Term Paper on Helminthes and Human Diseases | Microorganisms | Zoology

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Millions of people the world over lose vast amounts of their hard earned food and their life-giving blood to these parasitic worms which take a staggering toll in human sickness and pain. Their primary victims are children often from poor, under-fed and ill-educated families.

These highly infectious worms pass from person to person, infecting entire families, entire communities and often vast segments of nations and continents. In few countries is the danger greater than in India, especially in rural area.

The following three forms of helminthiasis are the most widespread:

1. Nematodiasis,

2. Trematodiasis and

3. Cestodiasis.

1. Term Paper on Nematodiasis:

Diseases caused by the nematodes constitute nematodiasis. More than 50 species are parasites of man, but there are four predominant nematode worms which afflict humans.

i. Ascariasis:

Ascariasis is a very common disease of human beings caused by the large-sized nematode (roundworm) Ascaris lumbricoides. There are an estimated 860 million people in world are victims of this disease. This roundworm is found in the intestine especially of children. In human beings the disease follows the ingestion of embryonated eggs with contaminated food (raw vegetables fruits) and drinking water.

Among children playing in the contaminated soil, there is also hand to mouth transfer of eggs by dirty fingers. Ascariasis is characterized by indigestion, protuberance of abdomen, loss of appetite and intestinal obstruction, insomnia, appendicitis, gastric ulcers, diarrhoea, liver disorders, etc., the larvae while pursuing a migratory course enters the lungs and their heavy infection affects the lungs (causing bronchits). Ascariasis can be successfully treated by oral administration of piperazine citerate syrup, alkendazole, mebendazole, santonin and oil of chenopodium.

ii. Ancylostomiasis:

Ancylostomiasis is caused by two hookworms, Ancylostoma duodenale and Necator americanus. Both nematodes are parasites within the intestine. They are most frequent in rural areas. Female hook-worms produce 5000-1000 eggs per day which pass out in the stools. Hookworms also thrive in warm and moist climate. India alone has 200 million of the world’s 700 million hookworm victims, most of whom are children.

Man acquires infection when the eggs hatch and the juveniles penetrate through the skin of hands and feet. They can also be swallowed with contaminated food or drink. They enter the blood vessels and are carried to the heart and lungs. Now they make their way to one of the bronchial tubes, pass into the small intestine and finally develop into adult worms.

Where roundworm takes its toll in protection only, hookworm also sucks blood and tissue juices of the host. The characteristic symptoms of ancylostomiasis are gastrointestinal disturbances, anaemia and nervous disorders. Patients appear pale and are often weak. They complain of dizziness, ringing in the ears and headache. Nausea and vomiting are frequent. In more severe case men may become important and women may cease to menstruate.

Hookworm infection can be drastically reduced by keeping the feet covered outside the house. Researches in Kanpur, Jhansi and some districts of Madhya Pradesh have proved that people habitually bearing chappals or shoes suffered far less infection than those who went about barefoot. In the treatment of hookworm, the safe and effective drugs are tetrachloroethane and carbon tetrachloride.

iii. Filariasis or Elephantiasis:

Filariasis is caused by Wuchereria bancrofti commonly called the filarial worm. The adult worm inhabits lymphate vessels of human beings, most frequently those in the lymph nodes, testes and epididymis.

Infection is spread through culex mosquito. Following copulation the viviparous female worm delivers juveniles called microfilariae. These exhibit a distinct periodicity of larval migration to the peripheral circulation, coinciding with the activity of mosquito (intermediate host).

The presence of parasite leads to short term lymphatic inflammation marked by pain and fever, mental depression and headache. The ultimate stage leads to elephantiasis which is characterized by great swelling of legs, scrotum and breast. Such swellings take place due to blockage of the lymph circulation by parasitic worms. The drug diethylcarbamazine (Hetrazan) is found effective in killing the microfilariae and possibly adult worms.

iv. Trichuriasis:

This disease is caused by Trichuris trichiura, commonly called whipworms. These worms inhabit the large intestine, mainly the caecum of vermiform appendix. The female lay enormous number of eggs daily that pass in the stools. The eggs gain entry to the human body with contaminated drinking water and raw fruits and vegetables. They may also be spread by flies. In the intestine the eggs hatch and the larvae develop into adult whipworms.

Most whipworm infections are mild and a little more than a nuisance. But they retard growth in small children. The patient suffering from whipworm disease complains of nausea, vomiting, diarrhoea or constipation, loss of weight, headache and even paroxylmal pains resembling appendicitis. In more severe cases, anemia and eosinophilia develop. The drugs most commonly used for the expulsion of whipworms are osarsol (acetarsone) are dithiazanine.

v. Trichinosis:

Trichinosis is caused by Trichinella spiralis. It is one of the smallest nematodes infecting human beings. Trichinosis is common and wide spread in Europe and America. Humans become infected by Trichinella by eating raw or under cooked meat (pork) containing its encysted larvae.

The early symptoms of trichinesis are nausea, vomiting, odema of face and eyelids and fever. After this, muscular pains are felt. The patient complains of pains in chewing, swallowing, breathing and in moving his arms and legs. The drugs thiabendazole is found to be effective in the treatment of trichinosis.

vi. Enterobiasis:

This disease is caused by Enterobius vermicularis, commonly called pinworms or seatworms. These are small white worms about 6 or 7 mm long and inhabit the upper part of the colon. The females migrate out through the colon and rectum and deposit enormous number of eggs in the skin folds about the anus, where they cause intense itching.

When the skin about the anus is scratched, eggs are easily picked upon the fingers and under the nails from where they find their way to food, and are swallowed. They hatch in the stomach and the juveniles migrate to the colon and develop into adult worms.

The infection is more frequent in children, than adults. The symptoms of the disease include severe itching around the anus, loss of appetite, sleeplessness, bed-wetting, grinding of teeth, nausea and vomiting. The victims spend a lot of time scratching the seat of their pants, often causing wounds and reinfections this way.

Piperazine is the most effective drug in the treatment of pinworms. The patient must wash his perianal region with warm water and soap before going to and on rising from bed.

vii. Strongyloidosis:

This disease is caused by Strongyloides stercoralis, commonly called threadworms. These invade the lining of the alimentary canal. The female lays large number of eggs that pass out in faeces and develop into rhabditiform larvae. These, then transform into infective filariform larvae that penetrate the skin of the bare feet, and thus enter the human body.

They enter blood vessels and pass to the lungs, where they invade alveoli. They ascend trachea, descend the oesophagus and mature to become pathenogenic females in the small intestine. Invading larvae cause dermatitis. Larva migrating through lungs tend to produce cough haemoptysis (= expectoration of blood in sputum) and dysponea. Severe infection of the intestine cause vomiting, diarrhoea and constipation. Its hyperinfection results in ulceration, oedoma, congestion, fibrosis and severe inflammation of the intestine. This disease can be treated by the drugs thiabendazole.

viii. Loiasis:

It is caused by the African eye worm Loa loa. It lives in the subcutaneous tissues of humans and baboons in Central and West Africa. Its infection is transmitted by mango flies (Chrysops species).

The worm migrates about in the tissue and sometimes passes across the eye ball. During its migration, Loa loa causes calabar swellings (i.e. transient subcutaneous swellings marking the migratory course through the tissues of the adult worm), itching, especially in the eyes. Other ocular symptoms include swelling of lids, congestion, itching and pain. The drug Hetrazan provides effective remedy of loiasis.

ix. Guinea Worm Disease:

It is caused by a largest known nematode Dracunculus medinensis, commonly called “guinea worm” or “fiery serpent”. Its life cycle includes two hosts- primary host is human and the intermediate host is Cyclops (a crustacean). Guinea worm lives in the general viscera (coelom) and subcutaneous tissues of arms, legs and shoulders of human beings. It also infests dogs, foxes, raccoons and minks. It is commonly found in dry regions of India, Arabia, Tropical Africa, South America, China, etc.

The female guinea worm is about 1 mm in diameter and up to 120 cm in length. After a period of development in the body cavity and connective tissue of the host, the gravid female migrates to the subcutaneous tissue and produces an ulcerated opening to the exterior.

If the ulcerated area of the host comes in contact with water, larvae are released. After a short free living stage, the larvae are ingested by species of Cyclops and continue their development in the host’s haemocoel. When definitive host (human being) swallows Cyclops in drinking water, the nematode larvae are released and penetrate the intestinal wall to reach the coelom or subcutaneous tissue.

Dracunculus secretes toxic substances that cause asthma, eosinophilia, itching vomiting diarrhea, and giddiness. The worm can be surgically removed. Intramuscular injection of phenothiazine emulsified in olive oil into a number of places close to worm kills the worm. Infection can be prevented by drinking filtered or boiled water.

2. Term Paper on Trematodiasis:

The diseases caused by the trematode helminthes constitute trematodiasis.

Some common such human diseases are as follows:

i. Fasciolopsiasis:

This disease is caused by the intestinal fluke, Fasciolopsis fuelleborni in India. It utilizes the snail as intermediate host in which it passes through an elaborate development cycle, producing metacercariae that leave the snail to be located on water plants. Infections are acquired by eating these water plants, particularly the water nuts. Within the intestine these metacercariae develop into adult worms within three months.

The worms cause erosion of intestinal lining, resulting in bleeding and pain. This is followed by diarrhoea, nausea, and vomiting. Hexylresorcinol and ‘Crystalloids’ anthelmintic are helpful in the eradication of the intestinal flukes.

ii. Schistosomiasis:

The blook 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 power.

For treatment of the disease, antimony compounds are recommended. Sanitary disposal of all human faeces and urine is essential for the control of Schistosomiasis.

iii. Opisthorchiasis (= Clonorchiasis):

This disease is caused by Opisthorchis (= Clonorchis) sinensis which inhabits the bile ducts. The disease is widespread in China, Japan, Korea, Vietnam and India. Human infections are acquired through eating raw or under-cooked fish which harbour metacercariae. Thousands of adult flukes are found in biliary ducts, causing the thickening of duct walls. Severe cases usually lead to cirrhosis and ultimate death.

Gentian Violet and Chloroquine prove helpful in curing infections. Most important is prevention. All fresh water fish should be thoroughly cooked before eating.

iv. Paragonimiasis:

This disease is caused by the long fluke. Paragonimus westermani-Infection is widespread in Asia, Africa and South and Central America. The flukes are found in the lungs in encapsulated form. The eggs are expelled out in sputum and when in contact with water these develop into miracidia. The miracidia find their way into the snail host where they develop into cercaria larvae.

The cercariae emerge end get into the crabs and crayfish and encyst into metacercarial cyst. Man acquires infection from eating raw or under-cooked crabs and crayfish. Excystment occurs in the intestine of man and the juveniles migrate into the lungs where they attain maturity and become encapsulated.

The lung flukes cause chronic cough with emission of bloody sputum. Heavy infections cause chest pain with pleurisy, shortness of breath, fever and anaemia. Emetine hydrochloride and sulpha drugs are recommended for the treatment of lung flukes.

3. Term Paper on Cestodiasis:

Cestodiasis is caused by tapeworms.

The two common forms of this disease are as under:

i. Taeniasis:

This disease is caused by the species belonging to the genus Taenia, which include mainly T. solium (pork tapeworm) and Taenia saginata (beef tapeworm). Man acquires the infection by eating raw or under-cooked pork or beef that contains the cysticerci. In the intestine the cysticerci develop into adult tapeworms.

The presence of tapeworms in the intestine causes gastrointestinal disorders. Some patients complain of hunger pain. Anaemic conditions may also develop. Atabrin or quinocrine hydrochloride is the drug of choice. Prevention requires the eating of thoroughly cooked pork of beef.

ii. Hydratid Disease:

This disease is caused by Echinocoecus granulosus, the hydatid worm. The primary host of this worm is dog. In the intestine the eggs are set free. These pass out in faeces and develop into onchospheres. Man acquires infection on eating food or drinking water contaminated with onchosphere-containing eggs.

In man the hydatid cysts develop in the liver, lungs and other tissues and represent the end of the parasitic life-line. The cysts cause inflammation of the tissues. Presence of cysts in the brain and kidney may prove fatal. The recommended drug is the same as for Taeniasis.