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| Laboratory diagnosis and treatment of ascaris lumbricoides |
Ascaris lumbricoides is an intestinal round worm and is the largest intestinal nematode to infect Human. Ascaris adult worm lives in small intestine and grow to a length that can reach more than 30 cm. It should be noted that Humans are the only natural host and reservoir of infection of these round worms.
Ascariasis infection occurs worldwide. The number of infected persons is estimated to be more than 2 billion. The main epidemic region with prevalence rate of approximately 10-90% includes countries on South east Asia, Africa and Latin America.
Morphology
It is sexually dimorphism and resemble earth worms but whitish in color. It is elongated tapering to both end, The anterior end being thinner than posterior. Freshly excreted Ascaris worm are yellowish pink in color, then gradually changes to white.
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| Morphology of ascaris lumbricoides |
Adult male measure 15-30 cm in length, 3-4 mm in diameter, tail curved
Adult female measures 20-40 cm length, 2-6mm diameter, tail straight longer than males.
Egg Morphology
Egg Are round or oval with 60*40 µm size,bile stained thick brown shell with rough surface. Fertile eggs are infective form of parasite especially those embryonated.
i) Un fertilized egg are large, more elongated (38-55*78-105) µm
ii) fertilized egg are ovoid (35-50*50-70)µm, golden brown color
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| eggs of ascaris lumbricoides |
Life cycle
The life cycle of Ascaris completes in single host. Human.
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| Life cycle of ascaris lumbricoides |
- Adult worm lives in small intestine
- Stages in life cycle:
Stage I: Eggs in faeces
Sexually mature female produces as many as 200,000 eggs per day, which are shed along with faeces in unembryonated form but they are non infective.
Stage II: Development in soil
Embryonation occurs in soil at an optimum temperature of 20-25C with sufficient moisture and O2
Infective larva develops within egg in about 3-6 weeks.
Stage III: Human infection and liberation of larvae
Human get infection by ingestion of embryonated egg contaminated food and water
Within embryonated state inside egg, first stage larvae will develops into second stage larvae. This second stage larvae is known as Rhabtitiform larvae form.
Then the Second stage larve is stimulated to hatch out by the presence of alkaline pH in small intestine and solubilization of its outer layer by bile.
Stage IV: migration of larvae through lungs
Hatched out larvae penetrates the intestinal wall and carried to liver through portal circulation
It then travels via the blood stream to the heart and to lungs by pulmonary circulation within 4-7 days of infection.
The larvae in lungs molds twice, enlarge and breaks into alveoli.
Stage V: Re-entry to stomach and small intestine
From alveoli, the Larvae then pass up through bronchi and into trachea and then swallowed.
The larvae passes down the oesophagus to the stomach and reached into small intestine once again.
Small intestine is the normal habitat of Ascaris and it colonises here.
Within intestine parasite molds twice and mature into adult worm.
Sexual maturation occurs with 6-10 weeks and the mature female discharges its eggs in intestinal lumen and excreted along with faeces, continuing the life cycle.
The life span of parasite is 12-18 months
Pathogenesis:
1. Mode of transmission:
faeco-oral route, by contaminated vegetables or water.
2. Pathogenesis:
Infection of A. lumbricoides in man is known as Ascariasis. There are two phase in ascariasis.
Phase I: migrating larvae
The migrating larvae causes pathological lesions. The severity of lesions depends upon the sensitivity of host, nutritional status of host and number of migrating larvae.
During migration and molding through lungs, larvae may causes pneumonia with low grade fever, cough and other allergic symptoms.
Phase II: Adult worm
Few worm in intestine produce no major symptoms and but some time give abdominal pain especially in children.
The adult worm produce trauma in host tissue and the wandering adults may block the appendical lumen or common bile duct and even small intestine.
Large number of adult worms affects the nutritional status of host by robbing the nutrition leading to malnutrition and growth retardation in children.
The metabolites of living or dead worm are toxic and immunogenic.
lumbricoides also produces various allergic toxin, which manifests fever, conjunctivitis and irritation.
Clinical manifestation:
Most Ascaris infection are asymptomatic.
There are 2 types of Symptomatic ascariasis which are Intestinal Ascariasis and Pulmonary Ascariasis
1. Intestinal ascariasis;
Nausea
Vomiting
Colicky abdominal pain
Abdominal distention
Weight loss and diarrhea
Malbasorption of nutrition
Growth retardation
Heavy worm in children leads to intussusception and total obstruction
Complications: Appendicitis, Biliary colic and perforation of bile duct, Hepatomegaly
2. Pulmonary ascariasis;
Transient eosinophilic pneumonitis (loeffler’s disease); elevated IgE
Bronchospasm
Dyspnea and wheezing
Fever
Non-productive cough and chest pain
Lab diagnosis:
Specimen: stool, sputum
Microscopy: examination of stool by saline emulsion 1
0X,40x or concentration by floatation methods employed to unembryonated egg
X-ray
Serodiagnosis: Indirect haemagglutination test, Immuno-fluorescence assay
Ultrasonography and CT scan
Other test: blood count shown peripheral eosinophilia
Treatment and prophylaxis:
Mebendazole: drug of choice, (100mg twice a day for 3 days)
Albendazole: 500mg single dose
Pyrantel pamoate: single dose of 1omg/kg weight
Piperazine citrate