(M) Theory of Disease Causation Flashcards
T or F
Disease and other health events do not occur randomly in a population
T
But disease/other health events are more likely to occur in some members of the population than others because of ?
Risk factors
that may not be distributed randomly in the population
T or F
One important use of epidemiology is to identify the factors that place some members at lesser risk than others.
F (Greater risk)
lame
What are the factors for Risk of disease
theres 3
- Host
- Agent
- Environment
ayan 3
Risk of Disease Is Not Equal
Components of Host
- Age affects risk
- Immunity
- Stress
Why extreme ages are more vulnerable to diseases?
because of their immune system
mas mavaba
Risk of Disease Is Not Equal
what are the 2 factors under immunity?
- Exposure
- Vaccination
Risk of Disease Is Not Equal
Components of Agent
- Variability in agents
- DIfferent agents
- Viral
Risk of Disease Is Not Equal
Components of Environment
- Season
- Politics
How do risk factor works together
What are the 5 relations of Agent, Host and Environment
use this card to familiarze i guess
- B is a proxy for A risk Factor for O
- A and B are overlapping Risk Factors for O
- A and B are independent risk factors for O
- B mediates the effect of A on O
- A moderates the effect of B on O
How Do We Identify Important Risk Factors?
what apporach are used?
Epidemiologic Approach
uses Decriptive and Analytic
How Do We Identify Important Risk Factors?
T or F
we Summarize disease occurince in sample
F (in population)
How Do We Identify Important Risk Factors? T or F
Compare risk of disease among animals with different exposures
T
How Do We Identify Important Risk Factors? T or F
measure comparison with disease occurence
F (associations)
Causes of Disease
Any (blank) that leads to new cases of disease
Exposure
Knowing the exposure can lead us preventing the disease
Two basic philosophies about causation of infectious diseases
- Presence of an agent → disease (Direct)
- Agent alone is not sufficient to produce disease (Need other factors)
The occurrence of disease follows certain biologic laws which apply to both communicable and non-communicable diseases, what are the 2 laws?
- disease results from an imbalance between a disease agent and man
- the nature and extent of the imbalance depends on the **nature and characteristics of the host and the agent. **
The characteristics of the two are influenced considerably by the conditions of their environment.
First recognized criteria for establishing cause
Henle-Koch Postulates
Henle-Koch Postulates - T or F
The organism is found in all disease cases.
T
e.g All of TB-positive should have mycobacterium tuberculosis
Henle-Koch Postulates - T or F
The organism is found in other individuals as a non-pathogenic parasite.
F (NOT FOUND)
You will not see the mycobacterium tuberculosis sa ibang tao na hindi TB-positive
Henle-Koch Postulates - T or F
It must be possible to produce a pure, sustainable culture of the organism.
T
The organism can be CULTURED or ISOLATED
Henle-Koch Postulates - T or F
It must be possible to experimentally reproduce the same disease in a susceptible host.
T
If the cultured/isolated organism were passed to another, the other should be positive from the disease
Henle-Koch Postulates - T or F
One Agent → Two Disease
F (one disease)
oa
was Henle-Koch postulates debunked?
yeah it was
Problems with Koch’s Postulates - T or F
Doesn’t directly relate to non-infectious diseases
T
You cannot isolate organism from a diabetic patient
Problems with Koch’s Postulates - T or F
Every exposed individual becomes infected
F (NOT EVERY)
It depends with the immunity of the person
Problems with Koch’s Postulates - T or F
Not all infected individuals develop disease.
T
- TB-exposure and TB-infected – no manifestation
- TB-Postive – manifested
Problems with Koch’s Postulates - T or F
Possible to recover infectious agents from all infected individuals or even all disease cases.
F (Not possible)
Some virus cannot be isolated
Did Koch identify THE cause?
Partly but not all
What is the conclusion for the henle-koch postulate
Conclusion: The epidemiologic concept maintains that there can be no single cause of disease.
These 3 factors:
contribute to the occurrence of disease
Agent, Host, and Environment
Models assist with in understanding and describing complex causal relationships
- Web of causation
- Path models
- Venn Diagrams
- Rothman Pie (Necessary, sufficient, and component causes)
a susceptible host (the person at risk for the disease), a disease agent (the proximate cause), and an environmental context for the interaction between host and agent.
The Epidemiological Triad
The Epidemiological Triad
the person at risk for the disease
host
The Epidemiological Triad
proximate cause
disease agent
The Epidemiological Triad
context for the interaction between host and agent.
environmental
Disease results from the interaction between the agent and the susceptible host in an environment that supports transmission of the agentfrom a source to that host
The Epidemiological Triad
– the aggregate of all external conditions and influence affecting the life and development of an organism, human behaviour or society
Environment
if u see this card
study the epidemiologic lever
● towards the agent - the agent has more of an ability to cause a disease
● towards the host - increased amount of ways a person is susceptible to a disease e.g. sleepless nights, unhealthy diet, consumption of unhealthy food
● towards the environment - plays a key role in how the agent and host are affected by a disease, where it is likely to spread, and its current location
Epidemiological Triad
Biologic, nutrients, chemical, physical, and mechanical
Agent
balance depends on age, race, sex, habits, customs, genetic factor, personality defense mechanism
Human
Epidemiologic Lever - T or F
Agent, host, and environmental factors interrelate in a variety of complex ways to produce disease.
T
Epidemiologic Lever - T or F
Different diseases require the same balances and interactions of these three components.
F (different)
Epidemiologic Lever - T or F
Development of appropriate, practical, and effective public health measures to control or prevent disease usually requires assessment of all three components and their interactions.
T
Even if one factor is addressed- that is a partial solution
designed to be shaped like a seesaw with the environment being the base, the host being on one side and the agent being on the other.
epidemiological lever
When the teeter-totter is balanced
the equilibrium state
what signifies a balanced epidemiological lever?
this state signifies that everything is healthy
Imbalance
considered as the agent having more of an ability to cause a disease on man
Imbalance towards the agent
Imbalance
the amount of ways a person is susceptible to a disease increased
Imbalance towards the host
Imbalance
Environment plays a key role in how the agent and host are affected by a disease, and where the disease is most likely to spread and where itis currently located
Imbalance towards the environment
Conclusion for The Epidemiological Triad
While the epidemiologic triad serves as a useful model for many diseases, it has proven inadequate for?
non-communicable diseases
BEST USED: Epidemiologic diseases
this model has shapes that overlaps with other
Venn Diagram
de-emphasizes the agent as the sole cause of disease while emphasizing the interplay of physical, biological, and social environments. It also brings genetics into the mix
The Wheel of Causation
Like the Wheel of Causation,this in explaining disease.
deemphasizes the agent in explaining disease
Provides for multifactorial causes that traverse various pathways.
Can be highly intricate and complex
Web of Causation
what model are like with the web of causation?
Wheel of Causation
how many factors web of causation provides
multifactorial
if u see this card
hanapan niyo si euly crush, yung moreno pls pls
Web of Causation
TOF. Easy and not complex
F (Can be highly intricate and complex)
Wider Application of the Web
devised to enhance search for understanding communicable disease
Epidemiologic Triad
Wider Application of the Web
devised to enhance understanding of non-communicable diseases /chronic diseases – can also be applied to communicable diseases
Web of Causation
use this card to see the example for wider application of the web
→ One interesting communicable disease example involves unanticipated consequences of economic development, and more particularly Trypanosomiasis or “sleeping sickness” that spread across Africa in the wake of new roads.
→ The agent was carried behind trucks by its vector, the tsetse fly, with fly bites being the mode of disease transmission.
→ in the Philippines, an ades mosquito was stuck in a luggage and then was brought to Taiwan.
this model is used sometimes in range of diseases and has a sequence before a disease manifest
Path Model
(Causal Sequence)
this model has this 3 components:
* Component Cause
* Sufficient Cause
* Necessary Cause
Causal Pies (Rothman, 1976)
Causal Pie
Any causal factor (Host, Agent, Env.
Component cause
Set of component causes that is capable of causing disease
Sufficient cause
T or F
Once all of the sufficient causes are present, disease WILL occur
T
Component cause that is REQUIRED for disease to occur
Necessary cause
Causal Pies
The complete pie, which might be considered a causal pathway is called
Sufficient Casue
Causal Pies
component cause can overlap?
yes they can! they may or may not obirlap
T or F
A single component cause is a rarely a sufficient cause by itself.
T
For example, even exposure to a highly infectious agent such as measles virus does not in variably result in measles disease.
Causal Pies - T or F
an agent that is usually harmless in healthy persons may cause devastating disease under different conditions.
T
i.e. Pneumocystis carinii is an organism that harmlessly colonizes the respiratory tract of some healthy persons, but can cause potentially lethal pneumonia in persons whose immune systems have been weakened by human immunodeficiency virus (HIV).
Causal Pies - T or F
Note that public health action does not depend on the identification of every component cause
T
kahit single component lang ma block goods na pero
pero this does mean na may others parin na pwede ma infect okay? oka
Causal Pies
Disease prevention can be accomplished by?
blocking any single component of a sufficient cause
at least through that pathway.
For example, the elimination of smoking (component B) would prevent lung cancer from sufficient causes I and II, although some lung cancer would still occur through sufficient cause III.
Modern concepts of disease Bradford–Hill criteria
Strong associations with higher risk ratios are more likely to be causal than a weak association – higher risk ratio, the more stronger it is
Strength of Association
Modern concepts of disease Bradford–Hill criteria
consistently finding an association a putative cause and a disease outcome in multiple studies by different investigators
Consistency
Modern concepts of disease Bradford–Hill criteria
If a factor is only associated With a specific disease It was said to be specific and considered more likely to be causal
Specificity
Modern concepts of disease Bradford–Hill criteria
The causal factor should precede the outcome it is proposed to be causing; nauuna exposure before sakit
Temporality
Modern concepts of disease Bradford–Hill criteria
A dose-response association IS supportive of a causal relationship; dependent sa amount na na consume
Biological Gradient
Modern concepts of disease Bradford–Hill criteria
Is the association biologically plausible?
Plausibility
Modern concepts of disease Bradford–Hill criteria
The proposed causal association should not contradict current scientific knowledge
Coherence
Modern concepts of disease Bradford–Hill criteria
A causal association is more likely if it is supported by results from controlled, randomized trials
experimental
Modern concepts of disease Bradford–Hill criteria
A causal association may be more likely If there are other examples of causal associations for analogous exposures and outcomes
Analogy
factor in epidemiological triad:
any element, substance, or force whether living or non-living, the presence or absence of which can initiate or perpetuate a disease process.
agent
Types of Agents
- Non-living, living and borderline (bacteria, virus, parasites, prions)
- ** Physical, Chemical and Mechanical** in nature (i.e. extremes of temperatures, light, electricity, physical trauma, etc.)
- Exogenous (i.e. common poisons), or endogenous – luob ng katawan (i.e. accumulation of toxic products of metabolism in acidosis of diabetes)
- Nutrients (deficiency agents and excess agents)
deficiency of Vitamin B
Beriberi
iron deficiency
Anemia
over-eating
Obesity
Components of Inherent Characteristics
Physical features, biologic requirements, chemical make-up, viability, and resistance.
Inherent Characteristics:
morphology, motility, presence or absence of capsules, whether the infecting agent comes in the form of spores or cysts, or whether they need to be in their vegetative forms to cause infection
Physical Features
Inherent Characteristics:
Refer to the things needed by the agent to survive
Biologic requirements