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.
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:
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
2. Maintain good food hygiene
* Please visit the website of Centre for Food Safety for more information on food safety.