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Ascariasis
Ascaris lumbricoides is an intestinal roundworm. It is the largest intestinal nematode that infects humans. Adult worms live in the small intestine and grow to a length of more than 30 cm. Humans are the only natural host and reservoir of infection. The roundworm infection occurs worldwide. The number of infected persons is estimated to be more than 2 billion. The main epidemic region with a prevalence rate of approx. 10-90% includes South East Asia, Africa and Latin America countries.
1.0Classification
- Phylum : Nematoda
- Class : Chromadorea
- Order : Ascaridida
- Genus : Ascaris
- Species : lubricoides
2.0Geographical Distribution
- Ascariasis is the most common human helminthic infection found worldwide.
- Infection is highest in tropical and subtropical regions, especially in areas with inadequate sanitation.
- The number of infected persons is estimated to be more than 2 billion.
- The main epidemic region, with a prevalence rate of approximately 10-90%, includes countries in Southeast Asia, Africa, and Latin America, including India.
- The infection is generally rare and absent in developed countries, but sporadic cases may occur in rural, impoverished regions of those countries.
- Some cases where human transmission is negligible in these areas have direct epidemiologic associations with pig farms.
- Ascaris lumbricoides is an intestinal endoparasite round worm. It is the largest intestinal nematode that infects humans.
- The adult worm lives in the small intestine and grows more than 30 cm in length. Humans are only the natural host and reservoir of infection.
- Many ancient people observed and reported this worm, but details about its life cycle were known only after 1916.
3.0Morphology - Adult
- The roundworm resembles the earthworm.
- It is elongated and tapering at both ends, with the anterior being thinner than the posterior.
- Fresh screwworms are yellowish-pink in colour, gradually changing to white.
- The worm is sexually dimorphic.
- Adult male: 15-30 cm long, 3-4 mm in diameter, tail curved.
- Adult female; 20-40 cm length, 2-6mm diameter, tail straight.
Egg
- Ascaris egg is round or oval, 60*40 µm size, thick brown shell and rough surface.
- It is the infective form of a parasite.
- Unfertilized egg; large, more elongated (38-55*78-105) µm
- Fertilized egg; ovoid (35-50*50-70)µm, golden brown colour
4.0Life Cycle of Ascaris
- The life cycle of Ascaris is completed in a single human host.
- The adult worm lives in the small intestine.
Stage I: Eggs in faeces
- A sexually mature female produces as many as 200,000 eggs per day, which are shed along with faeces in unembryonated form. 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. An infectious larva develops within the egg in about 3-6 weeks.
Stage III: Human infection and liberation of larvae
- Human infection and liberation of larvae
- Humans get infected by ingesting embryonated egg-contaminated food and water.
- Within the embryonated state inside the egg, first-stage larvae develop into second-stage larvae.
- This second stage larvae is known as Rhabtitiform larvae.
- Second-stage larvae are stimulated to hatch out by the presence of alkaline pH in the small intestine and the solubilization of their outer layer by bile.
Stage IV: Migration of larvae through lungs
- Hatched-out larvae penetrate the intestinal wall and are carried to the liver through the portal circulation.
- It then travels via blood to the heart and lungs through pulmonary circulation within 4-7 days of infection.
- The larvae in the lungs mould twice, enlarge and break into alveoli.
Stage V: Re-entry to the stomach and small intestine
- From the alveoli, the larvae pass up through the bronchi and into the trachea and are then swallowed.
- The larvae passed down the oesophagus to the stomach and again reached the small intestine.
- The small intestine is the normal habitat of Ascaris, and it colonizes here.
- Within the intestine, the parasite moulds twice and matures into adult worms.
- Sexual maturation occurs within 6-10 weeks, and the mature female discharges its eggs in the intestinal lumen and excretes along with faeces, continuing the life cycle.
- The life span of the parasite is 12-18 months.
5.0Pathogenicity of Ascaris Lumbricoides
- The adult worm produces the following pathogenic effects:
- Spoliative action: By robbing the host of its nutrition.
- Toxic action: The body fluid of Ascaris is toxic and causes anaphylactic reactions.
- Mechanical effect: Obstructing the tubular passages, such as the appendix, bile duct, pancreatic duct, and bronchus and perforating through ulcers in the alimentary canal.
6.0Clinical Manifestation of Ascaris Lumbricoides
- Ascariasis is an infection caused by the parasitic roundworm Ascaris lumbricoides.
- It is more frequently observed in children than in adults.
- While many cases remain asymptomatic, symptomatic infections are classified into two main types: intestinal ascariasis, which affects the digestive system, and pulmonary ascariasis, which impacts the respiratory tract.
Intestinal Ascariasis
Gastrointestinal Symptoms
- Nausea and vomiting
- Irregular bowel movements or diarrhea
- Cramping or colicky abdominal pain
- Abdominal bloating or distension
- Loss of appetite
- Unintentional weight loss
- Intestinal obstruction, leading to severe pain and vomiting
- Malabsorption of nutrients
- Growth delays, especially in children
- Presence of visible worms in the stool
Severe Cases and Complications
- Growth impairment in children due to poor nutrient absorption
- Severe worm infestation in children may lead to intussusception (where a section of the intestine folds into another) and complete intestinal obstruction
- Possible complications include:
- Appendicitis
- Biliary colic (pain due to bile duct obstruction)
- Perforation of the bile duct
- Hepatomegaly (enlarged liver)
- Generalized fatigue and weakness
- Fever in cases of heavy infestation
Pulmonary Ascariasis
- Transient eosinophilic pneumonitis (Loeffler’s disease); elevated IgE
- Bronchospasm
- Dyspnea
- Coughing and gagging
- Wheezing or shortness of breath
- Aspiration pneumonia (rarely).
- Blood in mucus Chest discomfort Fever
7.0Prophylaxis of Ascariasis Lumbricoides
- Ascariasis can be eliminated by preventing fecal contamination of soil.
- The Ascaris egg is highly resistant.
- Therefore, the use of night soil as manure will lead to the spreading of the infection, unless the destruction of the eggs is ensured by proper composting.
- Treatment of vegetables and other garden crops with water containing iodine 200 ppm for 15 minutes kills the eggs and larvae of Ascaris and other helminths.
- Avoid eating raw vegetables. Improvement of personal hygiene.
- Treatment of infected persons especially the children