Human Diseases > Communicable / Infectious Diseases - Modes of Transmission of Diseases through Pathogens

• Direct transmission: Pathogens are transferred directly from an infected person (or source) to a healthy person without any intermediate agent.
• Indirect transmission: Pathogens are transferred through an intermediate agent or medium such as vectors, contaminated food/water, air, or objects.

Direct transmission:

• Direct physical contact (touch, skin contact, sexual contact).
• Droplet infection by coughing, sneezing, talking at close range.
• Transfer via blood and other body fluids.
• Bites from infected animals.
• Transplacental (mother to foetus).

Indirect transmission:

• Vector‑borne: through insects or other animals carrying pathogens (mosquitoes, flies, ticks, dogs).
• Vehicle‑borne: through contaminated food, water, milk, serum, plasma.
• Fomite‑borne: via contaminated objects (towels, utensils, instruments).
• Air‑borne: via aerosols or dust carrying pathogens over a distance.
• Faecal-oral / unclean hands: poor hygiene leading to ingestion of pathogens.

Direct transmission:

• Measles, chickenpox, conjunctivitis (close contact, droplets).
• Common cold, influenza, mumps, COVID‑like respiratory infections (droplets).
• HIV, hepatitis B and C (blood, body fluids).
• Syphilis, gonorrhoea (sexual contact).
• Rabies (animal bite).
• HIV, some viral infections (mother to foetus).

Indirect transmission:

• Malaria, filariasis, dengue, Lyme disease (vector‑borne).
• Cholera, typhoid, diarrhoea, dysentery, hepatitis A/E (food‑ and water‑borne).
• Common cold, skin infections via shared towels, toys, and instruments (fomites).
• Measles, influenza, TB (air‑borne spread over distance).
• Amoebiasis and ascariasis are transmitted via unclean hands and poor sanitation.

• Direct transmission: Often fast within close‑contact groups (families, classrooms, wards) because transmission happens during direct interactions.
• Indirect transmission: Can cause community‑wide or large‑area outbreaks when water supply, food chains, or vector populations are widely contaminated.

Direct transmission:

• Isolation of infected persons where needed.
• Safe sexual practices.
• Use of gloves, masks, and safe injection practices.
• Screening and safe handling of blood and blood products.
• Wound care and avoidance of animal bites.

Indirect transmission:

• Vector control (eliminating mosquito breeding sites, fly control).
• Safe drinking water, proper cooking and food hygiene.
• Sanitation and hand‑washing with soap.
• Disinfection/sterilization of instruments and surfaces.
• Good ventilation and control of overcrowding.