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VET YEAR ONE > DISEASE E&E (Measuring Disease 1) > Flashcards

DISEASE E&E (Measuring Disease 1) Flashcards

1
Q

Iceberg of infectious disease: clinical spectrum

A

Below: subclinical
-exposure without infection
-infection without disease
Above:
-mild
-severe disease
-death

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2
Q

Johne’s disease:

A

-paratuberculosis
-caused by bacteria called MAP

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3
Q

Johne’s disease iceberg:

A

Below:
-susceptible heifer calves
-non-clinical, non-shedding
-non-clinical, shedding
Above
-clinical cases

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4
Q

Quantifying the course of a disease:

A

-1.Incubation period
-2. Illness
-1.Latent period
-2. Infectious
*expressed as averages, but significant variability between individuals

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5
Q

Incubation period:

A

-individual has no symptoms
Ex. 3-5years for Johne’s

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6
Q

Illness:

A

-individual has symptoms

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7
Q

Latent period:

A

-from when they are infected to when they are infectious
-sometimes shorter than the incubation period

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8
Q

Johne’s latent period:

A

-2-4 years
-shorter than the incubation period=great way to spread the disease

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9
Q

Infectious;

A

-host can transmit the pathogen

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10
Q

Quantifying the course of rabies:

A

-incubation period: 3-12weeks, depends where they were bitten
-illness: 7 days (then death)
-latent period: infectious after the virus reaches the brain
>similar to the incubation period

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11
Q

Characteristics of agent in relation to communicable disease (5):

A

-infectivity
-pathogenicity
-virulence
-immunogenicity
-physical stability

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12
Q

Infectivity:

A

-proportion of individuals that are exposed and who become infected

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13
Q

Pathogenicity:

A

-proportion of infected individuals who develop clinically apparent disease

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14
Q

Virulence:

A

-proportion of clinically apparent cases that are severe or fatal

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15
Q

Immunogenicity:

A

-capacity to produce specific and lasting immunity in the host

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16
Q

Physical stability:

A

-ability to survive independently in environment

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17
Q

Outbreak definition:

A

-an increase in observed number of cases of a disease or health problem compared with expected number for
>a given place
>a specific group of animals/people over a particular period of time

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18
Q

Epidemic definition:

A

-occurrence in a community or region of cases of an illness, specific health-related behaviour, or other health-related events, clearly in EXCESS of NORMAL expectancy

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19
Q

Outbreak vs. epidemic:

A

-often used for more localized epidemic
>within a village, town or specific institution

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20
Q

Pandemic:

A

-outbreak on a global scale

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21
Q

Endemic disease:

A

-disease which is “normally” present or “regularly found” in a population
Ex. Johne’s disease in cows in North America

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22
Q

Case definition:

A

-standard set of criteria that investigators in an epidemiological investigation use to decide whether an individual should be classified as having the disease of interest
-don’t all need to have a lab diagnostic test
*different from a clinical diagnosis

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23
Q

Importance of case definition:

A

-helps count cases CONSISTENTLY over time and from place to place
-helps with comparing expected and observed numbers to decide if there is a real outbreak

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24
Q

3 categories for case definitions:

A

-confirmed
-probable
-possible

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25
Q

Confirmed:

A

-typical clinical features AND a lab test or epidemiologic link to a lab confirmed case

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26
Q

Probable:

A

-typical clinical features but no lab confirmation or epi link

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27
Q

Possible:

A

-fewer typical clinical features and no lab confirmation or epi link

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28
Q

Identifying and counting cases:

A

-critical to success of an outbreak investigation
-not all may seek/get care
-not all cases get tested
*need to case find to get max info and better understand the epi of the disease

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29
Q

Reported cases may not:

A

-representative of all cases
>mild disease may not be reported

30
Q

Sometimes an ‘outbreak’ occurs because:

A

-we do a better job looking for or detecting cases
>new improved testing
>availability of diagnostics
>how hard we look

31
Q

Counting cases/number of animals infected: includes

A

-infected
-exposed
-diseased (cases)
-dead
*need a case definition
*help understand the timing (latent period, incubation period, illness duration)
*need a concept of size of the population at risk (DENOMINATOR)

32
Q

Clusters of cases:

A

-geographical or temporal collection of cases that seem GREATER than the EXPECTED number for that given place and/or time
*may help identify risk factors

33
Q

How should we orient cases?

A

-space
-time
-animal
*very important for diagnostic process at the population level

34
Q

Space:

A

-location
>province
>country
>farm
>kennel
>pen or pasture

35
Q

Animals:

A

-species
-class of animal
-age
-immune status

36
Q

Temporal variations of disease:

A

-seasonal patterns
-cyclical fluctuations (ex. measles, rabies)
-secular trends (long term movement)

37
Q

Secular trends can be a result of:

A

-environmental changes
-diagnostic changes
-medical changes

38
Q

Seasonal patterns:

A

-arthropod borne outbreaks
-related to environment and climate (foot rot in feedlot cattle)
-influenza in people (fall/winter)
-related to demographics in seasonal industry (calf scours in beef herds)

39
Q

Arthropod borne outbreaks (seasonal pattern)

A

-WNV
-Western equine encephalitis
-summer
*gradual build up or ‘amplification’

40
Q

Using a calendar as a tool:

A

-events in populations all take place in a continuum of time
-time=easily quantifiable

41
Q

Prevalence:

A

-sometimes referred to as prevalence rate or prevalence proportion
-proportion of cases or infections in a population at ONE PARTICULAR TIME
>no distinction between old and new cases (INCLUDES ALL CASES)
-snapshot in time
-a proportion (0-1 or 0-100%)

42
Q

Prevalence represents:

A

-the probability of an individual animal being infected AT a given POINT IN TIME
*important for diagnostic decision making

43
Q

Prevalence example:

A

-you walk through a herd of 200 dairy cows and 20 of the cows are lame
=20/200=0.1 or 10%

44
Q

Point prevalence:

A

-strictly considering the prevalence at a POINT in time
-can use an event as a ‘point of time’ (Ex. prevalence of hypocalcaemia at calving in dairy cows)

45
Q

Period prevalence:

A

-calculated the same way, but the population is assessed over a PERIOD of time
Ex. Johne’s disease prevalence: September 2014 to January 2015

46
Q

Johne’s disease prevalence:

A

-overall: 1.55%
-herd with at least one positive: 23.6%
-herd with 2 positives: 5.4%

47
Q

Other reasons for using prevalence:

A

-can be used to assess frequency of behaviours that might be risk or protective factors for disease
Ex. prevalence of smoking or vaccine use

48
Q

Incidence:

A

-measure of the occurrence of NEW CASES of disease during a span of time
-all measures should have a time component

49
Q

2 methods of calculating incidence:

A

-incidence risk
-incidence rate

50
Q

Incidence risk:

A

-probability that an INDIVIDUAL ANIMAL will contract or develop a disease during a defined period of time
-measure of RISK of becoming a case
-no units: ranges from 0-1

51
Q

Incidence risk equation:

A

-# of new cases in a period of time/total population at risk

52
Q

Incidence risk and length of observation period:

A

-longer the period=greater the risk

53
Q

When is using incidence risk good?

A

-best for static populations
-good when risk period is related to a specific event (ex. calving)

54
Q

Specific examples of incidence risk:

A

-attack rate
-case fatality rates

55
Q

Attack rates:

A

-describes the frequency of disease in outbreak situations
-measures of risk

56
Q

Attack rates equation:

A

=number of cases / size of population exposed

57
Q

Attack rates used where:

A

-risk period is limited
-all cases are likely to occur within the that risk period
Ex. going to a wedding and getting food poisoning

58
Q

Secondary attack rates:

A

-describes infectiousness of an agent
-ease of spread
-spread withing a herd or family and not ALL cases have resulted form a common source exposure

59
Q

Secondary attack rates equation:

A

-(number of cases – initial cases) / population at risk

60
Q

Case fatality rates:

A

-proportion of animals with a specific disease that die from it (within a specified time period)
-risk measure (proportion) instead of rate

61
Q

Case fatality rates describe the:

A

-impact of epidemic-type disease or severity of acute diseases

62
Q

Incidence rate:

A

-number of NEW cases of disease in a POPULATION per unit of ANIMAL-TIME during a given time period
-measures the rapidity with which new cases develop over time

63
Q

Incidence rate equation:

A

=number of cases of disease in a defined period / (number of animals-time units at risk during that period)

64
Q

Animal-time unit:

A

-one animal for a defined period of time
Ex. cow-mounth

65
Q

Incidence rates are usually calculated using:

A

-only the first occurrence of the disease for each animal
>no longer part of the population of risk
*make assumption that on AVERAGE they enter or leave halfway through the time period

66
Q

Incidence rate (approximate method):

A

=number of new cases of a disease that occurred in the population during a particular period of time / (# at risk at the start + # at risk at end)/2

67
Q

Incidence rate (approximate method): change in population at risk size

A

Animals that leave:
-withdrawals (culls, deaths)
-cases of the disease (no longer at risk)
Animals that enter:
-purchases
-births

68
Q

Incidence rate (exact method):

A

-sometimes called incidence density
-less commonly used
-denominator takes into account the EXACT amount of time each individual was at risk
-calculate per animal-time

69
Q

Prevalence vs. incidence:

A

-prevalence is AT
>P=I x D
-incidence is DURING

70
Q

Changes in prevalence can be due to:

A

Change in:
-incidence rate
-the average duration of the disease
-BOTH incidence and duration

VET YEAR ONE (108 decks)

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