19: Rabies Flashcards
deadliest viruses
by death rate - HIV/AIDS
by fatality rate - rabies
by total deaths - smallpox
history of rabies
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
rabies virus
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
rabies deaths
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
rabies transmission
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
all mammals can get rabies
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
rabies and children
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
primary strategy for rabies prevention in humans
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
rabies in the US
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
rabies detection
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
rabies infections
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
cost of annual rabies prevention
$300M
attempt to prevent contact with animals which introduce the virus into humans
- vaccination of skunks and all other animals for protection
most rabies exposure in the US from bats
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
rabies control in wildlife
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
rabies pathogenesis after animal exposure
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
rabies disease course and symptoms
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
2 forms of rabies disease
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
hydrophobia as an unusual symptom of rabies
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
symptoms of furious rabies
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
types of rabies treatment
preventive immunisation in people
post-exposure prophylaxis (PEP)
rabies treatment: preventive immunisation
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
rabies treatment: post-exposure prophylaxis (PEP)
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
why do we still see so many deaths from rabies when we have available/effective treatment?
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
situations when animals may be quarantined because of rabies concerns
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
