The Dynamics of Disease Transmission PDF

BSc Medical Sciences: Epidemiology Assistant Prof. Dr. Soza Th. Baban  Key aspects of Epidemiology It concerns with: Transmissibility Virulence of pathogens The course of clinical and sub-clinical infections Duration of protective immunity Human contact pattern Learning ob...

BSc Medical Sciences: Epidemiology Assistant Prof. Dr. Soza Th. Baban  Key aspects of Epidemiology It concerns with: Transmissibility Virulence of pathogens The course of clinical and sub-clinical infections Duration of protective immunity Human contact pattern Learning objectives 1. To learn modes of disease transmission by using epidemiologic model. 2. To define important terms related to the occurrence of disease in a population. 3. To calculate an attack rate and illustrate how it may be used to measure person-to-person transmission of a disease. 4. To describe the steps in an outbreak investigation and introduce how cross-tabulation may be used to identify the source.  I keep six honest serving-men (They taught me all I knew); Their names are What and Why and When And How and Where and Who. —Rudyard Kipling (1865–1936) Introduction to Disease Transmission Understanding how diseases spread within populations is crucial for public health. In this lecture, we'll explore the factors influencing the spread of infectious diseases, how we can identify their origins, and what can be done to prevent their spread. Key examples we'll look at include COVID-19 and malaria.  The epidemiologic triad of a disease Infectious disease is a disease caused by infectious agent or its toxic products. This agent can be transmitted by an infected person, an animal or a reservoir directly or indirectly through a vector. The epidemiologic triad is the relationship between an infectious agent and its host, its mode of transmission and the environment in which the transmission takes place or promotes the exposure. Human susceptibility factors– genetic, behavioural, nutritional, immunity  The epidemiologic triad of a disease The Epidemiological Triad explains how diseases are transmitted. Example: In malaria, the agent is the Plasmodium parasite, the host is humans, and the environment is areas where mosquitoes thrive.  Sources and Reservoirs of Infection Infectious diseases can originate from different sources: Human Reservoirs (People with the infection (symptomatic or carriers) Animal Reservoirs (zoonoses) Environmental Reservoirs Rabies (animal reservoir) Causative agent: Rebies virus Cholera (water as and environmental reservoir) Causative agent: Vibrio cholerae The epidemiologic triad of a disease Human susceptibility is determined by a variety of factors: genetic background and behavioral, nutritional, immunologic characteristics The immune status of an individual is determined by many factors including prior experience both with natural infection and with immunization. The factors that can cause human disease: biologic Physical chemical nutritional stress Behavioral  Modes of Transmission of Disease Direct transmission: Direct person-to-person contact Indirect transmission: Common vehicle Vector Different organisms spread in different ways, and the potential of a given organism for spreading and producing outbreaks depends on the, such as its characteristics of the organismate of growth, the route by which it is transmitted from one person to another, and the number of susceptible persons in the community.  Mode of Transmission of Respiratory Viruses Respiratory infections are spread by virus-containing droplets and aerosols exhaled by infected individuals during breathing, speaking, coughing, and sneezing. Droplets are categorized into two types: Respiratory droplets (>5–10 𝜇m in diameter) Aerosols (