Diseases can develop due to a number of factors including imbalance in diet, infection by microorganisms, malfunctioning of vital organs, allergic reactions, and unhealthy lifestyles. Diseases are classified as either acute, lasting a short period, or chronic, lasting a lifetime. Infectious diseases spread from person to person through various means such as direct contact, droplets, contaminated food or water, blood, or vectors like mosquitoes; while non-infectious diseases remain confined to the individual. Proper hygiene, sanitation, vaccination, and a balanced diet can help prevent the spread of infectious illnesses.

1. Why Do We Fall Ill
Introduction
Health is a state of physical, mental and social well being. The health of
an individual is dependent on his/her physical surroundings and his/
her economic status. We need food for health, and this food will have
to be earned by doing work. Our social environment, therefore, is an
important factor in our individual health. Cleanliness of the
surroundings and spread of disease are also related to each other.
Disease and its cause
A disease is opposite to health. Diseases upset our health. You feel
good when you are healthy. A disease occurs when the body is not
working correctly. Any disturbance in the working of the body is a
disease.
Acute and Chronic Disease:
Some disease last for only very short periods of time and these are
called acute disease, for e.g., cough and cold. On the other hand some
disease last for a long time, even as much as a lifetime and are called
chronic disease. An example is the infection causing elephantiasis,
which is very common in some parts of India.
Causes of Disease:
Diseases develop due to a number of factors or cause. Some of these
are given below:
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2. Diseases develop due to a number of factors or causes. Some of these
are given below:
1. Due to imbalance in the diet.
2. Due to infection by micro-organisms (example – cholera, malaria,
diarrhea and AIDS).
3. Due to malfunctioning of vital organs (example- diabetes, heart
disease, arthritis).
4. Due to allergic reactions of body to certain substances in the
environment (pollution and allergy related diseases like asthma and hay
fever due to dust, insecticides and pollen grains).
5. Due to smoking, alcoholism, drug addiction, unhealthy life style.
Infectious and non- infectious diseases:
Diseases which spread from one person to another are called
communicable or infectious diseases. These diseases are caused
through infection by micro- organisms. Examples - cholera, diphtheria,
typhoid, plague, mumps, cold, malaria, tuberculosis, AIDS.
Diseases which cannot be spread from one person to another and
remain confined to the diseased person only are called non-
communicable or non- infectious diseases.
Infectious diseases and their agents:
Infectious diseases are caused by different micro- organisms are given
below—

3. Virus – Common cold, Chicken pox, small pox, Measles, Polio, Rabies
Bacteria– Cholera, Tuberculosis, Typhoid, Diphtheria, Plague
Protozoa– Malaria, Dysentery
Fungi– Ringworm (skin disease). Means of spread:
Communicable diseases may be transmitted from the source of
infection to susceptible individual in many different ways:
1. Direct Transmission
a) Direct contact: Infection may be transmitted by direct contact
from skin to skin, e.g., leprosy, skin diseases and eye infections
(like conjunctivitis).
b) Droplet infection: Direct spray of droplets of saliva during
coughing, sneezing, speaking and splitting, e.g., whopping cough,
tuberculosis, diphtheria, common cold.
c) Contact with soil: For example, hookworm larvae, tetanus and
mycosis.
d) Inoculation into skin: The micro- organisms may be inoculated
directly into skin, e.g., rabies virus by dog bite, hepatitis
2. Indirect Transmission
This embraces a variety of mechanisms including the traditional
five F’s --- flies, fingers, fomites, food and fluid.
a) Transmission of micro- organisms through water and food:
e.g., acute diarrhea, typhoid, cholera, polio, hepatitis A, food

4. poisoning and intestinal parasites all are transmitted by
water and food.
b) Transmission through blood: e.g., hepatitis B, malaria.
Malaria causing microbes, entering through a mosquito bite
will go to the liver, and then to the red blood cells.
c) Transmission of micro-organism by an arthropod/any living
carrier (vector-borne), e.g., by mosquito ---- malaria,
dengue, filaria
d) Housefly ---- typhoid, cholera, poliomyelitis
e) Sand fly ---- kala azar and
f) Rat flea --- plague
Diseases due to malfunctioning of body organs:
Due to the improper functioning of various body organs problems or
disorders of sugar metabolism (diabetes), heart attacks, eye sight,
accumulation of waste products and arthritis may develop.
Diabetes: This is the disease caused by the malfunctioning of pancreas
in the body. Pancreas produce a hormone called Insulin regulates the
sugar level in the body. When enough insulin is not produced the sugar
level in the blood as well as urine .This disease is called diabetes.
Heart disease: In this disease the blood supply to the heart muscles is
reduced, leading to the reduced supply of oxygen to the muscles. This
can lead to a temporary pain in the chest.

5. Kidney disorders: sometimes, the waste products urea, uric acid, water
and salt keep accumulating in the blood as they are not removed from
the body. This condition is called uremia.
Principles of prevention
It is said that prevention is better than cure. So, how can we prevent
disease?
The general ways of preventing infections mostly related to preventing
exposure ----
 For air born microbes, we can prevent exposure by providing
living conditions that are not overcrowded.
 For water born – by providing safe drinking water. This can be
done by treating the water to kill any microbial contamination.
 For vector born – we can provide clean environment. In other
words, public hygiene is one basic key to the prevention of
infectious diseases,(animals carry the infecting agents from sick
person to another healthy person are called vectors).
The second basic principle of prevention of infectious disease is --
 The availability of proper and sufficient food for everyone. The
food should be kept in clean utensils and properly covered to
avoid contact with insects and flies.
 Proper life style and cleanliness are necessary for maintaining
good health.
Vaccination: our body has its own defence mechanism to fight against
the diseases. Vaccination is another method of making the body

6. immune to a particular disease. It was Edward Jenner who first
developed the technique of vaccination in 1798.
Some common vaccines
i. BCG (to develop immunity against tuberculosis)
ii. DPT (for protection against diphtheria, pertusis (whooping
cough) and tetanus.
iii. Oral polio vaccine
iv. MMR (for protection against measles, mumps and rubella).
v. Hepatitis B vaccine.