Skip to content

Common Intestinal Parasitic Infection

Common Intestinal Parasitic Infection

21 June 2019

Causative agents and mode of transmission

There are many intestinal parasites affecting humans. Common ones include roundworms, pinworms, hookworms, tapeworms and liver flukes.

Roundworms (Ascaris species) are round and long, and the length can reach 20 cm. They have pointed ends and are light brown or pink in colour. They live in the human small intestine and their eggs are passed out with stool. Infections are acquired through ingestion of food contaminated with their eggs. Hands with contaminated soil can also be the transmission media.

Pinworms (also called threadworms) are about 1 cm in length and whitish in colour, which resemble short pieces of threads. They inhabit the human large intestine and migrate to the anus at night to lay eggs. This may result in local itchiness. A patient's fingers may be contaminated during scratching. If the patient does not wash hands thoroughly before preparing food, ingestion of these contaminated foods by other persons could result in infection. Children are at higher risk of acquiring the infection.

Hookworms are about 1 cm long, round and curved. They inhabit the human intestine and attach to the intestinal wall, resulting in blood loss and causing the host to become anaemic. The eggs are passed out with stool and hatch into larvae in soil. Human contact with contaminated soil, such as working barefoot in fields, may result in these larvae penetrating through the skin and causing infection.

Tapeworms are flat and could be up to 6 m long. They are segmented and white or pale yellow in colour. They inhabit the human small intestine and their eggs are passed out with stool. If the eggs are ingested by pigs or cows, they will develop in their bodies and attach to the pork or beef as cysts. In addition, some tapeworm larva can occur in both freshwater and marine fish. Ingestion of these undercooked contaminated pork, beef or fish may result in infection.

Liver flukes are flat and about 1 to 2 cm long. They live in the human bile duct in the liver and their eggs are passed out with stool. After ingestion by snails and then released into water, they will come in contact and penetrate the flesh of some freshwater fish. Ingestion of these undercooked contaminated fish may result in infection.

Clinical features

Symptoms of parasitic infection depend on the type of parasite contracted. Infection with a small number of parasites may be asymptomatic. For those who have symptoms, the following may occur:

  • Abdominal discomfort and distention, vomiting, diarrhoea
  • Weight loss
  • Anal itchiness
  • In the case of tapeworm infection, passing tapeworm segments in stool
  • If a large number of parasites are present, they can result in more severe complications, e.g. intestinal obstruction, anaemia, obstruction and inflammation of bile ducts

Incubation period

The incubation period varies, depending on the type of parasite contracted.


Most parasitic infections can be completely eradicated by medication.


1. Maintain good personal hygiene

  • Perform hand hygiene frequently, especially before handling food or eating, and after using the toilet.
  • Wash hands with liquid soap and water, and rub for at least 20 seconds. Then rinse with water and dry with a disposable paper towel or hand dryer. If hand washing facilities are not available, or when hands are not visibly soiled, hand hygiene with 70 to 80% alcohol-based handrub is an effective alternative.
  • Regular trimming of fingernails.
  • Discourage children from sucking fingers or scratching anal area.
  • Wear footwear when working in fields.

2. Maintain good food hygiene

  • Drink only boiled water from the mains or bottled drinks from reliable sources.
  • Purchase fresh food from hygienic and reliable sources. Do not patronise illegal hawkers.
  • Avoid high-risk food like raw or undercooked meat, especially beef, pork and fish.
  • Clean and wash food thoroughly.
  • Cook all food thoroughly before consumption, especially when preparing food by barbecue or hot pot.
  • Adopt the 5 Keys to Food Safety in handling food, i.e. Choose (Choose safe raw materials); Clean (Keep hands and utensils clean); Separate (Separate raw and cooked food); Cook (Cook thoroughly); and Safe Temperature (Keep food at safe temperature) to prevent foodborne diseases.

* Please visit the website of Centre for Food Safety for more information on food safety.