Human Health and Diseases - Notes | Class 12 | Part 1: Common Infectious Diseases in Man


·   Health is a state of complete physical, mental & social well-being. It is affected by genetic disorders, infections, change in life style (food, water, rest, exercise, habits etc).

·     Mind influences immune system (through neural and endocrine systems) and thereby health.

·     When the functioning of organs or systems of the body is adversely affected, it is called a disease.

·     Diseases may be infectious (transmits from one person to another) or non-infectious (do not transmit. E.g. cancer).

·     Disease causing organisms are called Pathogens.  Parasites are pathogens as they harm the host.

Good humour hypothesis (by Hippocrates & Indian Ayurveda system): It states that health is a state of body & mind where there is a balance of certain humours. Persons with ‘black bile’ belong to hot personality and would have fevers.

William Harvey disproved this hypothesis. He discovered blood circulation and demonstrated normal body temperature in persons with black bile using thermometer.



a.    Typhoid: Pathogen is Salmonella typhi.

·   Mode of transmission: It enters small intestine through food & water and migrates to other organs via blood.

·   Symptoms: Sustained high fever (39o-40o C), headache, weakness, stomach pain, constipation & loss of appetite. Intestinal perforation and death may occur.

Widal test is used for confirmation of the disease.

Mary Mallon (Typhoid Mary) was a professional cook. She was a typhoid carrier who spread typhoid for several years through the food she prepared.

b.    Pneumonia: Pathogen is Streptococcus pneumoniae & Haemophilus influenzae.

It infects lung alveoli. The alveoli get filled with fluid leading to respiratory problems.

·  Mode of transmission: Inhaling the droplets/aerosols released by an infected person. Sharing glasses and utensils with an infected person.

·  Symptoms: Respiratory problems, fever, chills, cough, headache. In severe cases, lips and finger nails turn grey to bluish colour.

Other bacterial diseases: Dysentery, plague, diphtheria, etc.


a.    Common cold: Pathogen is Rhinoviruses.

It infects nose & respiratory passage but not lungs.

·   Mode of transmission: Inhaling droplets resulting from cough or sneezes. Through contaminated objects (pens, books, cups, doorknobs, computer accessories) etc.

·   Symptoms: Nasal congestion & discharge, fever, headache, sore throat, cough, hoarseness, tiredness etc.

   Common cold lasts for 3-7 days.


a.    Malaria: Pathogen is Plasmodium sp. (P. vivax, P. malariae & P. falciparum).

Most serious (malignant) malaria is caused by P. falciparum.

·   Mode of transmission: By female Anopheles mosquito.

·   Symptoms: Haemozoin (toxin released by Plasmodium) causes chill and high fever recurring every 3-4 days.


Life cycle of Plasmodium

b.    Amoebiasis (Amoebic dysentery): Pathogen is Entamoeba histolytica.

·    Mode of transmission: Houseflies (mechanical carriers) transmit parasites from faeces to food & water.

·   Symptoms: Constipation, abdominal pain and cramps, stools with excess mucus and blood clots.


a.    Ascariasis: Pathogen is Ascaris (Intestinal parasite).

·    Mode of transmission: Soil, water, vegetables, fruits etc. contaminated with faeces containing eggs of parasites.

·   Symptoms: Internal bleeding, muscular pain, fever, anaemia and blockage of intestinal passage.

b.    Filariasis (Elephantiasis): Pathogen is Filarial worms or Wuchereria (W. bancrofti & W. malayi).

·    Mode of transmission: Bite of female Culex mosquito.

·    Symptoms: Filarial worms live in lymphatic vessels (usually of lower limbs). It causes chronic inflammation of the organs in which they live for many years. Limbs and genital organs may be deformed.


a.    Ring worms: Pathogens are Microsporum, Trichophyton & Epidermophyton. They are seen in groin, b/w toes etc.

·    Mode of transmission: From soil or by using towels, cloths, comb etc. Heat and moisture help fungi to grow.

·    Symptoms: Dry, scaly lesions on skin, nails, scalp etc. Intense itching.


Personal hygiene

Keep the body clean. Use clean drinking water, food etc.

Public hygiene

a.    Proper disposal of wastes and excreta.

b.    Periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks.

c.    Avoid contact with infected persons or their belongings (to control air-borne diseases).

d.    Standard practices of hygiene in public catering.

e.    Control and eliminate the vectors (e.g. mosquitoes).

-    Avoid stagnation of water.

-    Regular cleaning of household coolers.

-    Use of mosquito nets.

-    Introduce larvivorous fishes like Gambusia in ponds.

-    Spraying insecticides in ditches, drainage and swamps.

-    Provide doors and windows with wire mesh.

These precautions can avoid vector-borne diseases like Malaria, Filariasis, Dengue & Chikun gunya.

Vaccines & immunisation helped to control diseases like smallpox, polio, diphtheria, pneumonia & tetanus. Drugs like antibiotics also helped to treat infectious diseases.


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