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Common Intestinal Parasitic Infection

Common Intestinal Parasitic Infection

21 March 2017

Causative agents and mode of transmission

There are many intestinal parasites affecting human. The common ones are roundworms, pinworms, hookworms, tapeworms and liver flukes.

Roundworms 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 transmitted through ingestion of food contaminated with their eggs. Dirty hands, flies and other insects can also be the transmission media.

Pinworms are also called threadworms. They are only 1 cm in length, whitish in colour, which resemble a short piece of thread. They inhabit the human large intestine and migrate to the anus at night to lay eggs. This may result in local itchiness. One's fingers may be contaminated during scratching. If one does not wash hands before preparing food, ingestion of these contaminated foods by other persons could result in infection. Children are particularly at risk of getting the illness.

Hookworms are 1 cm long, round and curved. They inhabit the human intestine, suck the host's blood and, cause the host to become anaemic. The eggs are passed out with stool, and hatch into larvae in soil. Human contact with contaminated soil like working barefoot in fields may result in these larvae penetrating through the skin and causing infection.

Tapeworms are flat and could be up to more than 6 m long. They are segmented, white or translucent 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 body and attach to the pork / beef as cysts. Ingestion of this under-cooked contaminated pork / beef may result in infection.

Liver flukes are flat and about 1 to 2 cm long. They live in the human liver and their eggs are passed out with stool. After ingestion by snails and then released into the water, they will attach themselves to the flesh of some fresh water fish. Ingestion of these under-cooked contaminated fish may result in infection.

Clinical features

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

  • Abdominal discomfort and distention, vomiting, diarrhoea
  • Loss of weight
  • Anal itchiness
  • Allergic skin reaction such as urticaria
  • If a great 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. Keep hands clean and fingernails trimmed.
  2. Wash hands thoroughly with liquid soap and water before handling food or eating, and after using toilet or handling faecal matter.
  3. Discourage children from sucking fingers or scratching anal area.
  4. Wear footwear when working in fields.
  5. Drink only boiled water from the mains or bottled drinks from reliable sources.
  6. Purchase fresh food from hygienic and reliable sources. Do not patronise illegal hawkers.
  7. Avoid high-risk food like raw or under-cooked beef, pork and fish.
  8. Clean and wash food thoroughly.
  9. Cook food thoroughly especially when preparing food by barbecue or hot pot. Fish has to be cooked thoroughly. Avoid eating raw or under-cooked fish congee. 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.