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AFNS 416 > 7 - Rabies > Flashcards

7 - Rabies Flashcards

1
Q

In latin, rabies means…

A

Madness, rage, fury

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2
Q

How many rabies cases worldwide? How many due to dog bites? Where do most deaths occur?

A

~60,000 deaths worldwide (most children in developing countries)
95% cases due to dog bites
99% deaths occur in Africa and Asia

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3
Q

Incubation period of rabies? signs of furious rabies

A

Typically 2-3 months, range from 1 week to 1 year
Furious rabies = signs of hyperactivity, excitable beh, hydrophobia, aerophobia. Cardio-respiratory arrest =death

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4
Q

Rabies dates back to…

A

Mesopotamians
Owner of a rabid dog was responsible for containment of the animal; pays for deaths

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5
Q

Aristotle on Rabies.

A

“Dogs suffer from the madness, this causes them to become irritable and all animals they bite become diseased”

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6
Q

Occurrence of rabies in europe and the americas

A
  • few human deaths
  • few transmissions from dogs (vaccinated)
  • primarily via wildlife (bats, foxes, skunks, raccoons)
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7
Q

Name countries that are recognized by the CFIA as being free of rabies

A
  • Australia
  • Finland
  • Ireland
  • UK
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8
Q

Canada rules on dog importation

A

It is restricted due to prevalence of rabies in some countries
Rabies vaccination required

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9
Q

Basics of the WHO’s response to rabies

A
  • involve all countries, emphasize one health approach
  • access to prophylactic treatment
  • can validate countries achieving 0 human deaths due to dog rabies
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10
Q

OIE is now the… What are their objectives

A

World Organization for Animal Health (WOAH): international org funded by UN

Objectives: transparency, scientific info, promote vet services, food safety, animal welfare

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11
Q

What % of dogs need to be vaccinated so no more human cases occur?

A

70%

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12
Q

What kind of virus is rabies? Shape?

A

RNA virus
Rhabdovirus family, Lyssavirus genus
Bullet shaped

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13
Q

Three Lyssavirus subgroups, what diseases they cause

A

Phylogroup 1: rabies virus, european bat lyssaviruses, australian bat lyssavirus

Phylogroup 2: lagos bat lyssavirus, mokola lyssavirus

Phylogroup 3: west caucasian bat lyssavirus

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14
Q

Describe the rabies RNA genome

A

12 kb negative sense genome
When it enters cell must be converted to positive sense through RNA polymerase

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15
Q

Outer coat of rabies virus? What does it do

A

Glycoprotein membrane
Interacts with cellular membrane to gain entrance into a cell; also is the target for neutralizing antibodies (antibodies to virus = antibodies to G protein)

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16
Q

Rabies virus is inactivated by:

A

Heat (50C for 15 min)
Sunlight, desiccation

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17
Q

Five structural proteins of the RNA virus

A
  • N nucleoprotein
  • P phosphoprotein
  • M matrix protein
  • G glycoprotein
  • L RNA dependent RNA polymerase
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18
Q

Majority of human rabies from dog reservoirs are in what countries?

A

South America, Asia, India

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19
Q

Stages of rabies virus spread in the body

A
  • peripheral nervous system to brain: 3-12 weeks
  • virus replicates rapidly in the brain
  • subsequent centrifugal spread to salivary glands and saliva
  • clinical symptoms after virus enters brain = death within 1 week

Slide 29

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20
Q

When does rabies treatment need to occur? Why?

A

PRIOR to clinical signs (post-infection)
Takes so long to progress to the brain, so it works

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21
Q

Why is there little/no rabies transmission during the preclinical phase

A

Because transmission occurs from saliva, which does not get infectivity until after brain infection

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22
Q

How does rabies spread in the body

A

Neurotrophic: spreads along neural pathways and invades CNS
Travels to spinal cord at a rate of 50 to 100 mm/day

23
Q

Why are clinical symptoms not useful for detecting rabies in dogs

A

Most of the infection is incubation or preclinical
Clinical symptoms can be difficult to identify

24
Q

Three methods of rabies detection

A

Direct Fluorescent Antibody Technique:
- brain tissue
- look for antibodies against viral nucleoprotein

Polymerase Chain Reaction
- primers to rabies genome

Direct Rapid Immunohistochemical Test:
- light microscopy
- used for wildlife surveillance

25
Q

How did Pasteur invent the live attenuated vaccine

A

Chicken Cholera
- bacterial disease of chickens
- Pasteur observed that old bacterial cultures lost virulence (did not produce disease but produced immune respone)

26
Q

Describe the creation of the first rabies vaccine

A

By Louis Pasteur
Live attenuated vaccine using rabies in rabbits

Spinal cord of rabies-infected rabbit ground, left out to dry

Longer it dried = less virulent
Led to canine vaccine

27
Q

First rabies vaccination of a human?

A

Joseph Meister
Young boy repeatedly bitten by rabid dog
Received 13 inoculations over 3 weeks from Pasteur (progressively more virulent samples)
Did not develop rabies

28
Q

Vaccination protocol for the 1911 rabies vaccine

A

25 injections total
- 3 on day 1
- 2 on day 2
- 2 no day 3
- 1 injection each day for 18 days
- each dose slightly more virulent

29
Q

Differences in rabies vaccination of dogs vs humans

A

Dogs: prevent infection
Humans: post bite

30
Q

Two steps of Rabies Postexposure Prophylaxis (PEP)

A

(rinse wound with soap and water thoroughly)

  1. dose of human rabies immune globulin (provides antibodies)
  2. rabies vaccine (on day of exposure, followed by days 3, 7 and 14)
31
Q

How many does of PEP administered worldwide? Deaths without it?

A

29 million /year
~ 3 million more deaths without it

32
Q

Average cost of PEP vs dog vaccination

A

Rabies treatment in humans per patient: US $108.07

Mass dog vaccination per dog: US $4.03

33
Q

Herd immunity level for rabies in dogs

A

70%

34
Q

What is R0?

A

Reproductive number of an infection (how fast its expected to spread; ability to spread between individuals)
- not necessarily a measure of severity

35
Q

A couple factors considered in calculating a pathogens R0?

A

Infectious period (length of time it is contagious)
Contact rate (# contacts while contagious - variable)
Mode of transmission (air = rapid transmission, direct contact = less transm)

36
Q

Example of pathogen with slow vs fast spread

A

Slow = ebola
Fast = measles

37
Q

Second definitely of R0

A

Expected number of secondary cases produced by a single infection in a completely susceptible population

38
Q

R0 values assume..

A

everyone in a population is completely vulnerable to the disease
i.e. nobody vaccinated, nobody has had the disease before, no ways of controlling the spread

39
Q

What is Re (or Rt)?

A

Numerical estimate that captures transmission once a virus becomes more common
Public health measures initiated

Typically lower than R0

40
Q

R0 <1 vs R0 = 1 vs R0 > 1

A

R0 <1 : disease will die out on its own, for every sick individual less than 1 new infection arises

R0 = 1 : existing infection causes one new infection. Stable rate (no epidemic)

R0 >1 : existing infection causes more than one new infection. Spread in pop can cause epidemic

41
Q

R0 of rabies in humans vs dogs

A

Humans = zero, dead-end host. Cannot decrease rabies by only treating humans

Dogs = >1 (social, interact with teeth)

42
Q

What is herd immunity? Provides…

A

When enough people are immune due to vaccination, previously having the disease and recovering this stops disease spread

Provides indirect protection to susceptible individuals when most of the pop is not susceptible

43
Q

How does R0 affect herd immunity? Herd immunity level (hC formula)

A

% needed to be vaccinated in pop affected by R0 (higher R0 = higher herd immunity needed)

hC = 1 - (1/R0)

44
Q

Why is dog vaccination not used in India? How could it help decrease cases?

A

Viewed as prohibitively expensive: say 70% number is not attainable due to cost, which is inhibiting vaccination bc they will not reach it

But if they vaccinate 200,000 stray dogs annually (13% of canine pop) could reduce human rabies by 90%

45
Q

Rabies in Sri Lanka

A

Has virtually been eliminated thanks to dog vaccination combined with PEP

46
Q

First rabies case in Canada

A

Charles Lennox, 4th Duke of Richmond
Fox bit his pet dog, he died of rabies

47
Q

Reservoirs in Canada

A

Artic foxes, red foxes, skunks, raccoons, bats

48
Q

Most rabies cases in Canada are in what animal?

A

Bats (70%)

49
Q

In Canada, rabies is common in what kind of bat?

A

The Big Brown Bat (5 to 10% of those tested were infected)

50
Q

Rabies in Mexico

A

No cases of dog-mediated rabies since 2006
Hs been improving its vaccination program
Validated by WHO in 2019 (free of human rabies transmitted by dogs)

51
Q

How do we go about vaccinating wild animals for rabies?

A

Oral vaccine bait (can significantly decrease cases)

  • does not work on bats
52
Q

Most recent human rabies case in Canada

A

2019
21 yr old male in BC
Bat ran into him, died of rabies

53
Q

Describe the five rabies deaths that occurred in the US in 2021

A
  • 80 year old illinois man: not vaccinated due to longstanding fear
  • idaho man and texas boy not vaccinated: did noy believe bat broke the skin
  • minnesota man bitten by bat: vaccinated but undiagnosed immune deficiency
  • man bitten by rabid dog in Philippines refused vaccination

Statistical blip

AFNS 416 (22 decks)

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