10.6 Human Health & Diseases

10.6 Human Health & Diseases

Why It Matters

According to the World Health Organization (WHO), health is a state of complete physical, mental and social well-being, not merely the absence of disease. RRB asks about the causes of common diseases, the vectors that carry them, and how vaccination builds immunity.

Disease: Two Broad Types

A disease is any condition that disrupts the normal functioning of the body. Diseases are broadly of two kinds:

1. Communicable (infectious) diseases — can spread from an infected person to a healthy one. Caused by pathogens: bacteria, viruses, fungi, protozoa or worms. Examples: common cold, influenza, malaria, dengue, typhoid, cholera, tuberculosis (TB), AIDS.
2. Non-communicable diseases — do NOT spread from person to person. Causes include deficiency of nutrients, genetic disorders, lifestyle and ageing. Examples: kwashiorkor (protein deficiency), marasmus (calorie deficiency), scurvy (vitamin C deficiency), rickets (vitamin D deficiency), anaemia (iron deficiency), diabetes, hypertension, cancer.

Common Communicable Diseases

Vectors are animals (usually insects) that carry a pathogen from one host to another. Common vectors:

• Female Anopheles mosquito — malaria.
• Aedes aegypti mosquito — dengue, chikungunya, yellow fever, Zika.
• Culex mosquito — filariasis (elephantiasis).
• Housefly — typhoid, cholera, diarrhoea (mechanical carrier on its body and legs).
• Sandfly — kala-azar (leishmaniasis).

Only the female Anopheles mosquito transmits malaria because it needs blood meals to nourish its eggs; males feed on plant juices.

Immunity and Vaccination

Immunity is the body's ability to defend itself against disease-causing organisms. There are two types:

• Innate (non-specific) immunity — the general barriers present from birth: skin, mucus, stomach acid, white blood cells.
• Acquired (specific) immunity — developed after exposure to a specific pathogen. Specialised cells called lymphocytes (a type of WBC) produce antibodies that recognise and neutralise the pathogen. The body also produces memory cells that 'remember' the pathogen and respond faster on the next exposure — this is the basis of vaccination.

Vaccination (immunization) is the introduction of a weakened, killed or inactivated pathogen (or a piece of it) into the body. The pathogen cannot cause disease, but it triggers the immune system to produce antibodies and memory cells against it. If the real pathogen ever enters, the immune system reacts quickly and prevents the disease. Examples of vaccines:

• BCG — against tuberculosis (given at birth).
• OPV (Oral Polio Vaccine) — against polio.
• DPT — against Diphtheria, Pertussis (whooping cough) and Tetanus. Note the initials: the D is diphtheria, not dengue, which is the distractor RRB reaches for most often.
• MMR — Measles, Mumps, Rubella.
• Hepatitis B vaccine.

The principle of vaccination was first applied by Edward Jenner in 1796, who noticed that milkmaids who had caught the mild cowpox disease were protected against the deadly smallpox; he used cowpox material to vaccinate against smallpox. The word 'vaccine' comes from vacca (cow).

Health, Hygiene and a Balanced Diet

Personal and public hygiene are essential to prevent disease:

• Wash hands with soap after using the toilet and before eating.
• Drink safe (boiled/filtered) water.
• Keep food covered to protect it from flies and dust.
• Dispose of garbage properly.
• Avoid spitting in public.
• Control mosquito breeding by not allowing water to stagnate (mosquitoes breed in stagnant water).

Balanced diet: a diet that contains all the nutrients — carbohydrates, proteins, fats, vitamins, minerals, water and roughage (dietary fibre) — in the right proportion. Important deficiency diseases:

• Protein deficiency in children → Kwashiorkor (swollen belly, poor growth) and Marasmus (extreme wasting due to calorie deficiency).
• Vitamin A deficiency → night blindness.
• Vitamin C deficiency → scurvy (bleeding gums).
• Vitamin D deficiency → rickets in children (soft, bent bones) and osteomalacia in adults.
• Iron deficiency → anaemia (low haemoglobin).
• Iodine deficiency → goitre (swollen neck) — covered in 10.3.

First Aid (Basic)

First aid is the immediate, temporary care given to an injured or suddenly ill person before proper medical help arrives. Important points:

• Bleeding: clean the wound, apply pressure with a clean cloth, raise the injured part.
• Burns: cool the area with running water (NOT ice); cover loosely with a clean cloth; do not apply ointments or butter.
• Fractures: immobilise the limb with a splint; do not try to set the bone.
• Snake bite: keep the person calm and still, lower the bitten part, tie a cloth above the bite, get to hospital quickly; do NOT cut the wound or suck the venom.
• Electric shock: switch off the current first (or use a non-conducting object like wood to separate the person from the source), then check breathing and give CPR if needed.

Exam Traps

1. Dengue is spread by Aedes (day-biting) mosquito, NOT Anopheles. Malaria is spread by female Anopheles.
2. Only the female Anopheles transmits malaria (males feed on plant juices).
3. DPT protects against Diphtheria, Pertussis and Tetanus — not Dengue.
4. HIV is the virus; AIDS is the disease. HIV destroys the immune system, so AIDS patients typically die of other infections (opportunistic infections), not AIDS itself.
5. Vaccination works by stimulating the body to make antibodies and memory cells — it does NOT directly kill the pathogen itself.
6. Rabies is fatal once symptoms appear — immediate vaccination after a dog bite is essential.