Ascaris lumbricoides is the most common parasitic worm in humans

Alpha University Somaliland

1. NEMATODES (ROUND WORMS) All the important human parasites of the Phylum Nemathelminths (Aschelminthes) belong to the Class Nematoda. GENERAL CHARACTERISTICS OF NEMATODES They are un-segmented, elongated and cylindrical bodies They have separate sexes with separate appearances. They have a tough protective covering or cuticle.

2. Cont…. They have a complete digestive tract with both oral and anal openings. The nematodes are free living (Majority) or parasites of humans, plants or animals . The adults vary greatly in size, from about a millimeter to a meter in length . The body cavity is a pseudocoele in which all the viscera are suspended.

3. Cont….. The digestive system consists of Anteriorly placed mouth. Esophagus which characteristically varies in shape and structure in different groups . The intestine with a single layer of columnar cells and leads to the rectum opening through the anus. In the male, the rectum and the ejaculatory duct open into the cloaca.

4. Cont….. The male reproductive system consists of a single delicate tubule differentiated into Testis V as deferens S eminal vesicle Ejaculatory duct which opens into the cloaca . The female reproductive system consists of ovary, oviduct

5. Cont….. S eminal receptacle Uterus Vagina. Nematodes may produce E ggs ( oviparous ) Larvae ( viviparous ) Some lay eggs containing larvae which immediately hatch out ( ovoviviparous ). The life cycle consists typically of four larval stages and the adult form.

6. The parasitic nematodes : The nematodes are generally light cream- white colored. Their life cycle includes: egg, larvae and adult. The parasitic nematodes are divided into: Intestinal nematodes Intestinal nematodes with tissue stage Ascaris lumbricoides Hookworms Strongyloides stercoralis

7. Cont….. Intestinal nematodes without tissue stage Enterobius vermicularis Trichuris trichiura. Tissue and blood dwelling nematodes Filarial worms Dracunculus medinensis

8. CLASSIFICATION Nematode parasites may be classified in various ways . Location of Adult in the Body Mode of Infection Based on Whether they Lay Eggs or Larvae

9. INTESTINAL NEMATODES WITH TISSUE STAGE ASCARIS LUMBRICOIDES These are common roundworms infecting more than 700 million people worldwide. The roundworm, Ascaris lumbricoides is the largest nematode parasite in the human intestine. Its specific name lumbricoides is derived from this resemblance ( Lumbricus , meaning earthworm in Latin ).

10. Cont…. It is the most common of human helminths and is distributed worldwide . A billion people are estimated to be infected with roundworms. An editorial in the Lancet in 1989 observed that if all the roundworms in all the people worldwide were placed end-to-end they would encircle the world 50 times.

11. Morphology Male adult worm measures 15-20 cm in length. The posterior end is curved ventrally. The female worm measures 20-40 cm in length. Its posterior end is straight Infective stage and modes of infection: The egg containing larva when ingested with contaminated raw vegetables causes Ascariasis.

12. Cont….. The adult worms live in the small intestines of infected persons. They are large cylindrical worms, with tapering ends, the anterior end being more pointed than the posterior . The mouth at the anterior end has three finely denticulated lips, one dorsal and two ventro-lateral.

13. Life cycle Ingested eggs hatch in the duodenum. The larvae penetrate the intestinal wall and circulate in the blood. From the heart they migrate to the lungs, ascend to the trachea, descend to the esophagus and finally reach the small intestine to become adult. The female pass immature eggs which pass to the soil and mature in 2 weeks.

14. Cont…. The larvae moult and develop into adults in the upper part of the small intestine . They become sexually mature in about 6 to 12 weeks and the gravid females start laying eggs . The adult worm has a lifespan of 12 to 20 months

15. Pathology and clinical features Larvae can cause pneumonitis with eosinophilia. Adult worms can cause obstruction of the small intestine, bile ducts and trachea; also appendicitis, pancreatitis and peritonitis. Children may vomit a bolus of adult worms or cough up immature worms . Adult worms in the intestine cause abdominal pain and may cause intestinal obstruction especially in children.

16. Cont…. Larvae in the lungs may cause inflammation of the lungs (Loeffler‘s syndrome) – pneumonia-like symptoms.

17. Laboratory diagnosis Ova may be recovered from feces by concentration methods. Rarely larvae can be found in sputum, and must be distinguished from those of Strongyloides. Eosinophilia is present in the larval invasion stage. No specific serology is currently available

18. Treatment Mebendazole Albendazole Piperazine