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BC07 — Diseases & Health

📖 BC07  ·  CDS General Knowledge — Biology CDS Level

Disease biology is highly practical — and AFCAT and CDS both test pathogen types, transmission routes, and prevention methods directly. This chapter also covers vitamins and their deficiency diseases — a favourite area for quick factual questions.

📌 CDS Focus: Malaria pathogen = Plasmodium (protozoan); vector = female Anopheles mosquito; TB = Mycobacterium tuberculosis (bacterial); HIV destroys T-helper (CD4) cells; Vitamin C deficiency = scurvy; Vitamin D = rickets; Vitamin A = night blindness; iodine deficiency = goitre. These are repeated direct questions.

1. Important Diseases — Pathogen and Transmission

Fig. 1 — Key Diseases: Pathogen Type, Causative Agent and Transmission
IMPORTANT DISEASES — Pathogen, Agent and Transmission Disease Type Causative Agent Transmission / Vector Key fact Malaria Protozoan Plasmodium (P. falciparum worst) Female Anopheles mosquito (vector) Quinine; liver and RBC affected Typhoid Bacterial Salmonella typhi Contaminated food/water (faecal-oral route) Widal test for diagnosis Tuberculosis Bacterial Mycobacterium tuberculosis Airborne droplets (coughing, sneezing) BCG vaccine; lungs affected HIV / AIDS Viral Human Immuno- deficiency Virus Blood, sexual contact, mother to child Destroys CD4 (T-helper) cells Dengue Viral Dengue virus (4 serotypes) Female Aedes aegypti mosquito Platelet count drops severely Cholera Bacterial Vibrio cholerae Contaminated water and food Severe watery diarrhoea; ORS treatment MOSQUITO-BORNE DISEASES COMPARISON Malaria: female Anopheles  |  Dengue/Chikungunya: female Aedes aegypti  |  Filariasis: Culex Malaria pathogen = Plasmodium (protozoan)  |  Dengue pathogen = Virus

2. Vitamin Deficiency Diseases

VitaminChemical NameDeficiency DiseaseSymptom ARetinolNight blindness / XerophthalmiaCannot see in dim light; dry cornea B₁ThiamineBeriberiNerve damage, muscle weakness B₃NiacinPellagraDermatitis, diarrhoea, dementia ("3 Ds") B₁₂CyanocobalaminPernicious anaemiaLarge, immature RBCs; nerve damage CAscorbic acidScurvyBleeding gums, poor wound healing DCalciferolRickets (children) / Osteomalacia (adults)Soft, bent bones; bowed legs KPhylloquinoneImpaired blood clottingExcessive bleeding; haemorrhage

3. Immunity — Innate and Acquired

Immunity is the body's ability to resist infection. Understanding the two types is important both for CDS and for understanding how vaccines work.

🛡 Innate (Non-Specific) Immunity

  • Present from birth; does not require prior exposure
  • First line of defence: Skin (physical barrier), mucus, tears, saliva
  • Second line: Fever, inflammation, phagocytes (neutrophils, macrophages), natural killer cells
  • Responds immediately but the same way to any pathogen
  • No memory — same response every time

🏰 Acquired (Adaptive) Immunity

  • Develops after exposure to an antigen (pathogen or vaccine)
  • Lymphocytes: B-cells (produce antibodies) + T-cells (kill infected cells)
  • Highly specific to each antigen
  • Has memory — faster, stronger response on second exposure (basis of vaccination)
  • Types: Active (body makes antibodies after exposure/vaccine) vs Passive (antibodies given externally — e.g., antivenom, mother's milk)
How Vaccines Work:

A vaccine introduces a weakened, killed, or partial form of a pathogen (or its antigen) into the body. The immune system mounts a response and creates memory B-cells and T-cells. On real exposure, the immune system recognises and attacks the pathogen much faster — before disease develops.

● Passive immunity from mother to infant: via placenta (IgG antibodies) and breast milk (IgA antibodies). This is why breastfed babies have fewer early infections.
● Herd immunity: When enough of a population is immune (via vaccination), the pathogen cannot spread — protecting even unvaccinated individuals.

4. Food & Nutrition — Macronutrients

NutrientPrimary RoleSourcesDeficiency CarbohydratesMain energy source (4 kcal/g); simple (sugars) and complex (starch, fibre)Rice, wheat, potato, fruits, sugarFatigue, weight loss ProteinsGrowth and repair of tissues; enzymes, antibodies, hormones (4 kcal/g)Legumes, eggs, milk, meat, fishKwashiorkor (protein deficiency in children); Marasmus (overall calorie + protein) Fats (Lipids)Energy store (9 kcal/g); fat-soluble vitamins A,D,E,K; cell membranes; insulationOils, butter, nuts, meatFat-soluble vitamin deficiencies; fatty acids deficiency MineralsStructural (Ca, P in bones); regulatory (Na, K in nerve impulse); enzymatic (Fe in haemoglobin)Iron: leafy greens; Calcium: milk; Iodine: seafoodIron: anaemia; Calcium: osteoporosis; Iodine: goitre WaterUniversal solvent; 70% of body mass; transport medium; temperature regulationDrinking water, fruits, vegetablesDehydration (even 2% loss impairs performance)

📝 CDS PYQs — Diseases & Health

Q1. Malaria is caused by which type of pathogen? CDS PYQ
(a) Bacteria(b) Virus(c) Protozoan(d) Fungus
✔ Answer: (c) Protozoan
Malaria is caused by Plasmodium, a protozoan parasite, transmitted by the female Anopheles mosquito. There are 4 species: P. falciparum (most dangerous, causes cerebral malaria), P. vivax (most common), P. malariae, P. ovale. The parasite undergoes part of its life cycle in the liver and part in RBCs — causing the characteristic fever cycles. Quinine (from cinchona bark) was the original treatment.
Q2. Deficiency of Vitamin C causes: CDS PYQ
(a) Rickets(b) Night blindness(c) Scurvy(d) Beriberi
✔ Answer: (c) Scurvy
Scurvy results from Vitamin C (ascorbic acid) deficiency. Symptoms: bleeding and swollen gums, slow wound healing, joint pain, and anaemia. Vitamin C is essential for collagen synthesis — without it, connective tissue weakens. Historically, scurvy affected sailors on long voyages. Rickets = Vitamin D; Night blindness = Vitamin A; Beriberi = Vitamin B₁. This deficiency-disease mapping is one of the most repeated CDS factual questions.
Q3. HIV destroys which type of cell in the human body? CDS PYQ
(a) Red blood cells(b) Platelets(c) CD4+ T-helper lymphocytes(d) Neutrophils
✔ Answer: (c) CD4+ T-helper lymphocytes
HIV (Human Immunodeficiency Virus) specifically targets and destroys CD4+ T-helper cells (a type of white blood cell). These cells coordinate the entire immune response — telling B-cells to make antibodies and cytotoxic T-cells to kill infected cells. When CD4 count falls below 200 cells/μL, the immune system collapses and AIDS develops, making the body vulnerable to opportunistic infections. This CD4 mechanism is directly tested in CDS.

🧠 Quick Memory Chart — BC07

🌟 Mosquito Diseases
  • Malaria: Plasmodium (protozoan)
  • Vector: female Anopheles
  • Dengue/Chikungunya: Aedes aegypti
  • Filariasis: Culex mosquito
  • P.falciparum = most dangerous malaria
📈 Vitamins & Deficiency
  • A: night blindness (Retinol)
  • B₁: Beriberi (Thiamine)
  • C: Scurvy (Ascorbic acid)
  • D: Rickets/Osteomalacia (Calciferol)
  • K: Impaired clotting (Phylloquinone)
🚩 Key Disease Facts
  • TB: Mycobacterium tuberculosis (airborne)
  • Typhoid: Salmonella (faecal-oral)
  • Cholera: Vibrio cholerae (water)
  • HIV: destroys CD4 T-helper cells
  • Widal test: Typhoid diagnosis

📝 Practice Exercise

E1. BCG vaccine protects against:
(a) Malaria(b) Cholera(c) Tuberculosis(d) Typhoid
E2. Iodine deficiency causes:
(a) Anaemia(b) Goitre (enlarged thyroid gland)(c) Rickets(d) Kwashiorkor
Answers:
E1 → (c) Tuberculosis [BCG = Bacille Calmette-Guérin; given to newborns; protects against TB meningitis]  |  E2 → (b) Goitre [Iodine needed to make thyroxine; deficiency → thyroid gland enlarges as it tries to compensate]
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