Overview
This lecture explains how infectious diseases are transmitted through people, objects, or vectors, and outlines methods for controlling and preventing their spread.
The Epidemiological Triad
- Infectious diseases occur through interaction between three components: agent (organism), host (person), and environment.
- The agent can be bacteria, viruses, parasites, or fungi.
- The environment provides external conditions that allow disease transmission.
Transmission of Infectious Diseases
- Transmission pathways are either direct (person-to-person contact, coughing) or indirect (contaminated objects, food/water, vectors like mosquitoes).
- Direct transmission occurs through physical contact or aerosol droplets.
- Indirect transmission uses intermediates such as fomites, food/water, or vectors.
Methods for Controlling Infectious Diseases
- Changing health behaviors (e.g., condom use, handwashing, healthy diet, insect repellant) can reduce infection risk.
- Vaccines have led to dramatic declines in diseases and contribute to herd immunity.
- Antimicrobial medications kill or inhibit microorganisms and can be used for prevention (pre/post-exposure prophylaxis).
Challenges in Disease Control
- Antimicrobial resistance develops when microorganisms adapt to drugs, often due to overuse or misuse of medications.
Surveillance and Notification
- Disease surveillance tracks trends, detects outbreaks, and guides disease control programs.
- Notifiable diseases are reported by law to health departments for monitoring and action.
Environmental and Institutional Controls
- Environmental modifications (vector control, clean water, sanitation) reduce disease spread.
- Infection control in healthcare includes sterilization, protective equipment, isolation, hand hygiene, and cleaning.
Broader Strategies and One Health
- Improving social determinants (education, employment), strengthening healthcare systems, and workforce development support disease control.
- The One Health concept highlights the link between human, animal, and environmental health, requiring multidisciplinary cooperation.
Key Terms & Definitions
- Epidemiological Triad — Model explaining disease via agent, host, and environment.
- Direct Transmission — Disease spread through immediate contact.
- Indirect Transmission — Spread via intermediates like objects or vectors.
- Vector — An organism (e.g., mosquito) transmitting pathogens.
- Herd Immunity — Community-level protection when enough people are immune.
- Antimicrobial Resistance — Microorganisms’ ability to withstand drugs that previously killed them.
- Surveillance — Continuous monitoring of disease patterns.
- Notifiable Diseases — Illnesses legally required to be reported to authorities.
- One Health — Approach recognizing human, animal, and environmental health are interlinked.
Action Items / Next Steps
- Review methods of disease transmission and control for upcoming quiz.
- Read assigned textbook chapter on epidemiological principles and public health interventions.