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What is a Parasite?

Mary McMahon
Updated Mar 05, 2024
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A parasite is an organism which exploits another organism for the purpose of staying alive. Some parasitic relationships are harmless, while in other cases a parasite can damage or even kill its host. The study of parasitism is an extensive field, because parasites can be found across the biological kingdoms, and many animals host one or more parasites during their lives. A number of organisms also go through a parasitic stage at some point during their lives.

The word is borrowed from the Greek parasitos, meaning “one who eats at the table of someone else.” In both Greece and Rome, some people made dining at the homes of others a full time occupation, sometimes being called “professional dinner guests.” Like biological parasites, these individuals exploited their hosts for food, and they brought nothing to the the table themselves, other than dinner conversation. The existence of parasites has long been known in biology, although the development of high quality microscopes greatly expanded human knowledge of parasites.

In order to be considered a parasite, an organism must depend on another for food, energy, or some other service, such as incubating and raising young. In addition, the parasite must bring nothing to the relationship, creating an arrangement which may be neutral or harmful, but never positive. Numerous organisms team up together to exploit their mutual strengths in a biological process called symbiosis—in this case, the arrangement is mutually beneficial to both creatures and it is not considered parasitism.

Some well known examples of parasites include mites, tapeworms, mistletoe, and fleas. Parasites live in a number of different ways; some, for example, cannot live once their host dies, while others can switch hosts or continue thriving on dead hosts until their nutrients are consumed. There is some dispute over whether bacteria and viruses should be considered parasites; in medical terms, a parasite is usually a eukaryotic organism, meaning that it has a complex cell structure, unlike a bacterium.

Parasites which live inside a host are called endoparasites or internal parasites. Many human diseases are caused by internal parasites, which may infest the intestinal tract, causing symptoms like diarrhea and vomiting. Various treatments are used for parasitic infection, depending on the organism involved. Ectoparasites live outside the host, and they are generally more capable of switching hosts. When a parasite preys on other parasites, it is known as an epiparasite.

Frequently Asked Questions

What exactly is a parasite?

A parasite is an organism that lives on or inside another organism, known as the host, from which it obtains nutrients and protection. Parasites can cause harm to their hosts, ranging from minor discomfort to serious diseases. They can be microscopic, like protozoa, or visible to the naked eye, such as worms or ectoparasites like ticks.

How do parasites affect their hosts?

Parasites can affect their hosts in various ways, depending on the type of parasite and the host's vulnerability. They may cause nutrient deficiencies, weaken the immune system, or induce illnesses. According to the World Health Organization, malaria, caused by Plasmodium parasites, resulted in an estimated 241 million cases globally in 2020, illustrating the significant impact parasites can have on health.

Can parasites be beneficial to their hosts in any way?

While typically considered harmful, some parasites can have beneficial effects on their hosts. For instance, certain gut parasites may help regulate the immune system and reduce the incidence of autoimmune diseases. This complex relationship is an area of ongoing research, with studies suggesting that a balanced parasitic environment might contribute to a healthier immune response.

What are some common methods of parasite transmission?

Parasites can be transmitted through various routes. They may be spread through contaminated food or water, by vectors like mosquitoes or ticks, through direct contact with infected individuals or animals, or even via the environment, as some parasites produce eggs or larvae that can survive outside the host for extended periods, waiting to infect a new host.

How can one prevent parasitic infections?

Preventing parasitic infections involves practicing good hygiene, such as regular handwashing, cooking meat thoroughly, and drinking clean water. Using insect repellent and wearing protective clothing can help avoid vector-borne parasites. Travelers should be aware of regional risks and take prophylactic measures, such as vaccines or antiparasitic medications, when visiting areas with high parasite prevalence.

Are there any treatments available for parasitic infections?

Yes, there are treatments available for parasitic infections, which vary depending on the type of parasite involved. Antiparasitic medications can effectively target specific parasites, such as antimalarials for malaria or anthelmintics for worm infestations. Early diagnosis is crucial for successful treatment, and ongoing research continues to develop new therapies to combat drug-resistant strains.

AllThingsNature is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments

By anon934953 — On Feb 22, 2014

I have been fighting intestinal parasites for almost a year. I couldn't get a diagnosis from a gastro doctor, so I decided to use a natural product: food grade diatomaceous earth. I took it for about four months. I got a lot better, but then the die-off symptoms got so bad I discontinued it. I kept seeing dead worms after that. I thought the problem was taken care of. Now I am sicker than before.

Now, in addition to the parasites, I now have pernicious anemia. I went to another gastro doctor this last week. She is going to have me tested and plans to do a colonoscopy, which the other doctor refused to do. I am so sick, and I need immediate help. Now.

By Renegade — On Feb 17, 2011


Intestinal parasites can cause unhealthy weight loss, and sometimes people who are unaware of this think that it is a good weight loss plan. The truth is, intestinal parasites are difficult to deal with, and may feed off of their hosts for a long time. This is not symbiosis, or mutually beneficial, but destructive to the host.

By JavaGhoul — On Feb 14, 2011

Intestinal parasites can be transmitted by consuming foods which are rotten or ingesting dirt of some sort. Children who are prone to bite their nails when dirty may be at risk for being infected with intestinal parasites.

By anon26417 — On Feb 13, 2009

how do you get this disease

Mary McMahon

Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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