1. USING THE EPIDEMIOLOGICAL TRIANGLE AND THE CHAIN OF
INFECTION 1
Using the Epidemiological Triangle and the Chain of Infection
Melissa Logan
Walden University

2. USING THE EPIDEMIOLOGICAL TRIANGLE AND THE CHAIN OF
INFECTION 2
The epidemiological triangle displays the three factors necessary to cause the
transmission of an infectious disease (Songer, n.d.) The three required factors include a host,
agent, and environment. In this paper I will discuss the epidemiological triangle and the chain of
infection for Lyme disease. The agent in the epidemiological triangle of Lyme disease is the
bacterium Borelia burgdorferi, also known as the deer tick or blacklegged tick (Centers for
Disease Control [CDC], 3013). Borelia burgdorferi is a biological agent (Laureate Education,
Inc., 2011). The host in this epidemiological triangle is a tick, and then a human, and the
environment is warm weather in wooded areas. “Note that hunting and dressing deer or squirrels
may bring you into close contact with infected ticks” (CDC, 2013, para. 8). Host factors include
personal traits and behaviors, such as hiking or running in wooded or bushy areas, not covering
exposed skin, or not using tick repellents on exposed skin (Songer, n.d.; CDC, 2011).
The chain of infection diagram is below. The first step in the chain of infection is the
existence of the pathogenic microorganism (Laureate Education, Inc., 2011). The pathogenic
microorganism is known as the agent in the epidemiological triangle. Step two in the chain of
infection, the reservoir, in the case of Lyme disease, is the deer tick. “The Lyme disease
bacterium, Borrelia burgdorferi, is spread through the bite of infected ticks” … “In most cases,
Host: Tick/Human
Agent: Borrelia burgdorferi Environment: Tick-infested woods

3. USING THE EPIDEMIOLOGICAL TRIANGLE AND THE CHAIN OF
INFECTION 3
the tick must be attached for 36-48 hours or more before the Lyme disease bacterium can be
transmitted” (CDC, 2013). This explains steps three and four in the chain of infection, known as
the portal of exit or means of escape and mode of transmission, respectively. The mode of
transmission is indirect and vector borne through the tick bite (Laureate Education, Inc., 2011).
The portal of entry into the new host, step five in the chain of infection, is the skin that has been
bitten by the tick (Laureate Education, Inc., 2011; CDC, 2013). Finally, step six in the portal of
entry is host susceptibility, the strength or weakness of the host’s immune system and the
pathogen’s virulence (Laureate Education, Inc., 2011; Krasner, & Riegelman, 2013).
#2
Reservoir#1 Pathogenic
microorganism
#3
Means of
Escape
#4
Mode of
Transmission
#5
Means of Entry
#6
Host Susceptibility

4. USING THE EPIDEMIOLOGICAL TRIANGLE AND THE CHAIN OF
INFECTION 4
References:
Centers for Disease Control. (2013). Lyme disease transmission. Retrieved from
http://www.cdc.gov/lyme/transmission/index.html
Centers for Disease Control. (2011). Preventing tick bites. Retrieved from
http://www.cdc.gov/lyme/prev/on_people.html
Krasner, R., & Riegelman, R. (2013). Human disease and prevention (Laureate Education, Inc.,
custom ed.). Burlington, MA: Jones & Bartlett Learning.
Laureate Education, Inc. (2011). Infectious disease process and chain of infection [PowerPoint
slides]. Baltimore, MD: Author.
Songer, T. (n.d.). Introduction to the fundamentals of epidemiology. University of Pittsburgh and
Aga Khan University. Retrieved from www.pitt.edu/~super7/19011-20001/19061.ppt