Parasitism

I. Definition: Parasitism is an intimate association between two organisms of different species, in which one species is benefited and the other is harmed.

a. The organism that is benefited is known as parasite

b. The organism that is harmed is known as host

Parasite gets nourishment and shelter from the host. Host suffer from diseases due to the parasite.

II. Types of parasites :

1. Ectoparasite: A parasite that lives on the surface of the body of host is called ectoparasite. e.g.: Head lice and itch mites in man ; ticks on dog, copepods on marine fish.

2. Endoparasite: A parasite that lives inside the body of host is known as endoparasite.

    a. Intra cellular parasite / cytozoic parasite : It lives inside the cells of host.

e.g.: Plasmodium in liver cells and RBC of man and Nosema in the body of Sphaerospora (unicellular animal).

    b. Inter cellular or histozoic parasite : It lives in the inter cellular spaces of tissues and organs of the host. e.g.: Entamoeba histolytica in mucosa and submucosa of intestine of man, Wuchereria in lymph of man.

    c. Coelozoic parasite: It lives in the cavities of organs of the host, (if it lives in cavity of alimentary canal, it is called enterozoic parasite) e.g.: Ascaris in intestine of man.

3. Hyperparasite: A parasite lives in or on the body of another parasite is called hyperparasite. e.g.: Sphaerospora is parasitic in urinary bladder of toad fish, Nosema notabilis is a hyperparasite lives in the body of Sphaerospora.

4. Monogenetic parasite: A parasite that completes its life cycle in a single type of host.  e.g.: Entamoeba histolytica, Ascaris lumbricoides.

5. Digenetic parasite: A parasite that completes its life cycle in two or more hosts. e.g.: Plasmodium, Wuchereria.

III. Types of hosts:

1. Primary or definitive host: The host that lodges adult stage or sexually mature stage of parasite or the host in which parasite performs sexual reproduction is called primary host or definitive host. e.g.: Female Anopheles for Plasmodium, man for Wuchereria.

2. Secondary or intermediate host: The host that harbours the developing stages (like larvae) or asexual stages of a parasite or the host in which parasite performs asexual reproduction is called intermediate host. e.g.: Man for Plasmodium, female Culex for Wuchereria.

3. Reservoir host: The host that lodges the infective stages of parasite when main host is not available is called reservoir host. In reservoir host parasite does not undergo any change and also does not cause any disease. e.g.: Monkey for Plasmodium. Gnu (african antelope) for Trypanosoma gambiense.

IV. Vector: Vector is generally an insect (arthropod). It transfers the parasite from one host to other. Vectors are of two types :

1. Mechanical vector: It transfers the insective stages of parasite but no part of development occur in it. e.g.: House fly for Entamoeba histolytica.

2. Biological vector: In this vector, parasite undergoes part of development before it gets transfered to another host. e.g.: Female Anopheles for Plasmodium, female Culex for Wuchereria.

EFFECTS OF PARASITES ON THEIR HOSTS

1. Hypertrophy: Increase of size of the affected host cells due to parasite is known as hypertrophy. e.g.: Increase of size of RBC due to Plasmodium.

2. Hyperplasia: Increase of number of cells in host tissue due to parasite is known as hyperplasia. e.g.: Fasciola hepatica (liver fluke) in bile duct of sheep.

3. Neoplasia: Some parasites causes abnormal growth of cells and form new structures in the tissue. This effect is called neoplasia. (Some tumours may lead to cancers). e.g.: some viruses.

4. Gigantism : Increase of size of the host due to parasite or its young stages is called gigantism. e.g.: Abnormal increase of size of snail due to larvae of Fasciola hepatica.

5. Parasitic castration : Degeneration of gonads of host due to parasite is known as parasitic castration. Thus host becomes sterile. e.g.: Sacculina degenerates the ovaries of its host - crab (Carcinus).

6. Parasites cause various diseases in the host

PARASITIC ADAPTATIONS

1. Most of the parasites (particularly those live in intestine) develop certain organs for   attachement to host tissues. e.g.: Hookes and suckers in Taenia solium (pork tapeworm).

2. Intestinal parasites have an enzyme resistant cuticle as body covering. e.g.: cuticle of Ascaris.

3. Intestinal parasites secrete antienzymes to neutralise the enzyme of the host.

4. Most of the parasites adopt anaerobic respiration. Some are obligatory anaerobes (e.g.:Entamoeba histolytica) and few are facultative anaerobes (e.g.: Ascaris).

5. Vast capacity of reproduction. e.g.: Ascaris lay 2,00,000 eggs / day.

6. Formation of cysts to with stand unfavourable condition. e.g.: Entamoeba histolytica.

7. Some parasites change their antigens frequently. (Hence development of vaccine is not possible). e.g.: Plasmodium, HIV.

HEALTH

A state of complete physical, mental and social well being and absence of any disease is known as health.

Health may be affected by :

1. Genetic disorders         2. Infections          3. Life style

ENTAMOEBA HISTOLYTICA

I. Introduction :

1. Entamoeba histolytica was discovered by Lambel. Its disease causing nature was described by Losch.

2. Entamoeba histolytica is a protozoan (unicellular) parasite found in intestine of man. It secrets histolysins, which cause ulcers and haemorrhage in intestine.

3. Entamoeba histolytica is responsible for the disease amoebiasis.

II. Structure :

1. Entamoeba histolytica is a protozoan, parasite found in mucosa and submucosa of intestine of man (histozoic parasite). It causes amoebiasis.

2. A fully grown, disease causing (pathogenic) phase of Entamoeba histolytica is known as trophozoite.

                                    
3. Trophozoite is oval in shape and is covered by a thin plasma lemma.

4. Cytoplasm is divisible into outer clear ectoplasm and inner, granular endoplasm.

5. In the centre of the body, there is nucleus which is like a wheel of a cart.

       a. Nucleus is covered by nuclear membrane

      b. In the centre of nucleus is an endosome

      c. Attached to inner surface of nuclear membrane, there are chromatin granules

      d. Extending between chromatin granules and endosome, spoke radii are present

6. Nutrition in Entamoeba histolytica is holozoic. Food vacuoles contain RBC, bacteria etc.

7. Cytoplasm contains all cell organelles except mitochondria. Hence it is an obligate anaerobe.

8. Trophozoite asexually reproduces by binary fission.

III. Life history:

1. Entamoeba histolytica is parasitic in the intestine (in mucosa and sub mucosa) of man and causes amoebiasis. Fully grown Entamoeba histolytica is known as trophozoite.

2. Trophozoite reproduces asexually by binary fission. After many binary fissions, some of the daughters fall into lumen (cavity) of intestine and become round precystic stages (nonpathogenic). In cytoplasm of precystic stages food materials are stored as glycogen and chromatoid bodies (ribonucleo proteins).

3. Then precystic stages are enclosed by a tough, chitinous cyst now they are called cystic stages.

4. Nucleus of cystic stages undergo two divisions and form four nuclei. These tetra nucleate cysts (infective stages) pass out through faces.

5. Tetra nucleate cysts reach human food / water by wind action or through house flies, cockroaches etc.

6. When man consumes contaminated food / water, tetra nucleate cysts reach his intestine, where, excystation takes place and the tetra nucleate body is released. It is called metacystic stage.

 The process of formation of protective cyst is called encystation.

 The process of break down of the cyst is known as excystation.

7. Each nucleus of metacystic stage divide once and thus eight nuclei are formed. This octa nucleate body undergoes three binary fissions and form eight daughter Entamoeba histolytica. They invade the mucosa and sub mucosa of intestine and become trophozoites.

IV. Pathogenic effects :

1. Entamoeba histolytica (trophozoite) causes amoebiasis in man.

2. Intestinal amoebiasis : Trophozoite of Entamoeba histolytica secrets histolysins, that cause ulcers and haemorrhage in intestine. Main symptoms of intestinal amoebiasis (amoebic dysentry) are abdominal pain, irregular motions, blood and mucus in stools etc.

3. Extra intestinal amoebiasis : In severe infection, some of the trophozoites of Entamoeba histolytica enter the blood circulation of man and reach vital organs like liver, heart, lungs, brain, kidneys etc., where they cause abscessess, which are fatal. (liver abscessess are common)

V. Prophylaxis :

1. Sanitary disposal of feces.

2. Washing of hands before eating.

3. Washing the fruits, vegetables etc., before consumption.

4. Protection of eatables from houseflies and other insects.

PLASMODIUM

I. Introduction :

1. Plasmodium is commonly known as malarial parasite. It causes malaria in man.

2. It is an inter cellular parasite found in liver cells and red blood cells (RBC) of man.

3. Plasmodium was discovered by Charles Laveran in the blood of a malarial patient.

4. Ronald Ross discovered cysts of Plasmodium in the wall of crop of female Anopheles (mosquito) for which, he was awarded the Nobel prize.

5. August 20th will be considered as World Malaria Day or World Mosquito Day.

6. Golgi described the life cycle of Plasmodium in RBC of man and Grassi and others in female Anopheles.

II. Species of Plasmodium :

III. Structure of sporozoites :

1. Sporozoite are the infective stages of Plasmodium.

2. It is sickle shaped with pointed ends.

3. Sporozoite is covered by an elastic pellicle. Cytoplasm contains organelles like mitochondria, Golgi body, ER, microtubules, nucleus etc.

4. In the anterior end, there is a small depression called apical cup (apical suker).

5. Opening into the apical sucker, there are two secretory organelles. They secrete a cytolytic enzyme that help the sporozoite to penetrate into the liver cell of man.

IV. Life history :

       Plasmodium completes its life cycle in two hosts, namely mosquito and man. Mosquito (female Anopheles) is the primary host and man is secondary host and monkey is reservoir host. In man, Plasmodium reproduces asexually (schizogony) and in mosquito sexually.

1. Life cycle of Plasmodium in man (human phase) or asexual cycle or schizogony :

Plasmodium is an intra cellular parasite found in liver cells and RBC of man. It reproduces asexually in man. Asexual multiplication of Plasmodium in man is called schizogony. It is divisible into hepatic (liver) schizogony and erythrocytic (RBC) schizogony.

A. Hepatic schizogony : It was explained by Short and Garnham. It takes place in liver cells (hepatocytes). Hepatic schizogony is divisible into two phases.

a. Preerythrocytic cycle : When a female Anopheles (mosquito infected by Plasmodium) bites a man, Plasmodium enters his blood in the form of sporozoites. With in 30 minutes, they reach liver and each one enters a hepatocyte (liver cell). In hepatocyte, sporozoite becomes trophozoite, grow in size and becomes a schizont. Nucleus and cytoplasm of schizont divide many times and form many small cryptozoites. Now the liver cell ruptures and they are liberated out.

b. Exoerythrocytic cycle : Cryptozoits again attack healthy hepatocytes, become trophozoites and then schizonts. Nucleus and cytoplasm of schizont divide and form two types of metacryptozoites, namely, micrometacryptozoites and macrometacryptozoites. When liver cell ruptures, they are liberated out. Macro metacryptozoites again attack healthy hepatocytes and continue the same cycle. Micro metacryptozoites enter the blood and attack RBC.

B. Erythrocytic schizogony or endoerythrocytic cycle or cycle of Golgi : In the blood micrometacryptozoits enter the RBC. In the RBC, it becomes trophozoite and begins to grow. A vacuole appears, grow and push the nucleus to one side. Hence, trophozoite looks like a ring. Hence it is called signet ring stage. Soon, the vacuole disappears and trophozoites becomes amoeba like (amoebiod stage). It feeds on haemoglobin, digest the globin and undigested haematin is stored as haemozoin(malaria pigment). By this time, in cytoplasm of RBC, red spots appear called Schuffner’s dots(these are probably antigens produced by plasmodium). Trophozoite grow further and become schizont. Nucleus and cytoplasm of schizont divide many times and form many spindle shaped erythrocytic merozoites. They are arranged like petals of flower in the RBC (rosette stage). By this time, RBC ruptures and erythrocytic merozoites are released into along with haemozoin and chemicals they cause malaria. Erythrocytic merozoites again attack healthy RBC and continue the same cycle.

Formation of gametocytes : After many endoerythrocytic cycles, some of the erythrocytic merozoits enter healthy RBC and become two types of gametocytes. Their further development takes place in female Anopheles (mosquito).

2. Life cycle in mosquito or mosquito phase or sexual cycle :

Plasmodium is an intra cellular parasite found in liver cells and RBC of man. It completes life cycle in two hosts, namely, man and female Anopheles (mosquito). In mosquito, it reproduces sexually. When a female Anopheles sucks, the blood from a malaria patient, all stages of Plasmodium reach the crop of mosquito. Except gametocytes, other stages are digested. pH and temperature in crop of mosquito are favourable for the development of gametocytes.

A. Gametogony : The formation of microgametes (male gametes) from microgametocyte and formation of macrogametes (female gametes) form macrogametocyte is called gametogony.

a. The nucleus of micro gametocyte divides two or three times and form 4 or 8 pro nuclei. They emerge out from gametocyte along with some cytoplasm as thread like structures. They show lashing movements and detached from present cells as microgametes. The process of detachement of microgametes from microgametocyte is known as exflagellation.

b. The macrogametocyte divide once and form a large cell and a small cell called polar body. Polar body distintegrates the large cell becomes macrogamete. It develops a small projection, known as fertilisation cone.

B. Fertilisation / Syngamy : Union of two gametes is called syngamy. If the gametes are dissimilar the syngamy is called anisogamy (In Plasmodium anisogamy takes place). A macrogamete (female gamete) is fertilised by a microgamete (male gamete). Thus a zygote is formed.

C. Ookinete and oocyst : The zygote becomes spindle shaped and move towards the wall of crop. This motile zygote is called ookinete or vermicule. It penetrates through the wall of crop of mosquito, reaches the underside of the outer most layer and becomes round. It grow in size and then encysted. Now it is called oocyst.

D. Sporogony or cycle of Ross : The formation of sporozoites from oocyst is known as sporogony. The nucleus of oocyst divide (first division of meiosis) many times and form large number of nuclei. Each nucleus is surrounded by some cytoplasm and form sporoblasts. Sporoblasts develop into sporozoites. When oocyst ruptures, sporozoites are released into the blood of mosquito, form where, they reach salivary glands and ready to infect a new host.

V. Prepatent period : The time interval between entry of Plasmodium into blood of man (as sporozoites) and second entry of Plasmodium into blood (from liver) is known as prepatent period. It is about eight days for Plasmodium vivax.

VI. Incubation period : The time interval between the entry of Plasmodium into blood of man (as sporozoites) and first appearance of symptoms of malaria is known as incubation period. It is about 10 - 14 days for Plasmodium vivax.

VII. Pathogenic effects :

1. Plasmodium vivax causes benign tertian malaria

2. Malaria is characterised by bouts of fever and it can be divided into 3 phases :

      a. Cold phase : Chills, shivering, headache, giddiness.

      b. Hot phase : High temperature, rapid breathing, pulse rate increases.

     c. Sweating phase : Profuse sweating and then temperature becomes normal.

3. Spleenomegaly (enlargement of spleen) and anaemia are other symptoms.

4. Sometimes, some macro metacryptozoites enter a state of rest in liver cells. They are called hypnozoites. They may activate again and continue to produce metacryptozoites which caused malaria again. It is called relapse of malaria.

VIII. Treatment :

Age old drug for malaria is Quinine. It is an alkaloid extracted from bark of Cinchona officinalis.

IX. Prophylaxis :

To control malaria, mosquito are to be eradicated / controlled by 

1. Keeping the water in drainage canals in constant flow.

2. Spraying kerosine on stagnant water, which form a film on water (prevents respiration of larvae and purpose of mosqutoes).

3. Spraying insecticides like DDT, BCH etc., in the areas where mosquitoes develop (DDT = Dichloro Diphenyl Trichloroethane, BCH = Benzene Hexa Chloride).

4. Biological control :

    a. Growing larvivorous fish Gambusia in drainage canals.

    b. Growing insectivorous plants like Utricularia.

ASCARIS LUMBRICOIDES

I. Introduction :

1. Ascaris is a nematode and is commonly called common roundworm.

2. It is parasitic in the intestine of man.

3. It causes Ascariasis.

II. Structure / external features :

1. Ascaris is commonly known as common roundworm and is parasitic in the intestine of man.

2. It is unisexual and exhibit sexual dimorphism.

3. Ascaris is elongated, round and cylindrical worm with pointed end.

4. In the anterior end, mouth is present, which is surrounded by three lips.

5. In the anterior end, amphids (chemoreceptors)and in the posterior end, phasmids (glandulo sensory) are present.

6. Near the anterior end, on the ventral side, an excretory pore is present.

III. Life history :

1. Ascaris is parasitic in the intestine of man. It is unisexual and exhibits sexual dimorphism.

2. Ascaris completes its life cycle in a single type of host, that is man.

3. After copulation, female lays 2,00,000 eggs per day. Each egg is covered by a protein coat with rippled surface. Hence, they are called mamillated eggs.

4. The zygote in eggs develops into a larva called rhabditiform larva (1st stage). Hence the eggs are called embryonated eggs.

5. Embryonated eggs pass out through faeces. In soil, larva in egg undergoes first moulting and becomes second stage larva.

6. By contaminated food and water the eggs reach the intestine of man, where the shell is dissolved and larva is set free.

7. Larva performs journey through different organs of human body and reach the intestine again. This journey is called extra intestinal migration.
 

8. The route of extra intestinal migration is :

2nd stage Rhabditiform larva - Hepatic portal vein - Liver - Hepatic veins - Post caval vein - Heart - Pulmonary arteries - Alveoli of lungs - 2nd moulting - 3rd stage larva - 3rd moulting - 4th stage larva - Bronchus - Trachea - Glottis - Throat - Oesophagus - Stomach - Intestine.

9. In intestine, 4th stage larva undergoes 4th moulting and develops into male or female Ascaris.

IV. Pathogenic effects :

1. Ascaris causes Ascariasis.

2. In mild infection (less number of worms), there are no symptoms.

3. In heavy infection (more number of worms) - it causes abdominal pain, weakness, and stunted growth in children.

V. Prophylaxis :

1. Sanitary disposal of feces.
2. Washing of hands before eating.
3. Washing the fruits, vegetables etc., before consumption.
4. Protection of eatables from houseflies and other insects.

WUCHERERIA BANCROFTI

I. Introduction :

1. Wuchereria bancrofti is commonly known as filarial worm

2. It causes Filariasis in man.

3. Sir Patrick Manson discovered that, it was spread by female Culex (mosquito).

II. Structure / external features :

1. Wuchereria bancrofti is commonly called filarial worm and is parasitic in lymph vessels and lymph glands of man.

2. Wuchereria bancrofti is unisexual and exhibit sexual dimorphism.

3. Anteriorly both male and female have mouth. Lips are absent. Near the anterior end excretory pore is present.

III. Life cycle (Life history) :

1. Wuchereria bancrofti is commonly called filarial worm and is parasitic in lymph vessels and lymph glands of man.

2. Wuchereria bancrofti is unisexual and exhibit sexual dimorphism. It completes its life in two hosts, namely man (primary host), and female culex (Intermediate host).

3. After copulation, female releases microfilariae. Each microfilarian is covered by a loose sheath. (Wuchereria is described as ovoviviparous).

4. Microfilariae enter the blood of man and exhibit nocturnal periodicity. (Tendency of larva to appear in peripheral circulation only at night is known as nocturnal periodicity).

5. When a female Culex (mosquito) sucks the blood from a filaria patient microfilariae reach its crop, where, sheath is dissolved.

6. The larva penetrates through wall of crop and reaches the thoracis muscles of mosquito, where it becomes sausage shaped larva (1st stage larva). After two moultings, it becomes 3rd stage larva. Then it reaches the labium of mosquito.

7. When this mosquito bites a man, 3rd stage larva enter his blood and then lymph. In lymph vessels, they undergo 3rd and 4th moultings and became adult.

IV. Pathogenic effects :

1. Wuchereria bancrofti causes Filaria and elephentiasis.

2. In mild infection, filarial fever is caused. Headache, mental depression etc. are its symptoms.

3. In general, Wuchereria bancrofti causes inflamation of lymph vessels (lymphangitis) and inflamation of lymph glands (lymphadentis).

4. In heavy infection, Wuchereria bancrofti obstruct lymph flow, resulting in swelling of affected organ called lymphoedema. Gradually fibrous tissue develops. In severe infection, sweat glands degenerate. Hence the skin becomes dry and rough leading to elephantiasis.

V. Control:

1. Keeping the water in drainage canals in constant flow.

2. Spraying kerosine on stagnant water, which form a film on water (prevents respiration of larvae and purpose of mosquitoes)

3. Spraying insecticides like DDT, BCH etc., in the areas where mosquitoes develop (DDT = Dichloro Diphenyl Trichloroethane, BCH = Benzene Hexa Chloride).

4. Biological control :

      a. Growing larvivorous fish Gambusia in drainage canals.

      b. Growing insectivorous plants like Utricularia.

BACTERIAL DISEASES

 

VIRAL DISEASE

Common cold :

1. It is caused by rhino group of viruses. They infect the respiratory passages - not lungs.

2. Infected through inhaling droplets of infected person or sharing his utensils.

3. The main symptoms are nasal congestion, discharge from nose, tiredness etc.

4. Common cold lasts for 3 - 7 days.

FUNGAL DISEASE

Ringworm diseases :

1. Many fungi belonging to the genera Microsporum, Trichophyton, Epidermophyton causes ringworm disease in man. They grow in hot and moist areas of skin.

2. Spread through sharing towels, cloths, comb etc.

3. Appearance of dry, scaly, usually round leisons on skin accompained by severe itching in various parts of body - skin, nails, scalp etc.

Preventation and control of microbial diseases (prophylaxis)

1. For bacterial and viral diseases : These diseases can be prevented by vaccination in time

2. Due to the advancement of biotechnology, new and safe vaccines are availabe to prevent many diseases.

3. Use of antibiotics under medical supervision.

TOBACCO, DRUGS AND ALCOHOL ABUSE (TDA ABUSE)

I. Tobacco

1. Tobacco contains a number of chemicals including an alkaloid - nicotine.

2. It is used in the form of smoking, chewed as gutka or inhaled as snuff.

3. Due to smoking, more carbon monoxide is released. CO readily combines with haemoglobin and affect the transport of O2 by blood.

4. Nicotine stimulate the adrenal gland and thus the levels of adrenalin and nor adrenalin increases. Thus heart rate and blood pressure increase.

5. Smoking causes bronchitis, emphasema, coronary heart disease, ulcers in stomach and also increase the chances of cancer.

6. Chewing of tobacco (gutka) causes the cancer in mouth cavity.

II. Drugs :

     The chemical substances used in treatment control and prevention of diseases so as to increase ones physical and mental well being are called drugs. Several plants, flowers, fruits with hallucinogenic properties have been in use.

      When these are taken for a purpose other than the medicinal use or in excess that impairs physical and psychological functions, it is described as drug abuse. Most of these drugs are produced by flowering plants and few by fungi.

1. Opioids :

   a. These are obtained from a plant Papaver somniferum (Opium poppy plant). The opioids are morphine and heroin.
   b. Morphine is extracted from the dried latex of the unripe seed capsule (pod) of poppy plant. It is in the form of white or colourless crystalline powder. It is taken orally or by injection. Morphine is an effective sedative and pain killer. It is widely used in surgeries.

    c. Heroin is prepared by acetylation of morphine. It is white, odourless, bitter powder. Chemically, it is diacetyl morphine and is commonly called smack. It is taken by snarting (inhalation) or by injection. Heroin acts as depressant and slows down the body function.

2. Cannaboids :

   a. These are a group of chemicals obtained from the plant Cannabis sativa (Indian hemp plant). The flower tops, leaves and resign of this plant along with other substances are used to produce marjuana, hashish, ganja.

   b. These are taken by inhalation or by injection.

   c. These substances show their effect on cardio (heart) vascular system.

3. Coca alkaloid or Cocaine :

    a. Cocaine is a white, crystalline powder, produced from the leaves of Erythroxylum coca.

   b. Cocaine is commonly called coke or crack.

   c. It is usually taken by inhalation (shorting).

   d. It acts on nervous system and interferes with neurotransmittor called dopamine. Hence it causes euphoria and increased energy.

   e. Excess use of cocaine causes hallucinations.

4. Other plants :

a. Some other plants also produce hallucinogenic properties by their products. They are :

     i. Atropa belladonna  ii. Datura

5. Other drugs :

   a. Barbiturates - Sleeping pills

   b. Amphitamines - Causes sleeplessness

   c. Benzodiazepines - Tranquilizers

   d. Lysergic acid dethylamide - LSD

The above drugs are used as medicines to treat patients with mental illness like depression, insomnia etc.

III. Alcohol :

Ethyl alcohol is consumed in mixing at various properties in different substances or by producing fermentation of grapes, barley etc.

Addiction and dependance TDA abuse leads to addiction and dependance.

1. Addiction : It is a psychological attachement to certain such as euphoria. The most important thing one fails to realise is the inherent addictive nature of tobacco, drugs and alcohol. It should be clearly borne in mind that use of TDA even once, can be a forerunner to addiction. Thus they enter into a vicious circle from which they may not be able to get out.

2. Dependance : The tendency of the body to main feast a characteristic and unpleasant situation if regular dose of alcohol or drugs is suddenly discontinued is called dependance.

This withdrawl syndrome is characterised by anxiety, shakiness, nausea, sweating etc. He resumes normal, if he takes the regular dose of alcohol / drug. Dependance leads the patients to ignore all social norms.