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Common Infectious disease in humans | NCERT 12th class


 What are the common diseases found in humans ? 

  1. Typhoid
  2. Pneumonia
  3. Common cold
  4. Malaria
  5. Ascariasis
  6. Elephantiasis / filariasis
  7. Ringworms

1. Typhoid fever

Causative agent :

 Salmonella typhi


Pathogenesis :- 


Pathogen enter through contaminated food and water.

Enter small intestine and migrate to other organs through blood.

Symptoms -

Higher fever (39° to 40°)
Weakness
Stomach pain
Constipation
Headache
Loss of appetite

Test perfomed -  

Widal test

2. Pneumonia

Causative agent : 


Streptococcus pneumonia

Haemophilus influenza

Pathogenesis :-


Pathogen enter through inhaling the droplets /aerosols released by infected person.

Infects alveoli (air filled sacs) of the lungs.

Alveoli get filled with fluid leading to severe problems in respiration.

Symptoms :-

Fever
Chills
Cough
Headache

How healthy person get infected ?


Healthy person get infected by inhaling the droplets /aerosols released by infected person through sharing glasses, utensils.

3. Common cold

Common cold is caused by virus infection in human body.

Causative agent :-


Rhino viruses

Pathogenesis :-

Enter through air and infect nose and respiratory passage

Symptoms :-


Nasal congestion & discharge
Hoarness
Cough
Headache
Tiredness

Incubation period : 3-7 days


How healthy person get infected ?


Through direct inhalation of cough & sneezes of an infected person.
Transmitted through pens, books, cups, doorknobs, computer keyboard, or mouse etc.

4. Malaria 

Causative agent : plasmodium (tiny protozoa)


Different species of plasmodium

1. Plasmodium vivax
2. Plasmodium malaria
3. Plasmodium falciparum 

Malignant malaria caused by -

Plasmodium falciparum 

Lifecycle of Malaria

Mosquito host

  1. Already Infected person with malaria
  2. Non infected Anopheles mosquito bites an Infected person
  3. Parasites enter the mosquito body
  4. Multiply within them
  5. Form Sporozoites in salivary gland
  6. This mosquito bites human , Sporozoites enter his/her body

Human host

  1. Infected female Anopheles mosquito bite human body.
  2. Plasmodium enters the human body as Sporozoites (infectious form )
  3. Parasites enter liver cell through blood and reproduce asexually.
  4. Liver cell get burst and parasites release into blood
  5. Then this parasite attack the Red blood cells
  6. Again asexually reproduce within red blood cells 
  7. Red blood cells get burst & haemozoin named toxic substances released with cause fever & chills.
  8. Again they infect new red blood cells
  9. In red blood cells , sexual stage(gametocytes) developed.
  10. When female mosquito bites infected person they takes up gametocytes with blood meal.
  11. Fertilization and development take place in the mosquito gut.
  12. Sporozoites ( mature infective stage ) escape from gut & migrate into the mosquito salivary glands.
  13. When the mosquito bites another human, Sporozoites are injected with bite.

At what stage symptoms visible in malaria 

When red blood cells are rupture and because of this toxic substances are released like haemozoin , which is responsible for the chill & high fever recurring every 3-4 days.

How many host does malarial parasite require to complete it's life cycle ?


Two host - human & mosquito

Who is the vector ( transmitting agent ) ?

Anopheles mosquito

Reference :

NCERT textbooks 12th class

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