Category : NEET
Diseases Caused by Helminthes
Diseases Caused by Helminthes : Helminthes (flatworms and roundworms) cause many diseases in man. The more common are taeniasis, ascariasis and filariasis (elephantiasis).
(a) Taeniasis : Taeniasis is caused by the pork tapeworm Taenia solium. This tapeworm lives in the human intestine, firmly anchored by hooks and suckers. It lacks mouth and absorbs host?s digested food through its skin (saprozoic nutrition). It is hermaphrodite and undergoes self-fertilization. There is normally a single worm in one host. This worm has enormous power of reproduction.
(1) Life-history : Taenia solium has about 4 metres long, white, flat, ribbon like body comprising a small knob-like scolex, a short neck and a very long strobila of about 850 proglottides. Capsules of the worm pass out in host?s faeces and are ingested by pigs. They release embryos which reach the pig?s striated muscles, encyst and develop into infective larvae. There may be about 3,000 larvae in 500 grams of pork. The infected pork has brownish spots and is called ?measly pork?. Man gets infection by taking raw or undercooked measly pork. Pink or red appearance of the pork, when cut into slices, is an indication of its being undercooked. In the human intestine, the cyst wall breaks down, releasing the larva. The latter grows into an adult worm in 3 to 4 months.
(2) Gravid proglottids : These segments are pregnant uterus, which possess fertilized ova, and all structures disintegrate in it the dropping of gravid proglottids is called apolysis.
(3) Effect on the Host (Pathogenicity) : The tapeworm infection produces little effect on a person with a sound health. Weak person may develop a disease named taeniasis. This disease is characterized by abdominal pain, indigestion, vomiting, constipation, loss of appetite (anorexia) and weight, insomnia, lowered resistance to other diseases and nervous disorder.
(4) Cysticercosis : Tapeworm infection can also occur by taking improperly washed vegetables and water contaminated with the tapeworm capsules. Thus, the vegetarians can also get tapeworm infection. The capsules release embryos which may reach eyes or brain, develop into larvae, called cysticerci, that encyst. The cysts so formed may cause blindness or epilepsy-like symptoms and prove fatal.
(b) Ascariasis : Ascariasis is caused by the roundworm Ascaris lumbricoides. This roundworm lives in the human small intestine. It lies free, having no organs for attachment. It takes host?s digested food by sucking through the mouth (holozoic nutrition).
(1) Life-history : Man gets infection by taking Ascaris eggs with food and water. Children become infected by ingesting soil. Eggs hatch in the host?s intestine in a few hours, each liberating a tiny (0.2 to 0.3 mm. long) worm called juvenile. The latter grows into an adult worm in 2 to 2.5 months. The adult worm has cylindrical body tapering at each end, 20 to 40 cm. long in female and 15-30 cm. long in male. Male?s hind end is curved ventrally. Mature male and female worms copulate in the host?s intestine, where the female later lays eggs. The eggs pass out in the faeces, and can remain alive in the soil for several years. The eggs are carried to food and drinking water by air, flies and cockroaches.
(c) Filariasis (Elephantiasis) : Filariasis is caused by the filarial worm, Wuchereria bancrofti.
(1) Life-history : The adult male and female worms are 40 mm. and 80 mm. long respectively. They live in the lymphatics and connective tissues. The worm is viviparous. The female delivers young worms called microfilariae. The latter shift to deep blood vessels. At night they migrate to the superficial blood vessels of the skin and are sucked by Culex mosquito, the intermediate host. The mosquito injects them into the blood of a healthy human being. Form the blood, they migrate to the lymph vessels and lymph glands. Here they grow into adults in about a year.
(2) Effect on the Host (Pathogenicity) : In acute cases the filarial infection causes fever. In chronic cases the worms block the lymph vessels. This causes enormous swelling of the affected part, which may be foot, leg, or scrotum. This is followed by thickening of skin and subcutaneous tissue. Enlargement of legs gives the disease its name, elephantiasis.
(d) Ancylostomiasis (Hookworm Disease) : Ancylostomiasis is caused by the hookworm, Ancylostoma duodenale. It lives in the small intestine firmly attached to its wall. It feeds on blood and bits of mucous membrane. A secretion from its pharyngeal gland prevents clotting of blood while the worm is feeding and causes considerable loss of blood after the worm has left the wound. Eggs laid by the female worm in the host?s intestine escape with the faeces and hatch in the moist soil. The larvae feed on organic debris and get into the human body by boring through the skin of the feet, causing ?ground itch.? They enter the veins, and passing through the heart, lungs, trachea, pharynx and oesophagus, reach the intestine. Here, they mature. Adult worms live for about 5 years. Male worm is 8-11 mm. long, and female 10-13 mm.
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