Vector: Female Anopheles mosquito.

Amoebiasis (Amoebic Dysentery):

Causative Agent: Entamoeba histolytica (protozoan parasite).
Infection Site: Large intestine.
Symptoms: Constipation, abdominal pain, cramps, stools with excess mucus and blood clots.
Transmission: Houseflies act as mechanical carriers, transmitting from infected faeces to food/water.

Ascariasis:

Causative Agent: Ascaris (roundworm, helminth).
Symptoms: Internal bleeding, muscular pain, fever, anemia, blockage of intestinal passage.
Transmission: Eggs excreted in faeces contaminate soil/water/plants; healthy person acquires via contaminated water/food.

Elephantiasis (Filariasis):

Causative Agents: Wuchereria bancrofti and W. malayi (filarial worms).
Symptoms: Slowly developing chronic inflammation, usually in lymphatic vessels of lower limbs; genital organs often affected, causing gross deformities.
Transmission: Female mosquito vectors.

Ringworms:

Causative Agents: Fungi (Microsporum, Trichophyton, Epidermophyton).
Symptoms: Dry, scaly lesions on skin, nails, scalp; intense itching.
Favorable Conditions: Heat and moisture (skin folds, groin, between toes).
Transmission: From soil, or using towels/clothes/combs of infected individuals.

Personal Hygiene: Keep body clean, consume clean food/water.
Public Hygiene: Proper waste/excreta disposal, periodic cleaning/disinfection of water reservoirs, control of vectors.
For Air-borne Diseases (e.g., Pneumonia, Common Cold): Avoid contact with infected persons and their belongings.
For Vector-borne Diseases (e.g., Malaria, Filariasis, Dengue, Chikungunya):
- Control/eliminate vectors and breeding places.
- Avoid water stagnation, regular cleaning of coolers.
- Use mosquito nets.
- Introduce fish like Gambusia in ponds (feed on mosquito larvae).
- Spray insecticides.
- Wire mesh on doors/windows to prevent mosquito entry.
Advancements: Vaccines (smallpox eradicated), antibiotics, and other drugs have significantly reduced infectious diseases.

The body's ability to defend itself against disease-causing organisms.

Innate Immunity:
- Non-specific defense, present at birth.
- Provides various barriers to foreign agents:
  - Physical Barriers: Skin, mucus coating (respiratory, GI, urogenital tracts).
  - Physiological Barriers: Acid in stomach, saliva in mouth, tears from eyes.
  - Cellular Barriers: Leukocytes (PMNLs), monocytes, natural killer cells, macrophages (phagocytose and destroy microbes).
  - Cytokine Barriers: Interferons (proteins secreted by virus-infected cells, protect non-infected cells).
Acquired Immunity:
- Pathogen-specific, characterized by memory.
- Primary Response: Low intensity on first encounter with pathogen.
- Secondary (Anamne