Unit 3: Biology and Human Welfare - Chapter 1: Human Health and Diseases

3.1 Human Health and Diseases

Health is defined by the World Health Organization (WHO) as a state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity.

Pathogens: Bacteria, Viruses, Protozoa, Helminths, Fungi

A pathogen is an organism that causes disease. Pathogens can belong to various groups:

• Bacteria: Unicellular prokaryotic organisms (e.g., Salmonella typhi, Streptococcus pneumoniae).
• Viruses: Non-cellular infectious agents that replicate only inside the living cells of other organisms (e.g., Rhinovirus, HIV, Dengue virus).
• Protozoa: Unicellular eukaryotic organisms (e.g., Entamoeba histolytica, Plasmodium).
• Helminths: Parasitic worms (e.g., Ascaris lumbricoides, Wuchereria bancrofti).
• Fungi: Eukaryotic organisms that include yeasts, molds, and mushrooms (e.g., Microsporum, Epidermophyton, Trichophyton).

Communicable Diseases: Causes, Transmission, Symptoms, Prevention

Communicable diseases (or infectious diseases) are diseases that can be transmitted from one person to another, or from animals to humans.

1. Viral Diseases

• Common Cold (Rhinitis):

  • Cause: Rhinoviruses.
  • Transmission: Droplet infection (coughing, sneezing), contaminated objects.
  • Symptoms: Nasal congestion and discharge, sore throat, hoarseness, cough, headache, fatigue. Usually lasts 3-7 days.
  • Prevention: Avoid contact with infected persons, maintain hygiene.

• Dengue Fever:

  • Cause: Dengue virus (DENV), transmitted by Aedes aegypti mosquito.
  • Transmission: Mosquito bite.
  • Symptoms: High fever, severe headache, pain behind the eyes, muscle and joint pains, rash, mild bleeding (nosebleed, gums).
  • Prevention: Mosquito control (eliminate breeding sites), use repellents, protective clothing.

• Chikungunya:

  • Cause: Chikungunya virus (CHIKV), transmitted by Aedes aegypti and Aedes albopictus mosquitoes.
  • Transmission: Mosquito bite.
  • Symptoms: Abrupt onset of fever, severe joint pain (often debilitating), headache, muscle pain, rash, nausea, fatigue.
  • Prevention: Mosquito control, personal protection from bites.

2. Bacterial Diseases

• Typhoid:

  • Cause: Salmonella typhi bacterium.
  • Transmission: Contaminated food and water.
  • Symptoms: Sustained high fever (39°C to 40°C), weakness, stomach pain, constipation, headache, loss of appetite. Intestinal perforation and death can occur in severe cases.
  • Diagnosis: Widal test is a serological test used to diagnose typhoid fever.
  • Prevention: Proper sanitation, safe drinking water, vaccination.

• Pneumonia:

  • Cause: Streptococcus pneumoniae and Haemophilus influenzae.
  • Transmission: Droplet infection (coughing, sneezing) from infected person.
  • Symptoms: Fever, chills, cough, headache. In severe cases, lips and fingernails may turn greyish to bluish due to lack of oxygen.
  • Prevention: Vaccination, avoid contact with infected persons.

• Plague:

  • Cause: Yersinia pestis bacterium.
  • Transmission: Flea bites (from infected rodents), direct contact with infected animals, or inhalation of infected droplets.
  • Symptoms: Fever, chills, headache, weakness, painful swollen lymph nodes (buboes - in bubonic plague), pneumonia (in pneumonic plague).
  • Prevention: Rodent control, flea control, vaccination (for high-risk individuals).

3. Protozoal Diseases

• Amoebiasis (Amoebic Dysentery):

  • Cause: Entamoeba histolytica (a protozoan parasite).
  • Transmission: Contaminated food and water (cysts are ingested).
  • Symptoms: Constipation, abdominal pain and cramps, stools with excess mucus and blood clots.
  • Prevention: Proper sanitation, hygiene, safe drinking water.

• Malaria:

  • Cause: Plasmodium species (P. vivax, P. malariae, P. ovale, P. falciparum - most severe).
  • Transmission: Bite of infected female Anopheles mosquito.
  • Symptoms: Recurring fever, chills, headache, nausea, vomiting, enlarged spleen and liver.
  • Life Cycle of Plasmodium:
    1. Infective Stage (Sporozoites): When an infected female Anopheles mosquito bites a human, sporozoites (infective form) are injected into the blood.
    2. Liver Stage: Sporozoites reach the liver cells, multiply asexually, and burst the liver cells, releasing merozoites.
    3. Red Blood Cell (RBC) Stage: Merozoites infect RBCs, multiply asexually, and cause the RBCs to rupture, releasing toxins (hemozoin) that cause fever and chills. This cycle repeats.
    4. Gametocytes: Some merozoites develop into male and female gametocytes in RBCs.
    5. Mosquito Stage: When a mosquito bites an infected human, gametocytes enter the mosquito's gut.
    6. Fertilization and Development: Gametocytes fertilize and develop into sporozoites in the mosquito's gut, which then migrate to the salivary glands, ready to infect a new human host.
  • Prevention: Mosquito control (larvicides, adulticides, eliminating breeding sites), use of mosquito nets, repellents, antimalarial drugs.

4. Helminthic Diseases

• Ascariasis:

  • Cause: Ascaris lumbricoides (roundworm).
  • Transmission: Ingestion of contaminated food/water containing Ascaris eggs.
  • Symptoms: Internal bleeding, muscular pain, fever, anemia, blockage of the intestinal passage.
  • Prevention: Proper hygiene, sanitation, avoid open defecation.

• Filariasis (Elephantiasis):

  • Cause: Wuchereria bancrofti and Wuchereria malayi (filarial worms).
  • Transmission: Bite of infected female Culex mosquito.
  • Symptoms: Chronic inflammation of the lymphatic vessels of the lower limbs, leading to gross deformities (elephantiasis). Genital organs may also be affected.
  • Prevention: Mosquito control, avoid mosquito bites.

5. Fungal Diseases

• Ringworm:
  • Cause: Fungi belonging to genera Microsporum, Epidermophyton, Trichophyton.
  • Transmission: Direct contact with infected persons or contaminated objects (towels, clothes).
  • Symptoms: Dry, scaly lesions on skin, nails, and scalp, accompanied by intense itching.
  • Prevention: Maintain personal hygiene, avoid sharing personal items.

Immunity: Innate, Acquired, Humoral, Cell-Mediated

Immunity is the ability of the host to fight against disease-causing organisms (pathogens) conferred by the immune system.

1. Innate Immunity (Non-specific Immunity):

   • Present from birth.
   • Provides non-specific defense against all types of pathogens.
   • Barriers:
     • Physical Barriers: Skin (prevents entry of microorganisms), mucus coating of respiratory, gastrointestinal, and urogenital tracts (traps microbes).
     • Physiological Barriers: Acid in the stomach, saliva in the mouth, tears from eyes (all prevent microbial growth).
     • Cellular Barriers: Phagocytic cells like neutrophils, monocytes, macrophages, and natural killer (NK) cells (destroy microbes).
     • Cytokine Barriers: Virus-infected cells secrete proteins called interferons, which protect non-infected cells from further viral infection.

2. Acquired Immunity (Adaptive/Specific Immunity):

   • Pathogen-specific, characterized by memory.

   • Develops after exposure to a pathogen.

   • Types:

     • Active Immunity: Produced when a host is exposed to antigens (naturally or artificially) and produces antibodies. It is slow but long-lasting.
       • Natural Active: Infection (e.g., recovering from measles).
       • Artificial Active: Vaccination.
     • Passive Immunity: Ready-made antibodies are directly given to protect the body. It is fast but short-lived.
       • Natural Passive: Antibodies from mother to fetus (via placenta) or infant (via colostrum).
       • Artificial Passive: Antivenom, antitoxins.

   • Humoral Immunity (Antibody-Mediated Immunity - AMI):

     • Mediated by B-lymphocytes (B-cells).
     • B-cells produce antibodies that circulate in the blood and lymph to fight pathogens.

   • Cell-Mediated Immunity (CMI):

     • Mediated by T-lymphocytes (T-cells).
     • T-cells directly attack infected cells or regulate other immune cells.
     • Responsible for graft rejection (e.g., organ transplants).

Antibodies: Structure, Types (IgG, IgA, IgM, IgD, IgE)

Antibodies (Immunoglobulins - Igs) are protein molecules produced by B-lymphocytes in response to antigens.

• Structure: Y-shaped molecule composed of four polypeptide chains: two identical light (L) chains and two identical heavy (H) chains. They are held together by disulfide bonds. Each chain has a variable region (antigen-binding site) and a constant region.

• Types (Isotypes): Based on the heavy chain type, there are five major classes of antibodies:

  • IgG: Most abundant antibody in serum, crosses placenta, provides passive immunity to fetus.
  • IgA: Found in secretions (colostrum, tears, saliva, mucus), protects mucous membranes.
  • IgM: Largest antibody, first antibody produced in primary immune response.
  • IgD: Found on the surface of B-cells, involved in B-cell activation.
  • IgE: Involved in allergic reactions and defense against parasites.

Immunisation & Vaccines

Immunisation is the process by which the body is made immune to a disease, typically by vaccination.

Vaccines are biological preparations that provide active acquired immunity to a particular infectious disease. They contain weakened or inactivated pathogens, or their components (antigens), which stimulate the immune system to produce antibodies and memory cells without causing the disease.

• Principle: The principle of immunisation is based on the property of 'memory' of the immune system. When a vaccine is administered, the body produces primary immune response and generates memory B and T cells. Subsequent exposure to the actual pathogen elicits a rapid and strong secondary immune response.
• Types of Vaccines: Live-attenuated, inactivated, toxoid, subunit, recombinant, mRNA vaccines.

AIDS: Cause (HIV), Transmission, ELISA Test, Replication, Prevention

AIDS (Acquired ImmunoDeficiency Syndrome) is a pandemic disease caused by the Human Immunodeficiency Virus (HIV).

• Cause: Human Immunodeficiency Virus (HIV), a retrovirus (contains RNA as genetic material).
• Replication of HIV:
  1. HIV enters the body and infects helper T-lymphocytes (T-cells).
  2. The viral RNA is reverse transcribed into viral DNA by the enzyme reverse transcriptase.
  3. The viral DNA integrates into the host cell's DNA.
  4. The infected cell produces new viral particles.
  5. New viruses are released and infect other helper T-cells, leading to a progressive decrease in the number of helper T-cells.
  6. This leads to immunodeficiency, making the person susceptible to various opportunistic infections.
• Transmission:
  • Sexual contact with an infected person.
  • Transfusion of contaminated blood and blood products.
  • Sharing infected needles (e.g., among intravenous drug abusers).
  • From infected mother to her child through the placenta.
• Diagnosis: ELISA (Enzyme-Linked Immunosorbent Assay) is a widely used diagnostic test for AIDS. Western blot is a confirmatory test.
• Prevention:
  • Avoid sexual contact with unknown partners.
  • Use condoms during sexual intercourse.
  • Avoid sharing needles.
  • Screen blood for HIV before transfusion.
  • Avoid drug abuse.
  • Public awareness campaigns.

Cancer: Benign/Malignant, Causes, Diagnosis, Treatment

Cancer is an abnormal, uncontrolled proliferation of cells that can invade and spread to other parts of the body.

• Types of Tumors:
  • Benign Tumors: Remain confined to their original location and do not spread to other parts of the body. They are generally less harmful.
  • Malignant Tumors: Are cancerous. They grow rapidly, invade surrounding normal tissues, and can spread to distant sites through blood or lymph (metastasis), forming secondary tumors.
• Causes of Cancer (Carcinogens):
  • Physical Carcinogens: Ionizing radiations (X-rays, gamma rays), non-ionizing radiations (UV rays).
  • Chemical Carcinogens: Tobacco smoke (lung cancer), certain dyes, asbestos.
  • Biological Carcinogens: Oncogenic viruses (e.g., Human Papillomavirus - HPV), certain parasites.
  • Oncogenes: Cellular oncogenes (c-onc) or proto-oncogenes, when activated under certain conditions, can lead to oncogenic transformation of cells.
• Diagnosis:
  • Biopsy and Histopathological Studies: Tissue samples are examined under a microscope.
  • Radiography (X-rays), CT (Computed Tomography) Scan, MRI (Magnetic Resonance Imaging): To detect tumors in internal organs.
  • Blood and Bone Marrow Tests: For leukemias.
  • Molecular Biology Techniques: To detect genes associated with cancer.
• Treatment:
  • Surgery: Removal of the tumor.
  • Radiotherapy: Cancer cells are irradiated lethally, taking care to protect surrounding normal tissue.
  • Chemotherapy: Drugs are used to kill cancer cells. Side effects include hair loss, anemia.
  • Immunotherapy: Patients are given biological response modifiers (e.g., alpha-interferon) to activate their immune system and help destroy the tumor.

Allergies: Causes, Symptoms

Allergy is the exaggerated response of the immune system to certain antigens present in the environment.

• Causes (Allergens): Substances that cause allergic reactions (e.g., pollen, dust mites, animal dander, certain foods, drugs).
• Mechanism: When exposed to allergens, the body produces IgE antibodies. These IgE antibodies bind to mast cells and basophils, causing them to release chemicals like histamine and serotonin.
• Symptoms: Sneezing, watery eyes, runny nose, difficulty breathing (asthma), skin rashes (hives).
• Treatment: Antihistamines, adrenaline, and steroids can quickly reduce the symptoms of allergy.

Drug & Alcohol Abuse: Effects, Types, Prevention

Drug abuse refers to the use of certain drugs for non-medical purposes, leading to physical, psychological, and social harm.

Alcohol abuse refers to excessive and harmful consumption of alcoholic beverages.

• Commonly Abused Drugs:

  • Opioids: Derived from the opium poppy (Papaver somniferum). Bind to opioid receptors in the CNS and gastrointestinal tract. Examples: Morphine, heroin (smack).
    • Effects: Sedative, painkiller, euphoria, drowsiness, constipation.
  • Cannabinoids: Obtained from the inflorescences of the cannabis plant (Cannabis sativa). Interact with cannabinoid receptors in the brain. Examples: Marijuana, hashish, charas, ganja.
    • Effects: Affect cardiovascular system, altered perception, hallucinations.
  • Cocaine (Coke/Crack): Obtained from coca plant (Erythroxylum coca). Interferes with the transport of dopamine.
    • Effects: Stimulant, sense of euphoria, increased energy. Excessive dosage causes hallucinations.
  • Other Drugs: Barbiturates, amphetamines, benzodiazepines (sedatives and tranquilizers), LSD (hallucinogen).

• Effects of Drug and Alcohol Abuse:

  • Short-term: Reckless behavior, violence, impaired judgment, mood swings, nausea, vomiting, loss of coordination.
  • Long-term: Liver cirrhosis (alcohol), nervous system damage, cardiovascular diseases, mental disorders, addiction, withdrawal symptoms, social and economic problems, increased risk of infections (e.g., AIDS, hepatitis due to shared needles).
  • Adolescent Abuse: Early age of initiation, peer pressure, curiosity, stress, family problems. Leads to poor academic performance, depression, aggression, isolation.

• Prevention and Control:

  • Avoid Undue Peer Pressure: Educate adolescents about the dangers.
  • Education and Counselling: Identify and counsel those at risk.
  • Seeking Help from Parents and Peers: Open communication.
  • Looking for Danger Signs: Changes in behavior, academic decline, withdrawal.
  • Seeking Professional and Medical Help: Rehabilitation programs.