GS Notes

3. Biology Notes 04

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Elaborate Notes

Classification and Nature of Diseases

A disease is a specific abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are broadly classified based on their onset and transmission.

  • Congenital Diseases: These are anatomical or physiological abnormalities present from birth.

    • Etymology: The term ‘congenital’ derives from Latin words con (“together”) and genitus (“born”).
    • Causes: They can be caused by genetic mutations (e.g., Down syndrome, Sickle-cell anemia), or environmental factors affecting the fetus during pregnancy. A notable historical example is the Thalidomide tragedy of the late 1950s and early 1960s, where the drug thalidomide, prescribed to pregnant women for morning sickness, led to severe birth defects (phocomelia). Other examples include congenital heart defects and cleft lip/palate.

  • Acquired Diseases: These diseases develop after birth and are not genetically inherited. They are further categorized into:

    • Communicable/Infectious Diseases: Caused by pathogenic microorganisms, such as bacteria, viruses, fungi, or protozoa. The pathogens can be transmitted from one person or organism to another.
      • Contagious Diseases: A subset of communicable diseases that spread very easily through direct physical contact (e.g., touching an infected person) or indirect contact (e.g., touching a contaminated surface). COVID-19 (caused by SARS-CoV-2 virus) and chickenpox are prime examples.
      • Non-contagious Communicable Diseases: These diseases are infectious but do not spread through casual direct contact. They require a specific mode of transmission, often involving a vector. A vector is an organism (e.g., an insect) that transmits a pathogen from an infected host to a new host without causing the disease itself. For example, Malaria is caused by the Plasmodium parasite but is transmitted by the female Anopheles mosquito. Polio spreads through the fecal-oral route, not typically by direct skin contact.
    • Non-Communicable/Non-Infectious Diseases (NCDs): These are chronic diseases that are not passed from person to person. They are of long duration and generally slow progression.
      • Causes: They are primarily caused by a combination of genetic, physiological, environmental, and behavioral factors (lifestyle choices). Major NCDs include cardiovascular diseases (like heart attacks and stroke), cancers, chronic respiratory diseases (such as asthma), and diabetes. The rise of NCDs is often referred to as an “epidemiological transition,” a concept developed by epidemiologist Abdel Omran (1971), describing the shift in disease patterns from infectious diseases to chronic, degenerative diseases as societies develop.

  • Acute vs. Chronic Diseases:

    • Acute Diseases: Characterized by a rapid onset and a short duration (e.g., common cold, influenza). Despite their short duration, they can be severe.
    • Chronic Diseases: Characterized by a slow progression and long duration, often lasting for the rest of a person’s life (e.g., diabetes, arthritis, cancer). They are typically of lower immediate severity but cause long-term health deterioration.

Pathogens and Associated Diseases

Bacteria

Bacteria are single-celled prokaryotic microorganisms belonging to the Kingdom Monera in the Whittaker’s Five Kingdom Classification (R.H. Whittaker, 1969). While many bacteria are harmless or beneficial, some are pathogenic.

  • Tuberculosis (TB):
    • Pathogen: Mycobacterium tuberculosis, a bacterium discovered by Robert Koch in 1882, for which he received the Nobel Prize in 1905.
    • Types:
      • Pulmonary TB: Affects the lungs and is the most common and infectious form. Symptoms include a persistent cough (lasting more than two weeks), fever (often rising in the afternoon, corresponding to the bacterium’s metabolic cycle), night sweats, weight loss, and hemoptysis (coughing up blood).
      • Extra-pulmonary TB: Occurs when the infection spreads from the lungs to other parts of the body, such as the brain (meningitis), bones, spine, and intestines.
    • Global Context: TB is a major global health issue. Its elimination is a key target under Sustainable Development Goal 3 (Target 3.3). The WHO’s Directly Observed Treatment, Short-course (DOTS) strategy has been a cornerstone of global TB control since the 1990s.
    • Treatment: TB is curable with a course of antibiotics, typically lasting six months. Non-compliance with the drug regimen is a major cause of the development of drug-resistant TB.

Viruses

Viruses are non-cellular, infectious agents that can only replicate inside the living cells of other organisms. They are considered obligate intracellular parasites. This is why they cannot be cultured in a synthetic (non-living) medium, which was the key to solving the UPSC Prelims 2021 question. In contrast, bacteria and fungi can be grown on artificial media like agar jelly.

  • Hepatitis:
    • Meaning: Inflammation of the liver (‘Hepatic’ refers to the liver).
    • Types: Caused by five main types of hepatitis viruses: A, B, C, D, and E.
      • Hepatitis A and E: Primarily transmitted through the fecal-oral route (contaminated food and water). They usually cause acute infections. Jaundice (yellowing of skin and eyes) is a common symptom.
      • Hepatitis B, C, and D: Transmitted through contact with infected body fluids (blood, semen). They can cause chronic infections, leading to cirrhosis and liver cancer. Hepatitis B and C account for the highest mortality. A vaccine exists for Hepatitis B, but not for C. The discovery of the Hepatitis C virus by Harvey J. Alter, Michael Houghton, and Charles M. Rice was awarded the Nobel Prize in Physiology or Medicine in 2020.
  • Zika Virus:
    • Vector: Transmitted primarily by Aedes mosquitoes (Aedes aegypti), the same vector responsible for Dengue and Chikungunya.
    • Other Modes of Transmission: Sexual contact and mother-to-fetus (congenital) transmission.
    • Major Symptom: A key concern is microcephaly, a congenital condition where a baby’s head is significantly smaller than expected, leading to developmental issues. The Zika outbreak in Brazil in 2015-16 highlighted this risk, leading the WHO to declare it a Public Health Emergency of International Concern (PHEIC).
  • Nipah Virus:
    • Zoonotic Origin: It is a zoonotic virus, meaning it transmits from animals to humans. The natural reservoir is fruit bats of the Pteropus genus.
    • Transmission: It can spread from bats to other animals like pigs, and then to humans, or directly from bats (e.g., through contaminated fruit) to humans. Human-to-human transmission occurs through close contact with an infected person’s bodily fluids.
    • Symptoms: It causes a range of illnesses, from asymptomatic infection to acute respiratory illness and fatal encephalitis (inflammation of the brain). Outbreaks in Kerala, India (2018, 2019, 2021, 2023) have raised significant public health concerns.

Antimicrobial Resistance (AMR)

  • Definition: AMR is the ability of a microorganism (like bacteria, viruses, fungi, or parasites) to stop an antimicrobial (such as antibiotics, antivirals, and antifungals) from working against it. As a result, standard treatments become ineffective, infections persist and may spread to others. Antibiotic resistance is a specific subset of AMR that refers to bacteria resisting antibiotics.
  • Mechanism: Resistance develops through natural evolutionary processes. When microbes are exposed to an antimicrobial drug, the susceptible ones are killed, but some may have genetic mutations that allow them to survive. These resistant microbes then multiply, passing on their resistant traits.
  • Causes:
    • Misuse in Humans: Over-prescription of antibiotics, patients not completing their full treatment course, and self-medication.
    • Overuse in Livestock: Widespread use of antibiotics in agriculture and livestock farming, not just for treating sick animals but also as growth promoters. This was a key point in the UPSC Prelims 2019 question.
  • Consequences: The emergence of “superbugs” (multi-drug resistant organisms like MRSA) poses a grave threat to global health, making common infections and minor injuries potentially lethal and complicating procedures like surgery and chemotherapy.

The Immune System

Immunity is the body’s capability to resist harmful microorganisms or toxins.

  • Innate Immunity:
    • Nature: The body’s first line of defense. It is non-specific, meaning it acts against all types of pathogens in the same way. It is present from birth.
    • Components:
      • Physical Barriers: Skin, mucous membranes lining the respiratory and gastrointestinal tracts.
      • Chemical Barriers: Acid in the stomach (HCl), enzymes like lysozyme in saliva and tears.
      • Cellular Barriers: Phagocytic cells like neutrophils and macrophages (types of White Blood Cells) that engulf and destroy pathogens.
  • Acquired/Adaptive Immunity:
    • Nature: This is a pathogen-specific immune response that develops after exposure to an antigen. It is characterized by immunological memory.
    • Lymphocytes: Key cells of the adaptive immune system.
      • B-lymphocytes (B cells): Mature in the Bone marrow. They produce proteins called antibodies in response to antigens. This is called humoral or antibody-mediated immunity.
      • T-lymphocytes (T cells): Originate in the bone marrow but mature in the Thymus gland. They are responsible for cell-mediated immunity. They can directly kill infected cells or help activate other immune cells.
  • Antigen-Antibody Interaction:
    • Antigen: Any substance (often a protein or polysaccharide on the surface of a pathogen) that triggers an immune response.
    • Antibody (Immunoglobulin): A Y-shaped protein produced by B cells that specifically binds to an antigen, neutralizing it or marking it for destruction. This interaction is highly specific, often compared to a lock and key mechanism.
  • Immunological Memory:
    • The adaptive immune system ‘remembers’ pathogens it has encountered before.
    • Primary Response: The first time the body encounters a specific antigen, the response is slow and relatively weak as B and T cells are activated.
    • Secondary Response: Upon subsequent exposure to the same antigen, the memory cells (specialized B and T cells) created during the primary response mount a much faster, stronger, and more effective response, often preventing the disease from developing. This is the principle behind both natural immunity after an infection (e.g., chickenpox) and vaccination.

Vaccination

  • Principle: Vaccination, or immunization, is the process of administering a biological preparation (a vaccine) to stimulate an individual’s immune system to develop adaptive immunity to a specific pathogen. It introduces a harmless form of the antigen to create immunological memory without causing the disease.
  • Historical Context: The practice was pioneered by Edward Jenner in 1796, who used cowpox material to create immunity to smallpox, laying the foundation for modern immunology.
  • Types of Vaccines:
    • Live-attenuated Vaccines: Use a weakened (attenuated) form of the live germ. They create a strong and long-lasting immune response. Examples: Oral Polio Vaccine (OPV), Measles, Mumps, Rubella (MMR), and BCG (for TB).
    • Inactivated (Killed) Vaccines: Use a killed version of the germ. They are less robust than live vaccines and may require booster shots. Examples: Inactivated Polio Vaccine (IPV), Covaxin (for COVID-19).
    • Subunit, Recombinant, and Polysaccharide Vaccines: Use only specific pieces of the germ, like its protein or polysaccharide (sugar) casing. This offers a very strong immune response targeted to key parts of the germ. Examples: Hepatitis B vaccine, vaccine for Whooping Cough (pertussis).
    • Conjugate Vaccines: A type of subunit vaccine that links a polysaccharide from the germ’s outer coat to a carrier protein. This helps the immature immune systems of infants recognize the polysaccharide and develop a response. Example: Pneumococcal Conjugate Vaccine (PCV).
    • Newer Platforms: Recent advancements include mRNA vaccines (e.g., Pfizer-BioNTech, Moderna) and Viral Vector vaccines (e.g., Oxford-AstraZeneca/Covishield), which use the body’s own cells to produce the antigen, triggering an immune response.

Healthcare Approaches

  • Curative Healthcare: Focuses on treating and curing diseases after they have developed. It includes medicines, surgeries, and therapies. This is often resource-intensive and treats individuals rather than populations.
  • Preventive Healthcare: Aims to prevent diseases from occurring in the first place. It includes vaccination, health education, sanitation (e.g., Swachh Bharat Mission), lifestyle modifications, and regular health screenings. It is generally more cost-effective and equitable as its benefits can extend to the entire population.

Prelims Pointers

  • Virus Culture: Viruses are obligate intracellular parasites and cannot be cultured in a non-living, artificial/synthetic medium.
  • Bacteria & Fungi Culture: Bacteria and fungi can be cultured in artificial/synthetic laboratory media.
  • Congenital Disease: An abnormality present at birth. Example: Cleft lip, Down syndrome.
  • Acquired Disease: A disease developed after birth.
  • Vector: An organism that transmits a pathogen but does not cause the disease itself (e.g., mosquito for malaria).
  • Bacteria: Unicellular, prokaryotic organisms belonging to the Kingdom Monera.
  • Tuberculosis (TB):
    • Causative agent: Mycobacterium tuberculosis.
    • Primarily affects: Lungs (Pulmonary TB).
    • India’s TB Elimination Target: 2025 (five years ahead of the global SDG target of 2030).
  • Antibiotic Resistance (AMR): The ability of a microbe to resist the effects of medication previously used to treat them.
  • Causes of AMR: Incorrect dosage of antibiotics, overuse of antibiotics in livestock farming.
  • Hepatitis: Inflammation of the liver. Hepatitis B and C cause the most deaths and can lead to chronic disease.
  • Vaccine for Hepatitis: A vaccine exists for Hepatitis B, but not for Hepatitis C.
  • Zika Virus:
    • Vector: Aedes mosquito.
    • Congenital Symptom: Microcephaly (abnormally small head in newborns).
  • Nipah Virus:
    • Type: Zoonotic virus.
    • Natural Reservoir: Fruit bats of the Pteropus genus.
  • Innate Immunity: The first line of defense; non-specific and present from birth.
  • Acquired/Adaptive Immunity: Pathogen-specific immunity developed after exposure; characterized by memory.
  • Lymphocytes: A type of White Blood Cell.
    • B cells: Mature in Bone marrow; produce antibodies (Humoral immunity).
    • T cells: Mature in the Thymus gland; responsible for cell-mediated immunity.
  • Antigen: Any substance that triggers an immune response.
  • Antibody: A protein produced by B cells to neutralize a specific antigen.
  • Phagocytosis: The process of a cell engulfing a large particle or another cell.
  • Immunological Memory: The ability of the immune system to respond more rapidly and effectively to a pathogen that has been encountered previously. This is the principle of vaccination.
  • Types of Vaccines:
    1. Live-attenuated: Weakened live virus (e.g., Oral Polio Vaccine, BCG).
    2. Inactivated (Killed): Killed virus (e.g., Injectable Polio Vaccine, Covaxin).
    3. Subunit: Uses only specific parts of the pathogen (e.g., vaccine for Whooping Cough).
    4. Conjugate: Links parts of the pathogen to a carrier protein (e.g., Pneumococcal Conjugate Vaccine).

Mains Insights

GS Paper II: Social Justice - Issues Relating to Health

  • Preventive vs. Curative Healthcare Debate:
    • Argument for Prevention: Investing in preventive healthcare (like vaccination, sanitation, nutrition programs - POSHAN Abhiyaan, and awareness campaigns) is more cost-effective and equitable than a purely curative approach. It reduces the disease burden on the healthcare system, lowers out-of-pocket expenditure for citizens, and improves overall productivity.
    • Policy Linkage: This aligns with the principles of the National Health Policy 2017, which emphasizes a “continuum of care” with a focus on wellness. It is also central to achieving Sustainable Development Goal 3 (Good Health and Well-being).
  • Disease Burden and Social Determinants of Health:
    • Diseases like Tuberculosis disproportionately affect marginalized sections of society. Factors like poverty, malnutrition, poor housing conditions, and overcrowding create a conducive environment for the spread of TB.
    • This highlights the need for a multi-sectoral approach to health, addressing the social determinants of health (SDOH) rather than just the biological causes of disease. Schemes like the Pradhan Mantri Awas Yojana (housing) and the National Food Security Act can have significant positive impacts on public health outcomes.

GS Paper III: Science & Technology; Environmental Conservation

  • Antimicrobial Resistance (AMR): A Silent Pandemic:
    • Threat Multiplier: AMR is not just a health crisis but also a major economic and security threat. It can render modern medicine ineffective, increasing mortality, healthcare costs, and threatening food security.
    • One Health Approach: The solution to AMR requires a ‘One Health’ approach, an integrated, unifying approach that aims to sustainably balance and optimize the health of people, animals, and ecosystems. It recognizes that human health is closely connected to animal health and the shared environment.
    • India’s Initiatives: India’s National Action Plan on AMR (2017-2021) and the ‘Red Line’ campaign on antibiotic packaging are steps in the right direction but require stricter implementation, especially in regulating the use of antibiotics in the poultry and livestock sectors.
  • Rise of Zoonotic Diseases: An Environmental Wake-up Call:
    • Cause-Effect Relationship: The increasing frequency of zoonotic diseases like Nipah, Zika, and COVID-19 is directly linked to anthropogenic environmental changes. Deforestation, habitat fragmentation, and climate change bring wildlife, livestock, and humans into closer contact, increasing the risk of pathogen spillover.
    • Policy Implications: This necessitates strengthening wildlife health surveillance (e.g., the One Health concept), regulating illegal wildlife trade, and integrating environmental conservation into public health planning. The line between environmental policy and health policy is blurring.
  • Biotechnology and Vaccine Development:
    • Innovation: The COVID-19 pandemic catalyzed unprecedented innovation in vaccine technology, particularly mRNA and viral vector platforms. These platforms allow for faster development and production of vaccines compared to traditional methods.
    • Challenges - Vaccine Equity: The pandemic also exposed deep inequalities in global health, leading to debates on “vaccine nationalism” versus “vaccine equity.” Issues like intellectual property rights (TRIPS waiver), technology transfer, and strengthening manufacturing capacity in developing countries are critical for ensuring preparedness for future pandemics.

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