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Infect Agent Cancer. 2017 Apr 12;12:21. doi: 10.1186/s13027-017-0131-z. eCollection 2017.

Predominance and association risk of Blastocystis hominis subtype I in colorectal cancer: a case control study.

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Laboratory Medicine, Faculty of Applied Medical Sciences, Umm Al-Qura University, Makkah, 7607 Saudi Arabia.
Clinical Laboratory Diagnosis, Department of Animal Medicine, Faculty of Veterinary Medicine, Assiut University, Assiut, Egypt.
Medical Parasitology, King Abdullah Medical City, Makkah, Saudi Arabia.
Parasitology Department, Faculty of Medicine, Ain-Shams University, Cairo, Egypt.
Oncology, King Abdullah Medical City, Makkah, Saudi Arabia.
Department of Internal Medicine, Medical Oncology, Mansoura University, Mansoura, Egypt.
Medical Parasitology, Al-Noor Specialist Hospital, Makkah, Saudi Arabia.
Parasitology Department, Faculty of Medicine, Assiut University, Assiut, Egypt.



Blastocystis, a genetically diverse intestinal parasite with controversial pathogenic potential, has increasingly been incriminated for diarrheal illness in immunocompromised individuals including colorectal cancer (CRC) patients. The aim of the current study was to assess the possible association between Blastocystis infection and CRC condition in Makkah, Saudi Arabia (KSA).


Stool samples were collected from 80 non-cancer (NC) and 138 cancer subjects including 74 CRC patients and 64 patients with other cancers outside gastrointestinal tract (COGT). Molecularly confirmed Blastocystis isolates were genetically grouped and subtyped using multiplex polymerase chain reaction with restriction fragment length polymorphism (PCR-RFLP) and sequence-tagged site primers-based PCR (PCR-STS), respectively.


Blastocystis hominis were confirmed in 29.7, 25 and 15% among CRC, COGT and NC patients, respectively. Obtained Blastocystis isolates were initially categorized into 2 groups (A and C), which were subsequently subtyped into 3 different subtypes; subtype-I (38%), subtype-II (44%) and subtype-V (22%). Interestingly, subtype-I was the most predominantly detected subtype (54.5%) among CRC patients with a significant association risk (COR 7.548; 95% CI: 1.629-34.987; P = 0.004).


To the best of our knowledge, the current study is the first to provide genetic insights on the prevalence of Blastocystis hominis among CRC patients in Makkah, KSA. Moreover, the study suggests for a possible association between subtype-I of Blastocystis hominis and CRC, which could indicate a potential influence of Blastocystis on CRC condition. Further studies are required to confirm this association risk and to investigate the possible underlying mechanism of postulated carcinogenic influence of Blastocystis hominis subtype-I.


Association risk; Blastocystis hominis; CRC; Genetic diversity; Subtypes-I

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