ascaris lumbricoids

ASCARIS

CLASSIFICATION.

• Family: Ascarididae• Genus: Ascaris• Species: Ascaris Lumbricoides and Ascaris

Suum.• Binomial name:Ascaris Lumbricoides

ASCARIS LUMBRICOIDES

Ascaris lumbricoides is the giant roundworm of humans, belonging to the phylum Nematoda. An ascarid nematode is responsible for the disease ascariasis in humans, and it is the largest and most common parasitic worm in humans.

MORPHOLOGY Ascaris is a large intestinal roundworm. It superficially resembles the common earthworms found in the soil. Female worms can be as long as 20-35cms, and males tend to be smaller, no larger than 30cms. They can be anywhere from 2-6 mm wide. Mature worms are cylindrical, creamy white or light brown. They tend to have tapered ends.The worms have a thick cuticle, 3 lips at its head, small teeth, and its own digestive tract. The fertilized eggs are oval shaped, and they are about 65 to 40um in size. The eggs are brown or yellow brown, and they have a thick shell.

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An adult male has a coiled posterior end and a female A. lumbricoides anterior ends are more slender than the posterior ends.

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EPIDEMIOLOGY

It is estimated that more than 1.4 billion people are infected with A. lumbricoides, representing 25 percent of the world population. A number of features account for its high prevalence including the durability of eggs under a variety of environmental conditions, the high number of eggs produced per parasite, and poor socioeconomic conditions that facilitate its spread.

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More than 2 billion people are affected by this infection. In the United States there is a reported prevalence of 0.8% of the total population as of 1987. Ascaris lumbricoides eggs are extremely resistant to strong chemicals and low temperatures. The eggs can remain viable in the soil for several months or even years.

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Although ascariasis occurs at all ages, it is most common in children 2 to 10 years old, and prevalence decreases over the age of 15 years. Infections tend to cluster in families, and worm burden correlates with the number of people living in a home. Infection rates for ascariasis have not been reported to be higher in patients infected with the human immunodeficiency virus (HIV) .

TRANSMISSION• Lumbricoides is transmitted primarily through fecal-oral

contamination. The transmission can occur by ingesting contaminated soil, water, or food(raw vegetables or fruits)

• Usually, ascariasis is caused by directly or indirectly eating soil contaminated with feces carrying these eggs.

• These eggs mature in the body, and adult female worms can then lay eggs that come out in the feces. Note, however, that in order for the eggs to be infective , the feces must have been infected 2-4 weeks before it is ingested. Infection with Ascaris eggs is so common because the eggs are frequently found in the environment due to poor sanitation practices.

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• Ascariasis can occur by way of trasnplacental transmission, since many neonatal cases have been documented.

• Occasionally inhalation of contaminated dust.

Reservoir; No reservoir for this type of Ascaris exists outside of humans Vector; No vector exists for Ascaris. Incubation period; between 4-16 days after ingestion of the eggs

LIFE CYCLE

LIFECYLE CONT…DLife Cycle from the Figure above ;– Adult worms (1) live in the lumen of the small intestine. A female

may produce approximately 200,000 eggs per day, which are passed with the feces.

(2). Unfertilized eggs may be ingested but are not infective. Fertile

eggs embryonate and become infective after 18 days to several weeks (3), depending on the environmental conditions (optimum: moist, warm, shaded soil).

After infective eggs are swallowed (4), the larvae hatch (5), invade the intestinal mucosa, and are carried via the portal, then systemic circulation to the lungs

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(6) The larvae mature further in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed (7) Upon reaching the small intestine.

They develop into adult worms; Between 2 and 3 months. Adult worms can live 1 to 2 years.

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SIGNS AND SYMPTOMS The main symptoms include the following:• Low grade fever• Cough and bloody sputum• Wheezing• Abdominal cramping and discomfort• Nausea • Vomiting worms• Anorexia• Diarrhoea and passing worms in stool• Small bowel obstruction (mainly in children)• Pancreatitis (worm migration)• Appendicitis (worm migration)

INVESTIGATIONS

• Abdominal x-ray or other imaging tests• Complete blood count • Eosinophil count• Stool ova and parasites exam• Liver Function Test may reveal liver damage

or low protein state.• Sputum for larva and eosinophil count.

FERTILE EGG IN HUMAN FAECES

INFERTILE EGG

FERTILE EGG SEEN IN A MICROSCOPE

WORMS IN THE INTESTINES AND THOSE PASSED FROM THE INTESTINAL TRACT

MANAGEMENT

• Pyrantel pamoate — Pyrantel pamoate (11 mg/kg up to a maximum of 1 g) is administered as a single dose.

• Mebendazole — Mebendazole (100 mg BD for 3 days or 500 mg as a single dose) • Albendazole — A single dose of albendazole:400 mg for 2years and above, 200mg for

12-24months

• Piperazine citrate — Piperazine citrate (50 to 75 mg/kg QD up to a maximum of 3.5 g for 2 days

• Levamisole — Levamisole (150 mg for adults and 5 mg/kg for children)

• Manage other signs and symptoms as they present

PREVENTION

• Good sanitation to prevent fecal contamination of soil.

• Health education program advising against the use of human feces as a fertilizer.

• Improved sanitation and hygiene. • routine or preventive (prophylactic) treatment

with deworming medications.

COMPLICATIONS

• Liver secretion (biliary tract) obstruction• Blockage in the intestine• Hole (perforation) in the gut

REFERENCES

• Et al cedric; 2004; medical microbiology; 3rd edition; mosby-elsevier limited; philadelphia

• www.cdc.gov/ncidod/dpd/parasites/ascaris