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

Human Health and Diseases: Common Infectious Diseases in Man

Common Infectious Diseases in Man

Health is a state of complete physical, mental & social well-being. It is affected by genetic disorders, infections, and changes in lifestyle (food, water, rest, exercise, habits, etc.).
Mind influences the 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.

Proposed by Hippocrates and the Indian Ayurveda system: Health is a state of body and mind where there is a balance of certain humours.
Persons with ‘black bile’ belong to a 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 a thermometer.

Pathogen is Salmonella typhi.
Mode of transmission: It enters the small intestine through food and water and migrates to other organs via blood.
Symptoms: Sustained high fever (39°-40° C), headache, weakness, stomach pain, constipation, and 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 and a typhoid carrier who spread typhoid for several years through the food she prepared.

Pathogen is Streptococcus pneumoniae and 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 fingernails turn grey to bluish color.
Other bacterial diseases: Dysentery, plague, diphtheria, etc.

Pathogen is Rhinoviruses.
It infects the nose and respiratory passage but not the lungs.
Mode of transmission: Inhaling droplets resulting from cough or sneezes. Through contaminated objects (pens, books, cups, doorknobs, computer accessories), etc.
Symptoms: Nasal congestion and discharge, fever, headache, sore throat, cough, hoarseness, tiredness, etc.
Common cold lasts for 3-7 days.

Pathogen is Plasmodium sp. (P. vivax, P. malariae, and 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.

Pathogen is Entamoeba histolytica.
Mode of transmission: Houseflies (mechanical carriers) transmit parasites from faeces to food and water.
Symptoms: Constipation, abdominal pain and cramps, stools with excess mucus and blood clots.

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, anemia, and blockage of intestinal passage.

Pathogen is Filarial worms or Wuchereria (W. bancrofti and 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.

Pathogens are Microsporum, Trichophyton, and Epidermophyton. They are seen in groin, between toes, etc.
Mode of transmission: From soil or by using towels, clothes, combs, etc. Heat and moisture help fungi to grow.
Symptoms: Dry, scaly lesions on skin, nails, scalp, etc. Intense itching.

Proper disposal of wastes and excreta.
Periodic cleaning and disinfection of water reservoirs, pools, cesspools, and tanks.
Avoid contact with infected persons or their belongings (to control air-borne diseases).
Standard practices of hygiene in public catering.
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, and Chikungunya.

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

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