Title: Blastocystis hominis and colorectal cancer

The protozoan parasite, blastocystis hominis, has been studied by transmission electron microscopy in the stool samples of 320 patients. Various ultrastructural characteristics are noted and the incidence of this parasite infestation studied. The vacuolar form is the most common form. There is a strong correlation between the disease condition and the presence of blastocystis hominis (p<00001).The commonest infection was seen in patients having pruritis ani (54.2%) or carcinoma of the colon/rectum confined to the bowel wall or regional lymph nodes (53%) compared with patients having other intestinal diseases (30%). The implications of this finding with respect to colorectal cancer and the aetiology of this condition are discussed. Index 1.1 Blastocystis hominis, the protozoan parasite 1.2 Materials and methods 2.1 Ultrastructure of blastocystis hominis 2.1.1 Vacuolar form of blastocystis hominis 2.1.2 Amoeboid form of blastocystis hominis 2.1.3 Cyst form of blastocystis hominis 2.1.4 Phagocytosed blastocystis hominis 3.1 Analysis of the ultrastructural data and the patient information 3.1.1 Incidence of blastocystis hominis 3.1.2 Time of year sample collected 3.1.3 Age of patient 3.1.4 Disease condition 3.1.4.1 Blastocystis hominis and colorectal cancer 4.1 Is such a result relevant to colorectal cancer? Can this result be supported by any existing evidence? 5.1 How can the environmental factors influence the adenoma – carcinoma sequence resulting in the development of colorectal cancer? 6.1 Conclusion 2 Paper 8 www.howardsteer.co.uk/papers/008 Copyright © Howard Steer 2007 1.1 Blastocystis hominis, the protozoan parasite Blastocystis hominis is a parasitic protozoan organism whose whole history has proved to be rather perplexing. The difficulties concerning this organism are reflected in the following facts: – difficulty establishing its parasitic protozoan status – difficulty in defining its taxonomy – its mode of transmission is unknown – its life cycle is uncertain – its significance is unknown – its association with disease states is uncertain. The lack of knowledge with respect to blastocystis hominis makes this organism ideal for study. What is known about the organism? Blastocystis hominis was initially considered to be a yeast. Although a flagellated cyst was described in the early twentieth century (Prowazek 1904; Alexeieff 1911) subsequent publications continued to call it a yeast (Brumpt 1912) and a fungus (Alexeieff 1917). In fact, for many years it continued to be described as a yeast in textbooks. The advent of electron microscopic techniques together with specific laboratory culture methods has enabled the true position of Blastocystis hominis as a protozoan parasite to be appreciated (see Zierdt, Rude and Bull 1967). The taxonomic position of Blastocystis hominis has remained uncertain. These uncertainties are discussed in the review article of Stenzel and Boreham (Stenzel and Boreham 1996). Although blastocystis hominis has been described as being a protozoan parasite causing intestinal disease (Zierdt 1983) the evidence for this has been provided mainly from case reports. The pathogenic potential of blastocystis hominis is uncertain. It is unknown whether “blastocystis hominis is a truly pathogenic organism or a commensal or perhaps is capable of being a pathogen in specific circumstances” (Stenzel and Boreham 1996). Epidemiological studies have been hampered by the initial difficulties defining the organism, the identification of the organism and the fact that the stool samples examined have usually been those submitted to a parasitology laboratory for the purpose of excluding an infection. The samples are therefore from a preselected group of patients. This has resulted in limited epidemiological studies. Electron microscopy has enabled the organism to be identified with greater accuracy so that epidemiological studies can now be performed using the electron microscope although such studies are more time consuming. There have been numerous ultrastructural reports which have refined the morphological details of blastocystis hominis (Zierdt, Rude and Bull 1967). With these facts in mind it has been decided to study the incidence of blastocystis hominis infection as assessed by transmission electron microscopy. 1.2 Material and Methods The patients involved in this study have been referred to hospital with lower gastrointestinal symptoms and seen in an outpatient clinic or as an inpatient. Following Paper 8 www.howardsteer.co.uk/papers/008 3 Copyright © Howard Steer 2007 full and informed consent from the patients the investigation of these patients has included a sigmoidoscopy of an unprepared rectum. During this examination faecal samples have been obtained. Ethical approval has been obtained for the study. This study has involved 320 patients who presented to a gastroenterological outpatient clinic with a variety of lower gastro-intestinal conditions. The diagnoses of the patients studied and the numbers of patients in each group are as follows: Diagnosis Number of patients Haemorrhoids (diagnosis 1) 46 Pruritis ani (diagnosis 2) 24 Chronic anal fissure (diagnosis 3) 27 Colo-rectal cancer (diagnosis 4) 83 Colonic adenoma (diagnosis 5) 35 Ulcerative colitis (diagnosis 6) 105