Transcript THE NEMATHELMINTHES OR ROUNWORMS

THE NEMATHELMINTHES
OR
ROUNDWORMS
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.
Morphology and Physiology
 The adult nematode is an elongated cylindrical
worm, primarily bilaterally symmetrical. The
anterior 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 cuticle
B. subcuticular epithelium
C. muscle cells layer
 The cuticle has various surface markings
and spines, bosses or sensory papillae. The
thin, syncytial , subcuticular layer is
thickened into four longitudinal cords –
dorsal, ventral, and two lateral that project
into the body cavity and separate the
somatic muscle cells into four groups.
Theses cords carry longitudinal nerves and
often lateral excretory canals. The body
wall surrounds a cavity, within which lie the
digestive, reproductive and parts of the
nervous and excretory system. It is line by
delicate connective tissues and a single
layer of muscle cells
Alimentary tract is a simple tube
extending from the mouth to the anus
which opens on the ventral surface a short
distance from the posterior extremity. The
mouth is surrounded by lips or papilae and
in some species is equipped by teeth or
plates. It leads into a tubular or funnelshaped 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
 The midgut is 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 opens
through 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.
 The nervous system consist of a ring or
commissure
of
connected
ganglia
surrounding the esophagus. From this
commissure six nerve trunks pass forward to
the head and circumolar region, and six
nerve trunks connected commissures extend
posteriorly.
 The excretory system consist of two lateral
canals that lie in the lateral longitudinal
cords. The lateral canals join in a bridge
from which the terminal duct leads to a
ventral pore in the region of the esophagus.
Nematodes possess only longitudinal muscle
which produce their typical sinuous
movement.
Reproductive organs
MALE – situated in the posterior third of the
body as a single coiled or convoluted tube,
the various parts of which are differentiated
as testis, vas deferens, seminal vesicle and
ejaculatory duct.
FEMALE – either a single or a bifurcated
tube, differentiated into ovary, oviduct,
seminal receptacle, uterus, ovejector, and
vagina. The daily output of a gravid female
ranges from 20 to 200,000 eggs
Position maintenance
 Ancylostoma – oral attachment to the
mucosa
 Trichuris – anchorage with their attenuated
ends
 Stronglyoides – penetration of the tissues
 Ascaris – retention in the folds of mucosa
and pressure against it.
Methods of obtaining food
 Ancylostoma – sucking with ingestion of
blood
 Trichuris – ingestion of lysed tissues and
blood embedded worms
 Ascaris – feeding on the intestinal contents
 Filarial worms – ingestion of nourishments
from the body fluids
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
Life cycle
 Larvae either resume their parasitic existence of
again 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 the
adult 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
Pathogenicity
 Since nematodes can rarely multiply in humans,
the number of parasites presents, or the intensity
of infection. Is a critical factor in determining the
amount of damage to the host. The local reaction
to adult worms in the intestine are generally
minimal; there maybe some irritations, some
degree of invasion to the intestinal wall or
mucosal damage from blood sucking. Tissue
reaction to nematode parasites can involve both
immediate hyper sensitivity, or allergic reactions
as well as delayed-type cell mediated reactions
with glaucoma and giant cell formation
Resistance and Immunity
 Inability of nematode parasites to infect a
host may be due to some innate, preexisting
incompatibility that renders the host
resistant or the immunity acquired from
previous exposure to the parasite. A variety
of immunologic reactions that take place at
the surface membrane of the nematodes are
complement
activation,
neutrophil
interaction to generate chemotactic factors
for eosinophils, and direct attack of larval
nematodes by eosinophils.
 Production
of
antibodies
of
the
immunoglobin class IgE, which fix to mast
cells
and
mediate
immediate
hypersensitivity reactions is a prominent
feature of many nematode infections.
 Immunopathology can be manifested y
allergic reactions, such as urticarial skin
eruptions during accute trichosis or visceral
larva migrans, or the bronchopasm and
cough of tropical pulmonary eosinophilia or
filariasis. Immunopathologic tissue damage
to the skin and eye is a prominent feature of
onchocerciasis.