CM7.2 | CM7.2 | Disease Transmission and Control Principles — Summary & Reflection

KEY TAKEAWAYS

Disease transmission — communicable or non-communicable — follows a chain of interacting elements: infectious agent (characterised by infectivity, pathogenicity, virulence), reservoir (where the agent normally lives), source (the proximate origin of transmission), portal of exit, mode of transmission (direct: contact, droplet, vertical; indirect: vehicle-borne, vector-borne, airborne), portal of entry, and susceptible host. Control strategies break the chain at its weakest link. Source-targeted strategies include treatment, isolation, quarantine, and contact tracing. Transmission-interrupting strategies include water/sanitation, vector control, infection-control precautions, and barrier methods. Host-protective strategies include vaccination (achieving herd immunity when coverage exceeds 1 − 1/R₀), passive immunisation, chemoprophylaxis, and protective behaviours. The framework applies equally to NCDs when risk factors replace the infectious agent. The distinction between quarantine (incubation period, exposed contacts) and isolation (communicable period, confirmed cases) is operationally critical for outbreak response.

REFLECT

Consider a dengue outbreak in your city. Identify each link in the chain of infection for dengue (Aedes aegypti as vector, human as reservoir) and propose one specific, implementable intervention at each link — not just the most obvious one (mosquito nets). Which intervention would you prioritise in the first 72 hours of an outbreak and why? How does your answer change if the outbreak occurs in a densely populated urban slum versus a rural village? Write three to four sentences addressing both scenarios, drawing on what you have learned about mode of transmission and herd immunity in this module.