A parasite is an organism that lives in or on another organism, known as a host, and obtains nutrients or other benefits from the host. Parasitic organisms can cause harm to their hosts, although the effects vary depending on the type of parasite and the host.

Parasites that infect humans can enter the body through contaminated food or water, insect bites, contact with contaminated soil or surfaces, or direct contact with an infected person or animal. Some parasites can live in the intestines, while others can infect tissues, blood, or other parts of the body.

However, it is impossible for humans to completely isolate themselves from parasites. According to the World Health Organization, parasitic infections remain an important global health problem, particularly in tropical and subtropical regions where inadequate sanitation, unsafe water, poor hygiene, and limited access to health care can increase the risk of infection. Diseases such as lymphatic filariasis, schistosomiasis, and soil-transmitted worm infections affect millions of people worldwide.

Parasites can cause a wide range of health problems, including abdominal pain, diarrhea, anemia, malnutrition, fever, and damage to organs or tissues. Lymphatic filariasis, for example, is caused by microscopic parasitic worms transmitted through mosquito bites and can lead to severe swelling and enlargement of affected parts of the body.

There may also be a beneficial side to the study of parasites. Researchers have investigated whether certain parasitic worms, known as helminths, or substances produced by them could help regulate an overactive immune system. This research has led to studies involving conditions such as inflammatory bowel disease and other immune-related disorders. However, helminth therapy remains an area of research and is not an established general treatment that can replace conventional medications.

作者：Michael Chiu，MWS，CI
Previously published in Ming Pao Daily News – Updated and Revised in 2026