Koch Question.docx

Koch's postulates are the following: 1. The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms. 2. The microorganism must be isolated from a diseased organism and grown in pure culture. 3. The cultured microorganism should cause disease when introduced into a healthy organism. 4. The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

In 1890 the German physician and bacteriologist Robert Koch set out his celebrated criteria for judging whether a given bacteria is the cause of a given disease. Koch's criteria brought some much-needed scientific clarity to what was then a very confused field. Koch's postulates are as follows: 

The bacteria must be present in every case of the disease.



The bacteria must be isolated from the host with the disease and grown in pure culture.



The specific disease must be reproduced when a pure culture of the bacteria is inoculated into a healthy susceptible host.

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The bacteria must be recoverable from the experimentally infected host.

However, Koch's postulates have their limitations and so may not always be the last word. They may not hold if: 

The particular bacteria (such as the one that causes leprosy) cannot be "grown in pure culture" in the laboratory.



There is no animal model of infection with that particular bacteria.

A harmless bacteria may cause disease if: 

It has acquired extra virulence factors making it pathogenic.

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It gains access to deep tissues via trauma, surgery, an IV line, etc.

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It infects an immunocompromised patient.

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Not all people infected by a bacteria may develop diseasesubclinical infection is usually more common than clinically obvious infection.

Despite such limitations, Koch's postulates are still a useful benchmark in judging whether there is a cause-and-effect relationship between a bacteria (or any other type of microorganism) and a clinical disease.

Question

Answer

What is CDC?

Centers for Disease Control and Prevention

What is OIE?

World Organisation for Animal Health (known by its French acronym Office International des Epizooties – OIE)

What is USDA- APHIS?

United States Department of

Agriculture- Animal and Plant Health Inspection Service what is USDA –FSIS?

United States Department of Agriculture - Food Safety and Inspection Service

what is AVMA?

American Veterinary Medical Association

Epidemiology is?

the greek of the word means... "the study of what is upon the population". SO, it is the Study of the occurrence and distribution of disease in populations (animal or human) (Emphasis on establishing the causal factors that influence disease occurrence)

what is a population?

the totality of individuals that share common attributes (sex, breed, ethnicity, location)

What is EBM (evidence based medicine)?

"the conscientious, explicit and judicious use of current best evidence in making decisions about the care of the individual patient.”

EBM uses POPULATION DATA to better understand these 4 areas

dx, prevention, tx, prognosis

What is endemic(human)/enzootic(animal) ?

Usual (constant) frequency of disease in a population. A disease is endemic when it occurs with predictable regularity in a population. (Note: Endemics can become epidemics if host-agent-environmental factors change)

What is Epidemic (epizootic)?

Often synonymous with the term outbreak and typically

used for infectious diseases. An epidemic disease is a disease that is rapidly spread and many individuals acquire disease over a short period. What is Pandemic?

A widespread epidemic/epizootic……involvin g more than one country. There is a more specific def. made by the WHO(World Health Organisation), which requires...: There must be a disease new to a population – or at least a disease that had not surfaced for a long time. This disease must be caused by diseasecausing agents that infect humans, causing serious illness. AND, The agents must spread easily and sustainably among humans causing high morbidity and high mortality

The WHO (world health organization) defines their "phase 6- pandemic phase" as

the pandemic phase, is characterized by community level outbreaks in at least one other country in a different WHO region in addition to the criteria defined in Phase 5. Designation of this phase will indicate that a global pandemic is under way.

"sporatic" disease occurance is defined as...

A disease that is NOT NEW & occurs infrequently (without regularity) in a population. Cases occur in small numbers, illness is not apparently connected with similar illnesses in any other animals/persons,

and it is not rapidly spread explain epidemic vs sporatic

Whilst an epidemic can be 1 case of a new disease, it is rapidly spread between animals /humans... BUT!!! A sporadic case refers to a person/animal whose illness is not rapidly spread and not apparently connected with similar illnesses in any other animals or humans

what is Public health surveillance?

Public health surveillance is the ongoing, systematic collection, analysis, interpretation, and dissemination of data regarding a health-related event for use in public health action to reduce morbidity and mortality and to improve health (CDC,2001).

what is passive surveillance?

System in which Vet agencies make no active efforts to collect disease info (But Problem: Some info on disease frequency but not accurate.)

what is Active surveillance?

Uses structured disease surveys to collect high quality disease info quickly. A survey: Trained veterinary staff examine only a sample of the population. (more costly but more accurate)

what is a host?

An individual (animal or human) that harbours an Infectious agent or is exposed to a potential causal agent of disease which is usually infectious. Typically used in

reference to infectious diseases although in general hosts are also susceptible to noninfectious and chronic diseases. What is a demographic?

Personal characteristics of an individual or group (age, sex, breed, occupation)

what is a case?

Individuals with a particular disease that meet selected criteria stated by the case definition

what are Causal factors or determinants?

A factor that directly influences the occurrence of disease. Synonymous with risk factor or exposure factor

what is infection?

Defined as the encounter of a potentially pathogenic agent with a susceptible human /animal host and the host shows an immunologic response to infection.

what is disease DEFINED as?

a clinically apparent infection — infection accompanied by overt illness.

Question

what are the three corners of the epidemeologic triangle? What is this triangle used for?

Answer

Host-Agent-Environment. It is used as A model to explain why diseases occur in a population.

Temporal (in time) disease occurance reporting uses what kinda terminology (list...)

Endemic (enzootic), Epidemic (epizootic), Pandemic (panzootic), Sporadic

how would you describe endemic in terms of temporal patterns?

dz occurs at expected frequency, present in population or region at all times, and Usually low and predictable level

how would you describe epidemic in terms of temporal patterns? how do you depict the occurrence of the dz?

disease occurs at greater than expected frequency. Occurrence depicted graphically as "Epidemic curves"

how would you describe pandemic in terms of temporal patterns?

sporatic

The shape of an epidemic curve tells us what two major things?

These are histograms depicting the no. of new cases (Y) axis over time (X) axis. Using this info, we can get info on probable time of exposure based on the incubation period, and also info on if the outbreak was due to a common or point source

what are the 3 basic curves of disease occurrence on the epidemic curve?

(1) Point epidemic (point source) (2) Continuous common source epidemic (3) Propagating epidemic

what is a "point source" epidemic curve? what does the curve look like on the graph?

animals or persons are subjected to the same BRIEF exposure over a limited, defined time period, usually within 1 incubation period. The graph looks like Curve commonly rises rapidly and

contains a definite peak at the top, followed by a decline once the point source is removed, no new cases occur (see slide 14) what is a "continuous(common) epidemic" epidemic curve? what does the curve look like on the graph?

Exposure to the source is prolonged over an extended period of time and may occur over > one incubation period. On the graph, The down slope of the curve may be very sharp if the common source is removed or gradual if the outbreak is allowed to exhaust itself (see slide 16)

what is a "propagating epidemic" epidemic curve? What does the curve look like on the graph?

Occurs when disease is introduced through a single (primary) source of infection in 1 animal and then transmitted to other animals. The graph has multiple peaks and regressions (see slide 20)

what is the frequency of an endemic like?

disease occurs at expected frequency

what is the frequency of an epidemic like?

disease occurs at greater than expected frequency

what is the frequency of "sporatic disease" occurance like? What is distinct about them?

only a small number of cases are observed during a short period of time, Disease occurs rarely and without regularity, and there are no secondary cases

look at slide 24 for sporatic vs endemic vs epidemic

epi and sporatic look similar, except sporatic is much fewer cases

what does a time series analysis

Uses the information on

do?

patterns of disease occurrence obtained from temporal occurrence data...the temporal occurrence data will identify periods of high/low risk (trends) of disease occurrence--> allows casual associations to be explored

what are the three trends of timeseries analysis?

short-term, cyclical (including seasonal), secular trends

what is a secular trend?

a long term trend, where the Data reflects an Overall inc or dec in incidence occurring gradually over long time periods

what is a cyclical trend like?

Rise and fall of disease over greater than 1 year Associated with regular, periodic fluctuations in level of disease occurrence

what are some factors which would make a cyclical trend a seasonal trend?

things like host density (all migrating together or sthing), Management practices, Vector borne diseases (fly season), Infectious agent survival due to environmental factors

Disease occurrence can be affected by host factors such as...

age, sex, breed

What is Incidence?

a measure of the frequency with which new cases occur over a specified time period (other explanations given are:)The proportion of a population, initially free of the outcome of interest, that

develops the disease over a given period of time. Incidence refers to NEW cases of disease What is prevalence?

The number of cases that are present in a given population (other explanations given are:) Proportion of the population at a given time that have the factor of interest

what is attack rate?

Measure of the proportion of the population that develops disease at the start of an outbreak among the total exposed

What is the math problem for incidence?

I(per 1,000)= the number of new cases in a population during a particular period of time, DIVIDED BY the number of individuals at risk of developing the disease during that period of time. All of this is multiplied by 1000.

how are units of population expressed?

Unit of population expressed as whole numbers and in the smallest multiples of 10

What is the math problem for prevalence?

# of individuals having a disease at a particular point in time DIVIDED BY # of individuals in the population at risk at that point in time

how is incidence expressed, versus prevalence?

incidence is usually expressed numerically in reference to population at risk (X out of a 1000 or whatever mult of 10).

Prevalence is usually expressed as a proportion between 0 and 1, OR a %, OR As a unit of population at risk what is point prevalence?

Number of cases in a population, at a particular point in time.

what does incidence account for that prevalence doesnt?

prevalence, (unlike incidence), does not take into account the duration of disease. It is a snapshot at this point in time.

What is period prevalence?

How many people have had the disease during a certain time period, for example over 1 calendar year. It is a combination of point prevalence and incidence

what is the math equation which relates incidence and prevalence?

Prevalence=Incidence x Duration of disease

check out prevalence vs incidence example starting on slide 53

helpful

what is a cluster analysis?

Geographical information systems used to measure disease occurrence in time and space... This allows us to ID geographical clustering of disease and define as endemic, epidemic, sporadic, pandemic based on timelocation

what is data modelling used for?

used to test hypotheses and plan health policies

what is a case definition?

set of uniformly applied criteria for a particular disease

Causal relationships Question

Answer

What is Infection?

ability of the agent to establish itself in a host

what is Pathogenic?

ability of agent to produce disease in host

what is Virulence?

Measure of severity of disease due to agent

Resistance to disease in populations is called...?

herd immunity

The stronger the association between a presumed causal factor and disease or outcome, the more likely a cause and effect relationship exists.This is which criteria for establishing a cause?

Strength of association

non-statistical strength of association means?

it happened by chance, no real cause or relation

Positive statistical association may indicate...?

causality

A negative statistical association may indicate...?

a protective factor

example/explanation of a causal factor being Necessary and sufficient?

Certain dose of virus required for infection

example/explanation of a causal factor being Necessary but not sufficient?

Occurrence of disease requires two or more factors are present

example/explanation of a causal factor being Sufficient but not necessary?

Passive smoking can cause feline lymphoma, but other causes of feline lymphoma exist

example/explanation of a causal factor being Neither sufficient nor necessary but can contribute to existing disease?

High fat diet and Cardiovascular disease

what is Temporal Precedence?

The evidence provided demonstrates that your cause happened before your disease occurrence.

Dose-response relationship...what must you remember about this criteria of causal factors?

disease may not develop until exposed to a certain level [ex: exposure/smoke]

"Reversible association" criteria of causal factors means/asks...

Does the removal of a factor results in a decreased or increased frequency of disease? (ex: Cessation of smoking leads to reduction of inflammatory & haemostatic markers for cardiovascular disease)

what is the strongest type of epidemiologic study providing EVIDENCE (NOT PROOF) that an association might be causal? What are the less strong types?

A Randomized clinical trial is Best evidence for causality! Other trials which are not randomized, so are less strong are: cohort and case control, cross sectional, cases series, case report

Relative Risk ratios are used in what studies? Odds Ratios are used in what studies? what do they both measure?

RR is used in cohort studies. OR is used in case-control studies. They measure the STRENGTH of the association between the causal/exposure factor and disease which is a Major criteria for judging causal inferences