Nursing College – Mosul UniversityCausality :
Causality refers to the relationship between a
cause and its effect .A purpose of
epidemiologic study has been to discover
causal relationships, so as understand why
conditions develop and offer effective
prevention . Over the years , however as
scientific knowledge of health and disease has
expanded, epidemiology has changed its view
of causality .
Chain of causation :As the scientific community ' s thinking about
disease causation and the tripartite model has grown
more complex , epidemiologist have used the idea of a
chain of causation . The chain begins by identifying
the reservoir ( where the causal agent can live and
multiply ) e. g. with plague, that the reservoir may be
other humans , rats , squirrels , and a few other animals
. But with malaria , infected humans are the major
reservoir for the parasitic agents, by bite of an
Anopheles mosquito which spend part of their life
cycle in the mosquito ' s body ; the mosquitoes in this
case is the mode of transmission
Fig 2.1 Chain of causation in infection diseaseMultiple of Causation:
A more advanced concept multiple of causation has
emerged to explain the existence of health and illness
states and provide guiding principles for
Dever's Epidemiological Model considers the health
status of the host and how it is compacted by human
biology, life - style, environment, and the health care
system. Sometimes referred to a "web of causation
"this model attempts to identify all possible influence
on the health and illness processes also the problems.
e.g. Causation for myocardial infarction or infant
As conditions that lead up to this criticalsituation exist for years and come from
many factors ,including heredity ,
lifestyle , environment ,and the health
care system . This is important to
recognition of multiple causes provides
many points of intervention for
prevention , health promotion , and
Web of Causation - CHDRS Bhopal
Model of cause's disease:There are a number of multiple causation models in
epidemiology, such as
Metaphoric - Krieger mode (1960 ).
Dever's model 1991 . All the models point to the inter play of
numerous factors in the presentation of a specific disease .
Some of these factors are very easier to change and other is
not . One way of remembering the categories of cause for
disease is the acronym used in the model (BEINGS) model .
Obviously the factors in some of these categories are harder to
change than others .
For example Genetic (G) factors remain the most difficult to
Whereas nutritional (N) factors are more easily changed .
BEINGS model of cause's disease.B: Biological factors and behavioral
E : Environmental factors
I : Immunological factors.
N : Nutritional factors.
G : Genetic factors.
S : Services, social, spiritual factors .
Biological agents.Animal origin .
E.g.: E. histolytica = amoebiasis P. spp. = malaria
L. tropica = Leshmania S. typhi = typhoid.
E.g. Round worm = Ascariasis ,
Flat worm = T. Saginata , T. solium
E.g. High bacteria = Actinomycosis
Lower bacteria = Cocci, Bacilli = many diseases
Yeast = Fungi = Many fungal diseases.
b. Non -cellular
E.g.: Viruses HBV HCV = hepatitis
HIV = AIDS
A - Inheritant Factor in Relation to theEnvironment :
1. Spore formation.
2 . Viability.
3 . Antigenicity .
4 . Host specificity.
Affected human (only),Cholera
Affected human & animal, Sal. typhimurum
5 . Sensitivity to chemotherapy and antibiotics.
6 . Toxicity
B - Inheritant factor in relation tothe host
Pathogenicity & Virulence.
Invasion & toxicity.
Tissue & selectivity.
Dose of agent.
C - It has specificity in it's action :1 - Endotoxin affected GIT
2 - Neurotoxin affected nerve cell.
e.g. Tetanus, Rabies.
3 - Diphtheria exotoxin affected
muscle of larynx, heart and nerve
4 - Erythrocyte toxin B Streptococcus
e.g. : Strep. pyogen affected RBC
Leading to scarlet fever .
Environment factors : ( B E INGS )Environment define as a collection of
external condition affected life and
development of microorganism also affect
human behaviors and society.
Environmental factors in causative disease
1 - Physical
2 - Biological
3 - Social and habitual
4 - Econical
1 - Physical factors : divided into :a - Geological as (soil factors) :
1 - Rocky or agricultural increase infections
2 - Amount of nutrient material in the soil
3 - Mineral deposit in the soil e.g. sulfa or calcium
decrease the growth of microorganisms.
4 - Type of water .
a - Underground water (Ph high) affected life and
survival in soil. e.g. : Clostridium. spp .
b - surface water (ph 7 ) life and survival e.g.
Shigella , E coli , Streptococcus
5 - Sanitation in the area .
b - Geographical factors :Town decrease infectious disease.
Port increase infectious disease.
c - Climate factors :
1 - Temperature.
2 - Humidity .
3 - Air movement.
4 - Rain
5 - Atmospheric pressure.
2 - Biological factors :Biological factors include plants and animals which
live with human by itself it affect :
a - Biological agent either animals or plants origin.
b - Reservoirs as brucellosis in cow .
c - Vectors as arthropod (intermediate host) .
3 - Social and habitual
a - population density
b - education
c - transportation
4 - Economical factors :a - poverty
b - bad housing as (sunlight, ventilation etc.)
c - bad sanitation as (no chlorination in water,
urination in water, bad sewage etc.)
d - malnourishment causing defect in disease
control and increase fatality, decrease
diagnosis, decrease treatment, increase
complication that increase fatality.
e - product of industrialization result in croup
and allergic conditions.
Genetic factors : (BEIN G S )Inheritant disease in certain families
depend on endocrinological factors or
depend on races in jaw - Tb , Negron Tb.
Rheumatoid arthritis, Tb, Rheumatic
fever not Inheritant but occurs in
families because :
( 1 ) overcrowding
( 2 ) malnutrition
( 3 ) low hygiene
❑ Age factor :( 1 ) Incidence
Incidence depend on exposure (Environment) and person
immunity which different in :
▪ Infant : incidence of infection disease is low because of
passive Abs from mother.
▪ 2 - 4 years : incidence of infection disease high because
high Infant exposure and low artificial immunity.
▪ 4 - 6 years : out door trauma and infections because intake
of food outside with flies and dirt causing typhoid, cholera,
▪ 6 - 14 years : infectious disease due to
(1 ) artificial immunization ,
▪ ( 2 ) sub clinical infection.
▪ Puberty : infectious disease due to :( 1 ) artificial immunization,
( 2 ) sub clinical infection.
▪ Adult & old age : Increase in venereal
disease, gonorrhea, AIDS
( 1 )Adult : Occupational disease ; like cancer
bilharzias, Ankylostoma. But woman
more than male in exposure.
( 2 )Old age : decrease exposure, slow
metabolism, inhibition of phagocyte
Cycles, stimulation for any foreign
Antigens is low, increase infectious
( 3 ) End result and severity :Sever and fatal result
Young age - pneumonia, measles .