BSc 1st Year Lower Non-chordates Helminths Sample Model Practice Question Answer Papers
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Q. 1. Give an account of Helminth parasites of man.
Write an essay on the economic importance of helminths.
Helminths are well known due to their parasitic mode of life. The great majority dwells inside the various organs of vertebrates, a few in plants, while these occur rarely as free living forms. They affect their host by their mode of life, by their size, number and the site of infection. The large number of parasites causes starvation of the host their large size leads to the robbery of a great amount of food and their heavy infection stunts the growth.
Not only the adult but also the larval forms are pathogenic. The adults cause anaemia, diarrhoea, eosinophilia, dysentry, headache, fever, etc., while the larvae moving from one organ to other cause destruction of the host tissue. Many diseases have been named according to the name of the parasite such as Fascioliasis, Taeniasis, Schistosomiasis, Ascariasis, Ancylostomiasis, etc. The fatality of the helminths can be discussed by considering the individuals of separate groups.
Economic Importance of Flatworms
The flatworms include Turbellarians, Trematodes and Cestodes.
1. Turbellarians: The turbellarians are mostly free-living and are utilized as food by fishes and amphibians.
2. Trematodes: The trematodes are exclusively parasitic, found in man and other domesticated animals. These mostly live in the organs like liver, intestine, bile ducts, blood vessels and the urinary bladder.
A few of them are as follows:
(i) Liverflukes: The liver flukes, Fasciola hepatica, in sheep and Clonorchis in man are parasites found in the bile passages of liver and cause liver rot or hepatitis, while their by products cause anaemia, diarrhoea and eosinophilia.
(ii) Blood flukes: The blood fluke of man is Schistosoma haematobium. It dwells in the mesenteric blood-vessels and the veins of hepatic portal system and is said to cause a disease known as schistosomiasis. The penetrating cercaria larva causes itching in the skin. During migration of the portal system these produce headache, general pain, eosinophilia, diarrhoea and dysentery. When eggs are laid by the adults, pain in the urinary bladder of the host is produced, Fever usually develops in late afternoon or evening. Finally the urinary bladder loses its contraction
(iii) Fasciolapsis buski : It is a common intestinal parasite of dogs and man and is especially found in India and other neighbouring countries.
3. Cestodes : Cestodes are mostly the intestinal parasites of vertebrates. However, their larval forms dwell in the muscles. A few of the cestodes are as follows:
(i) Taenia : Various species of Taenia are found in the intestine of man and other domesticated animals. These cause vomiting, nausea, abdominal pain and nervous disorders.
(ii) Moniezia: It is found in sheep, cattle and other ruminants and causes diarrhoea, anaemia and intestinal obstruction.
(iii) Diphyllobothrium latum : It is the largest and the most pathogenic cestode found in men, cats, dogs, bears and sea lions. It causes bothrioceophalus anaemia, erythropenia and haemorrhage.
(iv) Echinococcus granulosus : It is known as bladder worm or hydatid worm and occurs more commonly in the small intestine of cats, dogs and foxes but intermediate host is man, where the larva develops into a hydatid cyst. The cysts are harmful causing inflammation and development of fibrous tissue in the host. The hydatid causes diarrhoea, vomiting and abdominal pain.
Economic Importance of Roundworms
Roundworms belong to phylum Nemathelminthes. A great majority of them are free living while a few are found as parasite in man and some occur on plants. Human parasitic roundworms include:
(i) Ascaris lumbricoides : It is the most common roundworm found in the intestine especially of children. The disease caused by it is named Ascariasis and is characterised by indigestion, protuberance of abdomen, loss of appetite, insomnia, appendecitis, gastric ulcers, diarrhoea, etc. The larvae while pursuing a migratory course enter the lungs and their heavy infection affects the lungs.
(ii) Ancylostoma : The common hookworm found in the intestine of man is Ancylostoma duodenal. It causes itching in skin, haemorrhage and bronchial pneumonitis in the lungs in the larval condition and the adults produce constipation, diarrhoea, dyspnea, anaemia, etc.
(iii) Necator Americans: It is American hookworm of man found mostly in America and causes the same symptoms.
(iv) Enterobius vermicularis : It is the common pin worm or seat worm found in the caecum, appendix vermiform, colon or small intestine of man and enjoys a world-wide distribution. The gravid females cause intense itching in the perianal and parineal regions. The presence of worms causes loss of appetite, insomnia, hysteria and restlessness.
(v) Trichinella spiralis : Trichinella is found in the intestine of man, pigs and other vertebrates mostly in the United States and Arctic regions. It causes trichiniasis, characterised by haemorrhage, muscular pain, hypereosinophilia, thrombosis and restlessness.
(vi) Filaria bancrofti (Wuchereria bancrofti): It is causative agent of filariasisis in man and is found throughout the world. It occurs in the lymphatic and muscular systems and is transmitted by the bite of mosquito. The presence of parasite leads to filarial fever and mental depression of headache. The ultimate stage leads to elephantiasis, characterised by the swelling of legs, scrotum and mammary glands, etc.
(vii) Loa-loa : The common African eye-worm is Loa loa. It invades the subcutaneous tissue and during its migration causes itching, especially in the eyes. (BSc 1st Year Lower Non-chordates Helminths Sample Model Practice Question Answer Papers)
Thus we find the helminth parasites cause great harm not only to man but also to domesticated animals, but they never cause epidemics like protozoans.