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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
Confirmed:
-typical clinical features AND a lab test or epidemiologic link to a lab confirmed case
26
Probable:
-typical clinical features but no lab confirmation or epi link
27
Possible:
-fewer typical clinical features and no lab confirmation or epi link
28
Identifying and counting cases:
-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
29
Reported cases may not:
-representative of all cases >mild disease may not be reported
30
Sometimes an ‘outbreak’ occurs because:
-we do a better job looking for or detecting cases >new improved testing >availability of diagnostics >how hard we look
31
Counting cases/number of animals infected: includes
-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
Clusters of cases:
-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
How should we orient cases?
-space -time -animal *very important for diagnostic process at the population level
34
Space:
-location >province >country >farm >kennel >pen or pasture
35
Animals:
-species -class of animal -age -immune status
36
Temporal variations of disease:
-seasonal patterns -cyclical fluctuations (ex. measles, rabies) -secular trends (long term movement)
37
Secular trends can be a result of:
-environmental changes -diagnostic changes -medical changes
38
Seasonal patterns:
-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
Arthropod borne outbreaks (seasonal pattern)
-WNV -Western equine encephalitis -summer *gradual build up or ‘amplification’
40
Using a calendar as a tool:
-events in populations all take place in a continuum of time -time=easily quantifiable
41
Prevalence:
-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
Prevalence represents:
-the probability of an individual animal being infected AT a given POINT IN TIME *important for diagnostic decision making
43
Prevalence example:
-you walk through a herd of 200 dairy cows and 20 of the cows are lame =20/200=0.1 or 10%
44
Point prevalence:
-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
Period prevalence:
-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
Johne’s disease prevalence:
-overall: 1.55% -herd with at least one positive: 23.6% -herd with 2 positives: 5.4%
47
Other reasons for using prevalence:
-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
Incidence:
-measure of the occurrence of NEW CASES of disease during a span of time -all measures should have a time component
49
2 methods of calculating incidence:
-incidence risk -incidence rate
50
Incidence risk:
-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
Incidence risk equation:
-# of new cases in a period of time/total population at risk
52
Incidence risk and length of observation period:
-longer the period=greater the risk
53
When is using incidence risk good?
-best for static populations -good when risk period is related to a specific event (ex. calving)
54
Specific examples of incidence risk:
-attack rate -case fatality rates
55
Attack rates:
-describes the frequency of disease in outbreak situations -measures of risk
56
Attack rates equation:
=number of cases / size of population exposed
57
Attack rates used where:
-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
Secondary attack rates:
-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
Secondary attack rates equation:
-(number of cases – initial cases) / population at risk
60
Case fatality rates:
-proportion of animals with a specific disease that die from it (within a specified time period) -risk measure (proportion) instead of rate
61
Case fatality rates describe the:
-impact of epidemic-type disease or severity of acute diseases
62
Incidence rate:
-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
Incidence rate equation:
=number of cases of disease in a defined period / (number of animals-time units at risk during that period)
64
Animal-time unit:
-one animal for a defined period of time Ex. cow-mounth
65
Incidence rates are usually calculated using:
-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
Incidence rate (approximate method):
=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
Incidence rate (approximate method): change in population at risk size
Animals that leave: -withdrawals (culls, deaths) -cases of the disease (no longer at risk) Animals that enter: -purchases -births
68
Incidence rate (exact method):
-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
Prevalence vs. incidence:
-prevalence is AT >P=I x D -incidence is DURING
70
Changes in prevalence can be due to:
Change in: -incidence rate -the average duration of the disease -BOTH incidence and duration

VET YEAR ONE (108 decks)

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