Common Diseases in Humans

The major categories of disease and how they are caused.

Common Diseases in Humans

Human beings are affected by many diseases caused by pathogens, genetic abnormalities, nutritional deficiencies and other factors. In Class 12 Biology, special attention is given to common infectious diseases, their causative organisms, symptoms, modes of transmission and prevention.

कुछ diseases infectious होती हैं, अर्थात् वे pathogens के कारण होती हैं और एक व्यक्ति से दूसरे व्यक्ति तक फैल सकती हैं। कुछ diseases non-infectious होती हैं और व्यक्ति-से-व्यक्ति transmission नहीं होता।

What is a Disease?

A disease is a condition in which the normal structure or function of the body is disturbed.

Disease के कारण body के किसी organ, tissue या physiological process की normal functioning प्रभावित हो सकती है।

Types of Diseases

Type Meaning Examples
Infectious disease Caused by pathogens and may spread between individuals. Malaria, Typhoid, Pneumonia, AIDS
Non-infectious disease Does not spread from one person to another. Cancer, diabetes, genetic disorders

Pathogens

Pathogens are disease-causing organisms or infectious agents.

Important groups of pathogens include:

  • Bacteria
  • Viruses
  • Protozoans
  • Fungi
  • Helminths

Common Human Diseases

Important diseases discussed in NCERT include:

  • Typhoid
  • Pneumonia
  • Common cold
  • Malaria
  • Amoebiasis
  • Ascariasis
  • Filariasis
  • Ringworm
  • AIDS
  • Hepatitis-B

1. Typhoid

Typhoid is an infectious bacterial disease caused by Salmonella typhi.

यह bacteria contaminated food and water के माध्यम से digestive system में प्रवेश कर सकता है।

Mode of Transmission

Typhoid commonly spreads through contaminated food and water.

Poor sanitation and unsafe drinking water increase the risk of infection.

Symptoms

  • High fever
  • Weakness
  • Stomach pain
  • Headache
  • Loss of appetite
  • Constipation or diarrhoea in some cases

Diagnosis

The Widal test is commonly associated with the diagnosis of typhoid.

Important: Typhoid → Salmonella typhi → contaminated food and water → Widal test.

2. Pneumonia

Pneumonia is an infection of the lungs in which the alveoli may become filled with fluid or inflammatory material.

It may be caused by bacteria such as Streptococcus pneumoniae and Haemophilus influenzae.

Symptoms

  • Fever
  • Chills
  • Cough
  • Difficulty in breathing
  • Chest pain

Severe pneumonia can seriously affect gas exchange in the lungs.

Transmission

The infection can spread through respiratory droplets released by infected individuals.

3. Common Cold

Common cold is a common viral infection of the upper respiratory tract.

It is commonly caused by Rhinoviruses.

Symptoms

  • Nasal congestion
  • Nasal discharge
  • Sore throat
  • Cough
  • Headache
  • Mild fever

Common cold generally affects the nose and throat and usually resolves without serious complications.

4. Malaria

Malaria is a protozoan disease caused by parasites of the genus Plasmodium.

It is transmitted through the bite of an infected female Anopheles mosquito.

Important Plasmodium Species

  • Plasmodium vivax
  • Plasmodium falciparum

Plasmodium falciparum can cause severe and potentially fatal malaria.

Life Cycle of Plasmodium

The life cycle of Plasmodium involves two hosts:

  • Human: Intermediate host
  • Female Anopheles mosquito: Definitive host

When an infected female Anopheles mosquito bites a human, it injects sporozoites into the bloodstream.

ये sporozoites पहले liver cells में पहुँचते हैं और वहाँ multiplication करते हैं। बाद में parasites red blood cells को infect करते हैं।

Malaria and RBCs

Plasmodium multiplies inside red blood cells and eventually causes their rupture.

RBC rupture releases substances that contribute to the characteristic periodic fever and chills associated with malaria.

Board Point: Plasmodium → Malaria; female Anopheles → vector; RBC rupture → periodic fever and chills.

5. Amoebiasis

Amoebiasis is an intestinal disease caused by the protozoan Entamoeba histolytica.

The parasite commonly lives in the large intestine of humans.

Transmission

It spreads mainly through contaminated food and water.

Symptoms

  • Abdominal pain
  • Diarrhoea
  • Stool containing mucus
  • Blood in stool in severe cases

Houseflies can act as mechanical carriers by transferring infective material from contaminated matter to food.

6. Ascariasis

Ascariasis is caused by the parasitic roundworm Ascaris lumbricoides.

It is commonly acquired by consuming food or water contaminated with eggs of the parasite.

Symptoms

  • Abdominal pain
  • Internal bleeding in severe cases
  • Weakness
  • Impaired nutritional absorption
  • Intestinal blockage in heavy infections

In some cases, the larvae migrate through tissues including the lungs before returning to the intestine.

7. Filariasis

Filariasis is a parasitic disease caused by filarial worms.

Important causative organisms include Wuchereria bancrofti and Wuchereria malayi.

The infection is transmitted by mosquitoes.

Symptoms

Chronic infection can cause inflammation and enlargement of affected body parts, especially the limbs and genital organs.

A severe form of the disease may lead to elephantiasis.

8. Ringworm

Ringworm is a fungal infection of the skin.

Common causative fungi include:

  • Microsporum
  • Trichophyton
  • Epidermophyton

Ringworm commonly affects moist areas of the body.

Symptoms

  • Dry and scaly skin
  • Itching
  • Red circular patches
  • Skin irritation

It can spread through direct contact or through contaminated clothes, towels and other personal items.

9. AIDS

AIDS stands for Acquired Immuno Deficiency Syndrome.

It is caused by the Human Immunodeficiency Virus (HIV).

HIV attacks important cells of the immune system, particularly helper T-lymphocytes, weakening the body's ability to fight infections.

Transmission of HIV

HIV can be transmitted through:

  • Unprotected sexual contact with an infected person
  • Transfusion of infected blood
  • Sharing contaminated needles or syringes
  • Transmission from infected mother to child during pregnancy, childbirth or breastfeeding

HIV is not transmitted through casual contact such as shaking hands, hugging, sharing food or sitting together.

Effect on Immune System

HIV gradually reduces the number and functioning of helper T-cells.

As immunity decreases, the person becomes vulnerable to various opportunistic infections.

Diagnosis

HIV infection is commonly detected using antibody-based tests such as ELISA, with confirmatory testing as appropriate.

10. Hepatitis-B

Hepatitis-B is a viral infection that primarily affects the liver.

It is caused by the Hepatitis-B virus (HBV).

Transmission

  • Infected blood
  • Contaminated needles
  • Unprotected sexual contact
  • Mother-to-child transmission

Effects

Hepatitis-B can cause inflammation of the liver and, in chronic cases, may contribute to cirrhosis and liver cancer.

Common Diseases: Quick Comparison

Disease Causative Agent Main Transmission
Typhoid Salmonella typhi Contaminated food and water
Pneumonia Streptococcus pneumoniae, Haemophilus influenzae Respiratory droplets
Common cold Rhinoviruses Respiratory droplets/direct contact
Malaria Plasmodium Female Anopheles mosquito
Amoebiasis Entamoeba histolytica Contaminated food and water
Ascariasis Ascaris lumbricoides Contaminated food and water
Filariasis Wuchereria bancrofti, Wuchereria malayi Mosquito
Ringworm Fungi Direct contact/contaminated articles
AIDS HIV Blood, sexual contact, contaminated needles, mother-to-child
Hepatitis-B HBV Blood, sexual contact, contaminated needles, mother-to-child

Prevention of Infectious Diseases

Prevention is an important part of controlling infectious diseases.

  • Maintain personal hygiene.
  • Drink safe and clean water.
  • Eat properly cooked food.
  • Maintain proper sanitation.
  • Use mosquito-control measures.
  • Follow vaccination schedules.
  • Avoid sharing contaminated needles.
  • Use screened blood for transfusion.
  • Follow appropriate measures to prevent sexually transmitted infections.

Immunity and Vaccination

Immunity is the ability of the body to resist or fight disease-causing agents.

Vaccination stimulates the immune system to develop protection against specific infectious diseases.

Vaccines may contain weakened or inactivated forms of pathogens, components of pathogens, or other antigenic material capable of inducing an immune response.

Why Does Immunity Matter?

The immune system identifies foreign substances and pathogens and mounts responses against them.

In infectious diseases such as AIDS, impairment of immune function makes the person more susceptible to other infections.

Important Disease-Causing Organisms

Organism Disease
Salmonella typhi Typhoid
Streptococcus pneumoniae Pneumonia
Rhinovirus Common cold
Plasmodium Malaria
Entamoeba histolytica Amoebiasis
Ascaris lumbricoides Ascariasis
Wuchereria bancrofti Filariasis
Microsporum, Trichophyton, Epidermophyton Ringworm
HIV AIDS
HBV Hepatitis-B

How to Identify a Disease from the Question

Board exam में disease-related question देखकर पहले तीन चीजें identify करें:

  1. Causative organism: कौन-सा pathogen disease cause करता है?
  2. Mode of transmission: disease किस माध्यम से फैलती है?
  3. Characteristic symptom: कौन-सा symptom disease को identify करने में मदद करता है?

For example:

Female Anopheles mosquito + Plasmodium + periodic fever → Malaria

Salmonella typhi + contaminated food/water + high fever → Typhoid

HIV + decreased immunity + opportunistic infections → AIDS

Board Important Questions

Very Short Answer Questions

  1. What is a disease?
  2. What are pathogens?
  3. Name the causative organism of typhoid.
  4. Which test is commonly associated with typhoid diagnosis?
  5. Name the causative organisms of pneumonia mentioned in NCERT.
  6. Which virus commonly causes common cold?
  7. Which organism causes malaria?
  8. Which mosquito transmits malaria?
  9. What are sporozoites?
  10. Name the causative organism of amoebiasis.
  11. Name the causative organism of ascariasis.
  12. Name the causative organisms of filariasis.
  13. Name the fungi responsible for ringworm.
  14. What is the full form of AIDS?
  15. Which virus causes AIDS?
  16. Which cells of the immune system are attacked by HIV?
  17. What is the full form of HIV?
  18. Which virus causes Hepatitis-B?

Short Answer Questions

  1. Describe the symptoms and transmission of typhoid.
  2. Write a short note on pneumonia.
  3. Describe the symptoms of common cold.
  4. Explain the transmission of malaria.
  5. Describe the life cycle of Plasmodium in brief.
  6. Why does malaria cause periodic fever?
  7. Describe amoebiasis and its mode of transmission.
  8. Write a note on ascariasis.
  9. What is filariasis? Mention its causative organisms and transmission.
  10. Describe ringworm and its causative fungi.
  11. Explain how HIV affects the immune system.
  12. Write the major modes of transmission of HIV.
  13. Why is AIDS dangerous for the human body?
  14. Write a short note on Hepatitis-B.

Long Answer Questions

  1. Describe malaria with reference to its causative organism, vector, life cycle and symptoms.
  2. Explain the major infectious diseases of humans given in NCERT with their causative organisms and modes of transmission.
  3. Describe AIDS, its causative agent, mode of transmission and effect on the immune system.
  4. Explain the different modes of transmission and prevention of infectious diseases.
  5. Describe typhoid, pneumonia and common cold with their causative agents, symptoms and modes of transmission.

Multiple Choice Questions

  1. Typhoid is caused by:
    (A) HIV
    (B) Salmonella typhi
    (C) Plasmodium
    (D) Ascaris lumbricoides
    Answer: (B) Salmonella typhi
  2. Widal test is associated with:
    (A) Malaria
    (B) Typhoid
    (C) AIDS
    (D) Ringworm
    Answer: (B) Typhoid
  3. Common cold is commonly caused by:
    (A) Rhinoviruses
    (B) Plasmodium
    (C) HIV
    (D) Ascaris
    Answer: (A) Rhinoviruses
  4. Malaria is caused by:
    (A) Bacteria
    (B) Virus
    (C) Protozoan
    (D) Fungus
    Answer: (C) Protozoan
  5. The vector of malaria is:
    (A) Male Anopheles
    (B) Female Anopheles
    (C) Housefly
    (D) Aedes
    Answer: (B) Female Anopheles
  6. The causative organism of amoebiasis is:
    (A) Entamoeba histolytica
    (B) Salmonella typhi
    (C) HIV
    (D) Plasmodium
    Answer: (A) Entamoeba histolytica
  7. Ascariasis is caused by:
    (A) Ascaris lumbricoides
    (B) Wuchereria bancrofti
    (C) Rhinovirus
    (D) HIV
    Answer: (A) Ascaris lumbricoides
  8. Ringworm is caused by:
    (A) Viruses
    (B) Fungi
    (C) Protozoans
    (D) Bacteria
    Answer: (B) Fungi
  9. AIDS is caused by:
    (A) HBV
    (B) HIV
    (C) HPV
    (D) HCV
    Answer: (B) HIV
  10. HIV mainly attacks:
    (A) Red blood cells
    (B) Helper T-lymphocytes
    (C) Platelets
    (D) Bone cells
    Answer: (B) Helper T-lymphocytes
  11. Hepatitis-B primarily affects:
    (A) Heart
    (B) Liver
    (C) Kidney
    (D) Brain
    Answer: (B) Liver
  12. Which disease may be transmitted through contaminated food and water?
    (A) Typhoid
    (B) AIDS
    (C) Ringworm
    (D) Malaria
    Answer: (A) Typhoid
  13. Which disease is caused by a roundworm?
    (A) Ascariasis
    (B) Malaria
    (C) AIDS
    (D) Pneumonia
    Answer: (A) Ascariasis
  14. Elephantiasis is associated with:
    (A) Filariasis
    (B) Typhoid
    (C) Amoebiasis
    (D) Common cold
    Answer: (A) Filariasis
  15. Which of the following is a fungal disease?
    (A) Malaria
    (B) Ringworm
    (C) Typhoid
    (D) AIDS
    Answer: (B) Ringworm

Fill in the Blanks

  1. Typhoid is caused by ______.
  2. Widal test is associated with ______.
  3. Common cold is commonly caused by ______.
  4. Malaria is caused by ______.
  5. Malaria is transmitted by the bite of infected female ______ mosquito.
  6. Amoebiasis is caused by ______.
  7. Ascariasis is caused by ______.
  8. Filariasis may be caused by ______.
  9. Ringworm is caused by ______.
  10. AIDS is caused by ______.
  11. HIV mainly attacks ______ T-lymphocytes.
  12. Hepatitis-B is caused by ______.

Match the Following

Column A Column B
1. Typhoid a. HIV
2. Malaria b. Ascaris lumbricoides
3. AIDS c. Plasmodium
4. Ascariasis d. Salmonella typhi
5. Amoebiasis e. Entamoeba histolytica

Answers: 1-d, 2-c, 3-a, 4-b, 5-e

Assertion and Reason Practice

  1. Assertion: Malaria causes periodic fever.
    Reason: Plasmodium multiplies inside RBCs and their rupture is associated with release of substances that contribute to fever.
    Answer: Both Assertion and Reason are correct, and the Reason correctly explains the Assertion.
  2. Assertion: HIV infection can make a person susceptible to opportunistic infections.
    Reason: HIV damages the immune system by affecting helper T-lymphocytes.
    Answer: Both Assertion and Reason are correct, and the Reason correctly explains the Assertion.
  3. Assertion: Ringworm is caused by a virus.
    Reason: Ringworm is caused by fungi such as Microsporum and Trichophyton.
    Answer: Assertion is false, but Reason is true.
  4. Assertion: Contaminated food and water can transmit typhoid.
    Reason: Salmonella typhi can enter the body through contaminated food and water.
    Answer: Both Assertion and Reason are correct, and the Reason correctly explains the Assertion.

Practice Set: Identify the Disease

  1. A patient has high fever after consuming contaminated food and water. The causative bacterium is Salmonella typhi. Identify the disease.
  2. A disease is transmitted by an infected female Anopheles mosquito and is caused by Plasmodium. Identify the disease.
  3. A patient has diarrhoea and mucus in stool due to a protozoan living in the large intestine. Identify the disease.
  4. A fungal infection causes itchy, circular and scaly patches on the skin. Identify the disease.
  5. A viral infection progressively weakens immunity by affecting helper T-cells. Identify the disease.
  6. A parasitic roundworm infection occurs after ingestion of food contaminated with parasite eggs. Identify the disease.

Answers:

  1. Typhoid
  2. Malaria
  3. Amoebiasis
  4. Ringworm
  5. AIDS
  6. Ascariasis

Quick Revision

  • Typhoid → Salmonella typhi → Widal test
  • Pneumonia → Streptococcus pneumoniae / Haemophilus influenzae
  • Common cold → Rhinovirus
  • Malaria → Plasmodium → Female Anopheles
  • Amoebiasis → Entamoeba histolytica
  • Ascariasis → Ascaris lumbricoides
  • Filariasis → Wuchereria → Mosquito
  • Ringworm → Fungi
  • AIDS → HIV → Helper T-lymphocytes
  • Hepatitis-B → HBV → Liver

Remember: Disease → Causative agent → Transmission → Major symptoms → Prevention

Lesson 13 of 24
On This Page