Human Health and Disease

Human Health and Disease: An Overview

Health is more than just the absence of disease; it’s a state of complete physical, mental, and social well-being. When individuals are healthy, they are more efficient, which boosts productivity and economic prosperity. Health also increases longevity and reduces infant and maternal mortality.

Factors Affecting Health

Health is primarily influenced by:

• Genetic disorders: Deficiencies present from birth or inherited from parents.
• Infections.
• Lifestyle: This includes dietary habits, water intake, rest, exercise, and other personal habits.

Maintaining Good Health

Key practices for maintaining good health include:

• Balanced diet.
• Personal hygiene.
• Regular exercise, including practices like Yoga for physical and mental well-being.
• Awareness about diseases and their impact.
• Vaccination (immunisation) against infectious diseases.
• Proper disposal of wastes.
• Control of vectors.
• Maintaining hygiene in food and water resources.

Disease Classification

Diseases can be broadly classified into:

• Infectious diseases: Easily transmitted from one person to another (e.g., common cold, typhoid, AIDS). These are very common.
• Non-infectious diseases: Not easily transmitted (e.g., cancer, which is a major cause of death; drug and alcohol abuse also adversely affect health).

Common Diseases in Humans

Disease-causing organisms are known as pathogens. Most parasites act as pathogens, harming their hosts. Pathogens enter the body by various means, multiply, and interfere with normal vital activities, leading to morphological and functional damage. They must adapt to the host’s internal environment, such as surviving low pH in the stomach.

Bacterial Diseases

• Typhoid:

  • Cause: Salmonella typhi (pathogenic bacterium).
  • Transmission: Through contaminated food and water, entering the small intestine and migrating via blood to other organs.
  • Symptoms: Sustained high fever (39° to 40°C), weakness, stomach pain, constipation, headache, loss of appetite. Severe cases can lead to intestinal perforation and death.
  • Diagnosis: Widal test.
  • Notable Case: Mary Mallon (“Typhoid Mary”), a cook and carrier who spread typhoid for years.

• Pneumonia:

  • Cause: Bacteria like Streptococcus pneumoniae and Haemophilus influenzae.
  • Infection Site: Alveoli (air-filled sacs) of the lungs, which fill with fluid, causing severe respiratory problems.
  • Symptoms: Fever, chills, cough, headache. In severe cases, lips and fingernails may turn gray to bluish.
  • Transmission: Inhaling droplets/aerosols from an infected person or sharing contaminated objects (glasses, utensils).

• Other bacterial diseases: Dysentery, plague, diphtheria.

Viral Diseases

• Common Cold:
  • Cause: Rhino viruses.
  • Infection Site: Nose and respiratory passage (not lungs).
  • Symptoms: Nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness (usually lasting 3-7 days).
  • Transmission: Droplets from cough/sneeze (inhaled directly) or transmitted via contaminated objects (pens, books, doorknobs, keyboards).

Protozoan Diseases

• Malaria:

  • Cause: Plasmodium (a protozoan). Different species include P. vivax, P. malariae, and the most serious, potentially fatal P. falciparum (malignant malaria).
  • Life Cycle & Transmission:
    • Infectious form (sporozoites) enters humans via infected female Anopheles mosquito bite.
    • Parasites multiply in liver cells, then attack and rupture red blood cells (RBCs).
    • Rupture of RBCs releases haemozoin, causing chills and high fever every 3-4 days.
    • When mosquito bites an infected person, parasites enter mosquito, develop into sporozoites, and are stored in salivary glands.
    • Requires two hosts: human and mosquito (the mosquito is also the vector).

• Amoebiasis (Amoebic Dysentery):

  • Cause: Entamoeba histolytica (protozoan parasite) in the large intestine.
  • Symptoms: Constipation, abdominal pain and cramps, stools with excess mucous and blood clots.
  • Transmission: Houseflies act as mechanical carriers, transmitting parasites from infected faeces to food. Main source is drinking water and food contaminated by faecal matter.

Helminthic Diseases

• Ascariasis:

  • Cause: Ascaris (common roundworm), an intestinal parasite.
  • Symptoms: Internal bleeding, muscular pain, fever, anemia, blockage of intestinal passage.
  • Transmission: Eggs excreted in faeces contaminate soil, water, plants. Infection occurs through contaminated water, vegetables, fruits.

• Filariasis (Elephantiasis):

  • Cause: Wuchereria (filarial worms, e.g., W. bancrofti and W. malayi).
  • Symptoms: Slowly developing chronic inflammation of organs where they live for years, typically lymphatic vessels of lower limbs, leading to gross deformities. Genital organs can also be affected.
  • Transmission: Bite of female mosquito vectors.

Fungal Diseases

• Ringworms:
  • Cause: Fungi from genera Microsporum, Trichophyton, and Epidermophyton.
  • Symptoms: Dry, scaly lesions on skin, nails, and scalp, accompanied by intense itching.
  • Fungal Growth: Favored by heat and moisture, thriving in skin folds (e.g., groin, between toes).
  • Transmission: From soil or by using contaminated towels, clothes, or combs of infected individuals.

Prevention and Control of Infectious Diseases

General measures include:

• Personal hygiene: Keeping body clean, consuming clean drinking water, food, vegetables, fruits.
• Public hygiene: Proper disposal of waste and excreta, periodic cleaning and disinfection of water reservoirs, pools, cesspools, and tanks, observing standard hygiene in public catering. These are crucial for food- and water-borne diseases like typhoid, amoebiasis, and ascariasis.
• Air-borne diseases (pneumonia, common cold): Avoid close contact with infected persons or their belongings.
• Vector-borne diseases (malaria, filariasis, dengue, chikungunya):
  • Control/eliminate vectors and breeding places: Avoid water stagnation, regular cleaning of coolers, use mosquito nets.
  • Introduce fishes like Gambusia in ponds (feed on mosquito larvae).
  • Spray insecticides in ditches, drainage areas, swamps.
  • Install wire mesh on doors and windows to prevent mosquito entry.
• Advancements in biology: Use of vaccines and immunisation programmes have eradicated smallpox and controlled diseases like polio, diphtheria, pneumonia, and tetanus. Discovery of antibiotics and other drugs effectively treats infectious diseases.

Immunity

Immunity is the overall ability of the host to fight disease-causing organisms, conferred by the immune system.

Types of Immunity

1. Innate Immunity:

   • Non-specific defense present from birth.
   • Provides various barriers to prevent entry of foreign agents.
   • Four types of barriers:
     • Physical barriers: Skin (main barrier), mucus coating of respiratory, gastrointestinal, and urogenital tracts (trap microbes).
     • Physiological barriers: Acid in stomach, saliva in mouth, tears from eyes (all prevent microbial growth).
     • Cellular barriers: Certain leukocytes (WBCs) like PMNL-neutrophils, monocytes, natural killer cells, and macrophages in tissues can phagocytose and destroy microbes.
     • Cytokine barriers: Interferons (proteins secreted by virus-infected cells) protect non-infected cells from further viral infection.

2. Acquired Immunity:

   • Pathogen-specific and characterized by memory.
   • Primary response: Low intensity upon first encounter with a pathogen.
   • Secondary (anamnestic) response: Highly intensified upon subsequent encounter with the same pathogen, due to memory.
   • Carried out by B-lymphocytes and T-lymphocytes.
     • B-lymphocytes: Produce antibodies (proteins) that fight pathogens in the blood. This is called humoral immune response (or antibody-mediated immune response). Antibodies are represented as H₂L₂ (two heavy, two light chains); types include IgA, IgM, IgE, IgG.
     • T-lymphocytes: Do not secrete antibodies but help B cells produce them. They also mediate cell-mediated immune response (CMI).

Organ Transplantation and CMI

• Tissue matching and blood group matching are essential before organ transplantation.
• Grafts from different sources are rejected because the body differentiates ‘self’ from ‘non-self’.
• Cell-mediated immune response is responsible for graft rejection.
• Patients must take immunosuppressants for life after transplantation.

Active and Passive Immunity

• Active Immunity:

  • Produced when a host is exposed to antigens (living/dead microbes, proteins), leading to antibody production in the host body.
  • Slow and takes time for full effective response.
  • Induced by deliberate injection of microbes (immunisation) or natural infection.

• Passive Immunity:

  • Ready-made antibodies are directly given to protect the body.
  • Examples:
    • Mother’s milk (colostrum) containing abundant IgA antibodies protects newborns.
    • Foetus receives antibodies from mother through the placenta during pregnancy.
    • Injecting preformed antibodies or antitoxin (e.g., for tetanus, snakebites).

Vaccination and Immunisation

• Principle: Based on the ‘memory’ property of the immune system.
• Process: A vaccine (preparation of antigenic proteins or inactivated/weakened pathogen) is introduced into the body.
• Outcome:
  • Antibodies are produced, which neutralize pathogenic agents during actual infection.
  • Memory B and T-cells are generated, leading to a quick and massive antibody production upon subsequent exposure.
• Passive Immunisation: Direct injection of preformed antibodies when a quick immune response is needed (e.g., tetanus antitoxin, anti-snake venom).
• Modern Vaccines: Recombinant DNA technology allows large-scale production of antigenic polypeptides in bacteria or yeast (e.g., Hepatitis B vaccine from yeast).

Allergies

• Definition: An exaggerated response of the immune system to certain environmental antigens.
• Allergens: Substances causing allergy (e.g., mites in dust, pollens, animal dander).
• Antibodies Involved: Primarily IgE type.
• Symptoms: Sneezing, watery eyes, running nose, difficulty breathing.
• Cause of Symptoms: Release of chemicals like histamine and serotonin from mast cells.
• Diagnosis: Patient exposed to small doses of possible allergens, reactions studied.
• Treatment: Drugs like anti-histamine, adrenalin, and steroids quickly reduce symptoms.
• Modern Lifestyle Link: May lead to lowering of immunity and increased sensitivity to allergens, especially in children in metro cities.

Auto Immunity

• Basis: Higher vertebrates can distinguish ‘foreign’ organisms/molecules from ‘self-cells’.
• Auto-immune Disease: Sometimes, due to genetic or unknown reasons, the body attacks its own cells, causing damage.
• Example: Rheumatoid arthritis.

Immune System in the Body

The human immune system comprises lymphoid organs, tissues, cells, and soluble molecules like antibodies. It recognizes, responds to, and remembers foreign antigens, and plays a role in allergic reactions, auto-immune diseases, and organ transplantation.

• Lymphoid Organs: Sites for origin, maturation, and proliferation of lymphocytes.
  • Primary Lymphoid Organs:
    • Bone Marrow: Main lymphoid organ where all blood cells (including lymphocytes) are produced. Provides micro-environment for B-lymphocyte development and maturation.
    • Thymus: Lobed organ near heart, beneath breastbone. Large at birth, reduces with age. Provides micro-environment for T-lymphocyte maturation.
  • Secondary Lymphoid Organs: Lymphocytes migrate here after maturation. They provide sites for interaction with antigens, leading to proliferation into effector cells.
    • Spleen: Large bean-shaped organ, contains lymphocytes and phagocytes. Acts as a blood filter by trapping blood-borne micro-organisms. Also a reservoir of erythrocytes.
    • Lymph Nodes: Small, solid structures along lymphatic system. Trap micro-organisms/antigens from lymph and tissue fluid, activating lymphocytes and causing immune response.
    • Tonsils.
    • Peyer’s patches of small intestine.
    • Appendix.
• Mucosa-Associated Lymphoid Tissue (MALT): Lymphoid tissue within the lining of major tracts (respiratory, digestive, urogenital). Constitutes about 50% of lymphoid tissue in the human body.

AIDS (Acquired Immuno Deficiency Syndrome)

• Definition: A deficiency of the immune system acquired during an individual’s lifetime; not congenital. “Syndrome” refers to a group of symptoms.
• First Reported: 1981. Has spread globally, causing millions of deaths.
• Cause: Human Immuno deficiency Virus (HIV), a retrovirus (has an RNA genome within an envelope).

Transmission of HIV

Generally occurs by:

• Sexual contact with an infected person.
• Transfusion of contaminated blood and blood products.
• Sharing infected needles (e.g., among intravenous drug abusers).
• From an infected mother to her child through the placenta.
• High-risk groups: Individuals with multiple sexual partners, intravenous drug addicts, those requiring repeated blood transfusions, and children born to HIV-infected mothers.
• Important Note: HIV/AIDS is not spread by mere touch or physical contact; it spreads only through body fluids.

Mechanism of AIDS Virus Action

• Entry: Virus enters macrophages.
• Replication in Macrophages: Viral RNA genome replicates to form viral DNA using reverse transcriptase. This viral DNA incorporates into the host cell’s DNA, directing it to produce new virus particles. Macrophages act as “HIV factories”.
• Attack on Helper T-lymphocytes (T_H): HIV also enters T_H cells, replicates, and releases progeny viruses. These new viruses attack other T_H cells.
• Immune Deficiency: This leads to a progressive decrease in the number of helper T-lymphocytes.
• Symptoms: During this period, the person experiences bouts of fever, diarrhoea, and weight loss.
• Opportunistic Infections: Due to the severe decrease in T_H cells, the patient becomes immuno-deficient and suffers from infections that would normally be overcome, such as those caused by Mycobacterium (bacteria), viruses, fungi, and parasites like Toxoplasma. The patient cannot protect themselves against these.
• Time-lag: There’s a time-lag between infection and AIDS symptoms, varying from a few months to many years (typically 5-10 years).

Diagnosis and Treatment

• Diagnostic Test: ELISA (Enzyme Linked Immuno-Sorbent Assay) is widely used.
• Treatment: Anti-retroviral drugs are only partially effective; they prolong life but cannot prevent death.

Prevention of AIDS

Since there is no cure, prevention is the best approach:

• Awareness and Education: National AIDS Control Organisation (NACO) and NGOs educate people. WHO runs programs to prevent spread.
• Blood Safety: Making blood (from blood banks) safe from HIV.
• Sterile Equipment: Ensuring use of only disposable needles and syringes in healthcare settings.
• Condom Distribution: Free distribution.
• Drug Abuse Control.
• Safe Sex Advocacy.
• Regular HIV check-ups for susceptible populations.
• Social Support: HIV/AIDS-infected persons should not be isolated; they need help and sympathy. Society and medical fraternity must act together.

Cancer

Cancer is one of the most dreaded diseases and a major cause of death globally. Research into its development, treatment, and control is intense.

Characteristics of Cancer Cells

• Uncontrolled Growth: Normal cells have highly controlled growth and differentiation. Cancer cells lose these regulatory mechanisms.
• Loss of Contact Inhibition: Normal cells exhibit contact inhibition, where contact with other cells inhibits uncontrolled growth. Cancer cells lose this property.
• Tumor Formation: Uncontrolled division leads to masses of cells called tumors.

Types of Tumors

1. Benign Tumors:

   • Normally confined to their original location.
   • Do not spread to other parts of the body.
   • Cause little damage.

2. Malignant Tumors:

   • Mass of rapidly proliferating cells called neoplastic or tumor cells.
   • Grow very rapidly, invading and damaging surrounding normal tissues.
   • Compete for vital nutrients, starving normal cells.
   • Metastasis: The most feared property. Cells sloughed from these tumors can reach distant sites via blood, where they start new tumors.

Causes of Cancer (Carcinogens)

Transformation of normal cells into cancerous (neoplastic) cells can be induced by:

• Physical Agents:
  • Ionising radiations: X-rays, gamma rays (cause DNA damage).
  • Non-ionising radiations: UV radiation (cause DNA damage).
• Chemical Agents:
  • Chemical carcinogens in tobacco smoke are a major cause of lung cancer.
• Biological Agents:
  • Oncogenic viruses: Cancer-causing viruses with viral oncogenes.
  • Cellular oncogenes (c-onc) or proto-oncogenes: Genes present in normal cells that, when activated under certain conditions, can lead to oncogenic transformation.

Cancer Detection and Diagnosis

Early detection is essential for successful treatment.

• Biopsy and Histopathological Studies: A piece of suspected tissue is stained and examined under a microscope by a pathologist.
• Blood and Bone Marrow Tests: For increased cell counts in leukemias (blood cancers).
• Imaging Techniques: Useful for detecting internal organ cancers.
  • Radiography (X-rays).
  • CT (Computed Tomography): Uses X-rays to generate 3D images of internal organs.
  • MRI (Magnetic Resonance Imaging): Uses strong magnetic fields and non-ionizing radiations for accurate detection of pathological and physiological changes in living tissue.
• Antibodies: Used against cancer-specific antigens for detection.
• Molecular Biology Techniques: Can detect genes in individuals with inherited susceptibility to certain cancers. Identifying such genes helps in prevention by advising individuals to avoid specific carcinogens (e.g., tobacco smoke for lung cancer).

Treatment of Cancer

Common approaches:

• Surgery: To remove tumors.
• Radiation Therapy (Radiotherapy): Tumor cells are lethally irradiated, carefully protecting surrounding normal tissues.
• Chemotherapy: Uses chemotherapeutic drugs to kill cancerous cells. Some are tumor-specific. Side effects often include hair loss, anemia.
• Combination Therapy: Most cancers are treated by a combination of surgery, radiotherapy, and chemotherapy.
• Immunotherapy: Cancer cells can avoid immune detection. Patients are given biological response modifiers (e.g., alpha-interferon) to activate their immune system and destroy tumors.

Drugs and Alcohol Abuse

The rise in drug and alcohol abuse, especially among youth, is a significant concern due to its harmful effects. Proper education and guidance are crucial for prevention.

Commonly Abused Drugs

• Opioids:
  • Bind to specific opioid receptors in the central nervous system and gastrointestinal tract.
  • Heroin (smack): Chemically diacetylmorphine, a white, odorless, bitter crystalline compound.
  • Source: Obtained by acetylation of morphine, which is extracted from the latex of the poppy plant (Papaver somniferum).
  • Usage: Generally taken by snorting and injection.
  • Effect: A depressant that slows down body functions.
• Cannabinoids:
  • Interact with cannabinoid receptors primarily in the brain.
  • Source: Natural cannabinoids obtained from the inflorescences of the plant Cannabis sativa.
  • Forms: Flower tops, leaves, and resin are used in various combinations to produce marijuana, hashish, charas, and ganja.
  • Usage: Generally by inhalation and oral ingestion.
  • Effect: Known for effects on the cardiovascular system. Some sportspersons abuse cannabinoids.
• Coca Alkaloids (Cocaine):
  • Source: Obtained from the coca plant (Erythroxylum coca), native to South America.
  • Effect: Interferes with the transport of the neurotransmitter dopamine.
  • Common Name: Coke or crack. Usually snorted.
  • Action: Potent stimulating action on the central nervous system, producing euphoria and increased energy.
  • Overdose: Excessive dosage causes hallucinations.
  • Other hallucinogenic plants: Atropa belladona and Datura.
• Other Abused Drugs: Barbiturates, amphetamines, benzodiazepines. These are normally used as medicines for mental illnesses (depression, insomnia) but are often abused.
• Morphine: An effective sedative and painkiller, useful for post-surgery patients.
• Definition of Drug Abuse: Taking drugs for a purpose other than medicinal use, or in amounts/frequency that impairs physical, physiological, or psychological functions.

Tobacco Use

• Used for over 400 years, smoked, chewed, or used as snuff.
• Contains nicotine, an alkaloid.
• Nicotine’s Effect: Stimulates the adrenal gland to release adrenaline and nor-adrenaline, which raise blood pressure and increase heart rate.
• Health Risks of Smoking: Increased incidence of cancers of the lung, urinary bladder, and throat; bronchitis, emphysema, coronary heart disease, gastric ulcer.
• Health Risks of Tobacco Chewing: Increased risk of oral cavity cancer.
• Blood Oxygen: Smoking increases carbon monoxide (CO) in blood, reducing oxygen bound to haemoglobin, causing oxygen deficiency.
• Addictive Nature: Despite statutory warnings, smoking is prevalent. Addicts require counselling and medical help.

Adolescence and Drug/Alcohol Abuse

• Adolescence Period: Roughly 12-18 years of age, a bridge linking childhood and adulthood, marked by biological and behavioral changes. It’s a vulnerable phase of mental and psychological development.
• Motivations for Abuse:
  • Curiosity, need for adventure and excitement, experimentation.
  • Perceived benefits (e.g., escape from problems).
  • Stress from academic pressure or examinations.
  • Perception of being ‘cool’ or progressive, influenced by media (TV, movies, internet).
  • Unstable or unsupportive family structures.
  • Peer pressure.

Addiction and Dependence

• Addiction: A psychological attachment to certain effects of drugs/alcohol (e.g., euphoria, temporary well-being). Drives repeated use even when not needed or self-destructive.
• Tolerance: With repeated use, the body’s receptors increase their tolerance, requiring higher doses for the same effect, leading to greater intake and addiction.
• Vicious Circle: Even single use can lead to addiction, pulling the user into regular abuse from which it’s hard to escape without guidance.
• Dependence: The body manifests an unpleasant withdrawal syndrome if regular use is abruptly stopped.
  • Symptoms: Anxiety, shakiness, nausea, sweating.
  • Severity: Can be severe, even life-threatening, requiring medical supervision.
  • Social Impact: Leads to ignoring social norms to satiate needs, causing social adjustment problems.

Effects of Drug/Alcohol Abuse

• Immediate Adverse Effects: Reckless behavior, vandalism, violence.
• Overdose: Excessive doses can lead to coma and death due to respiratory failure, heart failure, or cerebral hemorrhage. Combining drugs or taking them with alcohol increases overdose risk.
• Warning Signs in Youth: Drop in academic performance, unexplained absence, lack of personal hygiene, withdrawal, isolation, depression, fatigue, aggressive behavior, deteriorating relationships, loss of interest in hobbies, changes in sleep/eating habits, weight fluctuations.
• Financial and Social Strain: Abusers may steal for money. Causes mental and financial distress to family and friends.
• Serious Infections: Intravenous drug users are at much higher risk of acquiring AIDS and Hepatitis B due to sharing infected needles/syringes. These are chronic and ultimately fatal, and can also be transmitted sexually.
• Long-term Health Damage:
  • Alcohol use during adolescence can lead to heavy drinking in adulthood.
  • Chronic use of drugs and alcohol damages the nervous system and liver (cirrhosis).
  • Drug/alcohol use during pregnancy adversely affects the foetus.
• Misuse by Sportspersons (Doping):
  • Abuse narcotic analgesics, anabolic steroids, diuretics, and certain hormones to increase muscle strength, bulk, aggressiveness, and athletic performance.
  • Side Effects of Anabolic Steroids:
    • Females: Masculinization, increased aggressiveness, mood swings, depression, abnormal menstrual cycles, excessive facial/body hair, clitoral enlargement, deepening of voice.
    • Males: Acne, increased aggressiveness, mood swings, depression, reduced testicle size, decreased sperm production, potential kidney/liver dysfunction, breast enlargement, premature baldness, prostate gland enlargement.
    • Both Adolescents: Severe facial/body acne, premature closure of growth centers of long bones (stunted growth).
  • Many of these effects can be permanent with prolonged use.

Prevention and Control of Drug/Alcohol Abuse

“Prevention is better than cure.” Habits often start young, especially during adolescence. Identifying situations that push adolescents towards abuse and taking timely remedial measures is key. Parents and teachers have a special responsibility.

• Avoid Undue Peer Pressure:
  • Respect and nurture each child’s individual choice and personality.
  • Do not push children beyond their threshold limits in studies, sports, or other activities.
• Education and Counselling:
  • Educate and counsel adolescents to face problems, stress, and accept disappointments/failures.
  • Channelize energy into healthy pursuits: sports, reading, music, yoga, extracurricular activities.
• Seeking Help from Parents and Peers:
  • Seek immediate help from parents and trusted friends for guidance.
  • Helps youngsters vent anxiety and guilt.
• Looking for Danger Signs:
  • Alert parents and teachers should identify warning signs like academic decline, changes in hygiene/mood, social withdrawal.
  • Friends should also report concerns to parents/teachers.
  • Appropriate measures for diagnosis and treatment should follow.
• Seeking Professional and Medical Help:
  • Qualified psychologists, psychiatrists, and de-addiction/rehabilitation programs are available.
  • With support, effort, and willpower, affected individuals can fully recover and lead normal, healthy lives.