The+Nemathelminthes

7/27/2019 The+Nemathelminthes

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Nemathelminthes - Nematoda

Includes numerous free-living and parasitic

species. They range in length from 2mm

(Stronglyoides stercoralis) to a more than a

meter ( Drancunculus medinensis) the sexes

are usually separate. The male is smaller

than the female and commonly has a curved

posterior end and in some species,copulatory spicules and a bursa.


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Morphology and Physiology

The adult nematode is an elongated cylindricalworm, primarily bilaterally symmetrical. Theanterior ends maybe equipped by hooks, teeth,

plates, setae, and papillae for purposes of abrasion,attachment and sensory response

The body wall is consist of:

A. an outer, hyaline, noncellular cuticleB. subcuticular epithelium

C. muscle cells layer


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The cuticle has various surface markingsand spines, bosses or sensory papillae. The

thin, syncytial , subcuticular layer isthickened into four longitudinal cords dorsal, ventral, and two lateral that projectinto the body cavity and separate thesomatic muscle cells into four groups.Theses cords carry longitudinal nerves andoften lateral excretory canals. The body

wall surrounds a cavity, within which lie thedigestive, reproductive and parts of thenervous and excretory system. It is line bydelicate connective tissues and a single

layer of muscle cells


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Alimentary tract is a simple tube

extending from the mouth to the anus

which opens on the ventral surface a shortdistance from the posterior extremity. The

mouthis surrounded by lips or papilae and

in some species is equipped by teeth orplates. It leads into a tubular or funnel-

shaped buccal cavity expanded for

sucking. The esophagus lined with an

extension of the buccal cuticle has striated

muscular wall, a triradiate lumen and

associated esophageal gland


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The midgutis a flattened with a wide lumen

that follows a straight course from the

esophagus to the rectum. In the female it

leads into a short rectum lined with cuticle.

In the male it joins with the genital duct to

form the common cloaca which opensthrough the anus.

There is no circulatory system. The fluid

of the body cavity contains hemoglobin,glucose, proteins, salts and vitamins and

fulfills the function of the blood.


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The nervous system consist of a ring orcommissure of connected gangliasurrounding the esophagus. From this

commissure six nerve trunks pass forward tothe head and circumolar region, and sixnerve trunks connected commissures extend

posteriorly.The excretory systemconsist of two lateral

canals that lie in the lateral longitudinalcords. The lateral canals join in a bridge

from which the terminal duct leads to aventral pore in the region of the esophagus.Nematodes possess only longitudinal muscle

which produce their typical sinuousmovement.


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Reproductive organs

MALE situated in the posterior third of thebody as a single coiled or convoluted tube,the various parts of which are differentiated

as testis, vas deferens, seminal vesicle andejaculatory duct.

FEMALE either a single or a bifurcatedtube, differentiated into ovary, oviduct,seminal receptacle, uterus, ovejector, andvagina. The daily output of a gravid femaleranges from 20 to 200,000 eggs


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Position maintenance

Ancylostomaoral attachment to the

mucosa

Trichuris

anchorage with their attenuated

ends

Stronglyoidespenetration of the tissues

Ascarisretention in the folds of mucosa

and pressure against it.


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Methods of obtaining food

Ancylostomasucking with ingestion of

blood

Trichurisingestion of lysed tissues and

blood embedded worms

Ascarisfeeding on the intestinal contents

Filarial worms

ingestion of nourishmentsfrom the body fluids


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Life span

The female Trichinella spiralis is passed

from the intestine 4 to 16 weeks

Enterobius vermucularis has a life span of 1

to 2 months

Ascaris lumbricoides may live for about a

year

Hook worms have been observed to persist

for about 14 years


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Life cycle

Larvae either resume their parasitic existence ofagain develop into mature free-living worms that

produce further generations. Some species have an

intermediate host in which the larva passes

through a cyclic development. The location of theadult parasite in the host , to a large extent,

governs the escape of the eggs and the character of

the life cycle. During larval development,

nematodes pass through several molts or ecdyses,

both inside and outside the host . Nematodes with

few exceptions do not multiply in humans,thus

differing from many other pathogenic organisms


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Pathogenicity

Since nematodes can rarely multiply in humans,the number of parasites presents, or the intensityof infection. Is a critical factor in determining theamount of damage to the host. The local reactionto adult worms in the intestine are generallyminimal; there maybe some irritations, somedegree of invasion to the intestinal wall ormucosal damage from blood sucking. Tissue

reaction to nematode parasites can involve bothimmediate hyper sensitivity, or allergic reactionsas well as delayed-type cell mediated reactionswith glaucoma and giant cell formation


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Resistance and Immunity

Inability of nematode parasites to infect ahost may be due to some innate, preexistingincompatibility that renders the host

resistant or the immunity acquired fromprevious exposure to the parasite. A varietyof immunologic reactions that take place atthe surface membrane of the nematodes are

complement activation, neutrophilinteraction to generate chemotactic factorsfor eosinophils, and direct attack of larval

nematodes by eosinophils.


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Production of antibodies of theimmunoglobin class IgE, which fix to mast

cells and mediate immediatehypersensitivity reactions is a prominentfeature of many nematode infections.

Immunopathology can be manifested yallergic reactions, such as urticarial skineruptions during accute trichosis or viscerallarva migrans, or the bronchopasm and

cough of tropical pulmonary eosinophilia orfilariasis. Immunopathologic tissue damageto the skin and eye is a prominent feature ofonchocerciasis.

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