The chapter Why Do We Fall Ill covers diseases, pathogens, immunity, and health. NCERT solutions for Class 9 Science provide clear explanations of types of diseases and preventive measures. Our class 9 notes summarize infections, immunity, and vaccination methods in a simple and exam-friendly format. Class 9 science tuition offers detailed discussions on immunity, microbes, and lifestyle diseases, making biology engaging and easier to retain. Personalized Class 9 tuitions help students remember important points, diagrams, and health concepts for scoring better in exams. Understanding this chapter builds a strong foundation for biology and health sciences in higher studies.
1. Health
The World Health Organization (WHO) in 1948 defined health as follows:
Health is a state of complete physical, mental and social well-being and not merely absence of disease or infirmity.
Therefore, WHO recognizes three dimensions of health:
Three Dimensions of Health
(i) Physical well-being: It refers to physical fitness of an individual at every stage of life. It implies 'perfect functioning' of all the body parts i.e., various organs and organ-systems.
(ii) Mental and emotional well-being: It implies harmony between the individual and its environment. An individual should be mentally strong and able to handle the emotions.
(iii) Social well-being: Human beings are social i.e. they live in groups, regularly interacting with each other. Social health implies that every person living in a society should possess basic requirements of life i.e. a clean place of living, good earning, good food, a happy family, cooperative interaction with neighbours and friends, leading a happy and cheerful life.
1.1 Personal and Community Health
The health of an individual and that of the community are closely linked. For good health, the actions of an individual are as important as those of the other members of his community, the civic services, the industries around him, etc. The basic conditions necessary for the health of an individual and a community are:
(i) Balanced diet: A balanced diet is the first condition necessary for good health. A balanced diet is the one that provides all the nutrients required by the body in correct proportions. The nutrients required by our body are proteins, carbohydrates, fats, vitamins and minerals. When our diet lacks one or more of these nutrients, we get deficiency diseases. For example, if our diet lacks the mineral iron, we may get a disease called anaemia.
(ii) Personal hygiene: Personal hygiene is extremely important for good health. We should bathe regularly and wear clean clothes.
(iii) Clean surroundings: Our health depends on the cleanliness of our surroundings. Flies and mosquitoes carry germs that cause diseases. People fall ill quite often if the area in which they live or work has uncleaned garbage, pools of stagnant water or open drains.
(iv) Clean food and water: Disease-causing organisms and chemicals can easily enter our bodies through the food we eat and the water we drink. Fruits, vegetables and food grains may be coated with pesticides and they may carry germs, insects and eggs of worms. Therefore, these should be thoroughly washed before cooking or eating. Cooked food should be kept in clean, covered utensils. Water carries a number of disease-causing organisms. Therefore, it is best to treat water to make it safe for drinking.
(v) Clean air: Clean air is a basic requirement for good health. Breathing polluted air causes respiratory diseases such as asthma and bronchitis.
(vi) Exercise and relaxation: Regular exercise keeps us fit. People who exercise regularly are less prone to heart attacks and strokes. Exercise keeps body weight under control. Relaxation and sleep are equally important for physical and mental health. They help in resting and recharging our bodies. They also reduce stress. We should have regular sleeping hours. We can relax by listening to music, strolling in a park, playing a game, reading and so on.
(vii) No addictions: Generally, when we talk about addiction, we mean the habit of smoking, drinking or taking drugs. An addiction causes health problems. Drinking alcohol reduces mental and physical alertness, and excessive use of alcohol may affect the nervous system and damage the liver. Smoking causes respiratory and heart diseases and cancer. Chewing tobacco can cause oral cancer and dental problems.
(viii) Good economic conditions: People who are poor cannot afford many of the things required for good health. For example, they may not be able to afford a balanced diet. Many of them live in overcrowded and unhygienic areas. They may also not have access to clean drinking water.
2. Disease
A disease is a disturbed state of body or mind. The term 'disease' means without ease or being uncomfortable. The disease can be in any part of the body organ. So, disease is defined as:
A condition of the body or some part or organ of the body in which its functions are disturbed or deranged.
2.1 Distinctions between 'Healthy and Diease Free'
The terms 'disease-free' and 'healthy' do not convey the same meaning. A person is considered 'disease free' if he does not have any discomfort or derangement of the functioning of the body. However, a 'disease free' person can be having a good health or poor health. If a person is not suffering from a disease, it does not mean he is healthy. For an individual, the term 'healthy' conveys different meanings under different situations. For instance, for a dancer, healthy may mean he is able to stretch his body into difficult but graceful positions.
Therefore, a person may have a poor health without actually suffering from a particular disease.
Difference between 'Disease-free' and 'Healthy'
| Disease-free | Healthy |
|---|---|
| 1. It is a state of absence of any discomfort or derangement of the functioning of the body. | 1. It is a state of physical, mental and social well being. |
| 2. It refers to an individual. | 2. It refers not only to the individual but also to its social and community environment. |
| 3. A 'disease-free' individual may have good health or poor health. | 3. A 'healthy' individual is one who is able to perform normally under given situation. |
2.2 What does Diease look like?
A disease is the malfunctioning of some body part. Whenever there is any malfunctioning of any organ or body part, it manifests itself in the form of certain symptoms and signs. The reason for this is that each and every body part and organ of our body has specific functions and whenever anything goes wrong, it will show in some way.
2.3 Diffrence between Symptoms and signs of a disease
Symptoms: It refers to the general visible changes and feelings when we feel there is something wrong. Symptoms of a number of diseases may look alike, hence symptoms do not indicate a specific disease. For example headache, loose motions, fever etc.
The symptom like headache could be due to stress, change in eyesight number, viral disease etc. There may be common symptoms of a number of diseases.
Signs: Signs of a disease means definite indications of a particular disease. On the basis of symptoms, a physician looks for specific signs of a disease. Physicians recommend specific tests on the basis of signs to identify the disease correctly.
2.4 Types of Dieases
Human diseases are classified in different ways.
Depending upon the duration for which a disease persists, diseases are grouped into two categories:
(i) Acute diseases: These diseases last for only short period of time and are severe. The acute diseases do not cause long term bad effects on our health. Examples of acute diseases are cold, cough, typhoid, cholera etc.
(ii) Chronic diseases: These diseases last for a long time, even as much as a lifetime. The chronic diseases have drastic long term effects on patient's health. Examples of chronic diseases are diabetes, tuberculosis, elephantiasis, cardio-vascular diseases, arthritis, cancer etc.
Differences between Acute and Chronic diseases
| Acute Diseases | Chronic Diseases |
|---|---|
| 1. These last for only short period of time. | 1. These last for a long time, even as much as a lifetime. |
| 2. These do not cause long term bad effects on human health. | 2. These cause drastic long term effects on human health. |
| 3. Examples include cold, cough, typhoid, cholera etc. | 3. Examples include elephantiasis, cardio-vascular diseases, tuberculosis, diabetes, arthritis, cancer etc. |
2.4.1 Chronic disease and poor health
Long duration of a chronic disease and prolonged use of medicines during the treatment have following effects on the body:
(i) Poor functioning of some vital organs of the body: Since chronic diseases last for a long time, they generally cause damage to the vital organs of the body, like heart, lungs or kidneys. For example, lungs get severely affected during tuberculosis.
(ii) Drastic bad effects on health: Not only vital organs but general health of the body deteriorates during a chronic disease. The person may lose weight, feel fatigue and feel tired.
(iii) Prolonged general poor health: It takes long to recover from a chronic disease and so in this long process, the person has prolonged general poor health. It is also related to malfunctioning of the vital organs of the body.
(iv) Drastic long-term effects: Apart from general poor health, chronic diseases also have many other economic and financial implications which may have drastic long term effect on the person.
2.4.2 Congenital and acquired diseases
On the basis whether the diseases occur since birth or after birth, these may be classified into two types:
(i) Congenital diseases: These diseases are those which are present since birth. They are caused due to genetic abnormality or due to metabolic disorders or malfunctioning of any organ. They are permanent, generally not easily curable and may be inherited by the children. For example, haemophilia, colour blindness, sickle-cell anaemia, Down's syndrome, etc.
(ii) Acquired diseases: These diseases are those which develop after birth. Acquired diseases can be broadly classified into two types:
- (a) Communicable or infectious diseases.
- (b) Non-communicable or non infectious diseases.
2.5 Cause of Dieases
When we think about the causes of diseases, we must remember that there are many levels of such causes. Let us study these causes at the following levels:
2.5.1 First Level
(i) It refers to the immediate cause i.e. to the agent that causes the disease. Viruses, bacteria, protozoans, and worms are the immediate causes.
For example, when a child suffers from loose motions, the immediate cause could be a virus or bacteria.
2.5.2 Second Level
(i) It deals with the reason of infection for the immediate cause like:
- (a) Where did the viruses come from?
- (b) Is it due to unclean drinking water?
- (c) Why did the other children not get it?
- (d) Is it due to poor health of the body?
- (e) Is it due to some genetic difference that makes a child more likely to get the disease when exposed to the virus or bacteria?
(ii) It refers to the contributory causes like lack of good nourishment, genetic difference, etc.
2.5.3 Third Level
(i) This also refers to the contributory causes like:
- (a) Poverty i.e., poor economic conditions.
- (b) Lack of public health services that a person is exposed to.
So, poverty or lack of public health services become third level causes. Therefore, all diseases have immediate causes and contributory causes and most of the diseases have more than a single cause.
2.6 Infections and Non-infections Disease
The diseases could be broadly classified into two types depending on the infectious and non-infectious causes.
Diseases
Infectious diseases (communicable diseases)
- Diseases that can be spread from diseased person to healthy person.
- These diseases can be transmitted from one person to another by means of air, water, food, contact and insects.
- These diseases are caused by infectious agents, mostly microorganisms like bacteria, viruses, protozoans and fungi.
Examples: Viral diseases like influenza, hepatitis etc. Bacterial diseases like tuberculosis, cholera etc.
Non-infectious diseases (non-communicable diseases)
- Diseases that cannot be spread from diseased person to healthy person. These diseases remain confined to the person only.
- These diseases do not get transmitted through air, water, food and contact.
- These diseases are due to many causes, but they are not external causes like microbes. Instead, these are mostly internal, non-infectious causes like malfunctioning of body organs, allergies, cancer or nutritional disorders.
Examples: High blood pressure, anaemia, cancer, scurvy, kwashiorkar, marasmus, goiter, beri-beri etc.
2.7 Infections Agents
As we have read above, infectious diseases can be passed from one person to another and are caused by organisms called infectious agents.
The infectious agents could be single-celled microorganisms like viruses, bacteria and protozoans or multicellular organisms like worms. The various infectious agents are:
(i) Virus (ii) Bacteria (iii) Fungi (iv) Protozoa (v) Worm
Some common diseases caused by these infectious agents:
| Infectious Agents | Diseases |
|---|---|
| I. Virus | 1. Common cold<br>2. Influenza<br>3. Dengue<br>4. Poliomyelitis<br>5. Hepatitis-B<br>6. AIDS (Acquired Immuno Deficiency Syndrome)<br>7. Chicken pox<br>8. Measles<br>9. Mumps |
| II. Bacteria | 1. Typhoid<br>2. Cholera<br>3. Tuberculosis<br>4. Anthrax<br>5. Tetanus<br>6. Food poisoning |
| III. Fungi | 1. Athlete's foot<br>2. Aspergillosis<br>3. Candidiasis |
| IV. Protozoan | 1. Malaria<br>2. Kala-azar<br>3. Amoebic dysentery<br>4. Sleeping sickness |
| V. Worm | 1. Intestinal worm infections<br>2. Elephantiasis |
Peptic Ulcer
Peptic Ulcer: Earlier, it was thought that peptic ulcer, which cause acidity-related pain and bleeding in the stomach and duodenum, were because of lifestyle reasons.
Then two Australians, Robin Warren and Barry Marshall, found out that small curved bacterium, Helicobacter pylori, was responsible for peptic ulcers. Their studies proved that peptic ulcers could be cured when the bacteria were killed off from the stomach by giving antibiotics. They received Nobel Prize for their achievement.
2.7.1 What is the need to know the categories of infectious agents?
It is important to know the category of the infectious agent as that helps in deciding the kind of treatment to be used to prevent or cure the disease.
Some important facts about infectious agents are:
(i) The viruses live inside the host cells whereas bacteria very rarely do.
(ii) Viruses, bacteria and fungi multiply very quickly but comparatively the worms multiply slowly.
(iii) All bacteria are closely related to each other but not to the viruses.
(iv) Many important life processes are similar in the bacteria but not in viruses.
2.7.2 Why do antibiotics work against bacteria but not against viruses?
(i) Antibiotics and bacteria: We often take antibiotics when suffering from bacterial infections. Antibiotics work in the following way:
Antibiotics commonly block important biochemical pathways of bacteria. For example, many bacteria make a cell-wall to protect them. The antibiotic blocks the biochemical pathways that build the cell wall. Hence, the bacteria are unable to make the cell wall and die away.
(ii) Antibiotics and Viruses: Antibiotics are not effective against viruses.
Viruses do not have the metabolic pathways as found in bacteria. Instead, viruses make use of the machinery and pathways of the host cell. Hence, antibiotics do not work against viral infections. For example, common cold is due to the viral infection. Now, if we take antibiotics during the viral cold, it is of no help. However if the bacterial infection also sets in along with the cold, the antibiotic will work only against the bacterial part of infection, not the viral infection.
Note: Since the human cells do not have a cell-wall, antibiotics do not affect human cells and affect the bacterial cells only.
2.8 Means of Spread
Since the infectious diseases can spread from a diseased person to a healthy person, they are also called as communicable diseases. The various means of spread are:
(i) Direct Contact: An infectious disease can spread by direct contact between the infected and the healthy person. It includes diseases like chicken pox, common cold etc. Direct contact or contact with the discharge from the sores, skin or infectious membranes cause the infection.
(ii) By Air: For the diseases that spread through air, tiny droplets are sufficient to cause an infection. The little droplets get thrown into air when an infected person sneezes, coughs or spits. They are laden with bacteria and viruses. By inhaling this air containing the droplets, one gets the infection. Example, like common cold, pneumonia, tuberculosis and influenza.
(iii) By Water: The diseases through water spread, when the excreta of an infected person suffering from an infectious disease like cholera, gets mixed with the drinking water. When people drink this contaminated water, they also get infected. Diseases of alimentary canal like typhoid, and cholera get transmitted this way.
(iv) Through contamination of food: The bacteria that cause infection of alimentary canal like dysentery, typhoid and Salmonella food poisoning are passed out in the faeces of infected person. They reach the food through unwashed hands, and enter the body through mouth.
(v) Sexually transmitted diseases: Syphillis, gonorrhoea and AIDS are sexually transmitted diseases (STD). They spread by sexual contact with the infected person. They do not spread by casual physical contact like handshake, hugs or sports like wrestling or by any other way in which we touch each other socially. For example, AIDS is a sexually transmitted disease. It can also spread through blood to blood contact (blood transfusion or using the same infected needle) with the infected person. If a mother has the disease, the infected mother can pass it to her baby during pregnancy or through breast feeding.
(vi) By Vector: Many times the transmission of the infecting agent to a healthy person is not direct but through an intermediary agent, called the vector or carriers.
- The common vectors are insects like cockroaches, houseflies, mosquitoes etc.
- Malaria spreads through female Anopheles mosquito. The female Anopheles carries the malarial parasite in its salivary glands which gets transferred during mosquito bite.
- In many species of mosquitoes, the females feed on the blood of warm-blooded animals. In this process, they transfer the diseases from one person to another.
(vii) By bite of an animal: Rabies or hydrophobia in man is caused by a virus that is transmitted through a dog bite. The virus is present in the saliva of the rabid animal and enters the healthy person through the wound.
Important Note: The infectious diseases can be transmitted by various means and if not controlled, can take an epidemic form.
2.9 Organ Specific and Tissues Specific Manifestations
The disease-causing microbes enter the body through different means like: (a) Nose, (b) Mouth, (c) Sexual contact, (d) Skin, (e) Blood etc.
Since these microbes enter the body through different parts, they reach different organs and tissues of the body where they cause infection.
Their point of entry in the body is directly related to the organ or tissue they infect. This can be understood by studying some examples given in the table.
| Point of entry of microbe in the body | Organ the microbe infects | Examples of disease caused |
|---|---|---|
| 1. Through nose from air | • Likely to go to lungs | • Bacteria causing tuberculosis enter through nose by the droplet infection. |
| 2. Through mouth (by food or water) | • Likely to go to alimentary canal or gut | • Bacteria causing typhoid infect the gut-lining. |
| • Some can go to liver also | • Jaundice is a water-borne disease, caused by a virus that infects the liver. | |
| 3. Through sexual contact | • Likely to go to sexual organs | • AIDS is caused by HIV that comes into the body through sexual contact. It then spreads to lymph nodes of the body and weakens the body immunity. |
| 4. Through mosquito bite (from skin to blood) | • Reaches blood directly | • Malaria is caused by malarial parasite Plasmodium that enters the blood through mosquito bite (female Anopheles mosquito). From there, it enters the red blood cells and liver cells and infects them.<br>• Japanese encephalitis or brain fever is caused by a virus that also enters through the mosquito bite. It then goes on to infect the brain cells. |
2.10 Tisseues Specific Manifestations
The signs and symptoms of the disease depend on the tissue or the organ, the infectious agent or microbe targets.
| Organ or tissue targeted | Tissue-specific manifestations/Symptoms |
|---|---|
| 1. Lungs | 1. Cough and breathlessness |
| 2. Liver | 2. Jaundice |
| 3. Brain | 3. Headache, vomiting, fits or unconsciousness |
| 4. Intestine | 4. Diarrhoea and loose motions |
2.11 Common Effects of Diseases
(i) Along with tissue-specific manifestations of the diseases, there are some common effects of the diseases too. Since these effects occur in many diseases, they do not point towards any specific disease, for example fever and headache are common to a number of diseases.
(ii) Common effects are due to the fact that the body's immune system gets activated, the moment an infection occurs in the body.
(iii) The activated immune system involves a number of cells which are sent to the affected organ to kill the disease causing microbes. This recruitment process of the active immune system is called inflammation.
(iv) This process of inflammation of the affected organ leads to both local and general effects.
- Local effects are swelling and pain of the infected area.
- General effect is fever (rise in temperature of the whole body).
2.12 Immune System and AIDS
Acquired Immuno Deficiency Syndrome commonly called AIDS is a fatal disease. It was first detected in USA in June 1981.
2.12.1 Cause
It is caused by a retrovirus HIV (human immuno deficiency virus). This virus attacks the white blood cells in the human blood and therefore weakens the human body's immunity or self-defence mechanism.
2.12.2 Modes of transmission
AIDS is transmitted only by the contact of infected cells containing blood of a patient with the blood of a healthy person. It spreads through:
(i) Unprotected sexual intercourse with an infected partner. (ii) Use of contaminated needles and syringes to inject drugs or vaccines. (iii) Use of contaminated razors for shaving. (iv) Use of contaminated needles for boring pinnae, (v) Transfusion of infected blood or blood products. (vi) Organ transplant. (vii) Artificial insemination. (viii) Mother to baby due to rupturing of blood vessels at the time of birth.
2.12.3 Symptoms
Since AIDS virus destroys the protective immune system of the body, the body can no longer fight back many minor infections that we encounter every day. The person becomes susceptible to other infections and diseases like pneumonia, tuberculosis and certain cancers. For example, the person suffering from AIDS cannot fight back common cold, and it may become pneumonia. A minor gut infection can lead to diarrhoea. The person may have persistent cough and fever and ultimately these infections may kill the people suffering from AIDS.
Important Note: Severity of a disease may depend upon the number of microbes infecting the body. If the number of microbes is small, then the infection may be minor or may go unnoticed. If the number of microbes is large, then, the infection may be severe and could be life-threatening.
Common symptoms of AIDS include:
(i) Sweating at night and weight loss. (ii) Swollen lymph nodes. (iii) Ulcers, repeated diarrhoea, prolonged cough. (iv) Decreased count of blood platelets resulting in haemorrhage. (v) Continuous fever. (vi) Severe brain damage. It may lead to loss of memory, speech and thinking ability. (vii) Susceptibility to other infections.
2.12.4 Treatment
Till date, there is no specific treatment against HIV infection.
2.13 Principles of Treatment
There are two ways to treat an infectious disease:
(i) Reduce the effects of the disease: For this, we take treatment to have some relief from the discomfort caused by the disease i.e.
- (a) Take medicines that bring down fever or pain.
- (b) Take bed rest to conserve the energy so that body can use energy for healing.
(ii) Kill the cause of the disease: In this, one takes the symptom-directed treatment and take medicines that kill microbes.
2.13.1 How do we kill microbes?
The microbes are of various types like bacteria, viruses, fungi and protozoa. Each one may need different medicines to kill the microbe.
Each group of organisms has some essential bio-chemical life processes that are specific to that group and not shared by other groups. These are used to kill the microbes.
2.13.2 Antibiotics
An ideal drug to cure a disease is the one that blocks the chemical pathway of the infecting agent without harming the host.
Antibiotics are such drugs that are used to cure bacterial infection.
Antibiotics cause the bacterial cell walls to break down by interfering with the biochemical path way that maintains it. Since these processes do not occur in animal cells, the animal tissues remain unaffected.
2.13.3 Drugs against viruses
There are very few effective drugs against viruses. It is because viruses have very few biochemical mechanisms of their own. They enter the cells and use the cell's machinery for their life processes. Hence, there are very few virus-specific targets to aim at. The virus is so closely involved in its host cell's physiology that any chemical that harms the virus will also harm the cell.
Despite the limitations, scientists have developed some effective anti-viral drugs.
2.14 Principles of Prevention
While treating an infectious disease, following three limitations are normally confronted:
(i) Once a person has a disease, some of the body functions may get damaged and may not recover completely.
(ii) The treatment of the disease always takes time, which means the person suffering from the disease is confined to bed or incapable of normal routine till proper treatment is given and the person recovers.
(iii) The person suffering from the infectious disease can serve as a source from where the infection may spread to other people.
Keeping in view these limitations, we can understand that prevention of diseases is much better than this cure. Preventing measures are precautionary measures taken to check the transmission of infectious diseases.
2.15 Ways of Prevention of Infectius Diseases
There are two ways of prevention of infectious diseases:
(i) General ways (ii) Specific ways
2.15.1 General ways of prevention
It relates to preventing the exposure to the infectious microbes. These include:
(i) Prevention by keeping the environment clean: The basic key to the prevention of infectious disease is by keeping clean environment and good public hygiene.
(a) For air borne microbes, we can prevent exposure by providing living conditions that are not overcrowding.
(b) For water-borne microbes, we can prevent drinking unsafe water. Water should be treated to kill the infectious microbes.
(c) For vector-borne infections, we can provide clean environment like clean, covered and hygienic food and drinks.
(d) We should not allow mosquito breeding, by keeping the drains clean or spraying with kerosene.
(ii) Proper and sufficient food: For a good immune system, it is important to have a healthy body. It means one should eat proper, balanced and sufficient food for a good active immune system.
(iii) Sterilization: Patient's surroundings and articles of use should be sterilized. Soap, phenyl, dettol, and antiseptic lotion may be used wherever necessary.
(iv) Isolation: A person suffering from an infectious disease should be segregated so that others do not catch infection from him.
(v) Education: People should be educated about the infectious diseases so that they may protect themselves against such infections.
2.15.2 Specific ways of prevention
It refers to a part of our immune system that reacts against specific microbes, recognizes them and kills them.
Immunity
Immunity is the capacity of the body to defend against the disease. Immunity can also be defined as the ability of the body to resist the disease.
The immunity can be of two types:
(i) Natural or In-born (ii) Acquired
Immunity Structure:
- Natural (present at the time of birth)
- Acquired (acquired after birth)
- Passive
- Active
(a) Natural or In-born immunity: It refers to the immunity present at the time of birth. During the development of the child, some antibodies from the mother pass through the placenta to the foetus. They protect the young child from number of diseases like measles and polio till body's own immune system becomes functional.
(b) Acquired immunity: It is the immunity acquired after birth. It could be active or passive.
(i) Active immunity: It can be natural or artificial.
(a) Natural active immunity: When the body is exposed to an antigen for the first time, it contracts the disease. The body not only produces antibodies, but also large number of memory cells. When the antigen strikes the second time, the memory cells produce large number of antibodies and the body does not contract a disease. It may last for a life time. This is the reason why some childhood diseases like measles, mumps, chicken pox etc., occur only once in a life time.
(b) Artificial active immunity: It is produced by injecting a small quantity of an antigen called the vaccine into the body. The process is called as immunization or vaccination. In active immunity the body manufactures the antibodies against the antigen and that is why such immunity lasts and protects the animal for a long time.
(ii) Passive Immunity: In this immunity, the organisms own body does not produce the antibodies, instead readymade antibodies from some other organism are introduced for protection against the disease. For protection against tetanus, diphtheria, rabies or Salmonella, the disease causing bacteria or virus is introduced into another animal like horse or sheep. Antibodies soon appear in the horse's or sheep's blood. From there, the antibodies are extracted and injected into humans to provide the passive immunity. Such immunity is short lived.
Historical Note: An English physician named Edward Jenner, realised that milkmaids who had cowpox did not catch smallpox even during epidemics. Cowpox is a very mild disease. Jenner tried deliberately giving cowpox to people and found that they were now resistant to smallpox. This was because the smallpox virus is closely related to the cowpox virus.
2.15.3 Vaccines
Antibody provoking agents are termed vaccines. The term vaccine is used for a preparation of antigenic proteins of pathogens or weakened or dead pathogens which on inoculation into a healthy person provides temporary or permanent immunity against the disease by inducing antibodies formation. Now, vaccines are available for preventing whole range of infectious diseases, e.g., tetanus, diptheria, whooping cough, measles, polio, hepatitis-B, cholera, tuberculosis, measles, plague, mumps etc. These form the public health programme of childhood immunization for preventing infectious diseases.
Vaccines against some common diseases:
| Vaccine | Disease |
|---|---|
| 1. DPT | 1. Diptheria, Pertussis (whooping cough), Tetanus |
| 2. Hepatitis-B | 2. Hepatitits |
| 3. Polio | 3. Poliomyelitis |
| 4. BCG (Bacillus Calmette Guerin) | 4. Tuberculosis |
2.16 Common Microbial Diseases and Their Prevention
The causative agent, symptoms, control and preventive measures of some common diseases are given below:
| Name of the disease | Name of causative organism | Symptoms | Prevention |
|---|---|---|---|
| 1. Typhoid | Bacteria: Salmonella typhi | Headache, fever abdominal pain weakness. | Community sanitation, use of boiled water, properly cooked food. |
| 2. Diarrhoea | Bacteria: Staphylococcus, clostridium, Escherichia coli etc. | Frequent discharge of semi-solid/liquid faecal matter, abdominal cramps nausea, vomiting, dehydration | Proper covering of eatables, use of boiled water, underground sewers for disposal of human excreta. |
| 3. Malaria | Protozoa: Plasmodium (transmitted by female Anopheles mosquito) | Tiredness, headache, muscular pain, paroxysms of chills, fever and sweating, enlarged liver and spleen. | Use of insect repellents to prevent mosquito bite, periodic spray of insecticides. |
| 4. Hepatitis | Virus: Hepatitis virus | Fever, loss of appetite, nausea, vomiting jaundice. | Eating hygienic food, drinking disinfected water, using disposable syringes. |
| 5. Rabies (Hydrophobia) | Virus: Rabies virus (Lyssavirus) | Severe headache, high fever, painful contraction of muscles of throat and chest, restlessness, inability to swallow even liquids. | Pet dogs and cats should be vaccinated. If the dog who has bitten someone develops rabies, then person should be given anti-rabies vaccine. |
| 6. Tuberculosis (T.B.) | Bacteria: Mycobacterium tuberculosis | Fever, cough, blood stained sputum, pain in chest, weight-loss | Sanitary surroundings, immunization with BCG vaccine, pasteurization of milk. |
| 7. Poliomyelitis or Polio | Virus: Polio virus | Headache and fever, stiffness of neck, paralysis of limbs. | Immunization with oral polio vaccine provides immunity against polio. |
2.17 Pulse Polio Programme
'Pulse polio immunization programme' was launched in 1995-1996 with an aim to eradicate polio disease from the world. It involves simultaneous administration of polio drops (polio vaccine) to whole of the high risk population (i.e., children under three years of age) on a single day throughout the nation.
This programme uses oral polio vaccine or OPV. As per the National Immunisation Schedule (NIS), a dose of 3 drops (0.5 ml) is given orally to the child, i.e., one dose each at 1.5, 2.5 and 3.5 month's age. Finally, a booster dose is given at the age of 1.5 years.
Aims:
(i) To immunize those children who are not earlier immunized or are partially immunized.
(ii) To boost the immunity of children already immunized.
(iii) To replace the disease-causing wild virus by harmless vaccine virus in the environment.