Chain of Transmission

What is the 'chain of transmission'?

The process by which infectious diseases spread, consisting of six linked elements.

What are the six links in the chain of transmission?

1. Infectious agent 2. Reservoir 3. Portal of exit 4. Mode of transmission 5. Portal of entry 6. Susceptible host

What is an infectious agent? Give examples.

A microorganism capable of causing disease (e.g., bacteria, viruses, fungi, parasites, protozoa).

What is a reservoir? Give examples.

The natural environment where the agent lives and multiplies (e.g., surfaces, soil, animals, humans, food, water, body fluids like urine, blood, sweat, tears, respiratory secretions).

What is a portal of exit? Give examples.

The path by which the agent leaves the reservoir (e.g., respiratory tract, GI tract, mouth, nose, blood, wounds, mucous membranes, urine, sexual secretions).

What are the modes of transmission?

Direct: Contact, droplet. - Indirect: Airborne, vehicle-borne (food, water, objects), vector-borne (mosquitoes, ticks).

What is a portal of entry? Give examples.

The way the agent enters the host (e.g., respiratory tract, GI tract, skin, mucous membranes, wounds).

What makes a host susceptible?

Weak or compromised immune system (e.g., immunocompromised person, neonates, elderly, cancer patients, wounds, burns, diabetes mellitus, immunosuppressive drugs).

How can infection be prevented in the chain of transmission?

Break any link by: - Eliminating the agent (sterilisation, antibiotics). - Controlling the reservoir (hygiene, sanitation). - Blocking portals of exit (PPE, cough etiquette). - Interrupting transmission (hand hygiene, isolation). - Protecting portals of entry (wound care, masks). - Strengthening host defences (vaccination, nutrition, rest).