19: Rabies

Question 1

deadliest viruses

Answer 1

by death rate - HIV/AIDS

by fatality rate - rabies

by total deaths - smallpox

Question 2

history of rabies

Answer 2

2300 BC - first written record

79 AD - pliny the elder and list of rabies cures

1703 - richard mead publishes opinion that rabies outbreaks are controlled by the moon

1753 - first documented case in the US

1804 - recognised as an infectious disease

1885 - first vaccine by pasteur

Question 3

rabies virus

Answer 3

virus from the genus lyssavirus (greek word for rage and fury)
- many other viruses within the genus which all cause rabies

enveloped, single-stranded negative-sense RNA virus with a helical capsid
- approximately 7nm in diameter and 180nm long

Question 4

rabies deaths

Answer 4

60,000 annually
- ~98% of human cases caused by dog bites

ancient disease but still deadly

disease of africa, asia and india
- neglected by countries with money that can help

Question 5

rabies transmission

Answer 5

rabid animal (most carnivores we know of)
- dogs, bats, racoons, foxes

almost always with a bite
- cannot enter intact skin
- needs to access muscle under the skin

non-bite transmission
- saliva from a rabid animal comes into contact with permeable mucous membranes or fresh skin lesions
- saliva then can enter muscles for replication

rarest forms of transmission
- inhalation of virus-containing aerosols
- human-human transmission where rabies hide in organs that may be transplanted to a new host

Question 6

all mammals can get rabies

Answer 6

most carnivores but also non-carnivores can be associated with rabies cases (rare since they aren’t bitten as much)

small rodents like squirrels, rats, rabbits, guinea pigs and hamsters are not usually transmitters of rabies

non-mammal pets like lizards, fish and birds never transmit rabies

Question 7

rabies and children

Answer 7

40-60% of all animal bite cases reported to occur in children

most cases in infants or toddlers since they’re not as scary

short stature so they are susceptible to bites on their face and scalp

also more susceptible since they play in open ground or streets

more likely to provoke an animal

might not report a bite, scratch or lick

Question 8

primary strategy for rabies prevention in humans

Answer 8

control of animal vectors through vaccination

typically target dogs as the most important animal vector for human transmission
- vaccination but hard to vaccination free-roaming dogs
- management of stray dog populations to reduce numbers

rabies can be controlled in the canine population if 70% of dogs are vaccinated with inactivated virus vaccine
- immunity lasts for 3 years

Question 9

rabies in the US

Answer 9

reversal of numbers of domestic and wild cases
- initially a lot of pets where we detected rabies

after vaccination, extremely rare to have a pet dog with rabies
- most cases in the wild population
- rabies existing in the US and is quite abundant but in wild animals

Question 10

rabies detection

Answer 10

no good immunological ways to detect it

only way to euthanise the dogs, cut tiny micro-slices of their brains, stain it for antibodies against rabies and check for a reaction

Question 11

rabies infections

Answer 11

1-3 cases reported annually
- 25 cases in the US from 2009-2018
- 7 of those acquired outside of the US

over 90% of animal rabies cases occur in wildlife

Question 12

cost of annual rabies prevention

Answer 12

$300M

attempt to prevent contact with animals which introduce the virus into humans
- vaccination of skunks and all other animals for protection

Question 13

most rabies exposure in the US from bats

Answer 13

issue that bats are small and you can’t feel the bite wound
- size of a hypodermic needle so people don’t know they are bitten and don’t seek out medical attention/PEP

1% of bats infected with rabies

Question 14

rabies control in wildlife

Answer 14

trap/vaccinate/release (TVR)
- effective in canada racoons (combined with oral baits)

oral baits with antivirus
- effective in europe and canada
- sprinkle vaccines into bait/chicken heads which can be thrown into bushes for animals

Question 15

rabies pathogenesis after animal exposure

Answer 15

disease from the bite, which is typically on the leg
- virus gets under the tissue and skin, infecting muscles
- replication in muscles

neurons adjacent to muscles take up virus
- transportation of virus to the brain (long and slow)

once in the brain, virus replicates and amplifies particularly in salivary glands
- become infectious to other people

process of developing rabies can be from months to years

Question 16

rabies disease course and symptoms

Answer 16

incubation period typically 2-3 months but may vary from 1 week to several years
- depends on location of virus entry and viral load

initial symptoms as non-specific
- fever, pain, tingling/pricking/burning at wound site

Question 17

2 forms of rabies disease

Answer 17

furious rabies
- signs of hyperactivity and hydrophobia
- death occurs a few days after due to cardio-respiratory arrest

paralytic rabies
- about 20% of total human cases
- slow development/degradation of a coma and death
- can be misdiagnosed, which contributes to under-reporting

Question 18

hydrophobia as an unusual symptom of rabies

Answer 18

virus spread through saliva so it increases spit production
- mouth is full of saliva and people feel like they’re drowning

painful spasms developing in muscles controlling breathing and swallowing

Question 19

symptoms of furious rabies

Answer 19

delirium, aggression, drooling, muscle spasms, dizziness, hallucinations

once you get rabies and symptoms, nothing can be done
- some cases where doctors induce artificial comas for a period of time to prevent hyperactivity and hallucination
- about 25 people in the world who survived rabies

Question 20

types of rabies treatment

Answer 20

preventive immunisation in people

post-exposure prophylaxis (PEP)

Question 21

rabies treatment: preventive immunisation

Answer 21

anyone who could be exposed to the live rabies virus takes this
- lab staff, vets, animal/bat handlers, wildlife officials

children traveling to/living in rabies-endemic area

travellers who might be more than 24h away from a medical centre with a post-exposure vaccine

Question 22

rabies treatment: post-exposure prophylaxis (PEP)

Answer 22

immediate treatment of bite victim after rabies exposure
- prevents virus entry into the CNS, which results in imminent death

extensive washing/local treatment of the wound

course of potent and effective rabies vaccine
- enough time for the immune system to generate a potent anti-immune response before it gets to the brain (since the virus takes weeks if not months to get from the infected tissue to the brain)

administration of rabies immunoglobulin (RIG)
- rabies antibodies injection so you’re protected in the first few weeks before your body generates its own antibodies

Question 23

why do we still see so many deaths from rabies when we have available/effective treatment?

Answer 23

majority of victims do not receive vaccination or do not complete the full course

use of RIG abysmally low
- expensive for individuals in poverty

serious lapse in PEP, lack of awareness about seriousness of animal bites, irregular supply of rabies vaccines and RIG

Question 24

situations when animals may be quarantined because of rabies concerns

Answer 24

after biting a person
- infectious dogs with rabies don’t live past 10 days so quarantine is 10 days
- vet quarantines pet and observes for developing signs of rabies

after potential exposure to a rabid animal
- typically when animals come from other countries they require quarantine to check whether they develop signs of rabies
- 6 months of quarantine since rabies can hide well and animals don’t develop a good immune response