Parasitic worm

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Parasitic worms or helminths are a division of eukaroytic parasites that, unlike external parasites such as lice and fleas, live inside their host. They are worm-like organisms that live and feed off living hosts, receiving nourishment and protection while disrupting their hosts' nutrient absorption, causing weakness and disease. Those that live inside the digestive tract are called intestinal parasites. They can live inside humans as well as other animals.

Helminthology is the study of parasitic worms and their effect on their hosts.

Parasitic worms are categorized into three groups: cestodes, nematodes, and trematodes.

These are the principal morphologic differences of the different families of helminths.

	Cestodes	Trematodes	Nematodes
Shape	segmented plane	plane no segmented	cylindrical
Celoma	NOT	NOT	Present
digestive tube	NOT	Ends in cecum	Ends in anus
Sex	Hermaphrodites	Hermaphrodites, except Shistosoma	Dioics
hook organ component	oral sucker, botridias and doble Rostellar hooks	Lips, teeth, filariform extreme and dentary plates

Diseases caused in humans by helminth infection include ascariasis, dracunculiasis, elephantiasis, hookworm, lymphatic filariasis, onchocerciasis, schistosomiasis, and trichuriasis.

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  Hookworms attached to the intestinal mucosa

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  The scolex, or head, of Taenia solium

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  Two pinworms, captured on emergence from the anus

(Images courtesy of Dr Imtiaz Ahmed Wani)

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  Enterotomy for worm removal

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  Ascaris lumbricoides caused gangrene of ileum (shown worms removed from a child)

Reproduction

Parasitic worms are sequential hermaphrodites and reproduce depending on the species of worm, either with the presence of a male and female worm, joining sperm and eggs, producing fertile eggs, such as hookworms, or by breaking off segments that contain both male and female sex organs that are able to produce fertile eggs without the presence of a male or female. (e.g., tapeworms)

All worm offspring are passed on through poorly-cooked meat, especially pork, wild fish, and beef, contaminated water, feces, mosquitoes, and, in general, areas of poor hygiene and food regulation standards such as parts of Africa, Central and South America, and Asia. However, it is estimated that 40 million Americans are infected with the most common roundworm, the pinworm. Medical experts theorize that widespread intestinal parasite infestation is leading to the rise of colon cancer in the United States.

Worm eggs or larvae or even adults enter the human body through the mouth, anus, nose, or skin, with most species attaching themselves to the intestinal tract. With the presence of digestive enzymes, worm egg shells are dissolved, releasing a brand-new worm; unlike its egg shell, the parasitic worm is protected from the body's powerful digestive enzymes by producing a protective keratin layer.

Immune response

The immune response to worm infection in humans is a Th2 response in the majority of cases. This results in inflammation of the gut, and results in cyst-like structures forming around the egg deposits throughout the body. The host's lymphatic system is also heavily taxed the longer helminths propagate, which excrete toxins after feeding. These toxins are released into the intestines to be absorbed by the host's bloodstream. This phenomena makes the host susceptible to more common diseases such as seasonal viruses and bacterial infection.

External Links

• Roundworms

ar:دودة طفيلية he:הלמינתולוגיה id:Cacing parasit th:พยาธิ uk:Гельмінтологія