Rabies

Rabies host susceptibility

• all mammals, wildlife & stray domestics at higher risk

• birds, reptiles, invertebrates, & fish non-susceptible

Human cases of rabies

• ~60-70k worldwide

• 95% in Asia + Africa

• 50% children <15

• males > females

• dogs are source of 99% of deaths

• bats larger issue in Americas

Rabies control & prevention

• mass dog vaccination

• dog population mgmt: licensing, shelters, euthanasia, sterilization

• education

• integrated bite mgmt: bite reporting + post-exposure prophylaxis

Rabies variants & distribution in the US

• 12 variants, 6 terrestrial + 6 bat

• bat variants endemic throughout US, source of most human rabies cases

• canine variant eradicated from US in 2007

• most common in wildlife (bats, raccoons, skunks, foxes)

• cats most likely domestic species to get rabies

  • bridge vector for raccoon variant

Variant

• specific subtype of rabies named for primary reservoir

• all variants can infect any mammal

Reservoir

• a species that maintains a rabies variant through transmission w/in a population

• majority of cases occur in this species

Spillover

• a case of rabies transmitted to a species that is not the typical reservoir

Vector species

• species likely to transmit rabies to another species

• can be reservoir species or different species likely to contact an infected reservoir

Oral rabies vaccination

• USDA wildlife services work w/local, state, & federal govt partners

• bait distributed to wildlife in targeted areas via aircraft, helicopter, & ground-baiting

• creates barrier of immunized raccoons who break transmission cycle to prevent expansion

Rabies virus etiology

• ssRNA enveloped bullet-shaped Lyssavirus

  • better able to evade host immune system

  • easily inactivated in environment

• neurotropic

Rabies pathogenesis

• incubation period variable by bite location (generally 1-3mos), not contagious at this time

• travels up peripheral nerves → spinal cord → brain → salivary gland

• prodromal phase (2-10 days): flu-like symptoms, pain around entry wound

• clinical phase: behavioral changes, hydrophobia + hyper-salivation, hypersensitivity, seizures + paralysis

  • in animals, excitatory → paralytic

• death w/in 4-6wks of clinical signs (people) or 7-10 days (animals)

Rabies exposures

• any mammal bite that breaks the skin

  • bats: known bite/scratch, direct bare-skin contact, finding bat in room w/something that can’t accurately communicate events

• inhalation of aerosolized rabies virus (rare)

• infectious material in contact w/broken skin or MM

• not exposures: dry-skin contact w/rabid animal, contact w/fomite contacted by rabid animal (unless wet w/saliva), contact w/feces, urine, blood, or skunk spray

Rabies reporting

• all dog bites & rabies exposures are required to be reported in all states regardless of vaccination status of dog

• typically report to designated public health authority (varies by state)

  • in OH, local health dept. in jurisdiction in which bite occurs

Public health rabies risk assessment

• based on type of exposure, species involved, circumstances of exposure, & geographic location

  • negligible risk: no further action needed

  • low risk: action may be dependent on risk tolerance of person involved

  • sufficient risk: quarantine or test biting animal, PEP for person

Options for rabies exposures

• quarantine: goal is to determine if biter was contagious at time of bite

  • 10 day quarantine for dogs, cats & ferrets regardless of vaccine status

    • if animal becomes ill/dies → euthanize & submit for testing

    • if animal is healthy → released once UTD on rabies vax

  • 14 day quarantine for livestock

• test: wildlife, hybrids, exotics, & other animals that can’t be confined (incubation & shedding period unknown) - exemptions possible

• PEP: animal is not traceable/available for testing or animal comes back positive

Rabies testing

• no reliable antemortem test

  • serum antibody: can’t differentiate infection from vaccination

  • antigen test: negative doesn’t rule out DZ

• direct fluorescent antibody test: requires brain sample (brainstem + cerebellum) sent to state lab, highly sensitive & specific

  • send entire head decapitated btwn occipital bone & atlas, place bagged specimen in Styrofoam cooler w/ice packs in rigid outer container

  • labeled as Biological Substance Category B

• direct rapid immunohistochemistry test: used by USDA wildlife services for enhanced rabies surveillance, not used for human exposures

Post-exposure prophylaxis for those not previously vaccinated

• day 0: clean wound w/soap & water ± virucidal agent

• any time btwn day 0-7: infiltrate Ig into & around wound, remaining can be given IM at site distant from vaccine site

• day 0, 3, 7, & 14: 1mL vax given IM into deltoid

Post-exposure prophylaxis for those previously vaccinated

• no Ig - body still has memory cells that will be stimulated by booster vaccine

• vaccine doses at days 0 & 3

• previous vaccination includes pre-exposure vaccines & past PEP

Mgmt of exposed animals

• report domestic animals to local health dept if they were bitten or had saliva exposure to…

  • rabies positive (or suspect)

  • raccoon, skunk, or other wild carnivore (foxes, coyotes)

  • bat

  • any mammal displaying signs of rabies

Vaccination status of domestic animals

• considered fully vaccinated 28 days after initial dose or immediately after booster dose (even if overdue)

• booster administered 1yr after initial vaccine, then every 3 years

• proven by valid rabies vaccination certificate signed by vet

• animals not considered vaccinated if overdue for a booster, vaccinated outside of veterinary supervision, or does not have proof of vaccination