopic results. In relation to rt-PCR results, 34 (38.6%) were normal, 26 (29.5%) colitis, 21(23.9%) colon cancer,
5 (5.7) inflammatory ulcer, and 2 (2.3%) had ileitis. No significant association between pathologic diagnosis and rt-PCR results.
Comparing the results of the 100 patients examined by microscopy and real time- PCR, no agreement was found between both techniques in detection of B. hominis in stool samples.