ICSE Class 9 Biology Chapter 16 Diseases Cause and Control

16 Diseases: Cause And Control

Syllabus: A brief introduction to communicable, non-communicable, endemic, pandemic and sporadic diseases. Modes of transmission.

Meaning of each of the above with examples: Bacterial, viral, protozoan, helminthic diseases.

Bacterial: cholera, typhoid, tuberculosis. Viral: AIDS, chicken pox, hepatitis. Protozoan: Malaria, amoeic dysentery, sleeping sickness. Helminthic: Ascariasis, taeniasis, filariasis.

Symptoms and measures to control the above diseases. (Scientific names of causative agents not required).

16.1 What Is A Disease?

The term "disease" is a condition in which the normal functioning of the body is disturbed. Many times such conditions are not very serious and get cured, but sometimes they become serious and even fatal.

Disease is a departure from normal health through structural or functional disorder of the body.

Early man looked at disease as an act of God or evil spirits. He used magical methods and sorcery for the treatment of the disease. Today, science looks at every disease to be a condition which has a definite cause and thereby making it possible to prevent it or cure it. To make people conscious of being healthy and disease-free, we celebrate:

World Health Day - April 7

Teacher's Note

Understanding disease as a biological condition rather than a supernatural phenomenon helps us make informed health decisions in our daily lives.

16.2 Categories Of Diseases

Diseases can be categorised in several ways, for example based on -

1. Extent of occurrence - Endemic, epidemic, pandemic, and sporadic.

2. Communicability - Whether infectious (caused due to germs) or non-infectious (due to the body's own poor functioning).

3. Kinds of pathogen - Whether bacterial, viral or some other types of germs.

4. Kinds of transmitting agent - Whether water-borne, food-borne, air-borne or insect-borne, etc.

16.3 Categories Of Diseases Based On The Extent Of Occurrence

1. Endemic when the disease is found in a certain area only attacking a fewer number of people, e.g. yellow fever in certain African countries, goitre in sub-Himalayan regions.

2. Epidemic when the disease breaks out and spreads from place to place affecting large numbers of people at the same time e.g. plague in India in 1994 (from Surat to many other places).

3. Pandemic when the disease is widely distributed worldwide, e.g. AIDS.

4. Sporadic when there are scattered individual cases of a disease e.g. malaria and cholera.

Teacher's Note

We observe these disease patterns in our communities - flu outbreaks in schools are epidemics, while the constant presence of malaria in certain regions makes it endemic.

16.4 Categories Of Diseases Based On Communicability

Diseases can also be classified into two major categories: non-communicable or non-infectious and communicable or infectious.

A. Non-Communicable Or Non-Infectious Diseases

In these diseases there is no germ of any kind and they cannot spread from a patient to another person by contact or by any other method, i.e. they are non-transmissible. Examples, diabetes, colour blindness, heart attack, beri-beri, etc.

B. Communicable Or Infectious Diseases

These are caused by some germs. The germs somehow must reach a new healthy person before he can suffer from the disease. The cause of the disease is called pathogen and its transmission from one person to another is called infection. An infectious disease usually does not appear immediately after the infection but it may take some time varying from a few hours to a few days; this period is called the incubation period. Common examples: cholera, smallpox, malaria, etc.

Teacher's Note

When someone in your family catches a cold, understanding its incubation period helps you know when you might develop symptoms too.

16.4.1 Non-Infectious Diseases

Given below is a simplified classification of non-infectious diseases with some common examples.

1. Nutritional deficiency - Beri-beri, scurvy, goitre, kwashiorkor, night-blindness, etc.

2. Metabolic - Diabetes (diabetes mellitus), goitre (hyperthyroidism),

3. Genetic - Haemophilia, Thalassemia,

4. Allergies - Hay fever, asthma

5. Degenerative (ageing) - Arthritis, cataract

[Arthritis is the inflammation of joints due to deteriorating metabolism. Arthritis is caused even due to infections.]

6. Physical and chemical causes - Injury, heat, cold, radiation, poisoning, etc.

7. Mental illness - Depression, schizophrenia.

8. Cancer - Breast cancer, prostate cancer, leukemia

[Cancer is an abnormal multiplication of cells. Their uncontrolled divisions may lead to a tumour. Cancers are usually fatal. Early detection and treatment improve chances of survival. Many causes are suggested for cancer and include chemicals, tars from tobacco smoking, tobacco chewing, drugs, pollution, certain radiations, and even certain viruses. Any agent that causes cancer is called carcinogen.]

Why the name - Cancer? Cancer has been given this name because it adheres to any part of the body which it siezes upon in an obstinate manner like the well-known crab Cancer.

Cancer occurs most commonly in those tissues in which cell division is a normal activity, e.g. skin, liver, lining of stomach, uterus, breasts, etc.

Teacher's Note

Recognizing that non-infectious diseases like diabetes often result from lifestyle choices empowers us to prevent them through diet and exercise.

16.4.2 Communicable Or Infectious Diseases

The infectious diseases are always due to some disease-causing organism called a pathogen (pathos: disease, gen: producing). The pathogens include a wide variety of organisms. Following is a list of some common pathogens and the diseases they produce. The syllabus includes only those diseases which are printed in blue letters:

Incubation Period

Incubation period is the period between the entry of germs and the appearance of the first symptoms of the disease.

All infectious diseases have a certain incubation period. Incubation periods (from the shortest to the longest) of some diseases are given in Table 18.1.

Teacher's Note

Knowing that chickenpox has a 14-21 day incubation period helps parents understand why their child might develop symptoms weeks after exposure.

16.5 Diseases Caused By Bacteria

Types of Bacteria. You have already read about types of bacteria in this book.

Some of the diseases caused by bacteria in humans are as follows:

1. Cholera

The disease attacks the intestinal tract, and is caused by a special bacterium called vibrio (vibrio cholerae). Incubation period is a few hours to 6 days. The patient suffers from vomiting and loose motions. There is very little or no urination because of the shortage of water in the body. Urea accumulates in the body, which is poisonous. The patient may die if not treated properly and promptly. The treatment includes saline water injection to supply water to the blood.

The cholera germ is spread through food and water (faeco-oral route). The contamination results due to dust and by direct transport through flies. The flies sit on excreta (faeces) of the patient and mechanically carry the germs which stick to their spiny legs and body, to the exposed food that is eaten up (through the mouth, i.e. oral).

Prevention methods include good sanitation, killing flies, keeping the food and cut fruit properly covered to prevent the flies reaching them, boiling water for drinking, and eating well-cooked food. Immunization by taking anti-cholera injection is very useful.

2. Typhoid Fever

Its major symptom is a continuous fever which usually rises in the afternoon. Reddish eruptions appear on the chest and abdomen. The causative germ (Salmonella typhi) is a flagellated bacterium which attacks the intestines. The patient passes out the germs in his excreta. Flies and direct contact spread the disease.

Prevention: Anti-typhoid inoculation should be repeated every year. Proper sanitation and control of flies reduces chances of the disease.

3. Tuberculosis (TB)

This is usually a disease of the lungs although other parts including brain, kidney and bones may also be affected. It is caused by a small rod-shaped bacterium (Mycobacterium tuberculosis), and spread by the sputum from the infected persons. The germs may be carried by air or dust. The incubation period is 2-10 weeks. In the body the surrounding tissues form a kind of wall or tubercle round the germs. The germs are widespread and almost every one receives them. Most people overcome minor infections. If the body resistance is low, the disease becomes severe. It requires treatment in its early stages. An antibiotic, Streptomycin is a very effective drug in curing tuberculosis; it inhibits the growth of bacteria.

Prevention: BCG vaccination has been found useful in developing immunity for tuberculosis. March 24 is observed as anti-tuberculosis day.

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