Biology + Human Disease Risk Flashcards
(135 cards)
strength of association (Hills Criteria)
strong associations are more likely to be causal than weak associations
consistency
repeated observations of an association in different populations under different circumstances
specificity
requires that a cause leads to a single effect, not multiple effects.
temporality
the necessity that the cause precedes the effect in nature
biologic gradient
refers to the presence of a uni-directional dose-response curve
Ex: more smoking = more carcinogenic exposure
plausability
refers to the biologic plausibility of the hypothesis;
often flawed
coherence
implies that a cause and effect interpretation for an association does not conflict with what is known of the natural history and biology of the disease
The Epidemiologic Triangle
models the relationship between:
agent - host - environment
Chain of Infection
Agent - Reservoir - Portal of Exit - Mode of Transmission - Portal of Entry - Susceptible Host
Agent
causes disease
ex: bacteria, viruses, parasites
Reservoir
habitat where agent normally lives, grows, and multiples
ex: humans, animals, environment (soil, water)
Zoonosis
an infectious disease that is transmissible under natural conditions from vertebrate animals to humans
Portal of exit
path by which an agent leaves the host
ex: mouth, cuts, urine or stool
Mode of Transmission
transfer of agent from reservoir to a host
Direct -or- Indirect
Direct transmission
direct contact (person or soil)
droplet spread (aerosols produced by sneezing, coughing, or talking)
Indirect transmission
airborne (dust or droplet suspension),
vehicles (food, water, blood, fomites)
vectors (mosquitos, fleas, ticks)
portal of entry
manner in which agent enters a susceptible host;
dermal, transplacental, oral, respiratory/inhalation
susceptible host
depends on genetics, immunity, or other determinants of health
Louis Pasteur
proved that germs caused disease (Germ Theory);
created first vaccines for rabies and anthrax
invented technique of treating milk to stop bacterial contamination (pasteurization)
Koch’s postulates
4 criteria to establish a causal relationship between agent and disease
anthrax; tuberculosis; later generalized to other diseases
Not all 4 postulates is required to demonstrate causality
Koch postulate 1
- agent must be found in all organisms with the disease, but not in healthy organisms
Koch postulate 2
- agent must be isolated from a diseased organism and grown in culture
Koch postulate 3
- cultured agent should cause disease in a healthy organism
Koch postulate 4
agent must be re-isolated and matched with original agent