1. Choose a current emerging disease or reemerging disease prevalent in your community or the larger community of the nation or world.
2. Complete an epidemiology triangle diagram for the chosen disease and thoroughly describe, using references, each factor and how it could contribute to an outbreak in your community.
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Detailed Description of Factors and Contribution to Outbreak
1. Agent: The Measles Virus
Description: The measles virus is a highly contagious, single-stranded RNA virus from the Paramyxoviridae family . Its primary mode of transmission is airborne (aerosols or droplets) and direct contact with infectious secretions.
Contribution to Outbreak: The virus is noted for its high basic reproduction number ($R_0$), which is typically cited as $12-18$ in a fully susceptible population, making it one of the most contagious human viruses (Smith et al., 2023). This extremely high contagiousness means that if even a small pocket of a community is under-vaccinated, a single imported case can rapidly infect a large number of susceptible hosts before public health measures can contain the spread.
2. Host: Susceptible and Immune Individuals
Description: The primary human host for measles is any person who has not been vaccinated or has not previously had the disease. Hosts include infants too young to be vaccinated, individuals with compromised immune systems, and those who have refused vaccination.
Contribution to Outbreak: In developed nations, the main driver of reemergence is the decline in effective herd immunity (Jones, 2024). When vaccination coverage falls below the necessary threshold (estimated to be about 93–95% for measles), a critical number of susceptible hosts accumulate. This accumulation creates "gaps" in community protection, turning densely populated areas with lower-than-average vaccination rates into vulnerable hotspots where the chain of transmission can be easily established and sustained.
3. Environment: Physical and Social Factors
Description: The environment encompasses both the physical (e.g., climate, housing density) and social/cultural (e.g., public health infrastructure, public trust, travel) factors.
Physical: Crowding in urban areas or schools facilitates close-quarters aerosol transmission, particularly during winter months when people spend more time indoors.
Sample Answer
Hypothetical Example Disease: Measles (Reemerging Disease)
Measles is an excellent example of a reemerging disease in many parts of the world due to declining vaccination rates and increased global travel.
The Epidemiology Triangle for Measles 📐
The Epidemiology Triangle is a model that describes how an infectious disease is transmitted. It consists of three parts: Agent, Host, and Environment. An outbreak results from changes or interactions among these three factors.