Ascaris

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Ascaris Lumbricoides

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Ascaris Lumbricoides

-Ascariasis is caused by the parasitic roundworm Ascaris

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

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Adult worm of A. lumbricoides

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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 severalyears.

4. Social customs and living habits.

5. Disposal of feces is unsuitable.

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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 theintestinal contents, where the fertilized female lays eggs. An adultfemale can produce approximately 200,000 eggs per day, whichare passed in feces. When passed, the eggs require outsidedevelopment of about three weeks until a motile embryo is formedwithin the egg.

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- After the ingestion of embryonated eggs (infective) incontaminated food or drink or from contaminated fingers, hostdigestive juices acts on the egg shell and liberate the larva intothe small intestine.

-These larvae penetrate the intestinal mucosa and enter lymphaticsand mesenteric vessels. They are carried by circulation to the

where they penetrate thefinally to the lungsandheartliver,capillaries into the alveoli in which they molt twice and stay for10-14days.

-Then they are carried, or migrate, up the bronchioles, bronchi, andtrachea to the thorate. When swallowed, the larvae pass down

.into adultsinto the small intestine where they develop-The time from the ingestion of embryonated eggs to oviposition bythe females is about 60-75 days. The adult worms live for aboutone-two year.

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Pathogenesis

There are two phase in ascariasis:

lung migration phase of the larvae:-. The blood1During the migration through the lungs, the larvaemay cause a pneumonia. The symptoms of thepneumonia are low fever, cough, blood-tinged

sputum, asthma. Large numbers of worms may giverise to allergic symptoms. Eosionophilia is generallypresent. These clinical manifestation is also called

.s syndrome’Loeffler

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. The intestinal phase of the adults.2

The presence of a few adult worms in the lumen of the small intestineusually produces no symptoms, but may give rise to vague abdominal

pains or intermittent colic, especially in children. A heavy worm.malnutritionburden can result in

-More serious manifestations have been observed. Adults worm mayblock the the common bile duct and even perforate the intestinal wall.

-Thus complications of ascariasis, that may occur include intestinalobstruction, 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 bowelby a bolus of worms (observed particularly in children). More than 796 Ascaris lumbricoides worms weighing 550 g [19 ounces] wererecovered at autopsy from a 2-year-old South African girl. The wormshad caused torsion and gangrene of the ileum, which was interpreted

as the cause of death.

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Source

Ingestion of infective eggs from soil contaminated with humanfeces or transmission and contaminated vegetables and water isthe primary route of infection.

-Intimate contact with pets which have been in contact withcontaminated soil may result in infection, while pets which are

infested themselves by a different type of roundworm can causeinfection with that type of worm.

-Transmission also comes through municipal recycling ofwastewater into crop fields. This is quite common in emergingindustrial economies, and poses serious risks for not only localcrop sales but also exports of contaminated vegetables. A 1986

outbreak of ascariasis in Italy was traced to irresponsiblewastewater recycling used to grow vegetable exports .

-Transmission from human to human by direct contact isimpossible.

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Diagnosis

The confirmative diagnosis depends on the recovery andidentification of the worm or its egg.

1. Ascaris pneumonitis: examination of sputum for Ascarislarvae 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 ofthe female oviposition, approximately 240,000 eggs per wormper day. So this method is the first choice.

(2) recovery of adult worms: when adults or adolescents arefound in feces or vomit and tissues and organs from the humaninfected with ascarids , the diagnosis may be defined.

(3) On X-ray, 15 –35 cm long filling defects, sometimes withwhirled appearance (bolus of worms).

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Albendazole-b

A broad-spectrum antihelminthic agent that decreases ATPproduction in the worm, causing energy depletion,immobilization, and finally death.

-It causes degenerative alterations in the intestinal cells of the wormby binding to the colchicine-sensitive site of tubulin, thusinhibiting its polymerization or assembly into microtubules. Theloss of the cytoplasmic microtubules leads to impaired uptake of

glucose by the larval and adult stages of the susceptibleparasites, and depletes their glycogen stores. Degenerativechanges in the endoplasmic reticulum, the mitochondria of thegerminal layer, and the subsequent release of lysosomes result indecreased production of adenosine triphosphate (ATP), which isthe energy required for the survival of the helminth. Due to

diminished energy production, the parasite is immobilized andeventually dies.

-Contraindicated during pregnancy and children under 2 years.

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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, stomachpain, easy bruising, mental/mood changes, verystiff neck, change in amount of urine. Allergicreactions are also possible.

-CBC and hepatic functions have to be obtainedregularly in patients receiving Albendazole.

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Thiabendazole-c

This may cause migration of the worm intothe esophagus, so it is usually combinedwith piperazine.

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Pyrantel pamoate-3It is a combination of pyrantel and pamoic acid.

-Pyrantel pamoate acts as a depolarizing neuromuscular blockingagent, thereby causing sudden contraction, followed byparalysis, of the helminths. This has the result of causing theworm to "lose its grip" on the intestinal wall and be passed outof the system by natural process. Since Pyrantel is poorlyabsorbed 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 wormload.

-Worms usually pass in normal stool or with diarrhea, straining,and occasional vomiting.

-Pregnancy category CP.S. : Pyrantel pamoate is considered adrug for use during pregnancy for humans

Ascaris

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