Parasitic Bugs in the Human Gut

Creepy-Crawlies in Us: The Parasitic Bugs in the Human Gut

When it comes to human gut health, intestinal parasitic infections are more common than you think. To avoid them, read on to understand them inside out.

Parasitic infections of the intestinal tract are less common in Singapore due to high standards of hygiene and good sanitation. However, with the rising trend of worldwide travel and immigration, the risk of parasitic infections is still present. This is particularly true when patients present symptoms that are not typical of common gastroenteritis after having returned or immigrated from countries with poor sanitation.

What are Intestinal Parasites?

These are organisms that infect the small and large intestines, and if left untreated, can lead to serious illness. The two main types are helminths and protozoa.


Multicelled helminths are also known as worms; the more common types found in humans are roundworms, tapeworms and pinworms. Adult-stage helminths generally do not multiply within their hosts. Instead, hosts are infected after ingesting parasitic eggs from contaminated soil or water. The eggs hatch, and the helminths then go through their life stages within the host.

Some helminths exhibit peculiar behaviours. For instance, pinworms live in the small intestine, but a pregnant female pinworm migrates to the anus (usually at night) and deposits her eggs in the skin folds around the anal region. This is why patients with pinworm infections complain of itchiness around the anal area. Once the eggs have hatched, the larvae re-enter the intestine from the anus, causing a retroinfection (an infection that is contrary to its usual course). The eggs may also contaminate the surroundings and infect another host.


Protozoa, unlike helminths, have only one cell. They can multiply within the human body and cause serious infections. Giardia is an example of intestinal protozoa; water contaminated by Giardia cysts is a major cause of diarrhoeal illness worldwide. Other protozoa include Cryptosporidium, Balantidium coli and Entamoeba histolytica.


Note that other diseases can have the same symptoms as intestinal parasitic infections. For example, inflammatory bowel disease may cause bloody stools and abdominal pain. An underlying colorectal carcinoma may lead to changes in bowel habits and weight loss in older individuals. Bacteria may also cause similar symptoms. It is important to distinguish between intestinal parasitic infections and other causes because the treatments are different.

Always consult a doctor for a formal assessment and medical opinion.

What are the Risk Factors?

Some of the risk factors associated with parasitic infections are:
• Travel to or living in a region with known parasitic infections
• Poor hygiene
• Poor sanitation (water and food)
• Compromised or suppressed immunity

How are Infections Managed?

Besides asking about your symptoms, your doctor will take your travel history and perform a physical examination. If an intestinal parasitic infection is suspected, he or she will order one or more stool samples to be collected for testing. In the case of a possible pinworm infection, your doctor may use the “tape” test, whereby adhesive tape is placed over the anus and then examined under the microscope for parasitic eggs. When your symptoms are severe and complications are a concern, or if your doctor is considering other diagnoses, they may order an X-ray or CT scan or perform a colonoscopy. Your doctor may also take biopsy specimens to be checked for parasitic eggs.
When the diagnosis is confirmed, your doctor will prescribe anti-parasitic medication. The treatment may take several weeks, and it is important to follow all steps as advised by your doctor.


A Final Tip

Prevention is key. Make washing your hands before eating a habit. When travelling to countries with poorer sanitation, drink only bottled water; avoid water from the tap or rivers. Note that the water used in cold desserts and for making ice usually comes directly from the tap, so take the necessary precautions.

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