Comprehensive Notes on Disease and Immunity

Health and Disease

Health vs. Disease

• Health: Defined as complete mental, physical, and social well-being, not just the absence of physical ailment.
• Disease: A condition where the health of an organism is impaired.

Types of Diseases

1. Pathogenic: Caused by parasitic organisms called pathogens (viruses, bacteria, fungi, protozoa, worms).
2. Deficiency: Caused by a lack of nutrients (vitamins or minerals) in the diet.
3. Hereditary: Caused by genes passed from one generation to the next.
4. Physiological: Caused by a malfunction of the body’s organs/systems.

Diseases are also categorized as communicable (transmissible) and non-communicable (non-transmissible).

• Non-Communicable Diseases (NCDs): Not directly transmitted (e.g., Parkinson's, autoimmune diseases, strokes, heart diseases, cancers, diabetes).
• Communicable Diseases: Spread from person to person via blood, bodily fluids, airborne viruses, or insect bites.

Examples, Causes, Symptoms, Treatment, and Control of Different Diseases

1. Pathogenic Diseases

• Cause: Parasitic organisms (pathogens) such as viruses, bacteria, fungi, protozoa, and worms.
• Example: Influenza (flu)
  • Cause: Virus that invades the body through contact with an infected person; airborne or droplet borne.
  • Symptoms: Headache, sore throat, muscular pains, fever.
  • Treatment: Rest and treatments for symptoms. Vaccines for specific strains.
  • Control: Prevent overcrowding to reduce virus spread. Minimize droplet infection through coughs and sneezes.

2. Deficiency Diseases

• Cause: Lack of a nutrient (vitamin or mineral) in the diet.
• Example: Iron-deficiency anaemia
  • Cause: Lack of iron, needed to make haemoglobin, a vital component of red blood cells that carries oxygen.
  • Symptoms: Weakness, fatigue, shortness of breath, pale appearance, increased heart beat.
  • Treatment: Eating iron-rich foods (red meat, dark green leafy vegetables). Taking iron tablets.
  • Control: Educating individuals about the importance of a balanced diet and specific nutrients.

3. Hereditary Diseases

• Cause: Genes passed on from one generation to the next.
• Example: Sickle cell anaemia
  • Cause: Inherited gene that causes red blood cells to have a sickle shape, reducing oxygen-carrying capacity.
  • Symptoms: Weakness, tiredness, weight loss, potentially leading to kidney and heart failure.
  • Treatment: No cure available, individuals should avoid situations with reduced oxygen.
  • Control: Genetic counselling.

4. Physiological Diseases

• Cause: Malfunction of an organ/system in the body.
• Example: Diabetes
  • Cause: Inability of the islet of Langerhans in the pancreas to produce insulin, preventing body cells from absorbing glucose.
  • Symptoms: Tiredness, continual thirst, weight loss, increased urination, coma.
  • Treatment: Insulin injection or tablets, low carbohydrate diet, exercise.
  • Control: Education on the importance of diet and exercise.

Global Distribution of Diseases

• Developed countries have fewer deaths from communicable diseases compared to developing countries.
• Developed countries have more deaths from physiological diseases like cancer and heart disease.
• This difference is due to wealth, standards, medical practices, overcrowding, clean water access, preventative medicine, and nutrition.

Pathogenic Diseases in Detail

• Pathogens are disease-causing organisms living on or inside a host.
• Transmission can occur through direct contact, dust particles, airborne droplets, contact with faeces, or vectors (animals).

Examples of Pathogens

• Cellular (Living):
  • Parasites (e.g., helminthes like tapeworm)
  • Protozoa (e.g., plasmodia causing malaria)
  • Fungi (e.g., tinea causing Athlete's foot)
  • Prokaryotes (i.e., bacteria causing Leprosy)
• Acellular (Non-Living):
  • Virus (e.g., HIV causing AIDS)
  • Prion (causing CJD)

Vectors

• Vectors are animals (mainly insects) that spread disease by transferring pathogens from host to host.
• Examples: flies, mosquitoes, rats.
• Mosquitoes are vectors for malaria.

Controlling Vectors

• Controlling vectors is a good way to control pathogenic diseases.
• Malaria spread has been controlled by controlling the mosquito population.
• Understanding the life cycle of the mosquito is important for control.

The Life Cycle of the Mosquito

1. Egg: Hatches when exposed to water.
2. Larva: (Wriggler) Lives in water, molts several times, surfaces to breathe air.
3. Pupa: (Tumbler) Does not feed, stage just before emerging as adult.
4. Adult: Flies shortly after emerging; only the female bites and feeds on blood.

Mosquito Eradication Program

• Knowing the mosquito life cycle helps control mosquito reproduction.
• Methods include using mosquito nets, pouring oil into open water, and cutting down bushes.

AIDS and Other STDs

• Pathogens vary in size and curability.
• Sexually transmitted diseases (STDs) or sexually transmitted infections (STIs) are acquired through sexual contact.
• Organisms (bacteria, viruses, or parasites) are transmitted through blood, semen, or vaginal and other bodily fluids.
• Spread through intimate contact with an infected person.

AIDS (Acquired Immune Deficiency Syndrome)

• Caused by the Human Immunodeficiency Virus (HIV).
• Transmitted through blood or semen during activities like blood transfusion, sexual intercourse, close contact with open wounds, or sharing needles. Infected mothers can pass the virus through the placenta or breastfeeding.
• HIV targets the body’s immune system, leaving it vulnerable to infections.
• Originated in Central Africa and has killed over 3 million people worldwide.

Symptoms and Control of STDs

1. AIDS:
   • Causative Agent: HIV (virus)
   • Symptoms: Persistent coughs, fever, skin rashes, swollen lymph glands, diarrhea, wasting away of body, weakness. Opportunistic infections (pneumonia, cancers, tuberculosis).
   • Control: Keep to one sexual partner, wear a condom during sex, sex education, vaccine development.
2. Gonorrhoea:
   • Causative Agent: Bacterium
   • Symptoms: Yellowish discharge from urethra, pain when urinating. May cause inflammation of the fallopian tubes and sperm ducts leading to sterility, arthritis, weakened heart, blindness.
   • Control: Keep to one sexual partner, wear a condom during sex, sex education, treatment by antibiotics (e.g., penicillin).
3. Syphilis:
   • Causative Agent: Bacterium
   • Symptoms: Painful ulcers in the genital area (primary), skin rash and sore throat (secondary), skin sore, scarred liver, blindness, insanity, paralysis, and heart failure (tertiary).
   • Control: Keep to one sexual partner, sex education. Effective antibiotic is penicillin, but it won't reverse damage of later symptoms.

• Stages of Syphilis: Primary, Secondary, Latent, Late (Tertiary).

1. Genital Herpes:
   • Causative Agent: Virus
   • Symptoms: Blisters in the genital area that burst forming ulcers. These may heal and reoccur.
   • Control: Keep to one sexual partner, avoid contact with blisters/ulcers. No known cure.

Common STDs

• Genital Herpes, Syphilis, Hepatitis B Virus (HBV), HIV.

Genital Herpes:

• A viral infection that can cause painful blisters or sores but many people have no symptoms.
• Transmitted through vaginal, oral, or anal sex, or skin-to-skin sexual contact.
• No cure, but medications can treat symptoms and reduce outbreaks.

Syphilis:

• A bacterial infection that can cause a single, painless sore/chancre and other symptoms may appear months later.
• Transmitted through vaginal, oral, or anal sex, and can cause damage to the brain, heart, and nervous system if untreated.
• Antibiotic treatment can cure it, but can't undo existing damage.

Hepatitis B Virus (HBV):

• A viral infection, either acute or chronic.
• Transmitted through vaginal, oral, or anal sex, sharing needles, or exposure to bodily fluids.
• May cause tiredness, aches, nausea, and yellowing of the skin. Acute HBV is treated with rest and chronic HBV may be treated with medicine.

HIV:

• HIV is the virus that causes AIDS.
• Transmitted through vaginal, oral, or anal sex, sharing needles, or from mother to child during pregnancy or breastfeeding.
• There is no cure for HIV or AIDS, but antiretroviral treatment can slow the progression of the disease.

Social and Economic Implications of STDs

• High costs for treatment and care.
• Reduction in workforce.
• Emotional and financial suffering for families.
• Significant global investment in HIV research.
• Stigma and alienation of people with AIDS.
• Millions of HIV-infected children worldwide.

The Role of Blood in Defending the Body

• The skin is the body’s first line of defense.
• Blood clots and scar tissue block openings in the skin barrier.
• Phagocytes (white blood cells) engulf and kill microorganisms.
• Lymphocytes produce and release antibodies to destroy dangerous foreign organisms (antigens).

How Lymphocytes Work

• Lymphocytes recognize specific pathogens and make antibodies.
• They can mobilize other lymphocytes to make antibodies.
• Antigens are foreign substances that cause antibody formation.

White Blood Cells

1. Kill the antigen
2. Cause antigens to clump together
3. Neutralize toxins produced by antigens
4. Prevent antigen entry into body cells

• It takes time for lymphocytes to recognize antigens and make antibodies which is why symptoms can present.
• After fighting the antigen, memory lymphocytes remain to quickly recognize future antigens and make antibodies.

Immunity

• Immunity: The ability to resist a particular infection or toxin by the action of specific antibodies or sensitized white blood cells
• Two main types of immunity:
  1. Natural immunity
  2. Artificial immunity

Natural Immunity

1. Actively Acquired:
   • Antigens enter the blood, lymphocytes make antibodies.
   • Antibody production takes time.
   • Eventually, pathogens are destroyed, leaving memory lymphocytes.
   • Immunity occurs if pathogens are destroyed before symptoms develop.
2. Passively Acquired:
   • Antibodies pass across the placenta or through breast milk.
   • Short-lived as the baby’s immune system has not actively made antibodies.

Artificial Immunity

1. Actively Acquired:
   • Achieved by vaccination.
   • Vaccines contain weakened, inactivated, or dead pathogens, prompting lymphocytes to make antibodies.
2. Passively Acquired:
   • Ready-made antibodies are administered (usually antitoxins).
   • Short-lived because lymphocytes do not learn to make antibodies.

Drug Use and Abuse

• Drug: A chemical that alters the functioning of living tissues.
• Drug abuse can lead to addiction and harm.

Types of Addiction

1. Physical Addiction: Body functions become dependent on the drug; withdrawal symptoms occur if the drug is discontinued.
2. Psychological Addiction: Mental functioning is altered to the point where the person feels they cannot function without the drug.

Use and Abuse of Alcohol

• Alcohol is a depressant of the central nervous system.
• Abuse involves repeated or excessive consumption.
• Continued abuse may lead to alcoholism.

Symptoms of Alcohol Abuse

• Impaired mental functioning
• Slowed muscular skills and loss of coordination
• Slurred speech
• Vasodilation
• Increased excretion of water
• Loss of consciousness
• Aggravation of hypertension
• Cirrhosis of the liver
• Intestinal, skeletal muscle or nervous system disorders
• Delirium tremens
• Fetal alcohol syndrome in children born to alcoholic mothers
• Death

Use and Abuse of Cocaine

• Used medically as a local anaesthetic.
• Abuse leads to addiction, stimulation of the central nervous system, and appetite suppression.

Symptoms of Cocaine Abuse

• Feelings of well-being, alertness, increased energy, confidence, and power
• Reduced need for sleep
• Loss of appetite
• Vasoconstriction leading to increased blood pressure, heart beat disruption, heart attack, stroke
• Increased respiratory rate, lung and nasal damage
• Increased body temperature leading to heat stroke
• Erratic, violent behaviour and hallucinations
• Schizophrenia, mental illness, and death.

Use and Abuse of Antibiotics

• Used to treat bacterial disease.
• Abuse involves overuse and incomplete courses.

Consequences of Antibiotic Abuse

• Development of antibiotic-resistant bacteria.
• Antibiotics become useless for patients who have developed resistance.
• Allergic reactions, potentially fatal.