Human Health and Disease

What is Health?

This chapter focuses on understanding Human health and disease, common human diseases, immunity mechanisms, AIDS, cancer, drug and alcohol abuse, and methods for prevention and control.

Historical Perspective (Old Beliefs)

• Hippocrates (Greece) and Ayurveda believed health depended on balance of body “humors” (body fluids).
  • People with ‘blackbile’ were thought to have hot personalities and fevers.
• Later scientific discoveries disproved the humor theory.
• William Harvey demonstrated blood circulation, advancing modern physiology.

Modern Scientific Understanding

• Health depends on proper coordination of:
  • Nervous system
  • Endocrine system
  • Immune system

Definition of Health

• Health = Complete physical, mental and social well-being
  • (Not merely absence of disease)
• Definition recognised by World Health Organization.

Importance of Good Health

• Increases efficiency and productivity
• Improves economic prosperity
• Enhances longevity
• Reduces infant and maternal mortality

World Health Day → 7 April

Factors Affecting Health

• Genetic Disorders:
  • Inherited from parents
  • Present at birth
• Infections:
  • Caused by pathogens (viruses, bacteria, fungi, protozoa, helminths)
• Lifestyle Factors:
  • Poor diet
  • Lack of exercise
  • Stress
  • Addiction
  • Poor hygiene

Maintaining Good Health

• Balanced diet
• Personal hygiene
• Regular exercise
• Yoga for physical and mental balance
• Vaccination awareness
• Safe drinking water
• Proper sanitation and waste disposal
• Vector (disease-carrying organisms) control

What is Disease?

• Definition
  • Disease = Condition where normal functioning of organs/systems is disturbed.
  • Characterised by signs and symptoms.

Classification of Diseases

1. Congenital Diseases
   • Present at birth
   • Genetic or developmental
2. Acquired Diseases
   • Develop after birth
     • a. Communicable (Infectious) – Spread from person to person
     • b. Non-communicable – Do not spread person to person

Pathogens

• Definition
  • Pathogens = Disease-causing organisms
• Include:
  • Bacteria
  • Viruses
  • Fungi
  • Protozoans
  • Helminths

• Mechanism
  • Enter host body
  • Multiply
  • Interfere with normal physiology
  • Cause tissue damage

Modes of Transmission

• Direct Transmission
  • Physical contact
  • Placental transfer
  • Animal bites
• Indirect Transmission
  • Air droplets (cough/sneeze)
  • Contaminated food and water
  • Vectors (mosquito, housefly)

Common Diseases in Humans

A. Bacterial Diseases

1. Typhoid

• Causative Agent (Pathogen)
  • Salmonella typhi
• Infection Route (Transmission)
  • Contaminated food and water
  • Oral-faecal transmission
• Incubation Period
  • 1–3 weeks
• Symptoms
  • Sustained high fever (39–40°C)
  • Weakness
  • Stomach pain
  • Constipation
  • Headache
  • Loss of appetite
• Severe Complications
  • Intestinal perforation
  • Death
• Diagnosis
  • Widal Test
• Important Case
  • Mary Mallon (“Typhoid Mary”), a cook – asymptomatic carrier who spread infection through food.

2. Pneumonia

• Causative Agents
  • Streptococcus pneumoniae
  • Haemophilus influenzae
• Site of Infection
  • Lung alveoli
• Pathology
  • Lung’s alveoli get filled with fluid
  • Impaired respiration
• Symptoms
  • Fever
  • Chills
  • Cough
  • Headache
  • Breathing difficulty
  • Bluish lips/nails (severe cases)
• Transmission
  • Inhalation of infected droplets
  • Sharing utensils
• Prevention
  • PCV vaccine
• Treatment
  • Antibiotics (e.g., Levofloxacin)

Other Important Bacterial Diseases

• Cholera – Vibrio cholerae
• Tuberculosis – Mycobacterium tuberculosis
• Diphtheria – Corynebacterium diphtheriae
• Tetanus – Clostridium tetani
• Pertussis – Bordetella pertussis
• Anthrax – Bacillus anthracis

Preventive Vaccines

• DPT vaccine
• BCG (Tuberculosis)
• Tetanus toxoid

B. Viral Diseases

• Concept
  • Viral diseases are caused by viruses (obligate intracellular parasites).
  • They enter host cells and use host cellular machinery to multiply.

1. Common Cold

• Causative Agent
  • Rhinovirus (100+ serotypes)
• Target Area
  • Nose
  • Upper respiratory tract
  • Does NOT infect lungs (important differentiator)
• Pathology
  • Inflammation of mucous membranes
• Symptoms
  • Nasal congestion
  • Runny nose
  • Sneezing
  • Sore throat
  • Cough
  • Hoarseness
  • Headache
  • Tiredness
  • Mild fever
• Transmission
  • Droplet infection (cough/sneeze)
  • Contaminated objects (fomites)

Core MCQ Point – Upper respiratory infection only — lungs remain unaffected.

Other Important Viral Diseases

1. Mumps (Infectious Parotitis)
   • Caused by Mumps virus
   • Inflammation of parotid salivary glands
   • Prevented by MMR vaccine
2. Measles (Rubeola)
   • Caused by Measles virus
   • Highly infectious childhood disease
3. Dengue
   • Caused by Dengue virus
   • Transmitted by Aedes aegypti
4. Poliomyelitis
   • Caused by Poliovirus
   • Transmitted via contaminated food and water
   • Prevented by OPV and Salk vaccine
5. Chickenpox
   • Caused by Varicella zoster virus
   • Characterised by vesicular skin rashes

C. Protozoan Diseases

• Protozoa = Single-celled eukaryotic parasites.
• Many require vectors or multiple hosts.

1. Amoebiasis (Amoebic Dysentery)

• Causative Agent
  • Entamoeba histolytica
• Site of Infection
  • Large intestine
• Symptoms
  • Constipation
  • Abdominal pain
  • Cramps
  • Stool with mucus
    • Blood clots in Stool
• Transmission
  • Contaminated food and water
  • Houseflies act as mechanical carriers
    (carry cysts from feces to food)
• Control
  • Proper sanitation
  • Protect food from flies
• Treatment
  • Metronidazole
  • Tinidazole

2. Malaria

• Causative Agent
  • Plasmodium (digenetic parasite)
• Important Species
  1. Plasmodium vivax
  2. Plasmodium malariae
  3. Plasmodium falciparum (most dangerous, malignant malaria)
  4. Plasmodium ovale
• Vector
  • Anopheles mosquito (Female)
  • Life Cycle Type – Digenetic
    1. Human → Intermediate host
    2. Mosquito → Definitive host & vector

Life Cycle of Plasmodium

• Entry into Human Body:
  • Mosquito bite injects sporozoites (infective stage of Plasmodium)

1. Liver Stage
   • Sporozoites reach liver via blood
   • Asexual multiplication
   • Liver cells rupture
2. RBC Stage
   • Parasites then infect Red Blood Cells
   • Multiply asexually
   • RBCs rupture
   • Release of Haemozoin
     • A toxic pigment released from ruptured RBCs
     • Causes chills and high fever
   • Fever Pattern – Recurs every 3–4 days (species dependent)
     1. Cold stage → chills & shivering
     2. Hot stage → high temperature
     3. Sweating stage → temperature falls

• Transmission to Mosquito
  • Mosquito bites infected human
  • Takes up gametocytes
• Sexual Reproduction in Mosquito
  • Fertilization in mosquito gut
  • Sporozoites formed
  • Move to salivary glands
• Re-infection
  • Next mosquito bite injects sporozoites
  • Cycle repeats

Important Clinical Points

• Plasmodium falciparum
  • Causes malignant tertian malaria
  • Most severe form
  • May cause cerebral malaria
• Symptoms before attack:
  • Headache
  • Muscular pain
  • Weakness

Control Measures

• Prevent stagnant water
• Wire mesh on doors/windows
• Mosquito nets
• Repellents
• Introduce Gambusia fish (eat larvae)
• Spray insecticides

Treatment

• Chloroquine
• Quinine
• Primaquine

Key Points

• Hosts:
  • Plasmodium requires two hosts to complete its life cycle: humans and mosquitoes.
• Vector:
  • The female Anopheles mosquito is both the host and the vector (transmitting agent).

D. Helminthic Diseases

• Definition
  • Helminths are parasitic worms belonging mainly to:
    • Phylum Platyhelminthes (flatworms)
    • Phylum Nematoda (roundworms)
• Most are endoparasites of:
  • Intestine
  • Blood
  • Lymphatic vessels

1. Ascariasis

• Causative Agent
  • Ascaris lumbricoides (roundworm).
• Site of Infection
  • Small intestine
• Mode of Transmission
  • Eggs excreted with feces
  • Contaminate soil, water, vegetables
  • Infection through contaminated food/water
• Symptoms
  • Internal bleeding
  • Muscular pain
  • Fever
  • Anaemia
  • Intestinal blockage
• Mechanism
  • Heavy worm load → Mechanical obstruction of intestine → Severe complication
• Prevention
  • Sanitation
  • Washing vegetables
  • Safe drinking water

2. Filariasis (Elephantiasis)

• Causative Agent – Filarial worms
  • Wuchereria bancrofti
  • Wuchereria malayi
• Site of Infection
  • Lymphatic vessels (lower limbs)
  • Genital organs
• Vector
  • Culex mosquito (Female)
• Host Type
  • Human → Definitive host
  • Mosquito → Intermediate host
• Symptoms
  • Chronic inflammation
  • Swollen lower limbs
  • Thickened skin
  • Genital deformities
• Pathology
  • Worms block lymphatic drainage → Accumulation of lymph → Massive swelling
• Prevention
  • Prevent mosquito bites
  • Vector control

Other Helminthic Diseases

• Taeniasis → Taenia solium
• Ancylostomiasis → Ancylostoma duodenale
• Schistosomiasis → Schistosoma

E. Fungal Diseases

• Fungal diseases may be:
  • Mycoses → Direct fungal infection
  • Toxicoses → Due to fungal toxins

1. Ringworm

• Causative Fungi
  • Microsporum
  • Trichophyton
  • Epidermophyton
• Transmission
  • Soil
  • Towels
  • Clothes
  • Combs
  • Personal items
• Symptoms
  • Dry scaly lesions on skin
  • Skin, nails, scalp affected
  • Intense itching
• Important Feature
  • Thrives in heat and moisture.
  • Common in:
    • Groin
    • Between toes
    • Skin folds
• Treatment
  • Griseofulvin
  • Miconazole

Prevention & Control of Infectious Diseases

• Personal Hygiene
  • Clean body
  • Safe food
  • Pure drinking water
• Public Hygiene
  • Proper waste disposal
  • Clean water sources
• Avoid Close Contact
  • With infected persons
• Vector Control
  • Avoid water stagnation
  • Clean coolers
  • Mosquito nets
  • Wire mesh
  • Gambusia fish
  • Insecticide spraying
• Prevents:
  • Malaria
  • Filariasis
  • Dengue
  • Chikungunya

Advancements in Disease Control

• Vaccines
  • Smallpox eradicated
  • Polio controlled
  • Diphtheria controlled
  • Tetanus controlled
  • Pneumonia controlled
• Biotechnology → New, Safer & improved vaccines development.

• Antibiotics
  • Effective against bacterial infections
  • Not effective against viral infections

Immunity

• Definition
  • Immunity = Ability of the body to resist/fight pathogens
• Two Types:
  1. Innate (Inborn, Non-specific)
  2. Acquired (Adaptive, Specific, Memory-based)

Innate Immunity

• Characteristics
  • Present at birth
  • Non-specific (defends against all pathogens equally).
  • Immediate response
  • First line of defence

Four Barriers

1. Physical Barriers
   • Skin
   • Mucus lining of respiratory, GI, urogenital tract
2. Physiological Barriers
   • Stomach acid
   • Saliva
   • Tears
3. Cellular Barriers
   • Neutrophils
   • Monocytes
   • Macrophages
   • Natural Killer (NK) cells
4. Cytokine Barriers
   • Interferons (a cytokine protein)
     • Released by virus-infected cells
     • Protect neighbouring cells

Acquired (Adaptive) Immunity

• Characteristics
  • Develops after birth
  • Pathogen-specific
  • Has memory
    • Differentiates self vs non-self

Immune Responses

• Primary Response
  • First exposure
  • Weak (low intensity)
  • Slow
• Secondary (Anamnestic) Response
  • Second/subsequent exposure
  • Rapid
  • Strong
  • Due to memory cells

Primary and secondary immune responses involve B-lymphocytes (B-cells) and T-lymphocytes (T-cells).

Types of Acquired Immunity

1. Humoral Immunity (Antibody Mediated Immunity – AMI)

• Main Cell
  • B-Lymphocytes
  • B-cells differentiate into:
    1. Plasma cells → Produce antibodies (proteins)
    2. Memory B-cells → Long-term immunity

• Antibodies (Immunoglobulins) – Types:
  1. IgG
  2. IgA
  3. IgM
  4. IgE
  5. IgD
• Structure: H₂L₂ structure
  • H₂L₂ structure
  • 2 Heavy chains
  • 2 Light chains
  • Antigen binding sites at tips

Important Fact: IgG can cross placenta.

2. Cell-Mediated Immunity (CMI)

• T-Cell Mediated
• Does NOT involve antibodies

Types of T-Cells

1. Helper T-cells
   • Stimulate B-cells
   • Release lymphokines
2. Cytotoxic (Killer) T-cells
   • Destroy infected cells
   • Release perforin
3. Suppressor T-cells
   • Prevent autoimmunity
4. Memory T-cells
   • Provide long-term protection

Transplantation & Immunity

Concept

• When an organ fails due to disease or injury, transplantation becomes necessary to save the patient’s life.
• However, organs cannot be taken from just any individual because the recipient’s immune system may recognise the transplanted organ as foreign.

Immunological Basis

• The immune system has the ability to differentiate between:
  • Self
  • Non-self
• If the transplanted tissue is recognised as non-self, the immune system mounts an immune response against it.
• This leads to graft rejection.

Why Rejection Occurs

• Surface antigens on donor organ differ from recipient
• Immune system recognises mismatch
• T-cells get activated
• Cytotoxic response damages graft tissue

Requirements for Successful Transplantation

1. Tissue Matching
   • Human Leukocyte Antigen (HLA) compatibility must be checked.
   • Closer match → Lower rejection risk
2. Blood Group Matching
   • ABO compatibility is essential.
3. Immunosuppressant Drugs
   • Even with good matching:
     • Patients must take immunosuppressive drugs
     • These suppress T-cell response
     • Prevent graft rejection

Graft rejection is an example of cell-mediated immune response (CMI).

Summary

Type	Description	Examples
Innate Immunity	Non-specific defense present at birth	Skin barrier, stomach acid, WBCs
Acquired Immunity	Pathogen-specific, memory-based	Antibodies from B-cells, T-cell response

Innate Immunity Barriers

Barrier Type	Examples
Physical Barriers	Skin, mucus lining
Physiological Barriers	Stomach acid, saliva, tears
Cellular Barriers	Neutrophils, monocytes, macrophages
Cytokine Barriers	Interferons

Acquired Immunity Responses

Response Type	Description	Cells Involved
Primary Response	First encounter with pathogen, low intensity	B-lymphocytes, T-cells
Secondary Response	Subsequent encounters, highly intensified	Memory B-cells, T-cells

TYPES OF ACQUIRED IMMUNITY

• Core Concept
  • Acquired Immunity = Specific + Memory Based
  • It develops after exposure to specific antigens and has the ability to remember previous encounters.
  • Two Major Types:
    1. Active Immunity
    2. Passive Immunity

Active Immunity

• Principle
  • Immunity developed when the host body produces its own antibodies after exposure to antigens.
• Nature of Antigens: Antigens may be:
  • Living microbes
  • Dead microbes
  • Attenuated (weakened) pathogens
  • Toxins
  • Proteins
• Key Features
  • Slow onset
  • Long lasting
  • Memory cells formed

Types of Active Immunity

A. Natural Active Immunity

• Mechanism
  • Natural infection → Pathogen enters body → Immune response develops → Memory cells formed
• Examples
  • Recovery from measles
  • Recovery from chickenpox

B. Artificial Active Immunity

• Mechanism
  • Deliberate exposure via vaccination → Antibody production → Memory cell formation
• Examples
  • Polio vaccine
  • Hepatitis B vaccine
  • DPT vaccine

Passive Immunity

• Principle
  • Ready-made antibodies are introduced directly into the body.
• Key Features
  • Immediate protection
  • No memory formation
  • Short duration

Types of Passive Immunity

A. Natural Passive Immunity

• Placental Transfer
  • IgG antibodies pass from mother to fetus through the placenta.
• Colostrum
  • First milk (colostrum) contains IgA
  • Protects newborn intestine

B. Artificial Passive Immunity

• Examples
  • Anti-tetanus serum (ATS)
  • Snake antivenom (serum)
  • Rabies immunoglobulin

Summary

Feature	Active Immunity	Passive Immunity
Antibody source	Produced by host in response to antigens	Given externally
Onset	Slow	Immediate
Memory	Present	Absent
Duration	Long lasting	Short term
Example	Vaccination	Antitoxin injection

VACCINATION & IMMUNISATION

• Definition of Vaccine
  • Preparation of dead/attenuated pathogens or antigenic proteins that induces active immunity.
• Vaccination
  • Process of introducing vaccine into body.
• Immunisation
  • Process by which body develops protection against disease.

Principle of Vaccination: Based on Immune Memory

• Stepwise Mechanism
  1. Vaccine introduces antigen
  2. Primary immune response triggered
  3. Memory B and T cells formed
  4. On real infection → Rapid secondary response
  5. Pathogen neutralised quickly

Types of Vaccination

• Live attenuated vaccines
• Killed/Inactivated vaccines
• Toxoid vaccines
• Subunit vaccines
• Recombinant vaccines

Recombinant DNA Vaccines

• Principle
  • Antigenic genes inserted into bacteria/yeast → Large-scale antigen production
• Example
  • Hepatitis B vaccine (produced in yeast)
• Advantages
  • Safer
  • Highly specific
  • Mass production possible

Summary

Type	Description	Examples
Vaccination	Introduction of antigenic proteins/weakened pathogens to generate memory cells	Polio vaccine, measles vaccine
Passive Immunisation	Injection of preformed antibodies or antitoxins	Tetanus antitoxin, snakebite antivenom
Recombinant DNA Vaccine	Vaccines produced using genetically engineered antigens	Hepatitis B vaccine

Allergies

• Definition
  • Exaggerated immune response to harmless environmental antigens.
• Allergens
  • Dust mites
  • Pollen
  • Animal dander
  • Food particles

• Immunological Basis
  • Allergen exposure
  • IgE antibodies produced
  • IgE binds to mast cells
  • On re-exposure → Mast cells release:
    1. Histamine
    2. Serotonin
  • Result → Inflammation

• Symptoms
  • Sneezing
  • Watery eyes
  • Runny nose
  • Breathing difficulty
• Treatment
  • Anti-histamines
  • Adrenaline
  • Steroids

Modern Observation – Urban children show increased allergy due to altered lifestyle & hygiene hypothesis.

Summary

Cause	Description	Examples
Environmental Allergens	Exaggerated immune response to environmental antigens	Pollen, dust mites, animal dander
Symptoms	Physical reactions to allergens	Sneezing, watery eyes, runny nose
Treatment	Medications to reduce symptoms	Anti-histamines, adrenaline, steroids

Auto Immunity

• Definition
  • When the body’s immune system attacks its own cells.
• Cause
  • Failure to differentiate self vs non-self.
  • Self antigens = Autoantigens
  • Due to genetic and other unknown reasons.
• Examples
  • Rheumatoid arthritis
  • Grave’s disease
  • Myasthenia gravis
  • Pernicious anemia
• Mechanism
  • Genetic predisposition + Environmental triggers

IMMUNE RESPONSE (PRIMARY vs SECONDARY)

• Primary Response
  • First exposure
  • Slow
  • Low antibody level
• Secondary Response
  • Subsequent exposure
  • Rapid
  • High antibody titer
  • Due to memory cells

Key Concept – Secondary response forms basis of vaccination success.

Immune System in the Body

• Components:
  • Lymphoid organs, tissues, cells, and soluble molecules like antibodies.
• Functions:
  • Recognizes and responds to foreign antigens, remembers them.
  • Plays a role in allergic reactions, auto-immune diseases, and organ transplantation.

Lymphoid Organs

• Definition
  • Organs where lymphocytes originate, mature and proliferate.
• Two Categories:
  1. Primary lymphoid organs
  2. Secondary lymphoid organs

PRIMARY LYMPHOID ORGANS

Bone Marrow

• Functions
  • Produces all blood cells
  • B-cell maturation

Thymus

• Location
  • Near heart, beneath sternum
• Functions
  • T-cell maturation
• Important Feature
  • Large at birth → Shrinks after puberty

SECONDARY LYMPHOID ORGANS

• Function
  • Site of antigen–lymphocyte interaction.

Spleen

• Bean-shaped
• Filters blood
• Traps blood-borne pathogens
• Reservoir of RBCs

Lymph Nodes

• Located along lymphatic vessels
• Trap antigens
• Activate lymphocytes

MALT (Mucosa Associated Lymphoid Tissue)

• Location
  • Respiratory tract
  • Digestive tract
  • Urogenital tract
• Fact
  • Constitutes ~50% of lymphoid tissue
• Includes
  • Tonsils
  • Peyer’s patches
  • Appendix

• Primary lymphoid organs: Organs where lymphocytes are formed and mature.
  • Bone marrow:
    • Produces all blood cells including lymphocytes.
  • Thymus:
    • A bilobed structure located near the heart, helps in the maturation of T-lymphocytes.
    • Large at birth but shrinks with age.
• Secondary lymphoid organs: Organs where mature lymphocytes interact with antigens and then proliferate to become effector cells.
  • Spleen:
    • Bean-shaped, contains lymphocytes and phagocytes, filters blood, traps blood-borne microorganisms.
    • Large reservoir of erythrocytes.
  • Lymph nodes:
    • Small solid structures along the lymphatic system, trap microorganisms and antigens, activate lymphocytes.
  • Mucosa-associated lymphoid tissue (MALT):
    • Located in the lining of respiratory, digestive, and urogenital tracts.
    • Constitutes about 50% of the lymphoid tissue in the body.

Summary

Type	Organs	Function
Primary Lymphoid Organs	Bone marrow, thymus	Production and maturation of lymphocytes
Secondary Lymphoid Organs	Spleen, lymph nodes, tonsils, Peyer’s patches, appendix	Interaction with antigens, proliferation of lymphocytes
Mucosa-Associated Lymphoid Tissue (MALT)	Located in respiratory, digestive, and urogenital tracts	Constitutes 50% of lymphoid tissue in the body

Complete Summary

Concept	Key Points
Types of Immunity	Innate (non-specific, present at birth), Acquired (specific, memory-based)
Innate Immunity Barriers	Physical (skin, mucus), Physiological (stomach acid, saliva), Cellular (WBCs), Cytokine (interferons)
Acquired Immunity Responses	Primary (first encounter, low intensity), Secondary (subsequent encounters, high intensity)
Types of Acquired Immunity	Active (host-produced antibodies), Passive (introduced antibodies)
Vaccination and Immunisation	Vaccination (antigen introduction), Passive Immunisation (preformed antibodies), Recombinant DNA Vaccine (genetically engineered antigens)
Allergies	Cause (environmental allergens), Symptoms (sneezing, watery eyes), Treatment (anti-histamines, adrenaline, steroids)
Auto Immunity	Immune system attacks self-cells, Example: Rheumatoid arthritis
Lymphoid Organs	Primary (bone marrow, thymus), Secondary (spleen, lymph nodes, tonsils, Peyer’s patches, appendix), MALT (respiratory, digestive, urogenital tracts)

AIDS (Acquired Immuno Deficiency Syndrome)

• Definition
  • AIDS = Acquired Immuno Deficiency Syndrome
  • Acquired → Develops during lifetime (not congenital)
  • Immuno Deficiency → Weakening of immune system
  • Syndrome → Group of symptoms

• History
  • 1981 – First reported in USA
  • Spread globally within 25 years
  • >25 million deaths worldwide
• Cause
  • Caused by Human Immunodeficiency Virus (HIV).
  • HIV is a retrovirus:
    • Enveloped virus
    • RNA genome
    • Contains reverse transcriptase enzyme

STRUCTURE & REPLICATION OF HIV

• Retrovirus Principle
  • RNA → DNA conversion using reverse transcriptase

Stepwise Life Cycle of HIV

1. Entry
   • Virus enters bloodstream
   • Infects macrophages
   • Infects helper T-cells (TH cells / CD4 cells)
2. Reverse Transcription
   • Viral RNA converted into viral DNA
   • Enzyme involved → Reverse transcriptase
3. Integration
   • Viral DNA integrates into host genome
4. Replication
   • Host cellular machinery produces viral RNA
   • Host machinery synthesizes viral proteins
5. Assembly and Release
   • New virions formed
   • Bud off from host cell
6. Destruction of T-Cells
   • Progressive depletion of helper T-cells
   • Severe immune deficiency develops

• Core Effect
  • Loss of CD4 T-cells → Failure of cell-mediated immunity
• Incubation Period
  • 6 months to 10 years
  • Average → 5–10 years

TRANSMISSION OF HIV

• Modes of Transmission
  • Sexual contact with infected person
  • Transfusion of contaminated blood
  • Sharing infected needles/syringes
  • Mother → Child (placenta, birth, breast milk)
  • Contaminated instruments (rare but possible)
• High-Risk Groups
  • Individuals with multiple sexual partners
  • Intravenous drug users
  • Patients requiring repeated transfusions
  • Children born to HIV-positive mothers

Non-Transmission

• HIV is NOT spread by:
  • Touch
  • Hugging
  • Sharing food
  • Casual contact
• Only spreads through specific body fluids.

SYMPTOMS OF AIDS

• Early Symptoms
  • Fever
  • Lethargy
  • Headache
  • Pharyngitis
  • Rashes
  • Weight loss
  • Diarrhea
• Advanced Stage – Opportunistic Infections
  • Due to immune failure:
    • Mycobacterium infections
    • Fungal infections
    • Viral infections
    • Toxoplasma (parasite)

Core Concept – AIDS patients die due to secondary infections, not directly due to HIV.

DIAGNOSIS

• ELISA Test
  • Enzyme Linked Immuno-Sorbent Assay
  • Detects antibodies against HIV
  • Widely used screening test
• Confirmatory tests may include:
  • Western blot
  • PCR

TREATMENT

• Anti-Retroviral Therapy (ART)
  • Controls viral replication
  • Prolongs life
  • Does NOT completely cure
• Limitation
  • Virus integrates into host DNA → Difficult to eliminate

PREVENTION OF HIV/AIDS

• Key Principle
  • Prevention is the only effective strategy.
• Preventive Measures
  • Safe blood transfusion
  • Use disposable syringes
  • Avoid needle sharing
  • Safe sex practices
  • Condom use
  • Control drug abuse
  • Regular testing in high-risk groups
• Institutional Efforts
  • NACO (National AIDS Control Organisation)
  • WHO programs
  • NGO awareness campaigns
• Social Message
  • “Don’t die of ignorance.”
  • Support HIV patients — avoid social isolation.

Symptoms:

• Initial symptoms: Bouts of fever, diarrhea, weight loss.
• Severe symptoms: Increased susceptibility to infections by bacteria (Mycobacterium), viruses, fungi, and parasites (Toxoplasma) due to immune system failure.
• The time lag (incubation period) between HIV infection and the onset of AIDS symptoms can be 5-10 years.

Diagnosis:

• Enzyme-linked immuno-sorbent assay (ELISA) test is commonly used.

Treatment:

• Anti-retroviral drugs: partially effective, can prolong life but can not cure the disease completely.

Prevention:

• No cure, so prevention is crucial.
• Preventive measures include:
  • Safe blood transfusions.
  • Use of disposable needles and syringes and avoid sharing needles..
  • Free distribution of condoms.
  • Controlling drug abuse.
  • Avoid unprotected sex and advocating safe sex.
  • Regular HIV check-ups for at-risk populations.
• Education and awareness are key; “Don’t die of ignorance.”

Efforts to Prevent HIV/AIDS:

• National AIDS Control Organisation (NACO) and NGOs educate people about AIDS..
• WHO programs to prevent HIV spread.
• Safe blood practices, disposable needles, free condoms, and safe sex advocacy.
• Regular check-ups for high-risk groups.

Social Support:

• Society must help and support HIV/AIDS-infected people instead of isolation.
• Collective action is needed to tackle and prevent the spread of AIDS.

• Normal Cells
  • Controlled growth
  • Regulated division
  • Show contact inhibition
• Cancer Cells
  • Loss of growth regulation
  • Loss of contact inhibition
  • Divide continuously
  • Form tumor mass

Contact Inhibition

• Normal cells stop dividing when in contact with neighboring cells.
• Cancer cells lose this property and continue dividing even after contact.

TYPES OF TUMORS

1. Benign Tumor
   • Remain localized
   • Do not spread
   • Generally less harmful
   • May cause pressure effects
2. Malignant Tumor
   • Rapid growth
   • Invade surrounding tissues
   • Spread via blood/lymph
   • Form secondary tumors

Metastasis

• Spread of cancer cells to distant sites.
• Most dangerous feature of cancer.

CAUSES OF CANCER (CARCINOGENS)

Carcinogens = Cancer-causing agents

1. Physical Carcinogens
   • X-rays
   • Gamma rays
   • UV radiation
2. Chemical Carcinogens
   • Tobacco smoke (major cause of lung cancer)
   • Mustard gas
   • Vinyl chloride
   • Nicotine
3. Biological Carcinogens
   • Oncogenic viruses

DETECTION & DIAGNOSIS

• Biopsy
  • Tissue sample taken
  • Stained
  • Examined microscopically (histopathology)
• Imaging Techniques
  • Radiography → X-rays
  • CT Scan → 3D X-ray imaging
  • MRI → Magnetic field imaging
• Blood & Bone Marrow Tests
  • Important for leukemia
• Antibody-Based Detection
  • Detect cancer-specific antigens
• Molecular Diagnosis
  • Identify inherited susceptibility genes

TREATMENT OF CANCER

• Surgery
  • Removal of tumor
• Radiation Therapy
  • High-energy rays destroy tumor cells
  • Care taken to protect normal tissue
• Chemotherapy
  • Drugs kill rapidly dividing cells
  • Side Effects
    • Hair loss
    • Anemia
    • Nausea
• Immunotherapy
  • Biological response modifiers
  • α-interferon activates immune system
  • Helps destroy tumor cells
• Combination Therapy
  • Often surgery + radiation + chemotherapy together.

Chapter Summary

CONCEPT OF HEALTH

• Modern Definition
• Health is not merely the absence of disease.
• It includes complete:
  • Physical well-being
  • Mental well-being
  • Social well-being
  • Psychological stability
• Significance
  • Healthy individuals are more productive.
  • Good health increases lifespan.
  • Reduces infant and maternal mortality.

DISEASES AND THEIR IMPACT

• Definition
  • Disease occurs when normal functioning of organs or systems is disturbed, producing signs and symptoms.
• Common Infectious Diseases
  • Typhoid
  • Cholera
  • Pneumonia
  • Fungal skin infections (e.g., ringworm)
  • Malaria

• Vector-Borne Diseases
  • Example: Malaria
• Caused by Plasmodium species
• Most dangerous: Plasmodium falciparum
• Spread by female Anopheles mosquito
• Can be fatal if untreated

• Impact of Diseases
  • Physical suffering
  • Economic burden
  • Reduced work efficiency
  • Increased mortality

PREVENTION OF INFECTIOUS DISEASES

• Personal Hygiene
  • Clean body
  • Clean food
  • Safe drinking water
• Public Health Measures
  • Proper waste disposal
  • Sanitation
  • Mosquito control
  • Avoid water stagnation
  • Safe blood transfusion
• Core Principle
  • Prevention is more effective than cure.

IMMUNE SYSTEM – BODY’S DEFENCE MECHANISM

A. Innate Immunity (Non-specific, present at birth)

1. Physical Barriers
   • Skin
   • Mucous membranes
2. Physiological Barriers
   • Stomach acid
   • Saliva
   • Tears
3. Cellular Barriers
   • Phagocytic cells
   • White blood cells

• Function
  • Prevents entry and destroys pathogens at initial stage.

B. Acquired (Adaptive) Immunity

• Pathogen-specific
• Develops during lifetime
• Possesses memory

• Primary Response
  • First exposure
  • Slow and weak
• Secondary Response
  • Subsequent exposure
  • Faster and stronger
  • Due to memory cells

• Basis of Vaccination
  • Vaccines stimulate immune memory so that future infections are rapidly neutralized.

MAJOR GLOBAL HEALTH CHALLENGES

A. AIDS

• Caused by HIV
• Weakens immune system
• Reduces helper T-lymphocytes
• Leads to opportunistic infections
• Prevention
  • Safe sex practices
  • Safe blood transfusion
  • Avoid needle sharing
  • Awareness and education
• No complete cure yet, but manageable with anti-retroviral therapy.

B. Cancer

• Definition
  • Uncontrolled and abnormal cell division forming tumors.
• Types
  1. Benign – Localized
  2. Malignant – Spreads (metastasis)
• Early Detection
  • Biopsy
  • CT scan
  • MRI
  • Blood tests
• Treatment
  • Surgery
  • Radiation therapy
  • Chemotherapy
  • Immunotherapy
• Many cancers are curable if detected early.

DRUG AND ALCOHOL ABUSE

• Concern
  • Increasing among youth due to curiosity, stress, peer pressure and perceived benefits.
• Nature of Addiction
  • Psychological attachment
  • Development of tolerance
  • Physical dependence
• Consequences
  • Health deterioration
  • Liver damage (alcohol)
  • Nervous system damage
  • Risk of AIDS (IV drug use)
  • Social and financial problems
• Solution
  • Education and awareness
  • Counseling
  • Professional medical help
  • Family support

CORE POINTS

• Health includes physical, mental and social well-being.
• Many infectious diseases are preventable through hygiene and sanitation.
• Immune system provides innate and adaptive protection.
• Vaccination works on immune memory.
• AIDS is preventable with precautions.
• Cancer is treatable if detected early.
• Drug and alcohol abuse can be prevented through awareness and guidance.