PHYLUM ASCHELMINTHES

Animal Diversity:
(Non-Chordates)
Phylum: Aschelhelminthes
Dr. Promila Madan
Associate Professor,
Department of Zoology,
Maitreyi College,
Bapudham Complex,
Chankyapuri,
New Delhi-110021.
24th September 2007
Contents
ASCARIS LUMBRICOIDES
Morphology
Body wall
Digestive System
Respiration
Excretory System
Nervous System
Sense Organs
Reproductive System
Life History
Pathogenicity
Parasitic Adaptations
Phylum Nematoda
Classification
I. The Class I. Aphasmida:
Orders
1. Enoplida,
2. Isolaimida,
3. Monochida,
4. Dorylaimida,
5. Trichocephlida,
6. Mermithida,
7. Muspiceida,
8. Chromadorida and
9. Araeolaimida.
II. The class II Scernentea or Phasmida
Orders
a. Rhabditida,
b.
c.
d.
e.
f.
g.
Strongylida,
Ascaridida,
Spirurida,
Camallanida,
Diplogasterida,
Tylenchida, and
h. Aphelenchida.
Ancylostoma (hook worm)
Wuchereria bancrofti
Enterobius vermicularis
ASCARIS LUMBRICOIDES
Ascaris is a common roundworm found in the small intestine of various vertebrates like chicken,
pig, cattle, horse and man. Among the roundworms the genus Ascaris is of the larger size. There
can be roughly one thousand to four thousand adult Ascaris in a single man. Ascaris is more
common in the children.
Morphology
Ascaris lumbricoides is an elongated, cylindrical, endoparastic and bisexual worm. It exhibit
marked sexual dimorphism. The female measures 20-41 cms and the male 15-31cms (Fig 1). The
tail of the female is straight while that of the male is curved like a hook. (Fig 2). They are
generally white or yellow in colour. The body is covered by tough and elastic cuticle. The mouth
lies at the anterior end of the body surrounded by three lips. (Fig 3). One is drosal in position and
the other two are ventro-lateral, so the mouth is triradiate. Ventrally, little behind the mouth is
the excretory pore. Ventrally, little before the hind end is anus in female and the cloacal aperture
in male. The female has a separate gonopore placed ventrally nearly one-third length from the
anterior side.
Body wall
The body wall is covered by thick tough non-chitinous cuticle resistant to the host’s digestive
enzymes but it is permeable to the salts and water. The cuticle is continuous with the cuticular
lining of the pharynx foregot and rectum hindgut. The cuticle is not smooth, it has wrinkles or
transverse striations. The cuticle is shed four times during the lifetime and is secreted by the, the
underlying epidermis secretes cuticle. (Fig 4).Below the cuticle is syncytial epidermis meaning
that the epidermis is having many nuclei but no cell membrane i.e. the cells limits are not
marked. The epidermis is thickened internally into ridges at four regions, commonly called cords
or ridges. The lateral cords are more conspicuous and contain the longitudinal excretory canals
along with lateral new card. The dorsal and the ventral thickenings contain the dorsal and the
ventral nerve cords respectively. The longitudinal muscles lie in four groups, which is separated
by four thickenings of the epidermis. There are no circular muscles present. Each cord has nearly
150 muscles cells.The muscle cell has two distinct portions. An outer and towards the epidermis
is the fibrillar portion, which is contractile, and the inner cytoplasmic portion, which has noncontractile supporting fibrils. The cytoplasmic zone is extended into a long narrow process, the
muscle tail. The muscle tails of the dorsal side extend dorsally to get inserted into the dorsal
epidermal cord. The muscle tails of the ventral side gets inserted into the ventral epidermal cord.
Body cavity is the space between the gut and the body wall. As it is not lined by mesodermal
epithelium,so it is not a coelom but a pseudocoelom. The body cavity has pesudocoelomic fluid,
which distributes the digested food and collects the waste material in it. The pesudocoel has five
giant cells the pseudocoelocytes. Their position is fixed in the epidermal cords. (Fig 5). The
pesudocoelocytes on the pharynx extend as membrane having delicate fibrous strands covering
the internal structures and organ of the pseudocoel.
Digestive System
The alimentary canal is complete divided into three parts foregut or pharynx, mid gut or the
intestine and hindgut or the rectum. (Fig6). The pharynx and the rectum are lined by the cuticle
and are ectodermal in origin. The mouth is tri-radiate in shape. In nematodes six lips or labia
surround the mouth. However in two Ascaris the mouth is surrounded by only three lips because
of the fusion of lips each, one is mid dorsal, the other two are latero ventral in position. The lips
have sensory structures on them (to be described later).
The pharynx or oesophagus is short, thick walled, having tri-radiate lumen, which is lined by
cuticle continuous with the body wall. (Fig7). The wall of the pharynx has radial muscles.
Posteriorly pharynx opens into the intestine, which is dorso-ventrally flattened and thin walled
as it is made up of a single layer of columnar epithelial cells. The free margin of the cells is
produced into microvilli to increase the surface area for absorption. The intestine opens into the
rectum, which is flattened dorsally and is lined by cuticle.(Fig8).The hindgut wall has tall
columnar cells, and few muscle fibers. In female the rectum opens into a transverse slit the anus
but in male it opens out by cloaca aperture because the male reproductive duct also joins the
rectum.
The food of the Ascaris contains blood and partly or fully digested food of the host. The
muscular pharynx sucks the food. Digestion in the intestine is mainly extra cellular, facilitated by
proteases, amylase and lipase. Some intracellular digestion also takes place. The digested food is
absorbed by the intestinal cells from there it diffuses into the pseudocoelomic fluid, and
distributed to the entire body cells.
Respiration
There are no respiratory structures. The oxygen concentration of the host’s intestine is very low
so anaerobic respiration takes place. Ascaris obtains energy by breaking down glycogen into
carbon dioxide and fatty acids. Whenever sufficient oxygen is present it goes for aerobic
respiration.
Excretory System
There is no protonephridia. The excretory system consists of two long longitudinal canals,
which are connected to each other by the transverse canalicular network below the pharynx. A
short terminal duct arises from the transverse canal and opens out as a minute excretory pore on
ventral side just behind the lips. The anterior canals are quite short and the posterior longitudinal
excretory canals run the entire length and are closed at both the ends. Fig 9
It was earlier thought that the entire excretory system is formed by the cytoplasm of a single
giant cell whose nucleus lies on the left side of the transverse canaliculi. A firm membrane lines
the entire system; there being no cilia or flagella. With the discovery of two more nuclei in the
excretory system it is now believed that the entire excretory system is made up of more than one
cell. The entire longitudinal excretory canals are intracellular excavations. The excretory waste
material is ammonia and urea and it is pushed forward towards the excretory pore probably by
the muscular undulations of the body of the Ascaris.
Nervous System
Nervous System is very well developed and quite complicated. The nerve cells are fixed in
number and position. Around the pharynx is circumpharnygeal nerve ring from which arise the
nerves. (Fig10)
Associated with the nerve rings are:
1.
2.
3.
4.
A Median dorsal ganglion
A pair of sub-dorsal ganglia
A pair of lateral ganglia each divided into six smaller ganglia
A large ventral ganglion
Anteriorly the nerve ring gives off eight nerves
1. Six papillary nerves, which innervate sensory papillae of the lips. Two of these nerves
are dorso-lateral, two laterals, and two ventro-lateral in position. Each papillary nerve
forms small papillary ganglia very near to its origin.
2. The two-amphidial nerves of each side arise from one of the six lateral ganglia and
innervate the sensory structure the amphids.
Posteriorly the nerve ring gives eight nerve or cords
1.
2.
3.
4.
5.
A dorsal nerve cord lying in the dorsal line.
Ventral ganglionated nerve cord lying in the ventral line, it is the main nerve cord.
A pair of lateral nerve cards
A pair of dorsolateral nerve cards
A pair of ventrolateral nerve cards
Various Transerverse connectives and commissures connect the eight nerves.
Sense Organs
The sense organs are very simple because Ascaris is an endoparasite. The sensory structures are
Papillae, Amphids and the Phasmids. The papillae are of three kinds labial,cervical and genital.
The papillae are projections of the cuticle. It is an elongated structure having fine sensory fibers
with some expansion below the cuticle, surrounded by supporting cells. The dorsal lip has two
double sensory structure the papilla, one on either end. Only one double sensory structure is
present on one side of the ventro lateral lip. On the other side of the lip there is a single papilla
and an amphid.
Each double sensory structure has a labial papilla & a cephalic papilla. First narrow and then
widens and ends below the surface of the cuticle. Genital papillae are present only in males.
There are fifty pairs of preanal and five pairs of post anal genital papillae (Fig 11). They help
during copulation.
The papillae are tango receptors.
Amphids: Each ventro-lateral lip has small pit just above the labial papillae containing sensory
cells. These are called amphids. They are chemoreceptors.
Phasmids are a pair of unicellular glands, which open out as a small pit one on each side of the
tail behind the anus they are chemoreceptors. (Fig 12)
Reproductive System
The gonads are thin, long and their walls are made up of single layer of cuboidal cells. It
has a central rachis, which is surrounded by large number of amoeboid cells. These are
developing gametes. The gonads are telogenic i.e. gametogonia are shed from the proximal
part of the gonad from a terminal cell.
Sexes are separate and sexual dimorphism is quite evident. The male has a curved tail and
female’s tail is straight. Female has a separate anus and a genital opening whereas male has a
cloaca and papillae around the cloaca.
Male Reproductive System: It consists of testis, vas deferens, seminal vesicle, ejaculatory duct
and penial setae confined to the posterior part of the body. The male reproductive system occurs
in single set i.e. monorchis. The single testis is long thread like convoluted having central rachis.
The posterior part of testis continues as vas deferens, which is thick, short and twisted, (Fig 13)
The vas deferens does not have the central rachis. The vas deferens opens into more
thicker,straight and muscular seminal vesicle, (Fig14)
The seminal vesicle opens into a narrow, short and muscular ejaculatory duct, which opens into
posterior part of the rectum to form the cloaca. The wall of the ejaculatory duct has a number of
prostate glands whose secretions help in copulation. The cloaca opens out ventrally by a
transverse cloacal apertune, little in front of the hind end.
Penial Setae: The cloaca evaginates on the dorsal side to form a pair of muscular penial sacs or
spicule pouches. The two spicule pouches join together and open into the cloaca. Each penial sac
secretes a cuticular spicule having a cytoplasmic core. The spicules sacs have protractor and
retractor muscles to protreude and withdraw the spicules from and into the cloacal aperture
respectively . The spicules serve to open the female genital pore during copulation to deposit the
sperms.
Female Reproductive System: Ascaris has a pair of long twisted ovaries lying in the posterior
two third of the pseudocoel. Each ovary continues posteriorly into a thicker and twisted oviduct
having a lumen. Each oviduct opens into a thicker and muscular uterus. The uterus is, lined by
cuticle. The first part of the uterus is called seminal receptacle, which store the sperms after
copulation, (Fig 15)
It is here that fertilization of eggs takes place. The distal part of the uterus store fertilized eggs.
The wall of the uterus has gland cells, which secretes yolk and material for eggshell.
The two uteri join together to form the vagina in the anterior third of the body. The vagina is
short and a highly muscular tube, which is entirely lined by the cuticle (Fig 16). The vagina
opens out mid ventrally as a female genital pore or vulva. Vulva is a transverse slit with lips and
is present near about one third of the body length from the anterior side.
Life History
Mature male and female worms copulate in the small intestine of the host, during copulation the
penial setae open the vulva and the motile amoeboid sperms move into the vagina and then to
seminal receptacle of the female Ascaris by amoeboid movement . Fertilization takes place in the
seminal receptacle where oocytes are also present. The unfertilized egg contains fat and glycogen
globules. After fertilization glycogen forms a fertilization membrane around the fertilized egg,
which hardens into a chitinous shell, (Fig 17). The fat globules accumulate below the shell and
form a lipoid layer. The distal part of the uterus forms thick, heavy protein membrane on the
shell. This wavy protein membrane is characteristic of Ascaris eggs. The fertilized eggs are
elliptical in shape measuring 60-70u by 40-50u.
The uteri of a single female may contain as many as 2,70,00,000 eggs. A female may lay as
many as 15,000 to 2,00,000 unsegmented eggs in a day. In the moist soil the eggs can remain
alive for several months but dry conditions can kill the eggs.
The eggs require a period of incubation before entering the human body. For further
development they require a temperature lower than human body. Favorable temperature is 85
degree F (about 30˚c) oxygen and moisture. The cleavage starts in the soil.
The cleavage is spiral and determinate. The sixteen-cell stage is like a hollow ball. This is the
blastula stage and the inner cavity the blastocoel. Blastula by invagination forms a gastrula. A
juvenile develops in 10-14 days. The juvenile has an alimentary canal, a lateral excretory system
and a nerve ring. This stage is called rhabditiform larva or rhabditoid (because of its resemblance
to a soil nematode called Rhabditis). The larva grows for a week and then moults within the shell
to become the second stage juvenile. This is the infectious stage of Ascaris and further
development requires high temperature which therefore can occur in the host’s intestine only.
Egg containing second stage juvenile enters the body of the host along with contaminated food
and water. The egg membranes are dissolved in the intestine and the juveniles are free within
few hours. The 0.02 - 0.03mm juvenile bores the intestinal wall and enters the blood vessels
(branches of hepatic portal). It moves along with the blood in the body for nearly ten days and
vein finally is large enough to damage the pulmonary capillary and reach the alveolar spaces.
Here it moults for the second time, and after growing for few days moults for the third time. The
fourth stage juvenile takes an upward journey passing through bronchus, trachea and then the
pharynx. It remains in the pharynx till it is coughed out through the nostrils or mouth or moves
down to enter the oesophagus. It then moves downward and reaches the intestine and measures
2-3 mm long. In the intestine the juvenile moults for the fourth and final time, becomes the adult,
and attains sexual maturity. The total period taken for the whole journey in host is about 25 days.
Generally it lives in the intestine for 9 –12 months.
Pathogenicity: The disease caused by Ascaris is called Ascariasis. Degree of pathogenesis
depends upon the number of worms present in the intestine. It causes more harm to the children
than adult.
Pathogenesis caused by adult Ascaris;
1. Abdominal discomforts like vomiting and colic pains, interferes in protein digestion
2. Absorb host’s digested food resulting in malnutrition and hence shunted growth.
3. Irritation of mucous membrane results in involuntary muscular contractions. Acute
infection can cause coma and death
4. Can cause appendicitis and hepatitis.
Larva: It may prove to be more harmful than the adult by causing hemorrhages. The circulating
juveniles can cause, serious damage to any vital organ like kidney, brain, eye, particularly to
lungs, which can result in pneumonia leading to death.
Treatment: Use of anti-helminth drugs like mixture of tetrachlorethylene and the oil of
chenopoduim is very effective; other drugs are hetrazan, pierazine hydrate dilhiazanine,
tetraezole etc.
Prevention: An effective sanitary system to dispose off the faeces. Vegetables should be
thoroughly washed or boiled before consuming them. Nails should be cut so that no dirt and eggs
collect below them. Always wash the hands with soap before eating.
Parasitic Adaptations
1. Long and elongated body of the allows to accommodate many Ascaris in the small
intestine of the host.
2. The cuticle protects the inner organs, and the antienzymes, counter act the digestive
enzymes and toxins of the host.
3. Muscular pharynx helps in the ingestion of the food.
4. The pseudocoelomic fluid helps in the distribution of food to various parts of the body
and transfer of waste substances to the excretory canal.
5. Anaerobic respiration enables the worm to service in oxygen free intestinal medium.
6. Production of large number of small sized eggs to continue the race.
7. The capsule protects the juvenile from all unfavorable environmental conditions.
8. Direct infection by the juvenile has higher chances of dispersal.
9. No intermediate host.
Mature male and
female in the lumen of
Man's intestine
Copulation
Fertilized Eggs
Leaves the
body of the
host
Egg Shell covered by
albuminous coat
Fourth
MOULT
Young Ascaris
Egg Shell with
embroyo in open
environment
Coughing
Developme
nt of the
larva 10-14
days
Alimentary canal
First stage
Rhabditiform larva
Upward
journey
Pharynx
First moult
within egg
shell
Non Infective stage
Third MOULT
after four
days
Fourth stage larva
Through
contaminate
d food and
water
Infective stage
Second
MOULT
Third stage larva
Second stage
Rhabditiform larva
Egg Shell in the lumen
of the alimentary canal
Second stage
Rhabditiform larva in
the Lumen of
Duodenum
Pierces the
wall of
duodenum
Lungs
larva liberated
from the egg shell
by the enzymes of
the intestine
remains for few
days, increase in
size and bores the
wall of the
capillary
Alveoli of Lung
Heart
Liver
Hepatic portal vein
Life Cycle of Ascaris
Phylum Nematoda
1. Nematoda is derived from a Greek word nematos meaning thread and eidos
meaning form. They are commonly called round worms or thread worms.
2. The body is tapering at both the ends and covered with thick cuticle, which is
secreted by the epidermis. The cuticle moults for growth.
3. The epidermis mostly cellular but synctial in some. The epidermis largely
disappears as a separate cellular layer.
4. A characteristic feature of the epidermis is enlargement of the cytoplasm into
pseudocoel along the mid-dorsal, mid-ventral and lateral lines as longitudinal
cords.
5. Nematode inhabits all kinds of habitats that can support life.
6. They are mostly free living but they are economically very important as plants,
human and animal parasites.
7. The alimentary canal is complete with mouth and anus.
8. They have cavity between the body wall and the alimentary canal, which is not a
coelom but a pseudocoel.
9. They are smooth rounded or flattened pseudocoelomate
10. Triploblastic, bilaterally symmetrical and has an elongated body.
11. Only longitudinal muscles present, circular muscles absent.
12. The number of cells is fixed in the adult.
13. The nervous system consists of a nerve ring having ganglia. From the nerve ring
the nerves extend anteriorly and posteriorly.
14. The important sense organs are papillae, amphids and phasmids.
15. The sexes are mostly separate with district sexual dimorphism and males
generally smaller than females. Life history usually complicated.
Classification
The phylum Nematoda is divided into two classes and has many orders.
III. The Class I. Aphasmida:
(a) Both free living and parasites.
(b) They have variable shaped amphids (without pores) behind the lips
(c) The free-living worm includes terrestrial, fresh water and almost all
marine forms.
There are 9 orders belonging to this class. These are
10. Enoplida,
11. Isolaimida,
12. Monochida,
13. Dorylaimida,
14. Trichocephlida,
15. Mermithida,
16. Muspiceida,
17. Chromadorida and
18. Araeolaimida.
IV. The class II Scernentea or Phasmida contains nematodes that usually posses pore
like amphids in the lateral lips. Mostly parasitic forms and free-living members
inhabiting soil. The 8 Orders are
1.
2.
3.
4.
5.
6.
7.
8.
Rhabditida,
Strongylida,
Ascaridida,
Spirurida,
Camallanida,
Diplogasterida,
Tylenchida, and
Aphelenchida.
Some Nematode parasites: Ancylostoma, Wuchereria, Enterobius
Ancylostoma (hook worm)
Most dangerous endoparasite in man. It is more common in rural areas where people
move barefooted. The adult male worm measures 8-11mm and female measures 11-13
mms. The anterior ends of both the sexes are curved dorsally. The posterior end of the
female is tapering but that of male is expanded like umbrella called copulatory bursa .The
mouth opens into a large buccal cavity lined by the cuticle and is provided with six
cutting plates or teeth. The animal holds to the wall of the intestine of the host by the
anterior capsule and the chitinous teeth cut holes in the intestinal wall. The worms secrete
an anti-coagulant and suck the blood. Even when the worm has shifted to another
location the blood keeps on oozing out because of the effect of anti-coagulant. This
causes anemia in the host. The life span of the adult worm in the intestine of the man is
three to five years.
Mode of infection: The infective stage is third stage juvenile or filariform larva present in
the soil or contaminated food or water. It penetrates the skin of the host and then enters
the lymphatics or small venules. It is then carried to the right side of the heart and
circulates along with the blood .The larva on reaching the lung breaks the wall of the
alveoli. From the alveolar spaces it ascends to reach the pharynx and during coughing it
gets swallowed into the oesophagus and finally reaches the intestine and gets attached to
the mucous lining, cut holes and suck the blood. They moult twice to become adult.
Pathogenicity: Penetration of the skin by larvae causes tiny irritating sores and
inflammation of the skin. Damage is done to the vital organs for example brain, heart,
kidney, particularly lungs by the circulating larva. The maximum damage is done by the
adult by forming wounds in the walls of the intestine from where the blood keeps on
flowing, causing blood stools, severe anemia, lower immunity and the host becomes
lethargic. The toxins secreted by the worm causes stomach disorders, pain, diarrhea or
constipation.
Wuchereria bancrofti
Wuchereria bancrofti is also called filarial worm. It is widely spread but mainly found in
tropics and sub tropics especially along the seacoast and near big rivers. Generally absent
from Europe and North America and Africa. Wuchereria bancrofti is a digenetic parasite
completing its life cycle in human beings, the primary host and a blood-sucking mosquito
of the genus Culex or Ades, as a secondary host.
The worm lives in the blood or lymph vessels or lymph glands where they block the flow
of lymph. The adult worms are long and filiform and both ends are tapering. The sexes
are separate.
The female measures 8 – 10 cm in length and the male measures 2.5– 4 cm in length.
Posterior end of the male is curved ventrally and contains two spicules of unequal length.
The tail end of the female is narrow, straight and pointed. Copulation takes place when
both male and female are present in the same lymph gland.
The females are ovo-viviparous i.e. laying eggs with well-developed embryos. The
females are much more numerous than males. The juveniles or microfilarae are very
small and immature measuring about 0.2 to 0.3 mm long.
A delicate cuticular covering covers the microfilariae. The embryos leave the lymph node
and enter the main lymphatic channel from there it reaches the blood stream. A
transparent sheath covers the microfilariae, which is longer than the larval body. During
the day the microflariae are present in the superficial blood vessels, so that they can be
sucked along with the blood by their intermediate host e.g. Ades or Culex. They die in
the blood if not sucked by the appropriate mosquito within seventy days.
Development in mosquito: In the stomach of the mosquito the microfilaria looses its
sheath and penetrates the stomach wall. Within a short time it reaches the thoracic
muscles. It is here that the parasite undergoes metamorphosis and grows. First it changes
into a thick sausage shaped organism, the first stage larva and then to an elongated form,
the second stage larva. At last it changes into a long (1.5mm) thin juvenile after two
months, which is the infective stage of the microfilariae. It moults twice in ten days to
become infective juvenile. By fourteen days several infective larva are coiled up in the
probosis sheath of the mosquito to infect man when the mosquito is sucking the blood.
The infective juveniles enter the primary host through the skin opening from where the
mosquito had sucked the blood. From the blood it reaches the lymph vessels and glands
where they develop into adult and mate and then the female realeases microfilariae and
the whole cycle is repeated.
Pathogenesis: The pathogenic effect caused by the adult Wuchereria is called
Wuchereriasis, more commonly filariasis. The incubation period can last for nearly one to
one and a half years during which the third stage larva becomes sexually mature. The
pathologic effects are due to the adult live worm, as well as the dead worm. The
microfilariae present in the blood do not cause any pathological effect. The adult worm
and the third stage developing larva can obstruct the lymph vessels preventing the flow of
lymph resulting in a inflammatory reaction of the lymphatic system lymphangitis because
of which affected body parts swells to enormous size because of oedema called
elephantiasis. Periodic attacks of fever are very common because of lymphangitis, small
blood vessels may rupture in the dilated lymphatics.
Treatment: The treatment has to focus on the three stages of the Wuchereria.
1. Adult worm
2. Microfilariae
3. Infective larvas
Arsenal preparations are good for adult stage. Diethylcarbamazine for microfilariae. Paramelamenyl phenyl stibonate (MSb) for infective larva and immature adult worms.
Prophylaxis
1. Use mosquito repellant creams on the exposed parts to avoid mosquito
bites.
2. Use of mosquito nets
3. Destruction of those habitat where the mosquitoes breed
4. Destruction of mosquitoes
5. To identify the carriers and then treat them using hetrazan.
Enterobius vermicularis
Commonly known as pinworm. It is one of the most common worm of the man
particularly children in all parts of the world. It is a thread like white or cream in color.
Sexual dimorphism is very distinct in the pinworm. The female measures 8-13mm in
length and the male measures 2-5mm long.
The adult lives in the small intestine of man, whereas the gravid females live in the large
intestine.
The characteristic feature of the pinworm is a pair of cuticular expansion just below the
mouth called the cephalic alae. The tail of female is long and pointed, while that of the
male is curved.
Generally at night the gravid female migrate to the peri-anal region and lays the egg on
the skin of the peri-anal region. The movement of the worm causes intense itching. When
the infected person scratches the peri-anal region the eggs get attached to the fingers and
under the nails. From here the eggs are transferred to the mouth, clothing, bed linen etc.
The eggs when reach the mouth enter the alimentary canal and in the duodenum they
hatch out as a larva. The larva moults twice and becomes adult, they mate in small
intestine and the gravid female again migrates to the peri-anal region. Sometimes the
larva hatch out in the peri-anal region and through anus enters the rectum. This is called
reintroduction.
The life span of the adult worm is 15 –30 days. If no re-infection takes place the infection
dies itself within a month.
Pathogenicity:
The pathogenic effects are collectively called enterobiasis. The movement of the female
around the peri-anal region causes intense itching. Scratching may damage the skin
around the peri-anal region, which can lead to eczematous condition.
The frequency of passing urine (micturition) also increases. Inflammation of the appendix
though not very common, can take place.
Treatment: Anthelmintics drugs effective for enterobiasis are used to kill the worms for
example piperazene salts, thiabendazole and mebendazole.
Control:
1. If the infection is heavy a course of specific anthelmintics drug is
necessary.
2. To avoid re-infection hands should always be washed properly before
eating, nails must be short.
3. In case of heavy infection linen should be washed and changed regularly
4. Treatment of all the people in case of heavy infection.