Revision: Health and Hygiene >> Diseases : Cause and Control Biology (English Medium) ICSE Class 9 CISCE

 Any disorder or abnormal working of an organ, part or system of the body leads to illness called as disease.

The ability of an organism to resist and overcome infection is called immunity.

Vaccination is a method of making the body immune to a particular disease by injecting killed or weakened disease causing microbe into a body to stimulate the formation of antibodies and develop immunity to that disease causing microbe.

The condition of nutrition in which the food is either in inadequate quantity or in excess or it lacks in some essential nutrient is called malnutrition.

Immunisation is body’s natural defence mechanism which acts by producing antibodies against the antigens infecting the body.

Atherosclerosis is a disease caused by the malfimtioning of heart wherein the arterial walls get hardened and thickened, reducing the flow of blood and raising the blood pressure.

A vaccine is a biological preparation of a weakened or killed pathogen (disease causing microbes) which stimulates the formation of antibodies and develops immunity against a particular disease.

Any organism that is capable of causing disease is called a pathogen.

Examples : bacteria, virus or other microorganism.

The diseases caused by inadequate intake of food or the lack of some essential nutrient in our diet are called deficiency diseases.

Deficiency in one or more of the nutrients causes various diseases. These are called deficiency diseases.

A disease not caused by pathogenic organisms and not transmitted from one person to another by direct or indirect contact is known as a non-communicable (non-infectious) disease.

or

The diseases which don’t spread from infected person to a healthy person are known as non-communicable or non-infectious diseases.

A disease caused by a specific pathogenic organism and capable of being transmitted to another individual by direct or indirect contact is known as communicable (infectious) disease.

Vector:
Vector is an agent that acts as an intermediate carrier of the pathogen.

• Communicable / Infectious diseases are caused by pathogens and spread from an infected to a healthy person via air, water, food, vectors, or contact.
• Common pathogens: bacteria (cholera, typhoid, TB), viruses (AIDS, hepatitis), protozoa (malaria), and helminths (ascariasis, filariasis).
• Incubation period: time between infection and symptoms — varies from hours (cholera) to years (HIV/AIDS, leprosy).
• TB (Mycobacterium tuberculosis) spreads through air; prevented by BCG vaccine, isolation, and DOTS.
• Hepatitis spreads through contaminated water, needles, or blood; prevented by boiled water and hygiene.
• Cholera, typhoid, and dysentery spread through contaminated food and water; prevented by hygiene, boiled water, ORS, and vaccination.

• Typhoid is caused by Salmonella typhi and spreads through contaminated food and water.
• Typhoid symptoms include high fever, weakness, stomach pain, and loss of appetite; confirmed by the Widal test.
• Pneumonia is caused by Streptococcus pneumoniae and Haemophilus influenzae and spreads through air droplets.
• Pneumonia affects the lungs, causing fluid-filled alveoli, cough, fever, and breathing difficulty.
• Other bacterial diseases include dysentery, cholera, tuberculosis, tetanus, and plague.
• These diseases spread through various modes like contaminated food/water, air droplets, direct contact, or insect vectors.
• Severe infections can lead to serious complications or death if untreated.

• Ascariasis is caused by Ascaris and spreads through faeces-contaminated soil, water, vegetables, and fruits.
• Symptoms of Ascariasis - internal bleeding, muscular pain, fever, anaemia, and intestinal blockage.
• Filariasis is caused by Wuchereria bancrofti and W. malayi, transmitted by female Culex mosquito bite.
• Filarial worms live in the lymphatic vessels of the lower limbs, causing chronic inflammation for many years.
• Filariasis leads to deformity of limbs and genital organs due to long-term swelling.

• Common cold is caused by Rhinovirus, spreads via droplets from cough/sneezes and contaminated objects, with symptoms like nasal congestion, sore throat, and headache, lasting 3-7 days.
• Dengue and Chikungunya are both spread by the Aedes mosquito; Dengue is caused by the Dengue virus and Chikungunya by the CHIK virus.
• Influenza spreads via coughing/sneezing, Measles spreads via droplets, while Mumps and Chickenpox spread through airborne droplets.
• German measles spreads via close contact, Smallpox via direct contact, and Rabies is transmitted through the bite of a rabid dog.
• Polio is caused by the polio virus and spreads via faeces and air, seriously affecting the nervous system.
• Avian flu is caused by the H5N1 virus and spreads through contact with infected poultry as well as through airborne spread.
• Chickenpox is caused by Varicella zoster and spreads via airborne droplets, while Smallpox, caused by Variola virus, spreads via direct contact and is now globally eradicated.