Transcript Ascaris Lumbricoides

Ascaris Lumbricoides
-Ascariasis is caused by the parasitic roundworm Ascaris
Ascaris Lumbricoides
lumbricoides. Perhaps as many as one quarter of the
world's people are infected. It is the largest of the
intestinal nematodes parasitizing humans.
-It is the most common worm found in human ,and it is
worldwide in distribution and most prevalent in
tropic areas with more prevalent in the countryside
than in the city
Adult worm of A. lumbricoides
Factors favoring the spread of the transmission:
1. Simple life cycle.
2. Enormous egg production ( 240,000 eggs/ day/ female)
3. These eggs are highly resistant to ordinary
disinfectants.The eggs may remain viable for several
years.
4. Social customs and living habits.
5. Disposal of feces is unsuitable.
Life Cycle
1. Site of inhabitation: small intestine
2. Infetive stage: embryonated eggs
3. Route of infection: by mouth
4. No intermediate and reservoir hosts
5. Life span of the adult worm: about 1 year
-This worm lives in the lumen of small intestine, feeding on the
intestinal contents, where the fertilized female lays eggs. An adult
female can produce approximately 200,000 eggs per day, which
are passed in feces. When passed, the eggs require outside
development of about three weeks until a motile embryo is formed
within the egg.
- After the ingestion of embryonated eggs (infective) in
contaminated food or drink or from contaminated fingers, host
digestive juices acts on the egg shell and liberate the larva into
the small intestine.
-These larvae penetrate the intestinal mucosa and enter lymphatics
and mesenteric vessels. They are carried by circulation to the
liver, heart and finally to the lungs where they penetrate the
capillaries into the alveoli in which they molt twice and stay for
10-14days.
-Then they are carried, or migrate, up the bronchioles, bronchi, and
trachea to the thorate. When swallowed, the larvae pass down
into the small intestine where they develop into adults.
-The time from the ingestion of embryonated eggs to oviposition by
the females is about 60-75 days. The adult worms live for about
one-two year.
Pathogenesis
There are two phase in ascariasis:
1. The blood-lung migration phase of the larvae:
During the migration through the lungs, the larvae
may cause a pneumonia. The symptoms of the
pneumonia are low fever, cough, blood-tinged
sputum, asthma. Large numbers of worms may give
rise to allergic symptoms. Eosionophilia is generally
present. These clinical manifestation is also called
Loeffler’s syndrome.
2. The intestinal phase of the adults.
The presence of a few adult worms in the lumen of the small intestine
usually produces no symptoms, but may give rise to vague abdominal
pains or intermittent colic, especially in children. A heavy worm
burden can result in malnutrition.
-More serious manifestations have been observed. Adults worm may
block the the common bile duct and even perforate the intestinal
wall.
-Thus complications of ascariasis, that may occur include intestinal
obstruction, appendicitis, biliary ascariasis, perforation of the intestine,
pancreatitis and peritonitis, enlargement of the liver or spleen, etc.
-other complications, sometimes fatal, include obstruction of the bowel
by a bolus of worms (observed particularly in children). More than 796
Ascaris lumbricoides worms weighing 550 g [19 ounces] were
recovered at autopsy from a 2-year-old South African girl. The worms
had caused torsion and gangrene of the ileum, which was interpreted
as the cause of death.
Source
Ingestion of infective eggs from soil contaminated with human
feces or transmission and contaminated vegetables and water is
the primary route of infection.
-Intimate contact with pets which have been in contact with
contaminated soil may result in infection, while pets which are
infested themselves by a different type of roundworm can cause
infection with that type of worm.
-Transmission also comes through municipal recycling of
wastewater into crop fields. This is quite common in emerging
industrial economies, and poses serious risks for not only local
crop sales but also exports of contaminated vegetables. A 1986
outbreak of ascariasis in Italy was traced to irresponsible
wastewater recycling used to grow vegetable exports .
-Transmission from human to human by direct contact is
impossible.
Diagnosis
The confirmative diagnosis depends on the recovery and 
identification of the worm or its egg.
1. Ascaris pneumonitis: examination of sputum for Ascaris
larvae is sometimes successful.
2. Intestinal ascariasis: feces are examined for the ascaris
eggs.
(1) direct fecal film: it is simple and effective. The
eggs are easily found using this way due to a large number of
the female oviposition, approximately 240,000 eggs per worm
per day. So this method is the first choice.
(2) recovery of adult worms: when adults or adolescents are
found in feces or vomit and tissues and organs from the human
infected with ascarids , the diagnosis may be defined.
(3) On X-ray, 15–35 cm long filling defects, sometimes with
whirled appearance (bolus of worms).
Treatment
Drugs that are used to kill roundworms are called ascaricides and
include:
1-Benzimidazole derivatives :
a-Mebendazole
Causes slow immobilization and death of the worms by selectively
and irreversibly blocking uptake of glucose and other nutrients
in susceptible adult intestine.
Drug interactions
-Carbamazepine and Phenytoin lowers serum levels of
mebendazole. Cimetidine raises serum mebendazole levels,
increasing its effectiveness.
-Stevens-Johnson syndrome (toxic epidermal necrolysis) when
Mebendazole is combined with high doses of Metronidazole.
b-Albendazole
A broad-spectrum antihelminthic agent that decreases ATP
production in the worm, causing energy depletion,
immobilization, and finally death.
It causes degenerative alterations in the intestinal cells of the worm by binding to the colchicine-sensitive site of tubulin, thus
inhibiting its polymerization or assembly into microtubules. The
loss of the cytoplasmic microtubules leads to impaired uptake of
glucose by the larval and adult stages of the susceptible
parasites, and depletes their glycogen stores. Degenerative
changes in the endoplasmic reticulum, the mitochondria of the
germinal layer, and the subsequent release of lysosomes result in
decreased production of adenosine triphosphate (ATP), which is
the energy required for the survival of the helminth. Due to
diminished energy production, the parasite is immobilized and
.eventually dies
-Contraindicated during pregnancy and children under 2 years.
Albendazole may cause dizziness, headache, fever,
.nausea, vomiting, or temporary hair loss
In rare cases it may cause persistent sore throat,
severe headache, seizures, vision problems,
yellowing eyes or skin, dark urine, stomach
pain, easy bruising, mental/mood changes, very
stiff neck, change in amount of urine. Allergic
.reactions are also possible
CBC and hepatic functions have to be obtained .regularly in patients receiving Albendazole
c-Thiabendazole
This may cause migration of the worm into
the esophagus, so it is usually combined
with piperazine.
2-Piperazine
-Piperazines were originally named because of their chemical similarity
with piperidine, a constituent of piperine in the black pepper plant
-Generally it acts by paralysing parasites, which allows the host body
to easily remove or expel the invading organism. This action is
mediated by its agonist effects upon the inhibitory GABA receptor.
Its selectivity for helminths is because vertebrates only use GABA in
the CNS and the helminths' GABA receptor is a different isoform to
the vertebrate's one.
-(i.e) It is a flaccid paralyzing agent that causes a blocking response of
ascaris muscle to acetylcholine. The narcotizing effect immobilizes
the worm, which prevents migration when treatment is
accomplished with other drugs such as albendazole. If used by
itself it causes the worm to be passed out in the feces.
3-Pyrantel pamoate
.It is a combination of pyrantel and pamoic acid
Pyrantel pamoate acts as a depolarizing neuromuscular blocking agent, thereby causing sudden contraction, followed by
paralysis, of the helminths. This has the result of causing the
worm to "lose its grip" on the intestinal wall and be passed out
of the system by natural process. Since Pyrantel is poorly
absorbed by the hosts intestine, the small dosage of medication
.used is completely ineffective to the host
-Spastic (tetanic) paralyzing agents, in particular pyrantel pamoate,
may induce complete intestinal obstruction in a heavy worm
load.
Worms usually pass in normal stool or with diarrhea, straining, .and occasional vomiting
P.S. : Pyrantel pamoate is considered a Pregnancy category C drug for use during pregnancy for humans