Diseases: Cause and Control

A. Major Disease Categories:

• Congenital Diseases: Present from birth due to chromosomal abnormalities or embryonic defects (e.g., Down syndrome, cleft palate, hemophilia).
• Acquired Diseases: Developed after birth during lifetime:
  • Communicable (Infectious): Transmitted from an infected person to a healthy person via air, water, food, physical contact, or animal vectors (e.g., Cholera, Malaria, Tuberculosis, AIDS).
  • Non-Communicable: Not transmitted from person to person:
    • Deficiency: Scurvy (Vit C), Kwashiorkor (Protein), Anaemia (Iron).
    • Degenerative: Heart disease, Osteoarthritis.
    • Allergies: Asthma (hypersensitivity to pollen/dust).
    • Cancer: Uncontrolled mitotic proliferation forming malignant tumors.

B. Key Epidemiological Terms:

• Pathogen: A disease-causing biological organism (bacterium, virus, protozoan, fungus, parasitic worm).
• Vector: An intermediate living organism (usually an insect) that carries a pathogen from an infected host to a healthy host without suffering from the disease (e.g., female Anopheles mosquito for malaria).
• Incubation Period: The time interval between the initial entry of the pathogen into the body and the appearance of the first clinical symptom of the disease.

A. Poliomyelitis (Polio):

• Pathogen: Poliovirus (enterovirus).
• Transmission: Faecal-oral route via contaminated water/food.
• Pathology: Virus multiplies in intestinal cells, enters bloodstream, and attacks the motor neurons of the spinal cord, causing muscular atrophy and permanent skeletal paralysis (usually in legs).
• Prevention: OPV (Oral Polio Vaccine / Sabin) and IPV (Salk vaccine) through Pulse Polio immunization.

B. Rabies (Hydrophobia):

• Pathogen: Rabies virus (rhabdovirus).
• Transmission: Bite of a rabid animal (dog, bat, monkey) carrying the virus in its saliva.
• Symptoms: Spasms of the throat muscles upon attempting to swallow liquids (Hydrophobia — extreme fear of water), delirium, fever, $100\%$ fatality once symptoms appear.
• Prevention: Immediate washing of wound with soap and water, followed by post-exposure anti-rabies vaccination.

C. AIDS (Acquired Immuno Deficiency Syndrome):

• Pathogen: HIV (Human Immunodeficiency Virus), an enveloped spherical retrovirus with RNA genome and reverse transcriptase.
• Mechanism: Selectively infects and destroys CD4+ Helper T-lymphocytes. As T-cell count crashes, the patient suffers complete immune collapse, dying from opportunistic infections (TB, fungal pneumonia, Kaposi sarcoma).
• Modes of Transmission:
  1. Unprotected sexual intercourse with an infected partner.
  2. Transfusion of contaminated blood or blood products.
  3. Sharing unsterilized hypodermic needles/syringes (intravenous drug abusers).
  4. From an infected mother to her child across the placenta or through breast milk.
• Non-Transmissible via: Shaking hands, hugging, coughing, sharing toilet seats, or mosquito bites!
• Diagnosis: ELISA (Enzyme-Linked Immunosorbent Assay) screening, confirmed by Western Blot test.

A. Malaria:

• Causative Protozoan: Plasmodium (P. vivax, P. falciparum, P. malariae).
• Vector: Female Anopheles mosquito (males feed only on plant nectar).
• Pathology & Symptoms:
  • Sporozoites enter blood via mosquito bite, multiply in liver cells, then infect and rupture Red Blood Cells (RBCs).
  • Rupture of RBCs releases a toxic crystalline chemical called Haemozoin into the bloodstream.
  • Haemozoin triggers the classic recurring paroxysms of malaria: Shivering cold stage → High fever hot stage ($104^\circ\text{F}$) → Profuse sweating stage every $48$ or $72\text{ hours}$.
• Treatment: Quinine (from bark of Cinchona tree), Chloroquine, Artemisinin.

B. Filariasis (Elephantiasis):

• Causative Agent: Filarial parasitic nematode worm Wuchereria bancrofti.
• Vector: Transmitted by the bite of Culex mosquito.
• Symptoms: Adult worms lodge in human lymphatic vessels, causing chronic inflammation and mechanical blockage of lymph drainage. This results in massive, grotesque swelling of limbs (usually lower legs and scrotum) resembling an elephant\'s foot (Elephantiasis).