Human Health and Diseases

1. Introduction

Human health is a state of physical, mental, and social well-being. This chapter covers common infectious and non-infectious diseases, the immune system, and the impact of lifestyle factors.

2. Common Diseases

2.1 Bacterial Diseases

Typhoid: Salmonella typhi. Spread by contaminated food/water. Widal test for diagnosis. Pneumonia: Streptococcus pneumoniae, Haemophilus influenzae. Affects lungs. Tuberculosis: Mycobacterium tuberculosis. Affects lungs primarily. DOTS treatment. Cholera: Vibrio cholerae. Severe diarrhoea. Spread by contaminated water.

2.2 Viral Diseases

Common cold: Rhinovirus. Respiratory infection. Influenza: Orthomyxovirus. Fever, cough, body ache. Dengue: Flavivirus (mosquito-borne). Severe fever, bleeding. Hepatitis: Hepatitis viruses (A, B, C). Liver inflammation.

2.3 Protozoan Diseases

Malaria: Plasmodium (P. vivax, P. falciparum). Mosquito-borne (Anopheles). Fever cycles. Amoebiasis: Entamoeba histolytica. Intestinal infection. Spread by contaminated food/water.

2.4 Fungal Diseases

Ringworm (Microsporum, Trichophyton). Skin infection, spread by contact.

3. Immunity

3.1 Innate Immunity

Non-specific, present from birth. Four barriers:

• Physical: Skin, mucous membranes.
• Physiological: Stomach acid, saliva, tears (lysozyme).
• Cellular: Neutrophils, macrophages, NK cells.
• Cytokine: Interferons (antiviral proteins).

3.2 Acquired (Adaptive) Immunity

Specific, develops after exposure. Two types:

• Humoral: B cells produce antibodies (immunoglobulins).
• Cell-mediated: T cells (helper T, cytotoxic T, memory T).

3.3 Active vs Passive Immunity

Active: Body produces its own antibodies (natural: infection; artificial: vaccination). Passive: Ready-made antibodies transferred (natural: mother to foetus; artificial: antivenom injection).

4. Vaccination

Principle: Exposure to weakened/inactivated pathogen stimulates immune memory without causing disease.

Types of vaccines: Killed (Salk polio), live attenuated (BCG, MMR), subunit (Hepatitis B), mRNA (COVID-19).

5. AIDS

Caused by HIV (Human Immunodeficiency Virus). Attacks helper T cells (CD4⁺).

Transmission: Unprotected sex, blood transfusion, needle sharing, mother to child (during pregnancy/birth/breastfeeding).

Stages: Acute HIV → Chronic HIV → AIDS (CD4⁺ count < 200/μL). Opportunistic infections (TB, pneumonia, Kaposi's sarcoma).

Treatment: Antiretroviral therapy (ART) — combination drugs. No cure, but manageable.

6. Cancer

Uncontrolled cell division. Types:

• Benign: Localized, non-invasive.
• Malignant: Invasive, metastasizes.

Causes: Chemical carcinogens, radiation, oncogenic viruses, genetic mutations.

Treatment: Surgery, radiation therapy, chemotherapy, immunotherapy (checkpoint inhibitors), targeted therapy.

7. Drugs and Alcohol Abuse

Common drugs: Opioids (heroin, morphine), cannabinoids (marijuana), cocaine, barbiturates, amphetamines.

Effects: Addiction, tolerance, withdrawal. Physical, mental, and social consequences.

Prevention: Education, counselling, rehabilitation.

8. Worked Problems

Problem 1: Differentiate between active and passive immunity with examples. Solution: Active immunity involves the body producing its own antibodies (vaccination, infection), provides long-term memory. Passive immunity involves receiving pre-made antibodies (maternal antibodies, antivenom), provides immediate but short-term protection.

9. Common Mistakes

'Students often think antibiotics work against all pathogens. Antibiotics are effective only against bacteria, not viruses, fungi, or protozoa.'

10. ISC Exam Focus

11. Self-Test Questions

1. Differentiate between innate and acquired immunity.
2. Describe the structure and life cycle of HIV.
3. What is the difference between benign and malignant tumours?
4. Explain the principle of vaccination with an example.
5. What are the effects of drug addiction on individuals and society?

12. Types of Vaccines