Ascaris lumbricoides - Philippines

Ascaris lumbricoides

Ascaris is a genus of parasitic nematode worms known as the "giant intestinal roundworms"

A.           lumbricoides is the largest intestinal roundworm and is the most common helminth infection of humans worldwide, an infection known as ascariasis. Infestation can cause morbidity, and sometimes death, by compromising nutritional status, affecting cognitive processes, inducing tissue reactions, such as granuloma, and provoking intestinal obstruction or rectal prolapse.

Scientific classification

Kingdom:                    Animalia

Phylum:                      Nematoda

 Class:                       Secernentea

Order:                       Ascaridida

 Family:                      Ascarididae

Genus:                        Ascaris

Species:                     A. lumbricoides

Binomial name           Ascaris lumbricoides
Linnaeus, 1758

Morphology

·         Adult: cylindrical shape, creamy white or pinkish in color.

·         Male: average 15–31 cm and is more slender than female.

·         Female: average 20–35 cm in length.

Symptoms

·         Bloody sputum

·         Cough

·         Low-grade fever

·         Vomiting worms

·         Passing of worm in stool

·         Gallstone formation

·         Liver abscesses

·         Pancreatitis

·         Pulmonary eosinophilia

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, with rates of 45% in Latin America and 95% in parts of Africa. 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. Certain genes have been identified in human populations that may increase the susceptibility to infection.

Infection occurs through ingestion of food contaminated with feces 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.

1. Adult worms 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.

Examination

·         Abdominal X-ray

·         Complete blood count

·         Stool ova and parasite exam

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).

PathologyRobbins & Cotran Pathologic Basis of Disease: With STUDENT CONSULT Online Access (Robbins Pathology)

Lung phase

A.lumbricoides is known as Ascaris pneumonitis. In the lung it causes hemorrhage, inflammation, bacterial infection. It also causes allergy in areas with seasonal transmission. Typically occurs at 6–15 days after initial exposure.

Intestinal phase

The intestinal phase causes malnourishment, intestinal blockage, verminous intoxication. A.lumbricoides will move around in the body in response to chemotherapy or fever. Typically occurs at 6 to 8 weeks after initial exposure.

Management

Early diagnosis can be performed by examination of stool for the worm eggs. The spread or infection of A.lumbricoides can be controlled by proper disposal of faeces and proper washing of food. Control of helminthiasis is based on drug treatment, improved sanitation and health education.

 

 

 

 

Defense Mechanism

As part of the parasite defense strategy, Ascaris roundworms secrete a series of inhibitors to target digestive and immune-related host proteases, which include pepsin, trypsin, chymotrypsin/elastase, cathepsins, and metallocarboxypeptidases (MCPs). Ascaris inhibits MCPs by releasing a enzyme known as Ascaris carboxypeptidase inhibitor (ACI). This enzyme binds to the active site of MCP and blocks the cleavage of its own proteins by the host MCP

Treatment

Infections with A.lumbricoides are easily treated with a number of anthelmintic drugs:

·         pyrantel pamoate given as a single dose of 10 mg/kg

·         levamisole given as a single dose of 2.5 mg/kg

·         mebendazole given as a single dose of 500 mg

·         albendazole given as a single dose of 400 mg.sup

The drugs' main target is the absorbing cells of the worm. The drugs prevent the worm from absorbing sugar in the intestine which is essential for its survival. This process leads to depletion of energy in worm and its eventual death within few days. The dead worm is then excreted from the gut in the stool. Albendazole is not well absorbed by the intestines and a high fat food or meal should be consumed with each dose.

Many parasitic disease specialists are seeing increased initial incidence and recurrence of roundworm in the U.S. and are thereby increasingly recommending follow up courses of medication to treat internal eggs which have not yet hatched, in addition to the initial treatment period as above. This consists of sporadic treatment with albendazole or similar for a period of three days each month for up to five months after the initial treatment period.

It has been theorized in work by Dr. Hulda Clark that a chemical found in jalapeno peppers may prevent Ascaris infection given the low infection rate in Mexicanos.

More severe cases, blockage of intestine or pancreatic ducts require surgical removal of worms.