Disease Spread and Control

Question 1

What is exponential spread?

Answer 1

spreading constantly

Question 2

Does R usually change over time?

Answer 2

Yes, it is not consistent over the period of time with the epidemic. Also, R doesn’t spread at the same rate with every individual (some are super spreaders)

Question 3

What are Hubs

Answer 3

netsworks. Where one individual spreads a lot (ex/ a bull breeding the herd of cows if it has a disease)
If you can control the one hub then it will have a big effect

Question 4

How can you reduce R?

Answer 4

If you can catch the disease early then you can same a huge amount of transmission. The longer the disease has to spread, the higher the transmission because of exponential spreading

Question 5

Describe the steps of disease response

Answer 5

1. you detect the disease and control it from spreading
2. trace the disease forward so that you can block the other half of R of that one individual (if R =2 ) so that one doesn’t spread
3. Trace backwards to see where the initial detected disease came from so you can see where the other half of the R is from that portion by tracing forwards again…at this point you haven’t detected a huge amount but every little bit helps

Question 6

What is important about disease detection?

Answer 6

The earlier the disease is detected, the more you can limit the spread of it and the better you can trace where it has spread to

Question 7

What are the 3 steps for disease control?

Answer 7

Prevention, detections and response!!

Question 8

What are some important considerations in disease control?

Answer 8

• diseases are not static, there are new pathogens, management and populations and they are constantly moving
• motivation is important for disease control programs– normally have more motivation when considering economic impacts, public health concerns and public opinions

Question 9

Describe disease eradication

Answer 9

• it is very rare, so instead it is typically referring to a regional elimination of an infectious disease
• you need to reduce prevalence to a point where transmission does not occur and so that it is no longer a major health problem

Question 10

What 3 things are necessary for the potential of disease eradication?

Answer 10

1. effective intervention is available to interrupt transmission (isolate, treat or kill infected animals)
2. practical diagnosis tool with sufficient sensitive and specificity available to detect low enough levels
3. no other reservoirs and disease doesn’t amplify in environment (can’t live in environment well)

Question 11

Economic considerations

Answer 11

We need to be able to justify using the money to eliminate the disease so it has to have health problems most likely

Question 12

Social and political criteria of eliminating the disease

Answer 12

• the eradication needs to be carried through until the end so it is a commitment
• needs to have the public health recognize it as important
• needs to have a national appeal
• need a specific reason for eradication

Question 13

Does eradication involve risk?

Answer 13

Yes, it always does, but if you know how risky it is then you don’t have to do a risk analysis and we just need to decide if we are comfortable in taking that risk

Question 14

What are two components of risk?

Answer 14

1. probability of harm

2. severity of impact of hazard

Question 15

What are some factors affecting risk perception?

Answer 15

• familiarity with subject
• understanding
• scientific certainty
• controllability
• impact on children

Question 16

What is disease control?

Answer 16

a term used to describe the reduction of morbidity and mortality. it is an on going process

Question 17

what is biosecurity?

Answer 17

any system or practice that prevents the spread of infectious agents from infected animals to susceptible animals.
Or any practice that prevents an infected animal getting introduced into a herd, region or country in which the infection has not occurred

Question 18

What are 3 factors that affect control?

Answer 18

• mode of transmission
• host specificity
• ease of spread

Question 19

What are some important facts in veterinary disease control programs?

Answer 19

• knowledge of cause, maintenance and transmission of disease
• vet infrastructure
• ability to diagnose
• availability to replace stock
• producers opinion and cooperations
• public opinion

Question 20

What are some important factors in disease control programs?

Answer 20

• public health
• requirement for legislation and compensation
• ecological consequences
• financial support

Question 21

What is one thing that will help diagnose a disease even if you don’t know what your treating

Answer 21

route of transmission

Question 22

What are pathognomonic tests?

Answer 22

absolute predictor of disease or disease agent

can have false negative (test negative but actually by positive) but if it is positive the it is absolutely positive

Question 23

What are surrogate tests?

Answer 23

detect secondary changes that will predict the presence or absence of disease.
Can have false negatives and false positives

Question 24

Gold standard tests?

Answer 24

should be backed by data comparing its accuracy to an appropriate standard.
can truely determine if a disease is present or absent
Post mortum is normally the ultimate conformational test
not many golf standard tests

Question 25

What does True prevalence =? and what is it?

Answer 25

(A + C)/N

It is when the disease is actually present

Question 26

What is apparent prevalence? and what is the equation?

Answer 26

The results that showed that the disease was present (included the false positive)
( A + B)/ N

Question 27

What is the sensitivity test? and what is the equation?

Answer 27

Tests to see how well the test detects the positives
A/ (A+C)
SnNout ( Sensitivity: negative the rule out disease)

Question 28

What is the specificity test? and what is the equation?

Answer 28

Determines the non diseased animals that test negative
D/ (B +D)
SpPin ( if positive then rule in disease)

Question 29

Is it better to have specificity or sensitivity?

Answer 29

It depends if you are trying to rule in the disease or rule out the disease
if rule in then use specificity and when rule out use sensitivity.
Also, it depends on how severe the disease is…if disastrous disease then use highly sensitive test at the cost of specificity because you want to avoid false negative at all costs
On the flip side, the cost of a false positive test could be potentially dangerous treatments or euthanasia so want to use highly specific tests

Question 30

What is selective slaughter?

Answer 30

slaughtering a minority of infected animals to protect healthy animals
works well in early disease outbreaks and slowly spreading diseases but it becomes more expensive as a disease becomes more rare
it is difficult to convince people

Question 31

What is depopulation?

Answer 31

sacrificing a whole population including non infected individuals
the disease is spreading rapidly or it is an exotic disease
in terminal stages of eradication program

Question 32

What is Quarantine?

Answer 32

physically separating the sick animals or potentially sick animals from healthy animals
restringing movement of exposed or infected animals that may be contaminated
can be at different levels…nationally or just within a herd

Question 33

What is reduction of contact?

Answer 33

reduce or prevent contact between infected and non infected animals by physically separating them or separating them in time (all in all out or different milking schedules)
closed herds will have maximum biosecurity and expanding herds will have much higher risk

Question 34

What is Mass treatment?

Answer 34

treating all animals whether they are sick or well
it combats diseases occurring at a high prevalence where depopulation and slaughter are not viable or economical
need safe and cheap and effective therapy

Question 35

What is mass immunization?

Answer 35

creating immunity in a population to limit the spread and impact of a disease
can decrease prevalence to a point when other techniques can be used for eradication
advantage: resistant individuals can freely move and have a lack of frequent dosages
but it is difficult in wild populations

Question 36

How can education help?

Answer 36

there can be programs that educate the public regarding disease control
often used in combination of other techniques

Question 37

Describe environmental control

Answer 37

many public health programs revolve around environmental hygiene
can control management, feeding, husbandry and environment

Question 38

How is ecology of the disease useful?

Answer 38

it can be used to prevent or control the disease using biological control mechanisms, or vector control

Question 39

How can genetic improvement help disease control?

Answer 39

do genetic screening to identify specific diseases and remove these individuals from the breeding population
also, can breed for disease resistance