Intestinal parasites update

The role of intestinal parasites such as Giardia Lamblia and Cryptosporidium in causing human disease is well known. More recently due to improvements in diagnostic tests, other parasites are also being recognized as pathogens. This is expanding the list of “single word answers” to chronic gastrointestinal complaints such as diarrhea predominant irritable bowel syndrome.

Dientamoeba Fragilis is a known human pathogen and a common cause of acute, subacute and chronic diarrhea, abdominal pain and bloating. Blastocystis Hominis was first discovered almost 100 years ago but its role in causing human disease has until recently been controversial. This controversy stems from the fact that only certain subspecies of the parasite are pathogenic in humans, that asymptomatic carriage is not uncommon and spontaneous clearance within 12 months more common than not.

Both parasites are usually contracted by faecal-oral transmission. Well known risk factors are overseas travel (especially to under developed countries), exposure to bodies of water (campers, swimmers) and ingestion of food contaminated by grey water (home vegetable patches especially), it is common to detect these parasites in symptomatic patients with no identifiable risks factors. It is therefore important that all patients with symptoms suggestive of infection with these agents is not denied screening on the basis of presence or absence of risk factors alone.

Detection, in the past, has been limited to simple direct stool examination but with the advent of fixed concentrated preparation examination and PCR based options, detection has been significantly improved.

The biggest issue surrounding infection with these agents is whether detection represents true pathogenic infection or just colonization. It is important that all patients with significant “red flag” symptoms (weight loss, rectal bleeding) are appropriately evaluated for more sinister causes. In the absence of these factors or other diagnostic tests being unenlightening it is not unreasonable to treat first with standard first line agents such as metronidazole. Often patients will experience at least transient benefit from this.

For resistant cases multiple novel anti-parasite treatments are now available (mostly via compounding chemists and not PBS subsidised).

Nathan ConnellyAUTHOR | Dr Nathan J Connelly (MBBS FRACP)
Dr Connelly has a longstanding commitment to gastroenterology and disease diagnosis, management and innovative techniques. He specialises in hepatology as well as gastroenterology. He performs endoscopy for diagnostic and preventative measures, capsule endoscopy, faecal microbiota transplant and much more.
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