Board exam focus — Human Health and Disease (CBSE & HBSE)

CBSE focuses on pathogens and diseases (malaria life cycle, typhoid, AIDS), immune system (innate vs adaptive, B and T cells, antibodies), vaccines, cancer (oncogenes, treatment), and drugs/alcohol abuse. HBSE emphasises definitions, disease causation, immunity types, AIDS, and drug addiction.

Pathogens and Common Infectious Diseases

Health and Disease

Health is defined by the WHO as "a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity." Health is influenced by genetic factors, environment, and lifestyle.

Disease: Any condition that impairs normal body function. Diseases are classified as:

• Infectious (Communicable): caused by pathogens; can spread
• Non-infectious: not caused by pathogens; cannot spread (e.g., cancer, diabetes, cardiovascular disease)

Pathogens: Disease-causing organisms — bacteria, viruses, fungi, protozoa, helminths (worms), and prions.

Common Infectious Diseases and Their Causative Agents:

Bacterial Diseases:

Typhoid Fever:

• Causative agent: Salmonella typhi (gram-negative bacterium)
• Transmission: contaminated food and water (faecal-oral route)
• Infection route: ingested bacteria → intestinal epithelium → lymph nodes → blood → systemic infection
• Symptoms: sustained high fever (39–40°C), headache, weakness, abdominal pain, constipation or diarrhoea, rose-coloured spots (rose spots on skin)
• Diagnosis: Widal test (detects antibodies against S. typhi); blood culture; stool culture
• Treatment: chloramphenicol, fluoroquinolones; vaccination with Ty21a or Vi polysaccharide vaccine

Pneumonia:

• Causative agent: Streptococcus pneumoniae (and Haemophilus influenzae)
• Transmission: respiratory droplets; affects lungs (alveoli fill with fluid)
• Symptoms: fever, chills, cough with rusty sputum, chest pain, difficulty breathing
• A person with pneumonia can infect others through droplets when coughing or sneezing

Plague:

• Causative agent: Yersinia pestis; transmitted by rat fleas; bubonic plague (buboes — swollen lymph nodes); pneumonic plague (lung involvement)

Viral Diseases:

Common Cold:

• Causative agent: Rhinovirus (over 100 serotypes); RNA virus
• Transmitted by: respiratory droplets and contaminated surfaces (fomites)
• Symptoms: nasal congestion, sore throat, mild fever, cough; lasts 3–7 days
• No effective vaccine due to large number of serotypes

Dengue:

• Causative agent: Dengue virus (4 serotypes: DENV 1–4); flavivirus
• Vector: Aedes aegypti mosquito (day-biting)
• Symptoms: high fever, severe headache, retro-orbital pain, myalgia, arthralgia ("breakbone fever"), rash
• Dengue Haemorrhagic Fever (DHF): severe form with bleeding; low platelet count
• No specific treatment; supportive care; dengvaxia vaccine available

Protozoan Diseases:

Malaria:

• Causative agent: Plasmodium species: P. falciparum (most dangerous), P. vivax, P. malariae, P. ovale
• Vector: female Anopheles mosquito (night-biting)
• Life cycle: mosquito injects sporozoites → liver (exoerythrocytic cycle: schizogony) → merozoites → RBC (erythrocytic cycle: rupture of RBC releases merozoites → fever/chills) → some form gametocytes (sexual stage)
• Transmission back to mosquito: female Anopheles bites infected human → gametocytes in mosquito gut → fertilisation → sporozoites in salivary glands → new infection
• Symptoms: high fever with chills (every 48 h for P. vivax — tertian malaria; every 72 h for P. malariae — quartan malaria), anaemia, splenomegaly
• Diagnosis: blood smear (microscopy), rapid antigen test, PCR
• Treatment: chloroquine (P. vivax); artemisinin combination therapy (P. falciparum)
• Prevention: DEET repellents, insecticide-treated bed nets, indoor residual spraying

Amoebiasis (Amoebic dysentery):

• Causative agent: Entamoeba histolytica
• Transmitted by: contaminated food/water (cysts ingested); houseflies as mechanical vectors
• Symptoms: abdominal pain, cramps, bloody/mucous stools (dysentery)

Helminthic Diseases:

Ascariasis:

• Causative agent: Ascaris lumbricoides (common roundworm)
• Transmitted by: ingestion of eggs from contaminated soil/food/water
• Symptoms: abdominal pain, intestinal obstruction in heavy infections, lung inflammation (Loeffler's syndrome) during larval migration

Filariasis (Lymphatic filariasis / Elephantiasis):

• Causative agent: Wuchereria bancrofti (and W. malayi)
• Vector: female Culex mosquito
• Larval worms block lymphatic vessels → lymphoedema → grotesque swelling of legs and genitals (elephantiasis)
• Microfilariae circulate in blood at night (nocturnal periodicity), taken up by Culex mosquito

Ringworm:

• Causative agent: Fungi — Microsporum, Trichophyton, Epidermophyton
• Transmitted by: direct contact or through clothes/towels/floor; spreads rapidly in warm/humid conditions
• Affects skin, hair, nails; intensely itchy circular lesions

Immune System, Vaccination and Allergy

The Immune System

The immune system protects the body against pathogens while distinguishing self from non-self. It has two major branches: innate (non-specific) and adaptive (specific) immunity.

Innate Immunity (Non-specific):

Provides immediate, non-specific defence. Present from birth; does not require prior exposure. Four types of barriers:

1. Physical/Anatomical barriers: skin (keratin layer), mucous membranes, cilia (trap and expel particles), wax in ears, tears (lysozyme)
2. Physiological barriers: body temperature (fever inhibits some pathogens), pH of secretions (acid in stomach — HCl, pH 1-2), lysozyme (enzyme in tears, saliva, mucus — degrades bacterial cell walls)
3. Phagocytic/Cellular barriers: neutrophils (most abundant; first responders; short-lived; engulf bacteria by phagocytosis), macrophages (derived from monocytes; long-lived; phagocytosis + antigen presentation; found in tissues — Kupffer cells in liver, alveolar macrophages), Natural Killer (NK) cells (kill virus-infected cells and tumour cells by releasing perforin/granzymes)
4. Cytokine barriers: interferons (IFN-alpha, IFN-beta) — secreted by virus-infected cells; alert neighbouring cells to produce antiviral proteins; activate NK cells; do not directly kill virus but prevent viral replication. Complement system (cascade of proteins in serum) — opsonisation (marking bacteria for destruction), membrane attack complex (MAC) that lyses bacteria, recruitment of immune cells.

Adaptive (Acquired/Specific) Immunity:

Develops after exposure to antigen; highly specific; has memory. Two arms:

A. Humoral Immunity (Antibody-mediated, AMI):

• Mediated by B lymphocytes (B cells), which mature in bone marrow
• Antigens are recognised by B cell surface immunoglobulin (BCR)
• T helper cells (CD4+) provide co-stimulation to B cells
• B cells differentiate into plasma cells (effector B cells) that secrete large amounts of antibodies (immunoglobulins)
• Memory B cells persist long-term; mount rapid secondary response on re-exposure

Antibodies (Immunoglobulins): Y-shaped glycoproteins with 2 heavy chains and 2 light chains linked by disulfide bonds. Classes: IgG (most abundant; crosses placenta), IgA (in secretions — saliva, breast milk), IgM (first antibody produced in primary response; pentameric), IgE (in allergies; binds mast cells), IgD (on B cell surface; function unclear). Functions: neutralisation, opsonisation (coating bacteria for phagocytosis), complement activation, ADCC (antibody-dependent cell-mediated cytotoxicity).

B. Cell-mediated Immunity (CMI):

• Mediated by T lymphocytes (T cells), which mature in thymus
• T cells recognise antigens presented by MHC molecules on antigen-presenting cells (APCs — macrophages, dendritic cells)
• MHC I (on all nucleated cells) presents endogenous (intracellular) antigens → recognised by cytotoxic T cells (CD8+) → kills infected cells
• MHC II (on APCs) presents exogenous (extracellular) antigens → recognised by helper T cells (CD4+) → activates B cells and macrophages
• Regulatory T cells prevent autoimmunity

Primary vs Secondary Immune Response:

• Primary response: slow (7–10 days), low titre antibody (mainly IgM); involves naive lymphocytes
• Secondary response (anamnestic/memory response): rapid (2–3 days), high titre antibody (mainly IgG); mediated by long-lived memory cells

Vaccination and Immunisation:

• Active immunity: host produces its own antibodies and memory cells
• Natural active: acquired through infection
• Artificial active (vaccination): weakened/killed pathogen or its parts → stimulates immune response + memory
• Passive immunity: preformed antibodies are transferred; no memory; temporary
• Natural passive: maternal IgG crosses placenta; IgA in breast milk
• Artificial passive: antiserum (e.g., anti-snake venom, anti-tetanus serum)

Types of vaccines: Live attenuated (OPV, MMR, BCG, varicella), killed/inactivated (IPV, hepatitis A, influenza), subunit (hepatitis B, pertussis component, pneumococcal conjugate), toxoid (diphtheria, tetanus), mRNA (COVID-19 — Pfizer, Moderna).

Allergy: Exaggerated immune response to non-pathogenic antigens (allergens — pollen, dust, food, drugs). Mechanism: IgE antibodies produced by plasma cells on first exposure → IgE binds mast cells and basophils → on re-exposure, allergen cross-links IgE on mast cells → degranulation → release of histamine, prostaglandins, leukotrienes → vasodilation, increased permeability, bronchoconstriction, mucus secretion. Symptoms: sneezing, running nose, urticaria, asthma, anaphylaxis. Treatment: antihistamines, corticosteroids, bronchodilators, epinephrine (for anaphylaxis).

Autoimmune Diseases: Immune system attacks self-antigens. Examples: Rheumatoid arthritis (joints), Type 1 diabetes (beta cells of pancreas), Multiple sclerosis (myelin sheath), Systemic Lupus Erythematosus (SLE).

AIDS, Cancer and Drugs and Alcohol Abuse

AIDS (Acquired Immunodeficiency Syndrome)

Causative agent: HIV (Human Immunodeficiency Virus) — a retrovirus (RNA genome; uses reverse transcriptase to make DNA from RNA).

Transmission:

1. Sexual contact with infected person (most common globally)
2. Blood transfusion with infected blood
3. Sharing contaminated needles/syringes (IV drug users)
4. Mother to child: during pregnancy (vertical transmission), childbirth, or breastfeeding

HIV is NOT transmitted by: casual contact, hugging, sharing utensils, mosquito bites.

Pathogenesis: HIV specifically targets CD4+ T helper lymphocytes (also macrophages and dendritic cells). Virus enters T cells, integrates into host DNA as a provirus, and replicates. Over years, CD4+ cell count declines. Normal CD4 count: 800–1200 cells/microlitre. AIDS is diagnosed when CD4 count falls below 200 cells/microlitre. With severely depleted T helper cells, cell-mediated and humoral immunity both fail → susceptibility to opportunistic infections (Pneumocystis carinii pneumonia, tuberculosis, toxoplasmosis) and certain cancers (Kaposi's sarcoma, lymphoma).

Diagnosis:

• ELISA (Enzyme-Linked Immunosorbent Assay): detects antibodies against HIV in blood; screening test; if positive, confirmed by Western blot
• PCR (Polymerase Chain Reaction): detects HIV RNA or DNA; used to monitor viral load and for early diagnosis in newborns

Treatment:

• ART (Anti-Retroviral Therapy): combination of drugs targeting different stages of HIV replication (reverse transcriptase inhibitors, protease inhibitors, integrase inhibitors). Highly Active ART (HAART) has transformed HIV from a death sentence to a manageable chronic condition. ART does not cure HIV but suppresses viral load to undetectable levels.
• No vaccine currently available.

Prevention (ABC): Abstinence; Be faithful (mutually monogamous); Condom use. Also: safe blood transfusion (blood screening), needle exchange programs, PMTCT (prevention of mother-to-child transmission — ART during pregnancy).

Cancer

Cancer is a group of diseases characterised by uncontrolled proliferation of abnormal cells.

Key concepts:

• Normal cells have contact inhibition — stop dividing when they come in contact with other cells. Cancer cells lose contact inhibition.
• Proto-oncogenes: normal genes that regulate cell growth and division. When mutated or overexpressed → oncogenes — cause uncontrolled cell proliferation.
• Tumour suppressor genes (anti-oncogenes): regulate cell cycle and prevent uncontrolled division (e.g., p53, Rb). Loss of function → cancer.
• Metastasis: spread of cancer cells from primary tumour to distant sites via blood or lymph. Most dangerous aspect of cancer.

Classification:

• Carcinoma: cancer of epithelial cells (skin, lung, breast, colon — most common cancers)
• Sarcoma: cancer of connective tissue (bone, muscle, cartilage)
• Leukaemia: cancer of blood/bone marrow (abnormal WBC production)
• Lymphoma: cancer of lymphoid tissue (Hodgkin's disease, Non-Hodgkin's lymphoma)

Carcinogens (cancer-causing agents):

• Chemical: tobacco smoke (polycyclic aromatic hydrocarbons, nitrosamines), asbestos, benzene, aflatoxin B1 (from Aspergillus flavus, contaminates stored grain)
• Physical: UV radiation (causes thymine dimers → skin cancer — melanoma, BCC, SCC); ionising radiation (X-rays, gamma rays, radon)
• Biological: oncogenic viruses — EBV (Epstein-Barr Virus → Burkitt's lymphoma, nasopharyngeal carcinoma), HPV (Human Papillomavirus → cervical cancer), HBV/HCV (hepatocellular carcinoma), HTLV-1 (T cell leukaemia)

Diagnosis: biopsy, imaging (X-ray, CT, MRI, PET scan), tumour markers (PSA for prostate, CA-125 for ovary, CEA for colon), blood tests.

Treatment:

1. Surgery: remove tumour mass
2. Radiotherapy: ionising radiation destroys cancer cells (more harmful to rapidly dividing cells); damages DNA
3. Chemotherapy: drugs that kill rapidly dividing cells (alkylating agents, antimetabolites, plant alkaloids — vincristine, vinblastine); significant side effects (hair loss, nausea, immunosuppression)
4. Immunotherapy: boost immune system against cancer (checkpoint inhibitors, CAR-T cell therapy, interferon)
5. Targeted therapy: drugs targeting specific molecular alterations (imatinib/Gleevec for BCR-ABL in CML)

Drugs and Alcohol Abuse

Commonly abused substances:

Opioids: bind opioid receptors in CNS; relieve pain; cause euphoria.

• Heroin (smack/diacetylmorphine): brown powder; synthesised from morphine; taken by smoking, snorting, or injection; highly addictive; depresses CNS; overdose causes respiratory failure
• Morphine: medical use as analgesic; source: Papaver somniferum (opium poppy)

Cannabinoids: THC (tetrahydrocannabinol) is the active compound; bind cannabinoid receptors in brain.

• Cannabis (marijuana/ganja/hashish/charas): from Cannabis sativa; inhaled or eaten; causes relaxation, euphoria, altered time sense, impaired short-term memory; link to psychosis with heavy use

Cocaine: from Erythroxylum coca (coca plant); white powder; snorted or injected; a stimulant; blocks dopamine, norepinephrine, serotonin reuptake → intense euphoria followed by crash; highly addictive; causes cardiovascular complications.

LSD (Lysergic acid diethylamide): hallucinogen; distorts perception, colours, sounds; causes "trips" (good or bad); no known therapeutic use; not physically addictive.

Tobacco/Nicotine: stimulant; highly addictive; causes: lung cancer, oral cancer, COPD, cardiovascular disease, emphysema.

Alcohol (ethanol): CNS depressant; causes euphoria then sedation; long-term: liver cirrhosis, alcohol-related brain damage (Wernicke-Korsakoff syndrome), pancreatitis, cardiomyopathy, addiction.

Effects on adolescents: impaired cognitive development, academic performance, mental health issues, risk of dependence.

Prevention: awareness programmes, counselling, de-addiction programs, rehabilitation.

Frequently asked questions

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Do these notes follow CBSE and HBSE?

Yes. The Human Health and Disease notes are NCERT-aligned and include guidance for both CBSE and Haryana Board (HBSE), with important questions and MCQs for revision.

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Concept explanations, key formulas and definitions, fully solved examples and board-pattern practice questions for Human Health and Disease.