Ascaris Lumbricoides

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Ascaris Lumbricoides

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- graphic image

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Ascaris Lumbricoides - Clinical Manifestations

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Symptoms correlate with worm load:light loads are asymptomatic; heavier loads cause abdominal symptoms, diarrhea, and sometimes malnutrition. A bolus of worms may obstruct the intestine. Migrating larvae can cause pneumonitis and eosinophilia.

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Ascaris Lumbricoides - Structure

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Ascaris lumbricoides is the largest intestinal nematode of humans. Females are up to 30 cm long; males are smaller. Three types of eggs may appear in feces: fertilized, unfertilized, and decorticated.

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Ascaris Lumbricoides - Multiplication and Life Cycle

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Adults in the small intestine produce eggs that pass in feces, embryonate in soil, are ingested, and hatch. The larvae migrate from the intestine to the lung and back to the intestine, where they mature.

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Ascaris Lumbricoides - Pathogenesis

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Migrating larvae cause eosinophilia and sometimes allergic reactions. Erratic adult worms may invade other organs. Heavy infections can impair nutrition.

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Ascaris lumbricoides - Host defenses

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Resistance increases with age; the mechanism is not clear.

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Ascaris lumbricoides - Epidemiology

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Egg viability is supported by warm, moist soil. Transmission is favored by unsanitary disposal of feces. Prevalence is highest in children.

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Ascaris lumbricoides - Diganosis

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Diagnosis is made most often by identifying eggs in stool; occasionally, erratic adults emerge from body orifices.

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Ascaris lumbricoides - Control

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Control is by sanitary disposal of feces and by education and treatment.

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Ascaris lumbricoides - Clinical Manifestations

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Adult A lumbricoides infections involving only a few worms are usually asymptomatic, but as the worm load increases, symptoms of abdominal discomfort, nausea, vomiting, weight loss, fever, and diarrhea develop. Allergic manifestations in hypersensitized persons lead to pneumonitis, cough, low-grade fever, and eosinophilia. Large numbers of worms may form a bolus and cause intestinal obstruction. Stimulation causes adult worms to become erratic and invade the appendix and bililary and pancreatic ducts. Worms may enter and block small orifices. Migrating adults have been vomited and passed from the nose and mouth, anus, umbilicus, and lacrimal glands. They can perforate the intestines and enter the peritoneal cavity, the respiratory tract, urethra, and vagina, and even the placenta and fetus. Excessive worm loads, especially among the malnourished, can lead to nutritional impairment because the worms interfere with the absorption of proteins, fats, and carbohydrates.

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Ascaris lumbricoides - Structure

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Ascaris lumbricoides is the largest and most common intestinal nematode of humans. Females are approximately 30 cm long; sexually mature males are smaller. The diameter varies from 2 to 6 mm. Mated females produce fertile eggs that are oval to subspherical, 45 to 75 μm by 35 to 50 μm, and are covered by a thick shell with a light brown, mammillated, albuminous outer coat. Unmated females (for example, in a single-sex infection), produce unfertilized eggs that are thin-shelled, ellipsoidal, and measure 78 to lO5 μm by 38 to 55 μm. The mammillated coat of unfertilized eggs is irregular and the contents are granular and disorganized. Some eggs are passed without the outer mammililated coat (decorticated eggs) and can be confused with eggs from hookworms or other worms.

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Ascaris lumbricoides - Structure labeling

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diagram

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Ascaris lumbricoides - Multiplication and Life Cycle

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Ascaris lumbricoides is found in the small intestine, particularly the jejunum. Females produce as many as 240,000 eggs per day and as many as 65 million in a lifetime. The eggs are unsegmented and are passed in the feces. In moist, warm, shady soil, the eggs embryonate, and an infective larva develops within the egg in about 3 weeks. After ingestion by a human, the eggs pass to the duodenum where they hatch; the released larvae penetrate the intestinal mucosa, enter the lymphatics and portal system, and are carried to the liver, heart, and lungs. This migratory phase requires a few days. The larvae then break out of the capillaries into the alveoli, pass up the respiratory tree, and are swallowed. They reach the intestines and continue their development, and 8 to 12 weeks after infection, become sexually mature adults. The adults live for about a year and are subsequently passed in the feces .

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Ascaris lumbricoides - Life Cycle diagrams

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life cycle diagrams

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Ascaris lumbricoides - Life Cycle diagrams

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life cycle diagrams

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Ascaris lumbricoides - Pathogenesis

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Pathogenesis
The initial pathology is associated with migrating larvae;
the severity depends upon:
1- number of invading organisms,
2- sensitivity of the host,
3- host's nutritional status.
Persons repeatedly infected become sensitized, and
migrating larvae may cause tissue reactions in the liver and lungs, with eosinophilic infiltration and granuloma formation. The reactions lead to pneumonitis and a condition known as Loeffler's syndrome.
Adult worms may cause blockage of the intestines, and migrating adults may provoke severe pathology when they wander into other organs. Acute pancreatitis and biliary stones may occur. The rare fatalities usually result from intestinal obstruction or biliary ascariasis. Furthermore, the pathogenicity of the worms may vary in different regions of the world.

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Ascaris lumbricoides - Pathogenesis diagram

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pathogenesis diagram

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Ascaris lumbricoides - Host defenses

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The fact that children are more often infected with A lumbricoides than adults suggests that resistance develops with age. The mechanisms underlying this resistance are not known. IgE antibodies are present in infected persons, and some persons can develop allergic manifestations such as urticaria, asthma, fever, conjunctivitis, and eosinophilia. Some parasitologists become sensitized and subsequently develop severe reactions when exposed to A lumbricoides antigens.

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Ascaris lumbricoides - Epidemiology

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Ascaris lumbricoides is distributed widely in tropical and subtropical areas, especially in the developing countries of South America, Africa, and Asia. More than one billion infections are estimated to exist at any given time.
In rural areas of Asia, it is not unusual to find 85 percent of the population passing Ascaris eggs. Prevalence rates are much lower in the United States. Some people appear to be predisposed to infection with intestinal helminths, including A lumbricoides. Some individuals are found to be constantly infected and usually have a higher intensity of infections than others.

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Ascaris lumbricoides - Diagnosis

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Symptomatic ascariasis is rarely diagnosed on clinical grounds alone because the pneumonitis, eosinophilia, and intestinal symptoms are similar to those caused by other infectious agents. Infections before the appearance of eggs in the feces, infections with only male worms, and extraintestinal infections are difficult to diagnose.
Radiologic computed tomography (CT) scan and ultrtasound examination may reveal adult worms in the intestine and bile ducts, but definitive diagnosis requires finding characteristic eggs in feces.
Eggs are usually so numerous in any infection involving female worms that simple microscopic examination of a fecal smear is all that is necessary. Concentration techniques involving flotation or sedimentation of eggs also may be used. Techniques are available to estimate the intensity of an infection on the basis of the number of eggs in a measured stool sample.

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Ascaris lumbricoides; Ultrasound imagery. Normal/ presence of Ascaris causes distention

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Ultrasound

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Ascaris lumbricoides; Control

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Control
The most effective method to control ascariasis, as well as other soil-transmitted helminthiasis, is sanitary disposal of feces. In some areas, this requires changing centuries-old habits and educating the population. Mass treatment programs have been initiated in many parts of the world and, in some Asian countries, efforts are being made to deworm all school children. In a pilot program in the Philippines aimed at eradication of the soil-transmitted helminths by periodic mass treatment of a barrio population, the prevalence of ascariasis decreased from 78 percent to less than 1 percent over 3 years. Mebendazole, the drug used, is effective against numerous intestinal nematode infections and causes few side effects. Levamisole is also useful, as are pyrantel pamoate, piperazine citrate, thiabendazole and albendazole. Care must be taken in treating mixed helminthic infections involving A lumbricoides,because an ineffective ascaricide may stimulate the parasite to migrate to another location. Persons in whom asymptomatic ascariasis is detected incidentally should be treated to prevent the possibility of a future abnormal migration of these large worms into extraintestinal sites.