First of all, let’s talk a little bit more about what a colonoscopy is exactly. This is a diagnostic procedure consisting of the visualisation of the interior of the anus, the rectum and the large intestine, also known as colon, by the introduction of a flexible endoscopic tube equipped with a camera. Some people can fear having to pass this type of tests, but patients are usually heavily sedated for this procedure and do not remember it afterwards. The annoying part of this procedure is really the day before where laxatives are given to clean the large intestine of all solid matters in order to facilitate the visualisation of the walls. Colonoscopy is usually used to detect and remove polyps before they can turn into colorectal cancer or for the formal detection of this type of cancer. This diagnostic test is then usually recommended every ten years for people over 50 years old. It is also frequently used to detect inflammatory bowel diseases and it is indicated when blood is found in the faeces without any known causes.

Colonoscopy is somewhat invasive and not currently a routine procedure to diagnose parasitic diseases, as blood tests and/or visualisation of parasites’ eggs in the faeces are better and less invasive diagnostic tools. However, it is possible that many faeces’ tests came back negative, even though the person is infected by an intestinal parasite. It is especially the case when the eggs are only present sporadically in the faeces. In that case, colonoscopy could be useful to find the real source of the experienced gastrointestinal symptoms. When looking for them, parasites, especially the ones that are able to hook themselves in the intestinal walls are easily visualised during a colonoscopy. The soil-transmitted helminth Trichuris trichiura, also known as whipworm, is one of the common examples of parasites that can be diagnose and correctly identify by its characteristic shape during a colonoscopy. It is especially true if the patient is infected only by few male worms and consequently testing for eggs in the faeces always come back negative. In that case, the part of the endoscopic tube discussed earlier that is usually used to remove polyps can be used to unhook worms from the intestinal walls. However, parasites that are not able to hook or attach themselves to the intestinal walls might be missed because that the laxative preparation prior to the colonoscopy might have flushed them away. In that case, it is possible that eggs are still present and that the parasite will come back after, as parasite’s eggs are not usually seen during a colonoscopy. Furthermore, characteristic damages to the intestinal walls caused by parasites could also be seen during this procedure.

Finally, it is interesting to note that, even with the great amount of colonoscopy performed as a colorectal cancer prevention tool each year in developed countries, it is quite rare to accidentally detect parasites during this type of procedure. However, as parasitic infections could be asymptomatic, this surprising but rare finding during routine colonoscopy has therefore been documented in the medical literature.