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Ascariasis

2007 Schools Wikipedia Selection. Related subjects: Health and medicine

             iAscaris lumbricoides
   An adult female Ascaris worm.
   An adult female Ascaris worm.
           Scientific classification

   Kingdom: Animalia
   Phylum:  Nematoda
   Class:   Secernentea
   Order:   Ascaridida
   Family:  Ascarididae
   Genus:   Ascaris
   Species: A. lumbricoides

                                Binomial name

   Ascaris lumbricoides
   Linnaeus, 1758

   CAPTION: Ascariasis
   Classifications and external resources

    ICD- 10   B 77.
     ICD- 9   127.0
   DiseasesDB 934

   Ascariasis is a human disease caused by the parasitic roundworm Ascaris
   lumbricoides. Perhaps as many as one quarter of the world's people are
   infected , and ascariasis is particularly prevalent in tropical regions
   and in areas of poor hygiene. Other species of the genus Ascaris are
   parasitic and can cause disease in domestic animals.

   Infection occurs through ingestion of food contaminated with fecal
   matter containing Ascaris eggs. The larvae hatch, burrow through the
   intestine, reach the lungs, and finally migrate up the respiratory
   tract. From there they are then reswallowed and mature in the
   intestine, growing up to 30 cm (12 in.) in length and anchoring
   themselves to the intestinal wall.

   Infections are usually asymptomatic, especially if the number of worms
   is small. They may however be accompanied by inflammation, fever, and
   diarrhea, and serious problems may develop if the worms migrate to
   other parts of the body.

Prevalence

   Roughly 1.5 billion individuals are infected with this worm^ .
   Ascariasis is endemic in the United States including Gulf Coast and
   Ozark Mountains; in Nigeria and in Southeast Asia. One study indicated
   that the prevalence of ascariasis in the United States at about 4
   million (2%). In a survey of a rural Nova Scotia community, 28.1% of
   431 individuals tested were positive for Ascaris, all of them being
   under age 20, while all 276 tested in metropolitan Halifax were
   negative^ .

   Deposition of ova (eggs) in sewage hints at the degree of ascariasis
   incidence. A 1978 study showed about 75% of all sewage sludge samples
   sampled in United States urban catchments contained Ascaris ova, with
   rates as high as 5 to 100 eggs per litre. In Frankfort, Indiana, 87.5%
   of the sludge samples were positive with Ascaris, Toxocara, Trichuris,
   and hookworm. In Macon, Georgia, one of the 13 soil samples tested
   positive for Ascaris. Municipal wastewater in Riyadh, Saudi Arabia
   detected over 100 eggs per litre of wastewater ^and in Czechoslovakia
   was as high as 240-1050 eggs per litre ^.

   Ascariasis sources can often be measured by examining food for ova. In
   one field study in Marrakech, Morocco, where raw sewage is used to
   fertilize crop fields, Ascaris eggs were detected at the rate of 0.18
   eggs/kg in potatoes, 0.27 eggs/kg in turnip, 4.63 eggs/kg in mint, 0.7
   eggs/kg in carrots, and 1.64 eggs/kg in radish^ . A similar study in
   the same area showed that 73% of children working on these farms were
   infected with helminths, particularly Ascaris, probably as a result of
   exposure to the raw sewage.

Life cycle

   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 . The larvae mature
   further in the lungs (6) (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 (8).
   Between 2 and 3 months are required from ingestion of the infective
   eggs to oviposition by the adult female. Adult worms can live 1 to 2
   years.
   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 . The larvae mature
   further in the lungs (6) (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 (8).
   Between 2 and 3 months are required from ingestion of the infective
   eggs to oviposition by the adult female. Adult worms can live 1 to 2
   years.

   First appearance of eggs in stools is 60-70 days. In larval ascariasis,
   symptoms occur 4-16 days after infection. The final symptoms are
   gastrointestinal discomfort, colic and vomiting, fever; observation of
   live worms in stools. Some patients may have pulmonary symptoms or
   neurological disorders during migration of the larvae. However there
   are generally few or no symptoms. A bolus of worms may obstruct the
   intestine; migrating larvae may cause pneumonitis and eosinophilia.

Diagnosis

   The diagnosis is usually incidental when the host passes a worm in the
   stool or vomit. Stool samples for ova and parasites will demonstrate
   Ascaris eggs. Larvae may be found in gastric or respiratory secretions
   in pulmonary disease. Blood counts may demonstrate peripheral
   eosinophilia. On X-ray, 15-35 cm long filling defects, sometimes with
   whirled appearance (bolus of worms).

Symptoms

   Patients can remain Asymptomatic for very long periods of time. As
   larval stages travel through the body, they may cause visceral damage,
   peritonitis and inflammation, enlargement of the liver or spleen,
   toxicity, and pneumonia. A heavy worm infestation may cause nutritional
   deficiency; other complications, sometimes fatal, include obstruction
   of the bowel by a bolus of worms (observed particularly in children),
   obstruction of bile or pancreatic duct. 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^ .

   Ascaris takes most of its nutrients from the partially digested host
   food in the intestine. There is limited evidence that it can also
   pierce the intestinal mucous membrane and feed on blood, but this is
   not its usual source of nutrition. As a result, Ascaris infection does
   not produce the anaemia associated with some other roundworm
   infections.

Treatment

   Native Americans have traditionally used epazote (Chenopodium
   ambrisioides) for treatment, which was not as powerful as
   pharmaceutical compounds, but spontaneous passage of Ascarids provided
   some proof of efficacy.

   Some recent studies exist in the medical literature suggesting that
   sun-dried papaya and watermelon seeds may reduce infections by a large
   factor. The adult dosage is one tablespoon of the seed powder in a
   glass of sugar water once a week for two weeks. The sugar makes the
   bitter taste palatable and acts as a laxative.

   Pharmaceutical treatments include:
     * Mebendazole (Vermox) (C[16]H[13]N[3]O[2]). Causes slow
       immobilization and death of the worms by selectively and
       irreversibly blocking uptake of glucose and other nutrients in
       susceptible adult intestine where helminths dwell. Oral dosage is
       100 mg 12 hourly for 3 days.
     * Piperazine (C[4]H[10]N[2].C[6]H[10]O[4]). 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 weak drugs
       such as thiabendazole. If used by itself it causes the worm to be
       passed out in the feces. Dosage is 75 mg/kg (max 3.5 g) as a single
       oral dose.
     * Pyrantel pamoate (Antiminth, Pin-Rid, Pin-X)
       (C[11]H[14]N[2]S.C[23]H[16]O[6]) Depolarizes ganglionic block of
       nicotinic neuromuscular transmission, resulting in spastic
       paralysis of the worm. Spastic (tetanic) paralyzing agents, in
       particular pyrantel pamoate, may induce complete intestinal
       obstruction in a heavy worm load. Dosage is 11 mg/kg not to exceed
       1 g as a single dose.
     * Albendazole (C[12]H[15]N[3]O[2]S) A broad-spectrum antihelminthic
       agent that decreases ATP production in the worm, causing energy
       depletion, immobilization, and finally death. Dosage is 400 mg
       given as single oral dose (contraindicated during pregnancy and
       children under 2 years).
     * Thiabendazole. This may cause migration of the worm into the
       esophagus, so it is usually combined with piperazine.

   Also, corticosteroids can treat some of the symptoms, such as
   inflammation.

Prevention

   Prevention includes; use of toilet facilities; safe excreta disposal;
   protection of food from dirt and soil; thorough washing of produce;
   hand washing; and common-sense sanitary measures.

   Food dropped on the floor should never be eaten without washing or
   cooking, particularly in endemic areas. Vegetables originating from
   third-world countries should always be washed thoroughly before
   consumption.

Animal models for Ascaris infestation

   There are two animal models for studying Ascaris infection:
     * Mouse- Ascaris suum test model. (Howes HL Jr. J Parasitol. 1971
       Jun; 57(3): 487-93.)
     * Ascaris suum in experimentally infected pigs. (Lichtensteiger CA et
       al; 1999)

Trivia

     * Ascariasis may result in allergies to shrimp and dustmites due to
       the shared antigen, tropomyosin.
     * Worm infestation, including ascaris lumbricoides, may provide some
       protection against developing asthma.
     * Ascaris have an aversion to some general anesthetics and may exit
       the body, sometimes through the mouth.

   Retrieved from " http://en.wikipedia.org/wiki/Ascariasis"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
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