biology

Parasitic worm

Parasitic worm is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Parasitic worm rather than just read about it. In short: Parasitic worms, also known as helminths, are a polyphyletic group of large macroparasites; adults can generally be seen with the naked eye. Many are intestinal worms that are soil-transmitted and infect the gastrointestinal tract.

Key takeaways

Parasitic worm belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Parasitic worm to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Parasitic worm from memory before moving on to harder problems.

Reference excerpt

Parasitic worms, also known as helminths, are a polyphyletic group of large macroparasites; adults can generally be seen with the naked eye. Many are intestinal worms that are soil-transmitted and infect the gastrointestinal tract. Other parasitic worms such as schistosomes reside in blood vessels. Some parasitic worms, including leeches and monogeneans, are ectoparasites – thus, they are not classified as helminths, which are endoparasites. Parasitic worms live in and feed in living hosts. They receive nourishment and protection while disrupting their hosts' ability to absorb nutrients. This can cause weakness and disease in the host, and poses a global health and economic problem. Parasitic worms cannot reproduce entirely within their host's body; they have a life cycle that includes some stages that need to take place outside of the host. Helminths are able to survive in their mammalian hosts for many years due to their ability to manipulate the host's immune response by secreting immunomodulatory products. All parasitic worms produce eggs during reproduction. These eggs have a strong shell that protects them against a range of environmental conditions. The eggs can therefore survive in the environment for many months or years. Many of the worms referred to as helminths are intestinal parasites. An infection by a helminth is known as helminthiasis, helminth infection, or intestinal worm infection. There is a naming convention which applies to all helminths: the ending "-asis" (or in veterinary science: "-osis") is added at the end of the name of the worm to denote the infection with that particular worm. For example, Ascaris is the name of a type of helminth, and ascariasis is the name of the infection caused by that helminth.

Taxonomy

Helminths are a group of organisms which share a similar form but are not necessarily evolutionarily related, which makes "helminth" is a polyphyletic assemblage. There is no real consensus on the taxonomy (or groupings) of the helminths, particularly within the nematodes. The term "helminth" contains a number of phyla, many of which are completely unrelated. However, for practical considerations the term is currently used to describe four phyla with superficial similarities: Annelida (ringed or segmented worms), Platyhelminthes (flatworms), Nematoda (roundworms), and Acanthocephala (thorny-headed worms). The phylum Platyhelminthes includes two classes of worms of particular medical significance: the cestodes (tapeworms) and the trematodes (flukes and blood flukes), depending on whether or not they have segmented bodies. There may be as many as 300,000 species of parasites affecting vertebrates, and as many as 300 affecting humans alone. Helminths of importance in the sanitation field are the human parasites, and are classified as Nemathelminthes (nematodes) and Platyhelminthes, depending on whether they possess a round or flattened body, respectively. Ringworm (dermatophytosis) is actually caused by various fungi, and not by a parasitic worm.

Reproduction and life cycle The lifetime of adult worms varies tremendously from one species to another but is generally in the range of 1 to 8 years (see following table). This lifetime of several years is a result of their ability to manipulate the immune response of their hosts by secreting immunomodulatory products. Helminths can be either hermaphroditic (having the sex organs of both sexes), like tapeworms and flukes (not including the blood fluke), or have their sexes differentiated, like the roundworms. All helminths produce eggs (also called ova) for reproduction.

Eggs Generally, thousands or even hundreds of thousands of eggs are produced each time the female worm deposits its eggs - a process called oviposition. There is a large variation in the number of eggs produced by different species of worm at one time; it varies in the range of 3,000 to 700,000. The frequency of egg deposition from an adult helminth is generally daily, and can occur up to six times per day for some Taenia species. Adult trematodes lay smaller numbers of eggs compared to cestodes or nematodes. However, the egg develops into a miracidia from which thousands of cercariae, or swimming larvae, develop. This means that one egg may produce thousands of adult worms. Helminth eggs remain viable for 1–2 months in crops and for many months in soil, fresh water, and sewage, or even for several years in feces, fecal sludge (historically called night soil), and sewage sludge – a period that is much longer compared to other microorganisms.

Helminth eggs are resistant to various environmental conditions due to the composition of the egg shell. Each helminth egg species has 3 to 4 layers with different physical and chemical characteristics:

Larvae Larvae hatch from eggs, either inside or outside the host, depending on the type of helminth. For eggs in moist soil at optimal temperature and oxygen levels, the embryo develops into an infective larva after 2 to 4 weeks, named "second-stage larva". Once ingested by a host, this larva has the ability to get out of the egg, hatch in the small intestine and migrate to different organs. These infective larvae (or "infective eggs") may remain viable in soil for two years or longer. The process of larval maturation in the host can take from about two weeks up to four months, depending on the helminth species. The following table shows the principal morphological and reproductive distinctions for three helminth groups:

Draft genomes for all categories of helminth have been sequenced in recent years and are available through the ParaSite sub-portal of WormBase.

Use in medicine

… excerpt ends here. Continue reading the full article.

Illustrations

Parasitic worm: Two pinworms — Two pinworms

Worked examples

Example 1 — a first encounter with Parasitic worm

Start with the simplest possible case. Write down what Parasitic worm claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Parasitic worm before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Parasitic worm ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Parasitic worm

In research: Parasitic worm appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Parasitic worm in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Parasitic worm is common in secondary-school and first-year university syllabi. It links to neighbouring topics Conditions diagnosed by stool test, Foodborne illnesses, Helminthiases, so understanding it makes those chapters shorter.
In everyday life: Look for Parasitic worm outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Parasitic worm in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Parasitic worm means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Parasitic worm out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Parasitic worm in simple terms?

Why does Parasitic worm matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Parasitic worm?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Parasitic worm.