| General Description | Commonly called as human roundworm. One of the most common and best known gastro-intestinal parasites. Body is elongate, cylindrical and gradually tapering at both ends. Sexes are separate with distinct sexual dimorphism. Cuticle covering the body has transverse striations, giving a pseudo-segmented appearance to the worm. |
| Parasitic Adaptations | Tough, thick and resistant cuticle. Covers the body and shields against the action of host digestive enzymes. It also secretes anti-enzymes that protect it from host digestive enzymes. Power of locomotion counteracts peristalsis of host’s intestine. Compensates for the absence of adhesive suckers and spines. Muscular Pharynx facilitates ingestion of food by sucking action. Because there is a constant supply of food, the alimentary canal is simple with no provisions for storage. No elaborate digestive glands, because the ingested food is pre-digested. No circulatory system. Pseudo-coelomic fluid serves for absorption, transport and distribution of food, oxygen and wastes, so that there is no circulatory system. Extremely low metabolic rate and anaerobic respiration enables the worm to live inside the host’s intestine, where free oxygen is negligible. Because the parasite remains well-protected inside the host, there is no need for complicated sensory organs. Transfer to a new host is entirely passive, depending on ingestion of embryonated eggs. After that it must have the adequate conditions to develop. Resistant covering or shell provides safety to the zygotes and embryonated eggs from unfavourable environmental factors. This way, they remain viable for years. Minute size and resistant nature of eggs affords far and wide dispersal of the parasite. Infection of a new human is direct, without an intermediate host, which makes the process easier. |
| Life History | 1. Adult worms live in the small intestine of people. There, females may produce about 200,000 eggs per day. The eggs are excreted with stool. 2. Only fertilized eggs cause infection. 3. The fertilized eggs develop in the soil. The eggs develop best in moist, warm, shaded soil. 4. People become infected when they swallow Ascaris eggs, often in food that came in contact with soil contaminated with human stool containing fertilized Ascaris eggs. 5. The eggs hatch and release larvae in the intestine. 6. The larvae penetrate the wall of the small intestine and travel through the lymphatic vessels and bloodstream to the lungs. 7. Once inside the lungs, larvae pass into air sacs (alveoli) in the lungs, move up the respiratory tract and into the throat, and are swallowed. When the larvae reach the small intestine, they develop into adult worms. |
| Pathogenicity | Ascariasis Infection is caused by Ascaris following ingestion of embryonated eggs with contaminated food and drinking water. Symptoms: Abdominal pains, vomiting, headache, irritability, diarrhoea, salivation. May spread to other organs and cause – Appendicitis, Gall Bladder trouble and Liver disease. Bronchitis in lungs. Treatment: Piperazine citrate syrup, Hexylresorcinol tablets. |