EPIDEMIOLOGY Flashcards
homeostasis
temporary or permanent anatomical, physiological or behavioural change of the organism to reduce or overcome health-threatening influences.
- Specific: environmental temperature high perspiration and vasodilation.
- Aspecific: stress, nonspecific reaction to a stimulus/stressor
general adaptation syndrome
- By activation of the hypothalamic pituitary adrenal circuit (endocrinology)
- 3 phases:
o Alarm reaction: first slight drop to below normal then increase to above normal
o Resistance: phase of adaptation
o Exhaustion: with long term exposure to the same stressor with eventually dead
hyperthermia
fever. Abnormally high body temperature
hypothermia
undercooling. exposed to very cold temperatures. your body then looses heat faster.
serological testing
can determine whether a person has been exposed to a particular microorganism.
- pathogen/antigen, best proof of current infection
- antibodies evidence of current and previous infection
blood composition
adv: fast and cheap ; con: false positive and false negative
zoonosis
disease that can be transmitted from animal to humans
suckling period
the drawing of milk into the mouth from the nipple or teat of a mammary gland
epizooties
(of diseases) spreading quickly among animals.
notifiable diseases
o Can quickly expand
o May cause serious damage to the species concerned
o Cannot be prevented or controlled by normal measures
o Causes serious economic damage to animal keepers and to EU countries
outbreak OIE
the occurrence of one or more cases in an epidemiological unit
ECDC
european centre for disease prevention and ctronl
EFSA
european food safety authority
OIE
office international des Epizooties
WHO
World health organsization
epidemiology
study of the emergency and spread of diseases
aetiology
study of the cause
multifunctional disease
traits and conditions that are caused by more than one gene occurring together
causal model
causal model I
Sufficient: if it is inevitably produces an effect. Always comprises a range of component causes
Necessary: if a cause is a component of every sufficient cause then it is necessary. The necessary cause must always be present to produce an effect
causal model II:
direct and indirect
preventive methods pathogen
disinfection
medication
stamping out/culling
isolation
preventive methods host
vaccination passive immunisation genetic resistance tolerance/resilience host
morbidity
medical problems caused by a treatment
prevalence
dominant, acceptance, having greater power
BSE
bovine spongiform encephalopathy. Affects the nervous system of cattle and kills them. misfolded protein.
horizontal transmission
transmission from one individual to another
vertical transmission
transmission of infection from one generation to the next by infection of the embryo of fetus.
prevent control or eradicate
stamping out
used in eradicating major epidemic notifiable diseases (OIE list of diseases). Legislation and with government funding
PREVENT CONTROL OR ERADITATE
control:
used for other major (zoonotic) diseases (OIE list). Legislation, not fully funded.
PREVENT CONTROL OR ERADICATE
endemic diseases
are the responsibility of producers to prevent them (own costs), also zoonoses even though these seldom cause disease or economic losses in animals.
most money in endemic diseases
VACCINATION STRATEGIES
emergency vaccination
to prevent the further spread of disease when epidemics occur. E.g. ring vaccination around an infected region.
VACCINATION STRATEGIES
barrier vaccination:
to prevent pathogens to enter in free areas, usually countries
VACCINATION STRATEGIES
suppressive vaccination
within and around an infected region. ring vaccination
passive immunisation
immune system is not sitmulated,
protection is temporary for a short time
via maternal antibodies, serum.
tolerance of animals
3
- Resistance: ability of an animal to control a pathogen burden.
- Tolerance: an animal got an increased pathogen and the animal can coope with it. Some animals more tolerant than others. -Ability of animal to maintain performance with increasing pathogen burden
- Resilience: animals have a good resistance. Combination fo resistance and tolerance
types of epidemiological studies
monitoring, surveillance, screening
tell me about monitoring survellance and screening
making of routine observations on health, productivity, and environmental factors and the recording and transmission of these observations.
Surveillance = more intensive form of monitoring
• With registration of origin of individuals and often part of a control programme
• Trace-back
• Often all (free) farms, but samble of animals within farms
Is a more intensive form of data recording than monitoring. Originally, surveillance was used to describe the tracing and observation of people qho where in contact with cases of infectious diseases. It is now used in much a wider sense to include all types of disease
Screening = testing of all animals in the population. Identification of undiagnosed cases of disease using rapid test or examinations. Aim is to separate healthy idnivicuals that probably have a disease from those that probably do not. Not intended to be diagnostic. Individuals with positive test results usually require further investigation for definite diagnosis.
- Mass screening: investigation of the total investigation
- Strategic screening: targeted at animals only in aresas where there have been cases of diseases
- Prescriptive screening: aims early identification of diseases that can be controlled better if they are detected early in their pathogenesis
surveys can be..
- cross-sectional: recors events occuring at a particlar point in time
- longitudinal: records events over a period of time. Prospectively(present to future) or retrospectively (past events)
observational studies
- Cross-sectional studies: investigates relationships between disease and hypothesized causal factos in a specified population. Animals catagorized according to the presence and absence of disease and hypothesized causal factors.
- Case-control studies: compares a group of diseased animals with a group of healthy animals with respect to exposure to hypothesized causal factos
- Cohort studies: a group exposed to factors is compared with a group not exposed to the facros with respect to the development of a disease. It is then possible to calculate the level or fisk of developing the disease in relation to exposure to the hypothesized causal factor.
experimental studies
the investigator has the ability to allocate animals to various groups according to factors that the investigator can randomly assig to animals
postulates of Koch
a micro-organism is causal if:
o It is present in all cases of the disease
o It does not occur in another disease
o It is isolated in pure culture form an animal, repeatedly passaged, it induces the same disease in other animal
Con: this monocausal model is too rigid, and doesn’t account for environmental factors, and not applicable to diseases with non-infectious cause.
Evan’s rules
- the proportion of individuals with the disease should be significantly higher in those exposed to the supposed cause than in those who are not;
- exposure to the supposed cause should be present more commonly in those with than those without the disease, when all other risk factors are held constant
- the number of new cases of disease should be significantly higher in those exposed to the supposed cause than in those not so exposed, as shown in prospective studies
- temporally, the disease should follow exposure to the supposed cause with a distribution of incubation period on a bell-shaped curve
- a spectrum of host responses, from mild to severe, should follow exposure to the supposed cause along a logical biological gradient
- a measurable host responsible (e.g. antibody, cancer etc.) should appear regularly following exposure to the supposed cause in those lacking this response before exposure, or should increase in magnitude if present before exposure; this pattern should not occur in individuals not so exposed
- experimental reproduction of the disease should occur with greater frequency in animals or people appropriately exposed to the supposed cause than in those not so exposed; this exposure may be deliberate in volunteers, experimentally induced in t he laboratory or demonstrated in a controlled regulation of nature exposure
- elimination or modification of the suppose cause should decrease the frequency of occurrence of the disease
- prevention or modification of the host’s response should decrease or eliminate the disease that normally occurs on exposure to the supposed cause
- all relationships and associations should be biologically and epidemiologically credible
causal model I
o Sufficient causes: often a range of causes that contribute component causes
o Necessary: is present in all sufficient causes
causal model II
- takes interactions into account. Factors depdent.
- A disease has several causes that lead to the onset of the disease separately or together
- One cause can show several symptoms
- In this model, causal relationships are considered as degrees of directness, and could be depicted in a causal web
formulating causal hypothesis
description of…
- Population. How many hearts, how many animals
- Environment ( hypothetical causal factors, in time and place
- Disease occurrence
Hil’s criteria
- time sequence of the events: cause must precede effect in a bacteriological survey.
- strength of the association: if a factor is causal, then there will be a strong positive statistical association between the factors and the disease.
- Biological gradient: if a dose responds relationship can be found between a factor and a disease, the plausibility of a factor being casual is increased
- Consistency: if an association exists in a number of different circumstances, then a causal relationship is probable
- Compatibility with existing knowledge: it is more reasonable to infer that a factor causes disease if a plausible biological mechanism has been identified than if such a mechanism is not known.
Hil’s criteria has achieved notable success, although the philosophical origin of the criteria remains unclear
describing disease occurrence
-Endemic: predictable presence of disease in
a population like masitits. Notifiable
diseases are never endemic because they
should not be there.
1. Normal level
2. Constant presence (at high level called
hyperendemic)
3. Balance between several factors
-Epidemic: unpredictable increase in cases
1. Sudden increase in incidence of disease
2. Imbalance between various factors
Different graphics for epidemic and
endemic. Endemic being more stable and
epidemic rising, action and decreasing
-Pandemic: worldwide epidemic
-Sporadic outbreak: a single case or cluster of
cases in areas where it was before absent
Kendall’s Threshold theorem
Threshold level: a minimum number of susceptible animals and density are required for the occurrence of an epidemic by contact.
reproduction ratio
Definition R_0: the average number of secondary classes caused by a typical infected individual during his entire infectious period in a fully susceptible population
reproduction ratio
Definition R_0: the average number of secondary classes caused by a typical infected individual during his entire infectious period in a fully susceptible population
morbidity
amount of disease infection
mortality
amount of death
mortality
amount of death
ratio
value after division of 2 numbers
proportion
special type of ratio e.g. the numerator is a part of the denominator also expressed as %
rate
ratio that represents the change in the numerator when there is a change in the denominator per unit. E.g. speed in km/h, cases of disease/ year.
two types of disease occurrence
Prevalence: without distinction between old and new case (ratio)
- Point prevalence: at a particular point in
time
- Period prevalence: during a specific
period
Incidence: only new cases that occur in a known population over a specified period of time
- Cumulative incidence (ratio)
- Incidence rate (rate, in literature also
used as incidence density)
two types of disease occurrence
Prevalence: without distinction between old and new case (ratio)
- Point prevalence: at a particular point in
time
- Period prevalence: during a specific
period
Incidence: only new cases that occur in a known population over a specified period of time
- Cumulative incidence (ratio)
- Incidence rate (rate, in literature also
used as incidence density)
case fatality
proportion of diseased animals that die
cohort study
A study design where one or more samples (called cohorts) are followed prospectively and subsequent status evaluations with respect to a disease or outcome are conducted to determine which initial participants exposure characteristics (risk factors) are associated with it.
cohort study adv and dis
- Advantages: incidence estimation, above table is based on cumulative incidence. Most effective for causal hypothesis testing
- Disadvantages: exposure prevalence cannot be determined, large numbers required for rare diseases, relatively expensive and long-term, follow-up loss is a risk
case-control study adv and disadv
- Benefits: very suitable for rare diseases, relatively fast and cheap, use of existing records, no risk for individuals
- Disadvantages: no prevalence/ incidence determination, recall, bias controls difficult to choose.
cross-sectional study adv and disadv
- Adventages: relatively fast, cheap, multiple factors, no risk for individuals
- Disadvantages: not suitable for rare diseases or diseases with short duration, cause and effect cannot be determined only association.
causal inferance
In a causal inference, one reasons to the conclusion that something is, or is likely to be, the cause of something else. For example, from the fact that one hears the sound of piano music, one may infer that someone is (or was) playing a piano.
three types of observational- analytical research makes use of the 3 rules of Evans:
- prevalence significantly higher in exposed subjects CS
- exposure occurs significantly more frequently among the infected (provided that other factors are equally prevalent CC
- incidence significantly higher is exposed group CH. the more postulates that apply the stronger causality reasoning is.
relative risk RR
ratio of disease in exposed group and disease in unexposed group
bias
any systematic error in the design, conduct or analysis of a study that makes the results invalid
