HLTA01 - Final Exam Notes.docx

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Published on 5 Feb 2013
Plague highly infectious ,usually fatal epidemic disease
Etiology (3)
o Changes in environment = change in habits, food & conditions; parasites & disease become prevalent due to pop. Growth
o Dense cities & close knit communities = easy transmission
o “URUK” 5,500 years ago – development of ancient cities enabled:
Closer proximity to neighbours, smaller living spaces, waste secreted back into environment
o 3 factors (revolutions) of population growth
Tool making
Cereal grains were harvested w/ ease b/c of tools, storage & processing of these grains
Used: baskets, mortar & pestles, techniques, storage pits
Population was less dense but people started domesticating animals & adopting sedentary lifestyle (food
growth = exposure to parasites
Economic trade, ties, political structures & religious practices occur; selective advantages to those in control
(group cohesion)
Irrigation practices = favorable environments for parasites b/c of abundant moisture liquid medium of
Consequences: increase in human disease (easily transmitted), exposure of disease b/c of fertilization (favored
disease), domestication (zoonotic)
Technological advancements can speed disease control AND disease transmission; efficiency in transportation
Religion, “opiate of the masses” was a competitive advantage over societies = political stratification, governed
the “settled” & commerce, baking & writing was invented = urbanization
(TWO checks needed to occur to set equilibrium of deaths/births (population growth)
1) External/environmental factors: limited food, space, resources, etc.
2) Self-regulating factors: fewer births, deliberate killing of offspring, OR increase in deaths b/c of accidents/
more virulent parasites
o ** host resistance is counterbalance to virulence of parasite/degree of harm; how negatively a host will be affected is
determined by host resistance and virulence
Virulence how mutation is filtered through natural selection: lethal vs. mild outbreak of disease, R0 must be > 1
o Factors that affect spread of disease
Size of population, overcrowding, density
Close association w/ domestic animals
Seasonal patterns, climate
Communal activities that bring susceptible
ppl in contact w/ infectious
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Character & quality of water supply, food, shelter
Practice of using human excrement (night soil) as
fertilizer = transmission of infective stages
Counter measures used (quarantine,
immunization, etc.)
Disease Ecology (7)
o Main factors that influence the occurrence of a disease:
Host (to get sick), environment (exposure to contagion), agent (parasite)
o Factors necessary for spread of disease
Must be infectious individuals
Must be susceptible individuals
Must have a means of transmission b/w the 2
NOTE: for an infection to persist in a population, each infected person must transmit the infection to at least 1
o Reproductive ratio “multiplier of disease” is the # of individuals each infected person infects at the beginning of the
epidemic (R0)
Greater the population size = greater (R0)
Change in the high (R0) = greater proportion of hosts infected (prevalence) & burden (incidence) of disease
R0 > 1, transmission stages = expanding disease (epidemic) BUT in time, susceptibility is consumed & the epidemic
may burn itself out/await new hosts through birth & immigration
R0 < 1, parasite cannot establish itself
Size of population needed to maintain infection varies INVERSELY w/ transmission efficiency & DIRECTLY w/
death rate (virulence)
Therefore, virulent parasites (those that cause high # of deaths) need large population to be sustained
o Modes of disease transmission
Direct from person to person
Indirect through a common route/vector
Portal of entry
Dermal through skin
Ingestion through mouth
Inhalation during respiration
Aspiration airway entry
o Types of diseases
Iceberg concept broad spectrum of disease severity
Peak see from a distance (common), know symptoms & how to avoid
Below surface SUBCLINICAL, most severe b/c has infections but no symptoms = easy spread of outbreak
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o Types of disease outbreaks
Endemic usual occurrence of a disease given within a geographical area; normal
Epidemic occurrence of a disease in excess of normal expectancy; exceeds normal tendencies
Pandemic worldwide epidemic
o Types of epidemic
TYPE 1 population is large & shows regular series of outbreaks but never completely disappears endemic, cases
# of susceptible ppl large enough to remain transmittable, R0 > 1
TYPE 2 peaks of infection are discontinuous but w/ regular pattern of occurrence cases; no endemicity, temporary
absences of disease
# of susceptible ppl is not enough to keep chain of transmission, R0 < 1
TYPE 3 occurs in populations of less than 10,000 w/ an increase in cases during irregular intervals & long periods
of no disease
Chain of infection is interrupted b/c of remoteness, R0 < 1
o Determinants of disease outbreaks [# of ppl immune/not at risk of disease VERSUS # of ppl susceptible/ at risk of
Herd immunity resistance of a group to a disease attack due to immunity (Ex: Measles, 94% population immune)
Incubation period short = low disease outbreaks (contagious), longer = high disease outbreak (contagious during)
** Attack rate ratio of the # of ppl in whom a certain illness develops ÷ total # of ppl at risk
Terminology (7)
o Parasites organism that grows, feeds & is sheltered on or in a different organism & that does not contribute to the
survival of its host (Ex: bacteria, protozoa unicellular)
Unable to live on their own, must rely on host for nutrition & replication, can be in different forms:
Parasitism the association of 2 different kinds of organisms (species) wherein 1 benefits (parasite) at the expense
of others (the host) = harm
o Virus ultimate micro parasite, smaller than bacteria; neither cells or organisms & can only reproduce in host
Collection of genetic material engulfed in protein, only seen w/ electron microscope killed when RNA/DNA
o Macro parasite compose of many cells (multicellular) & cycles through transmission stages of eggs & larvae which
pass into the external environment (Ex: plasmodium, ticks, flies)
Use the host for multiplication & cycles of transmission, can live on surfaces & the human body w/ complex or
simple life durations
o 3 kinds of bacteria
Spherical (coccus), rod shaped (bacillus) & corkscrew (sprillium/spirochete)
o Transmission movement of a parasite from host to host
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