Health is more than absence of disease — WHO defines it as complete physical, mental and social well-being. CBSE Class 12 dedicates a chapter to Human Health and Disease. NEET asks about specific pathogens, immunity and drug abuse.
Core Concepts
Types of diseases
Infectious (caused by pathogens) and non-infectious (lifestyle, genetic, degenerative). Infectious includes bacterial (TB, cholera, typhoid), viral (flu, polio, COVID-19), fungal (ringworm) and protozoan (malaria, amoebiasis).
Infectious diseases — detailed pathogen table:
| Disease | Pathogen | Type | Transmission | Key symptom |
|---|---|---|---|---|
| Typhoid | Salmonella typhi | Bacteria | Contaminated water/food | Sustained high fever, Widal test positive |
| Pneumonia | Streptococcus pneumoniae | Bacteria | Droplet inhalation | Cough, chest pain, fluid in alveoli |
| TB | Mycobacterium tuberculosis | Bacteria | Airborne droplets | Chronic cough, night sweats, weight loss |
| Cholera | Vibrio cholerae | Bacteria | Contaminated water | Severe watery diarrhoea, dehydration |
| Malaria | Plasmodium vivax/falciparum | Protozoa | Anopheles mosquito bite | Cyclic fever with chills and rigors |
| Amoebiasis | Entamoeba histolytica | Protozoa | Contaminated water/food | Bloody diarrhoea, abdominal cramps |
| Ascariasis | Ascaris lumbricoides | Helminth | Faecal-oral route | Abdominal pain, malnutrition |
| Filariasis | Wuchereria bancrofti | Helminth | Culex mosquito bite | Lymphoedema (elephantiasis) |
| Ringworm | Microsporum, Trichophyton | Fungus | Direct/indirect contact | Ring-shaped itchy patches on skin |
| AIDS | HIV (retrovirus) | Virus | Blood, sexual, vertical | Immune deficiency, opportunistic infections |
| Dengue | Dengue virus | Virus | Aedes mosquito bite | High fever, joint pain, low platelets |
NEET asks “which pathogen causes X?” as a direct question almost every year. The table above covers the most frequently tested diseases. Memorise at least 10 pathogen-disease pairs.
Malaria life cycle
Plasmodium has the most complex life cycle among NCERT pathogens, and NEET tests it repeatedly.
Male and female gametocytes taken up by Anopheles during blood meal → fertilisation in mosquito gut → oocyst on gut wall → sporozoites migrate to salivary glands.
Sporozoites injected during mosquito bite → travel to liver → multiply in liver cells (schizogony) → release merozoites into blood.
Merozoites infect RBCs → multiply (erythrocytic schizogony) → burst RBCs (haemolysis) → release more merozoites + toxins. This bursting causes the cyclic fever. Some merozoites form gametocytes → picked up by next mosquito.
P. vivax causes fever every 48 hours (tertian malaria). P. falciparum causes the most dangerous form (cerebral malaria, can be fatal).
Common pathogens and their diseases
Plasmodium — malaria. Entamoeba histolytica — amoebiasis. Ascaris — ascariasis. Wuchereria — filariasis. Streptococcus — pneumonia. Salmonella typhi — typhoid.
Immunity basics
Innate (non-specific) — barriers, phagocytes, inflammation. Acquired (specific) — B cells make antibodies, T cells kill infected cells. Acquired can be active (from infection or vaccine) or passive (from antibody transfer, like mother to baby).
Vaccines
Weakened or killed pathogen, or parts of it, trigger the immune system to make memory cells. Next infection, the response is fast and strong. India’s universal immunisation programme covers BCG, OPV, DPT, measles and hepatitis B.
India’s Immunisation Schedule (key vaccines):
| Vaccine | Against | When given |
|---|---|---|
| BCG | Tuberculosis | At birth |
| OPV | Polio | At birth, 6, 10, 14 weeks |
| DPT | Diphtheria, Pertussis, Tetanus | 6, 10, 14 weeks |
| Hepatitis B | Hepatitis B | At birth, 6, 14 weeks |
| Measles | Measles | 9-12 months |
| MMR | Measles, Mumps, Rubella | 15 months |
Cancer
Uncontrolled cell division due to mutations in proto-oncogenes (become oncogenes) or tumour suppressor genes (like p53). Benign tumours stay localised. Malignant tumours invade other tissues (metastasis) — this is cancer.
Causes of cancer (carcinogens): Chemical (tobacco tar, asbestos), physical (UV radiation, X-rays), biological (certain viruses — HPV causes cervical cancer, EBV causes Burkitt’s lymphoma).
Detection: Biopsy, blood tests for tumour markers (PSA for prostate), imaging (CT, MRI, PET scan), molecular diagnosis (PCR for cancer-associated mutations).
Treatment: Surgery, radiation therapy, chemotherapy, immunotherapy (monoclonal antibodies), hormone therapy.
Drug and alcohol abuse
Opioids (heroin), cannabinoids (marijuana), cocaine, tobacco. Effects — dependence, withdrawal, organ damage, social breakdown. Prevention relies on education, parental involvement and professional help.
Categories of commonly abused drugs:
| Category | Example | Effect | Danger |
|---|---|---|---|
| Opioids | Heroin (smack) | Euphoria, pain relief, sedation | Highly addictive, respiratory depression |
| Cannabinoids | Marijuana (ganja) | Altered perception, relaxation | Affects memory, may trigger psychosis |
| Stimulants | Cocaine, amphetamines | Energy, alertness, euphoria | Cardiac arrest, paranoia |
| Depressants | Alcohol, barbiturates | Relaxation, reduced inhibition | Liver damage, dependence |
| Hallucinogens | LSD | Altered perception, hallucinations | Bad trips, flashbacks |
| Nicotine | Tobacco | Mild stimulation, stress relief | Lung cancer, heart disease, COPD |
Worked Examples
Plasmodium has a complex life cycle with two hosts — mosquito and human. Vaccines are hard because the parasite changes surface proteins. Control relies on mosquito nets, repellents and drugs like artemisinin.
A child getting measles vaccine develops active immunity — their own B cells make antibodies and memory lasts years. A baby getting antibodies through mother’s milk has passive immunity — quick but temporary.
When antibiotics are overused or not completed, bacteria with resistance mutations survive and multiply. These resistant bacteria spread, making infections harder to treat. MRSA (methicillin-resistant Staphylococcus aureus) is a dangerous example — it resists most common antibiotics.
Common Mistakes
Calling TB a viral disease. It is bacterial — caused by Mycobacterium tuberculosis.
Confusing active and passive immunity. Active is made by your own body; passive is received pre-made.
Writing that antibiotics work against viruses. They do not — viruses need antivirals.
Confusing benign and malignant tumours. Benign tumours are localised and non-invasive. Malignant tumours spread to other tissues (metastasis) and are cancerous.
Saying malaria is transmitted by Aedes mosquito. Malaria is transmitted by Anopheles. Aedes transmits dengue and chikungunya.
Exam Weightage and Revision
NEET 2023 asked about the vector for filariasis. NEET 2022 tested the malaria life cycle. CBSE boards ask five-mark questions on diseases and their prevention. This chapter accounts for 2-3 NEET questions every year — one of the easiest to score.
When a question gives a scenario, identify the core mechanism first, then match it to the concepts above. Most wrong answers come from reading the scenario too quickly.
Make a two-column table — disease and its pathogen. About 15 entries. That table answers most NEET single-line questions on health.
Practice Questions
Q1. Name the causative organism and vector for malaria.
Causative organism: Plasmodium (P. vivax and P. falciparum are most common in India). Vector: Female Anopheles mosquito. The parasite completes its sexual cycle in the mosquito and asexual cycle in humans.
Q2. What is the Widal test?
The Widal test is a serological test for typhoid fever. It detects antibodies against Salmonella typhi in the patient’s blood. A positive Widal test (significant titre of anti-O and anti-H antibodies) confirms typhoid infection.
Q3. Differentiate between oncogenes and tumour suppressor genes.
Oncogenes are mutated forms of proto-oncogenes — they promote uncontrolled cell division (accelerator stuck on). Tumour suppressor genes normally inhibit cell division — when they are mutated and lose function, cell division goes unchecked (brakes removed). Cancer often requires mutations in both types.
Q4. Why is completing a full course of antibiotics important?
Stopping early kills only the most susceptible bacteria. The slightly more resistant ones survive and multiply, potentially producing a population that is resistant to the antibiotic. Completing the full course ensures all bacteria (including partially resistant ones) are killed, preventing the emergence of resistant strains.
Q5. Name two diseases transmitted by Aedes mosquito.
Dengue fever and chikungunya. Both are viral diseases transmitted by Aedes aegypti. The mosquito breeds in clean stagnant water (unlike Anopheles, which breeds in dirty water). Prevention: eliminating standing water, using repellents, wearing long sleeves.
FAQs
What is the difference between epidemic and pandemic? An epidemic is a disease outbreak in a particular community or region. A pandemic is an epidemic that spreads across countries or continents. COVID-19 was declared a pandemic by WHO in March 2020 because it affected nearly every country simultaneously.
Why is cancer not considered an infectious disease? Cancer is caused by mutations in a person’s own cells — it is not transmitted from person to person by pathogens. However, some cancers are caused by infectious agents (HPV causes cervical cancer, Hepatitis B causes liver cancer). The infection can be transmitted, but the cancer itself is not.
What is the difference between vaccination and immunisation? Vaccination is the act of receiving a vaccine (the injection). Immunisation is the process of becoming immune — it includes the body’s immune response to the vaccine. Vaccination leads to immunisation in most people, but not always (some individuals may not mount a strong enough response).
Health chapter rewards recognition. Know the pathogen, know the disease, know the control — three facts per row, ten rows, done.