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Veterinary Epidemiology > Infectious Diseases > Flashcards

Infectious Diseases Flashcards

1
Q

What is an infectious disease?

A

an illness due to a specific infectious agent or its toxic products that arises through transmission from an infected person, animal, or reservoir to a susceptible host, either directly or indirectly through an intermediate plant or animal host, vector, or inanimate environment

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2
Q

What are the 2 basic mechanisms of transmission of infectious agents?

A
  1. DIRECT TRANSMISSION from an infected host to a susceptible host
  2. INDIRECT TRANSMISSION to a vector IH that typically does not show clinical signs and then to a susceptible host
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3
Q

What are the 6 features of infectious diseases?

A
  1. dseases are caused by microorganisms
  2. a case may also be a risk factor (presence of an infected individual starts the spread)
  3. individuals may be immune
  4. a case may be a source without being recognizedas a case (no clinical signs)
  5. preventative measures usually have a scientific bases
  6. there is sometimes a need for urgency
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4
Q

What is infectivity? How is it calculated?

A

ability to invade a host

(# infected / # exposed to agent) x 100

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5
Q

What is pathogenicity? How is it calculated?

A

ability to induce disease

(# with clinical disease / # infected) x 100

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6
Q

What is virulence? How is it calculated?

A

ability to cause severe disease

(# severely ill / # with clinical disease) x 100

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7
Q

What are the most common infectious agents? Vectors?

A
  • viruses
  • bacteria
  • parasites
  • fungi
  • prions

biting arthropods - mosquitos, ticks, lice, fleas, mites, blood sucking flies/bugs (midges, sandflies)

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8
Q

What are the 3 types of hosts of epidemiological importance?

A
  1. domestic animals/humans
  2. sympatric (exist in the same area, like rodents)
  3. wild
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9
Q

What is the epidemiological triad?

A

the idea that diseases result from the interactions between the HOST, AGENT, and ENVIRONMENT
(sometimes including a vector or intermediate hosts/reservoirs/carriers)

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10
Q

What are 2 common factors that determine the host susceptibility to and infectious agent?

A
  1. genetics
  2. immunological condition (stressed/well-nourished/vaccinated)
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11
Q

What drives pathogen life cycles? What conditions fvor survival and transmission of infectious agents?

A

modes of transmission and maintenance of infection (hosts, vectors, agents)

interactions among host, vectors, and the environment

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12
Q

JEV life cycle:

A
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13
Q

Trichinella life cycle:

A
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14
Q

Body surfaces as sites of horizontal infection and shedding of infectious agents:

A
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15
Q

How does vertical transmission occur?

A

transplacental transmission with direct contact through blood from mother results in birth of offspring with the infectous agent

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16
Q

What are the 2 modes of contact (horizontal) transmission?

A
  1. DIRECT - handshaking, bites, breeding, colostrum/milk
  2. INDIRECT - droplets from sneezing/coughing, fomites (needles, dirty boots, palpation gloves, milking equipment, transport trucks)
17
Q

What are the 3 modes of vehicle (horizontal) transmission?

A
  1. AIRBORNE - dust particles, strong winds (influenza, PRRS, histoplasmosis)
  2. WATERBORNE - water troughs, streams, pools (Campylobacter, cholera, Giardia)
  3. FOODBORNE - contaminated food, “food poisoning,” under-cooked contaminated food
18
Q

What are the 2 modes of vector (horizontal) transmission?

A
  1. MECHANICAL - present ON insect bodies, like on the feet and mouthparts (E. coli, salmonellosis, pink eye)
  2. BIOLGICAL - present IN insect bodies, like gut and salivary glands (Lyme disease, malaria)
19
Q

What is the chain of infection? What affects the agent’s ability to cause infection, transmission, and host’s ability to be infected?

A

how the infection moves in a population from agent to host

AGENT - pathogenicity, infection dose, reservoir, source
TRANSMISSION - contact, common vehicle, airborne, vectors
HOST - individual host factors, non-specific resistance, specific immunity

20
Q

What is the difference between infection and disease?

A

infection must include invasion of agent into host, multiplicaion of agent, and reaction of the host tissues to the agent +/- toxins, leading to inflammation and WBC reaction

disease is a disorder (so much of a host reaction) of the structure or function of the host, associated with clinical signs

21
Q

You submit a sample for PCR test and it comes back positive. What do you actually know?

A

agent DNA/RNA is present —> don’t know if it’s alive or causing disease

22
Q

What are the transmission time periods of infection and disease in the first patient?

A

INFECTION: latent period —> infectious period —-> extended period leading to carrier/reservoir status OR infection of a second susceptible host

DISEASE: incubation period —> clinical disease —> dead/suscpetiblility/immunity

23
Q

What is propagative spread? What 3 types of cases are found?

A

spread of an infectious agent from one animal to another

  1. INDEX = first case identified
  2. PRIMARY = case that brings the infection into a population (can be the index)
  3. SECONDARY = infection from primary
    (tertiary and onward)
24
Q

What does maintenance of population-level infection depend on?

A

successful transmission to new host
- characteristics of infectious agents
- susceptibility of host
- population dynamics (size and density)

25
Q

If the number of susceptible individuals in a population is low, what is the probability of the infective host to contact susceptible hosts?

A

LOW

26
Q

How do agents with short infective periods spread?

A

quickly - require rapid contact with susceptible hosts

(HIV lasts long, so it doesn’t need to jump from person to person immediately)

27
Q

What is a common intervention strategy to decrease spread of an infectious agent?

A

resducing the susceptible population

28
Q

What is herd immunity? What happens when herd immunity is high? Low?

A

collective immunological status of a population with regard to the amount of susceptible individuals

HIGH = low susceptible population = less chance of spread (vaccination)

LOW = high susceptible population = high chance of spread (new crop of animals entering a farm)

29
Q

What does the critical threshold to determine the amout of susceptible/immune in a population to determine herd immunity status depend on?

A

disease-specific and related to the potential for transmission

30
Q

What is basic reproductive number (Ro, or R-naught)?

A

mean number of secondary cases an infectious individual will cause when introduced into a SUSCEPTIBLE (naive) population

if Ro = 2-7, one individual infected 2-7 other individuals on average

31
Q

What is the effective reproductive number (Rt)?

A

mean number of secondary cases an infectious individual will cause when introduced into the WHOLE population

disease progression = change over time

32
Q

What is happening in a population when R < 1, R = 1, and R > 1?

A

R < 1: disease is no longer spreading to others, it has been snuffed out and disappears

R = 1: disease is passing on average to one other individual - becomes ENDEMIC

R > 1: disease spread is growing exponentially - becomes epidemic

33
Q

What is the relationship between herd immunity and reproductive number?

A

a higher reproductive number (Ro) means that a higher number of individuals need to be vaccinated in order to control spread and reach herd immunity status —> need to get a proper amount of individuals immune so that R </= 1

34
Q

What is the compartmental model?

A

mathematical model for propagating epidemics where individuals are put into specific states (Susceptible-Infectious-Recovered or Susceptible-Exposed-Infectious-Recovered) and the rate of change between disease states are estimated

35
Q

What is the agent-based model?

A

mathematical model for propagating epidemics where free agents (individual entities, NOT infectious agents) are simulated with set parameters, taking into account different individual characteristics that can affect infeciton or spread

  • requires huge computational power!
36
Q

What is the overall goal of population models that propagate epidemics? What should be assumed about all models?

A

better understand and predict disease spread in a dynamic population

all models are wrongs, but some may be useful - they use assumptions and biological basis

37
Q

What is the basic Reed-Frost model?

A

compartmental model - case —> spread —> recover —> immune

38
Q

What are the 3 main goals when coming up with mitigation strategies?

A
  1. reduce the number of infected/shedding animals - treating, culling, screening/testing before moving or breeding
  2. reduce transmission of agent - cleaning the environment, removing vectors/reservoirs, quarantining/isolating infected, avoiding high risk practices
  3. reduce number of susceptible - vaccinate, isolate, cull, don’t move/mix populations

Veterinary Epidemiology (13 decks)

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