Dynamics of Disease transmission. Chapter - 2 Flashcards
What is the epidemiological triad?
It is the product of interaction of the human host, an infectious or
other type of agent, and the environment that promotes the exposure. A vector, such as the mosquito or the deer tick, may be involved. For such an interaction to take place, the host must be
susceptible.
- Host (top of the traingle)
- Agent (left of the triangle)
- Vector (middle of the triangle)
- Environment (right of the triangle)
Define host in epidemiological triad.
The person who is infected by the disease.
Characteristics of the host
- Age
- Sex
- Race
-Religion…
Define agent in epidemiological triad.
The pathological agent that has infected the host.
Biologic
- Bacteria, virus, fungi
Chemical
- Heavy metal, alcohol, smoke
Physical
- Trauma, radiation, fire
Nutrional
- lack of or excess of
Define vector in epidemiological triad.
Living organisms that trasmit pathogens between humans or from organisms to humans.
Rats, Mosquitos, lice, ticks, flies
Define environment in epidemiological triad.
**Environment/place that promotes the exposure of the agent to the host eventually causing the disease.
- Temperature
- Humidity
- Water
- Air
- Milk
- Food
- Noise…
What are the modes of disease transmission?
-
Direct transmission
- through person to person contact -
Indirect transmission
- through two ways
* a. Common vehicle which is a contaminated source such as air, water
* b. Vector
What is a carrier?
A carrier is an individual who harbors the organism but is not infected as measured by serologic studies (no evidence of an antibody response) or shows no evidence of clinical illness. e.g. Typhoid Mary
Outbreak
Sudden increase in cases of the disease in a localized place (region, instiution)
- Caused by common vehicle exposure - air, water, food
- Cases are limited to the people who shared the common exposure. e.g. food poisioning at the party
Immunity
Not at risk of developing a disease through immunization or other genetic factors
Susceptibility
At risk of getting infected by a disease
Herd immunity
Resistance to a disease on a larger scale; i.e. a large proportion of the population is immune to the disease this can be done through immunization
Incubation period
The incubation period is defined as the interval from receipt of
infection to the time of onset of clinical illness (the onset of recognizable symptoms). It may reflect the time needed for the organism to replicate sufficiently until it reaches the critical mass needed for clinical disease to result.
Reducing outbreaks
-
Remove the reservoir
- recall food, boil water, quarantine
2. Interrupt transmission
- masks, physical distancing, hand washing -
Reduce host susceptibility
- Vaccinate
Primary Case
Cases whose symptoms appeared following exposure to the source (within the minimum and maximum limits of the incubation period)
Secondary Case
Cases whose symptom appeard following the contact with the primary case and without exposure to the source
