CBSE Class 9 Science Why Do We Fall Ill Notes

WHY DO WE FALL ILL

HUMAN HEALTH & DISEASE 

Every living organism, may be plant or animal, requires food (nutrition) for its survival, maintenance, growth and development. Nutrition is required in specific amounts. Proper dietary habits lead to sound health and proper mental development. A person is said to be healthy if one: 

1. has no symptoms of disease and anxiety.
2. has no physical deformity.
3. has no mental problems and social tensions.
4. has no psychological tensions.
5. has all the body organs functioning properly.
6. has purposeful life.
7. has sufficient balanced diet.

The most widely accepted definition is (1947) World Health Organization’s description that states “Health is a state of physical, mental and social well being and not merely the absence of disease or infirmity”.

1.”Health” is a state of being well enough to function well physically, mentally, and socially.

2.”Disease”( disturbed ease) means being uncomfortable. One or more systems of the body will change, give rise to “Symptoms” ( Cough, loose motions, pus formation, headache, fever, breathlessness, vomiting, fits, unconsciousness, inflammation , swelling and general effects - a Doctor look for the basis of symptoms). Diseases are basically two types- Acute Disease & Chronic Disease

3. Acute Disease: The disease which lasts for only a short period of time is called Acute Disease Ex. Common Cold.

4.Chronic Disease: The disease which lasts for long period of time is called Chronic Disease Ex. Tuberculosis.

5. Causes of Diseases : Most of the diseases have many causes, rather than one single cause, like unclean water, nourishment, genetic differences, genetic abnormalities e.g. Based on the causes diseases are of two types: Non-Infectious Diseases and Infectious Diseases.

9. Principles of Treatment:

1. Antibiotics- many bacteria make a cell wall to protect themselves, the antibiotic (Penicillin) blocks the bacterial process that builds cell wall and blocks the biochemical pathways. Antibiotics do not work against viral infection Antiviral medicine is harder than making Antibacterial medicine because Virus has only few biochemical mechanisms of their own. Other medicines bring down fever, reduce pain or loose motions. We can take bed rest to conserve energy.

10. Principles of Prevention : Following three limitation are normally confronted while treating an infectious disease:

• Once someone has disease, their body functions are damaged and may never recover completely.

• Treatment will take time, which means that someone suffering from a disease is likely to be bedridden for some time even if we can give proper treatment.

• The person suffering from an infectious disease can serve as the source from where the infection may spread to other people.

General ways of preventing infectious disease :

• Air-borne – We can prevent exposure by providing living condition that are not overcrowded.

• Water-borne – prevent by providing safe drinking water. This is done by treating the water to kill any microbial contamination.

• Vector-borne – We can provide clean environment, which would not allow mosquito breeding.

11. Immunity: Even in cells there is repair mechanism called” Immunity”. Immune cells manage to kill off the infectious agent Smallpox disease is eliminated by developing memory cells for particular infection by mimics the microbes, called” Vaccine”. The basis of Immunization- if you had smallpox once, there was no chance of suffering from it again. Proper nutrition is essential to maintain body immunity. There are vaccines against tetanus, diphtheria, whooping cough, measles, polio and many other diseases.

12. Prevention of disease is better than cure. Hygiene is the basic key to maintain good health.

(a)Significance of Health :

Good health is “health body with a healthy mind and healthy attitude”. Good health increases our efficiency for doing work. The increased efficiency of a man due to good health contributes to his own progress, the progress of community and the progress of nation as a whole. Good health also make a man happy and cheerful. It allows a person to have the initiative for betterment. It makes living a joyful experience. It keep a person not only happy but also provides cheerfulness to the people. Good health is a condition for our purposeful existence in this world.

(b)Community and Personal Health :-

Health of a person depends upon his personal habits as well as his environment. One cannot remain healthy, if his environment is not clean. Good economic condition and job are needed for individual health, so that the person can have balanced diet and be healthy. Social equality and harmony in the community are also important to maintain individual’s health. If neighbors of a person are healthy, but possess no civic sense (i.e., they are in the habit of throwing garbage in an open space and there), files, mosquitoes, and other disease causing microorganisms will grow on the filth (foul matter) thrown by them. These microorganisms will infect nearby foodstuffs thereby spreading diseases. Thus, a person with his clean home, but unclean neighborhood will become sick. Similarly, the health of the whole community depends on the personal habits of various individuals who constitute the community. So community health can be defined as “All the personal health along with the environmental services for the improvement of health of community.” It comprises of all efforts for maintaining, protecting and improving the health of the people. WHO is doing remarkable work in community health.

(c)Difference Between Personal Health and Community Health :

The various activities involved in maintaining community health are as follows :

(i)Maintaining proper sanitation of the environment by :

1. Providing cleans and safe drinking water.
2. Providing good sewage and rain wate disposal systems (through underground pipes).
3. Proper garbage disposal.
4. Strict enforcement of antipollution laws, management of different types of environmental pollution by Central and State Control Boards.

(ii)Providing proper facilities for prevention and control of diseases such as :

1. Preventive vaccinations against a number of diseases like tuberculosis, diphtheria, whooping cough, tetanus, measles, hepatitis, polio, mumps, etc.
2. Spraying mosquito and germ killing chemicals (insecticides, pesticides etc.) at regular intervals.

(iii)Providing health education : to people about the mode of transmission of diseases and mechanism to control communicable diseases; importance of balanced diet; effects of bad habits Like alcoholism, addiction, etc.

(iv)Establishment of health care services: primary Health Centres, District Hospitals, Community Health Centres, Medical Colleges, All India institutes, Regional Hospitals, etc.

(v)Prevention of food adulteration.

(vi)Providing maternity and child care centres: so that mortality rate among children is reduced to a great extent. Provision of family planning advice and medical care to school going children.

WHAT IS A DISEASE?

A disease is a condition of the body or a part of it in which functions are disturbed. Disease may also be defined as morphological (structural), physiological (functional) or psychological disturbance in the body of body parts caused by external agencies which may be nonparasitic e.g. Deficiency of nutrients or may be parasitic e.g. Caused by vieuses, bacteria, fungi, etc. The term disease means dis-ease or discomfort or without ease. In short, it can be defined as “disease is disorder of body.”

(a) Distinction Between Healthy and Disease Free :

The term disease is used when we find a specific and particular cause for discomfort. We may not be knowing the main cause of the discomfort, but still we can use the term disease. A person may not be suffering from any disease but may be in poor health. This is particularly true for social and mental health, where we can be in poor health without there being a cause in the form of an actual disease. This is the reason why, when we think about health, we think about societies and communities. On the other hand, when we think about disease, we think about individual sufferers.

(b) Manifestation of Diseases :

There are number of tissue in the body, which aggregate together to form organ while a number of organs make up an organ system. Each organ system is performing a specific function. Each organ in the organ system also has a specific role to play. For example, in digestive, system, teeth help in mastication, stomach and intestine help in digestion, kidneys take part in excretion, bones and muscles hold the body parts together to form a musculoskeletal system that helps the body to move. When a person is suffering from any disease, then the physiological processes (functioning) or the appearance of organs in organ systems will change. These changes give rise to symptoms and signs of disease. symptoms are evidences of the patient’s feeling of being wrong. For example, headache, loose motions or a wound with pus are symptoms which may indicate the occurrence of discomfort. Headache may be due to examination stress, meningitis. The symptoms give an indication of the presence of a particular disease. The physicians will also get laboratory tests done to identify the disease further.

(c) Acute and Chronic Diseases :

The manifestations of diseases are different depending upon a number of factors. one of the factor is     duration of disease. on the basis of duration serious disease can be acute or chronic.

1. Acute disease : actual disease is the one which has a short duration by relatively severe course. most people with acute illness can expect to return to normal health. a case of cough and common cold is an example of an acute illness which lasts only for a few days. afterwards the patient becomes well without any bad effect, loss of weight, feeling of tiredness or short of breath.
2. Chronic disease : chronic disease is the one which is long lasting is usually slow to develop, often having a major effect on health, reducing the person’s ability to do work efficiently, learning in school o r doing work. the patient will also weight and feel tired all the time. examples of chronic diseases include tuberculosis, diabetes, asthma, hypertension, kidney disease, depression, etc. in these diseases we can develop a treatment plan to manage symptoms and prevent complications with the help of doctor.

(d) Causes of Diseases :

The various causes of diseases are

(i) Pathogens : They are disease causing organism like bacteria, viruses, fungi, protozoans, worms, etc. The pathogens are transferred to human being through air, contaminated food, water, soil and animals. Pathogens are primary cause of infectious diseases. However, every body does not suffer equally from infectious agents. There are some contributory causes that increase the proneness of an individual to catch the disease. 

(ii) Lack of nutrition diet: it is a second level cause of disease as absence of nutritious diet makes a person unhealthy. Unhealthy persons are susceptible to various diseases in comparison to healthier persons. Another contributory cause can be poor heredity which increases proneness of individual to a particular disease.

(iii) Lack of public services: Government should provide clean drinking water, good sewage disposal, proper garbage disposal, etc. If the public services are poor, there are more chances of contamination of food and water. They are the third level cause of disease. Poor people, due to poverty, live in unclean surroundings where even basic amenities are lacking, there are three level causes of diseases. These are infection with pathogen (1^st level), lack of nutrition diet and poor heredity (2^nd level) and lack of public services (3^rd level).

1. Congenital Diseases : Congenital diseases are present right from the birth. They are caused either due to genetic disorders or environmental factors during development or due to combination of these factors. These diseases pass on from generation to generation e.g. hemophilia, colour blindness, sickle cell anemia, Down ’s syndrome, albinism etc.
2. Acquired Diseases : These disease are acquired by an organism after birth and are not inheritable i.e., do not pass on from one generation to another. These are futher classified into categories; 

1. Communicable or infectious diseases: These diseases are caused by pathogens/infectious agents such as bacteria, viruses, fungi, protozoans, worms, etc. These diseases can spread from diseased person to healthy parson by means of air (droplet method), water, food, insects, physical contact, etc.,e.g. tuberculosis, malaria, diarrhea etc. 
2. Non-Communicable or Non-Infectious diseases: These diseases can’t be spread through infected persons to healthy persons. e.g. Scurvy

INFECTIOUS DISEASES

 (a)infectious Agents :

The various infectious agents are-bacteria, viruses, protozoans, helminthes (worms) and fungi.

1. Bacteria : They are unicellular, prokaryotic, microscopic organism. they reproduce very quickly. Some common diseases caused by bacteria are typhoid, cholera, tuberculosis, anthrax, diphtheria, tetanus, etc.
2. Viruses : They are submicroscopic organisms. They cannot reproduce by  themselves because they do not have their own metabolic machinery. They utilise the metabolic machinery of the host cell and multiply. The various diseases caused by viruses are common cold, influenza, dengue fever, AIDS , measles, mumps, polio, small pox, chicken pox, etc.
3. Protozoans : They are microscopic unicellular, eukaryotic organisms. The various diseases caused by protozoa are malaria (caused by Plasmodium), kala-azar (caused by Leishmania), etc.
4. Helminthes : Helminthes are multicellular worms which are mostly present in intestine. They cause taeniasis (caused by tapeworm), ascariasis (caused by worm), elephantiasis (caused by filariasis worm, hence also know as filariasis), etc.
5. Fungi : They are also multicellular, eukaryotic, heterotrophic organisms. They cause ring worm, athlete’s foot and other skin infections.

(b)Reason for Categorization of infectious Agents :

it is important to categories infectious agents because each group of organisms have some common traits and many similar biochemical pathways. As a result, a drug that blocks one of the biochemical pathways peculiar to one group would be effective against many members. Antibiotics are used for killing bacteria. They inhibit wall synthesis (e.g. penicillin), inhibit ribosome function (e.g. erythromycin, streptomycin) or DNA replication (e.g., ciprofloxacin). However, antibiotics are not effective against viruses. Protozoan infections are treated by different types of drugs. Antifungal drugs are useful against all types of fungi. Vermicides are used for overcoming worm infection.

(c)Means of Spread :

Infection diseases are called communicable diseases because they can spread   from affected persons to a healthy person. The means of communication or spread are different for different pathogens.

(i)Direct transmission. The pathogens are transmitted from an infected person to a healthy person directly without an intermediate agent. It occurs in the Following ways:

1. Contact with infected person ; Diseases like chicken pox, small pox, ring worm are spread by actual contact between infected person and a healthy person. Such diseases are called contagious diseases. The sexual contact is one of the closest physical contacts two people can have with each other. Diseases like syphilis, gonorrhea (both caused bybacteria0 and AIDS (caused by virus) are transmitted by sexual contact from one partner (infected) to the other (healthy).
2. Contact with Soil : The infectious agent of tetanus can enter the human body from soil through injuries.
3. Animal bites : The rabies virus is injected in the human body by the bite of rabied dog or monkey.
4. Transplacental Transmission : The diseases like AIDS, German measles and syphilis can also be transmitted from infected mother to the foetus though placenta.
5. Droplet infection : Pathogens spread by way of sneezing, coughing, spitting and taking as in common cold, influenza, diphtheria, tuberculosis, pneumonia etc.

(ii)indirect transmission : They pathogens of some diseases are carried through some intermediate agents. It occurs in the following ways :

1. Vectors : They are living organisms which spread their pathogens from an infected person to a healthy person. Usually, a part of life cycle of the pathogen is passed in the body of the vector. Some animals like housefly transfer the pathogen without taking them in their bodies. They are called carriers. Housefly is carrier of cholera, dysentery, typhoid, diarrhoea, etc. Female mosquitoes of many species are vectors of several diseases. They require blood meal in order to obtain nutrients for laying eggs. Female Anopheles spreads malaria while Culex spreads Filaria.
2. Through contaminated food and water. Cholera, hepatitis B, diarrhoea, ascariasis, etc. are some diseases which are transmitted through contaminated food and water.
3. Air borne diseases : Infectious agents can get transferred from infected person to healthy person through air, dust and droplets (emitted on sneezing, coughing or spitting), e.g., common cold, pneumonia, tuberculosis.
4. Fomite borne : Articles coming in contact with patients are a source of infection, e.g., door handles, taps, garments, currency, utensils, crockery.
5. Pathogenicity : Pathogens can harm their hosts in a number of ways such as by

(i)destruction of body tissues and

(ii)release of toxins or poisons which may be endotoxins. The entry of the pathogen in the body is called infection. After entering into the body, the pathogens multiply till they produce enough toxins to make the symptoms of the disease appear The interval between infection and appearance of first symptom of the disease is called incubation period.

MANIFEST ATION

(a)Organ or Tissue Specific Effects :

A microorganisms enters the body through different points like nose, mouth, sex organs etc. Which decides the organ or tissue that micro organism invades. At the same time the signs and symptoms of an infectious diseases also depends upon the tissue being invaded. e.g. If bacteria causing tuberculosis enters through nose, it invades respiratory passage and lungs and its symptoms are cough and breathlessness, but in some cases they may infect other organs also.

 Common Effects :

This category includes effects like inflammation in which swelling, reddening and pain in infected area and increase in body temperature occurs. These effects arise due to the active involvement of immune system to provide defence to body by producing some specific chemicals from WBC’s, against that microbe and this is not confined to a particular organ or tissue but seen in whole body.

(b)Severity of Effects :

It directly depends upon the no. of microorganisms. if microbes are smaller in number their effects are minor and can be overcame by our immune system in a lesser time but if the number of micro organisms inside the body is very high the effects are more severe and long lasting.

TREATMENT OF INFECTIOUS DISEASES

The basic concept behind the treatment process is to target the biochemical pathways occurring inside an organism for this certain drugs like antibiotics are prepared to after or stop the biochemical reaction of the microbes at some stage to stop them to produce infections, toxins or to kill them or to check their further growth and multiplication. There are two ways in which these diseases are treated they are :

1. Reducing the symptoms : By this, infection is not cured but some of the symptoms like fever, pain, aches, inflammation can be reduced to make the patient full comfortable. this is done by medicines like pain killers etc.
2. killing infectious agents : this can be done by targeting the biochemical pathways of infectious agents using specific drugs.

(a)Drugs :

chemical compounds that targets a particular reaction among the chain of reactions involved in the biochemical pathway by reacting with some substrates of that reaction and resulting in an undesirable product so that reaction cannot proceed further and stop infections and can kill the microbes. they do not affect human cells.

(b)Antibiotics :

Antibiotic are chemicals that kill or stop the growth of certain kinds of microbes. They help our body to fight against diseases. The development of antibiotics began with the discovery of penicillin by sir Alexander Flemming in 1928. Flemming noticed that an agar plate inoculated with bacterium Staphylococcus aureus had become contaminated with a mould. He future noticed the presence of a clear zone in the agar plate in which breakdown of the bacterial cells had occurred. Detailed studies led to the isolation of an inhibitory substance from the mould. As the mould was identified as Pencillium, Flemming called the antibiotic penicillin. Soon other antibiotics were isolated. Some well know antibiotics are streptomycin, gramicidin and tetracycline. the antibiotics have been obtained from either bacteria or fungi.

1. These are the drugs specific for curing bacterial diseases. they either ceases the formation of cell wall or interferes in their metabolic activities like production of proteins. This kills or stops the growth of bacteria.
2. Antibiotics are not effective for viruses or it is difficult to make antiviral diseases because Viruses are acellular entities which only have nucleic acid and protein but lacks cytoplasm, cell wall and cell organelles they do not have their own metabolic system but they use the host’s metabolic machinery to grow & multiply so drugs are not effective for them. 

PREVENTION OF INFECTIOUS DISEASES 

Preventive measures are categorized into two distinct groups:

(a)General preventive measures :

It includes:

1. Safe drinking water :Drinking water should be filtered to remove suspended particles And boiled, ozonized and treated with chlorine before drinking to avoid water borne diseases like typhoid, cholera, hepatitis etc.
2. Proper disposal of waste: Garbage should not be dumped here and there rather it should be thrown in covered garbage cans and burnt or buried for disposal. Sewage carrying drains should be covered for proper treatment of diseases of stomach and intestine.
3. Control of vectors : Growth and breeding of animals like mosquitoes, rats, flies, Cockroaches should be controlled, by keeping surrounding clean, spraying insecticides, removing stagnant water from populated areas.
4. Strong immune system: It helps to defence our body against invading microbes and can be made strong by proper diet and nourishment.

(a)Immune system: our body possesses a special type of defence mechanism called immune it provides resistance against disease causing microorganisms. immunity is the ability of the body to resist the infections. Two specific types of cells are present in our body that provide immunity.

(b)They are WBC (leucocytes) in blood and lymphocytes in lymph when any foreign body attacks our body these cells are released to all parts of body, they isolate, engulf, kill and digest the infectious agents and thus defend our body against any type of infection.

(b)Specific Preventive Measures :

This can be done two ways :

1. Immunization: Stimulating the body to produce antibodies by artificial means. our Immune system is misleader, to develop a memory against particular infection by introducing something into the body that mimics the specific microbe. Specific prevention is provided by the immune system. it produces specific molecules called antibodies that fight against the invading microorganism or their products called antigens. Antibodies are pertinacious molecules made by WBC’s and lymphocytes to fight against foreign bodies or other harmful chemicals. Antigens are also proteins or other harmful chemicals that are present on surface of invaders. Whenever there occurs attack of a foreign body specific Antibodies are produced corresponding to that antigen and an antigen antibody reaction occurs. it either engulfs and phagocyte it or makes it harmless and then makes them unable to grow and multiply. Besides  this  immune system also possesses memory. once antibodies are produced they remain in the body and at the second infection they recognize the antigens and show a much faster response. 
2. Vaccination: A vaccine is a suspension of disease- producing micro-organisms which is Modified by killing or wreaking  (attenuated) so that the suspension will not cause disease. Rather it stimulates the formation of antibodies upon inoculation. The antibodies remain in blood for long and when the germs of a particular disease enter the body, the antibodies destroy them. This is the basis of immunization. 

Some common vaccines :

1. DPT vaccine, for protection against diphtheria, whooping cough and tetanus
2. BCG vaccine, for protection against tuberculosis
3. Polio (OPV) vaccine ÝTyphoid vaccine  ÝMeasles vaccine ÝTT vaccine, against tetanus

1.  Pulse polio programme: The aim of this programme it to eradicate polio from our country. it was first held in our country in December, 1995. Polio vaccine called Oral polio vaccine (OPV) is given to children orally (through the mouth), as per the National Immunisation Schedule (NIS),NON

INFEOTIOUS / NON COMMUNICABLE DISEASES

These diseases which remain confined to a person. they are neither present at birth nor spread from one person to another. The diseases are caused due to some specific factors. They may be caused due to improper functioning of an organ (short sighted, hypertension, arthritis), hormonal imbalance (diabetes, dwarfism), allergy, cancer, inadequate diet (anaemia, goitre), etc.

1. These diseases are of following types :
2. Deficiency diseases : caused due to lack of some nutrient materials in our body like Vitamins, minerals, protein etc.
3. Degenerative diseases : caused due to ageing or malfunctioning of any organ or part of Body.
4. Allergies : caused due to hypersensitivity of an organism to certain type of material like Pollen grains, dust etc.
5. Uncontrolled growth of cells: this can cause cancer and tumor.
6. Mental disorders
7. Occupational diseases
8. Addiction: caused due to excessive intake of drugs tobacco, alcohol etc. 

COMMUNICABLE DISEASES

NON COMMUNICABLE DISEASES

Chapter: Why do we fall ill

Chapter Notes

Key learnings:

1) Our body’s well-being is dependent on the proper functioning of its cells and tissues.

2) All our body parts and activities are greatly interconnected. Hence dysfunction of any body part will affect the entire body.

3) When we are healthy, we are able to perform our physical, mental and social functions well.

4) Our physical and social environment plays an important role in maintaining good health.

5) In addition to personal hygiene, public cleanliness should also be maintained for ensuring that we remain healthy.

6) Many other factors like financial conditions, availability of nutritious food and social equality also influence the health of an individual.

7) A person suffering from a disease is in a state of discomfort.

8) Being in poor health is different from being diseased.

9) Symptoms and signs of the disease appear as a result of dysfunction of the affected body parts. These help to identify the disease that a person is suffering from.

10) Depending on their duration, diseases may be classified as acute or chronic.

11) Acute diseases last for a short time and do not cause major health effects. E.g. Common cold. On the other hand chronic diseases persist for a long time and hence cause prolonged ill health. E.g. TB of lungs. D

12) Causes of diseases may be immediate (first level cause) or contributory. For e.g. – The immediate cause of a person suffering from diarrhoea is the causative agent. The contributory causes could be i) lack of good nourishment or genetic difference (second level cause), ii) poverty or lack of public services (third level cause)

13) Diseases may be infectious or non-infectious. Infectious diseases are caused by microbes or other infectious agents (e.g. Malaria) whereas non-infectious diseases have internal, non-infectious causes (e.g. High blood pressure).

14) The infectious agents may be viruses

15) The type of treatment of a disease depends on the category of the infectious agent.

16) Organisms belonging to one category will share several important life processes, which will be different from those of organisms belonging to other categories.

17) Drugs working by interfering with life processes of one category of organisms will not be effective against members of another category. E.g. Antibiotics act against bacteria, but not viruses, since viruses do not share bacterial pathways.

18) Penicillin interferes with bacterial cell wall production, thus killing the bacteria. Due to lack of cell walls, penicillin does not affect human cells.

19) Many infectious diseases are called ‘communicable diseases’ since they can spread from one person to another.

20) Communicable diseases can spread through air, water, food, sexual contact or vectors.

21) The droplets released during coughing or sneezing of an infected person causes the spread of air-borne diseases like common cold, pneumonia, tuberculosis etc.

22) Air-borne diseases spread quickly in overcrowded and poorly ventilated living conditions.

23) Water-borne diseases like cholera spread when drinking water gets contaminated with the infectious agents.

24) Sexual contact causes the spread of diseases like AIDS and syphilis from the infected person to a healthy one. AIDS virus can also spread through blood transfusions, use of infected needles or during pregnancy and breast-feeding by an infected mother.

25) Vectors are intermediate animals causing the spread of disease causing agents from an infected person to a healthy person. For example – Female mosquitoes transmit many diseases like malaria when they feed on the blood of animals and humans.

26) On entering the body, the infectious agents reach their specific target organs. In certain cases the target organ is related to their point of entry. For e.g. – Typhoid causing bacteria enter through mouth and reside in gut lining.

27) In other instances, the target organ of the microbe has no relation to their point of entry. For e.g. HIV enters through the sexual organs but spreads to all the lymph nodes.

28) The symptoms of a disease depend on the target organ infected by the microbe. For e.g. cough and breathing problems are seen when lungs are infected. So based on the signs and symptoms of a disease, we can get an idea of the target organ of the microbe.

29) During infection, the body’s activated immune system sends specialized cells to destroy the microbes, causing inflammation, with associated local effects.

30) The AIDS causing virus destroys the functioning of the immune system, due to which the body becomes unable to fight even minor infections. Ultimately the patient succumbs to such infections.

31) The severity of a disease is directly proportional to the number of infectious agents present in body.

32) An infectious disease can be treated in 2 ways:

i) Reduce the symptoms of the disease by providing treatment

ii) Kill the infectious agent causing the disease.

33) Medicines used in killing an infectious agent aim to disrupt some pathway of a vital life function peculiar to that group of organisms. These pathways are not present in other microbial groups or in humans.

34) On entering human cells, viruses use our cellular machinery for carrying out all their life processes. There are very few virus-specific biochemical pathways that can be targeted to produce anti-viral drugs.

35) The approach of treatment of an infectious disease has three drawbacks:

i) Recovery of the patient may not be complete in certain case

ii) Treatment requires time; hence the patient suffers from the disease and may be bedridden.

iii) The patient serves as the source of spread of infection to others.

36) It is desirable to prevent a disease than to treat it completely.

37) There are general and specific ways of preventing diseases.

38) Infectious diseases can be generally prevented by public health hygiene methods, which aim to reduce exposure to infectious microbes. Public hygiene measures include providing safe drinking water, clean environments and adequately spacious conditions for living.

39) Another general method of preventing infectious diseases requires the availability of sufficient and balanced diet for the proper functioning of the immune system. The immune system ensures that we do not develop a disease each time we are exposed to an infectious agent, by destroying the agent before it multiplies greatly.

40) During smallpox epidemics, it was noted that people who survived after suffering form smallpox, did not get infected with it again. Such observations led to the birth of immunization, which is a specific method of preventing infectious diseases.

41) The principle of immunization is based on the memory of the immune system on encountering an infectious agent. On subsequent encounters with the same or related microbe, the response of the immune system is multiplied greatly, leading to quick elimination of the infection.

42) During immunization, a vaccine (containing weakened or killed pathogen or a specific part of the pathogen) is introduced into the body to fool the immune system into remembering a particular infection. Hence the body does not suffer even on further exposures to that pathogen or its close relatives.

43) Nowadays, vaccines preventing many infectious diseases like tetanus, polio and measles are used extensively especially in child health immunization programmes.

44) Everyone in the community should have access to public hygiene and immunization for effective prevention of infectious diseases.

1) Health – A state of being well enough to function well physically, mentally and socially.

2) Disease - Lack of a feeling of ease due to impairment of health or a condition of abnormal functioning.

3) Acute disease – Disease lasting for a short period of time.

4) Chronic disease – Disease lasting for a long time, even as much as a lifetime.

5) Vectors – The intermediate animals causing the spread of infecting agents from a sick person to another potential host.

6) Infectious diseases – Disease where microbes are the immediate causes.

7) Communicable disease - A disease capable of being transmitted from an infected person to a healthy person.

8) Immediate cause of disease - The cause which immediately kindles a disease into action, when there occurs a predisposition towards it.

9) Contributary cause of disease – A cause or condition whose presence makes it more probable that a particular disorder will occur, but that cause is neither necessary nor sufficient for the occurrence of the disease.

10) Antibiotics - A substance produced by bacteria or fungi that destroys or prevents the growth of bacteria and other microorganisms.

11) Immunisation - The process of inducing immunity by administering a vaccine to allow the immune system to prevent infection or illness when it subsequently encounters the infectious agent.

12) Vaccine – A preparation of a weakened or killed pathogen or of a portion of the pathogen's structure that upon administration stimulates the immune system to fight against the pathogen but is incapable of causing severe infection.

13) Pathogen - Any disease-producing agent such as a virus or bacterium or other microorganism.