RABIES

  • A chronic viral infection of the nervous system of mammals that is transmitted through saliva only (bites usually,) moves progressively up the peripheral nerves to the central nervous system shielded from the immune system, and operates by blockade of neurotransmitters without causing much tissue damage
  • Essentially 100% fatal once it enters the nervous system
  • Nearly 100% preventable if treated properly; thus treatment constitutes a medical emergency; vaccine-preventable
  • ANY mammal can become infected and ALL will die. Globally, unvaccinated dogs are the major reservoir for humans and account for 99% of deaths. In the US (2014), the main reservoirs are raccoon-30.2%, bat 29.1%, skunk 26.3%, and fox 5.2%; however, bats account for almost all human cases acquired in the US. No bat reservoir in most of NV, but there are around us. Cats are the major reservoir for domesticated animals in US; cattle, monkeys can be source. Rodents and rabbits are safe
  • Globally 30-50K deaths per year, 10 M post-exposure treatments. Rabies rare now in US with only 1 case in 2014
  • Of 56 bat-related cases (usually proven by viral DNA type) from US and Canada from 1950-2007, 39% were bites, 16% had “contact,” 11% found bat in the home, especially the bedroom, and 34% provided no clear history for transmission. Bat bites can be very subtle, especially if person sleeping etc. The virus is aerosolized in bat-infested closed spaces with inhalation as the mechanism
  • Incubation period, where virus slowly ascends to CNS with no symptoms, usually 20-90 days, 90% within 1 year, documented to be as long as 17 years. Depends partly on how close to head wounds are, and how extensive the inoculum
  • Prodromal phase, when the virus reaches the spinal cord ganglion causing pain/paresthesia/itch at original wound site in 50%, often with nonspecific flu-like symptoms, lasting 2-10 days
  • Acute neurologic phase, when the virus reaches the brain full blast, leading to death in 2-10days if no supportive treatment. Muscle twitching, focal or generalized seizure, paralysis in various patterns. Can have “furious” episodes of extreme agitation often briefly over 5 mins. Autonomic instability with especially labile blood pressure, excessive respiratory secretions (foaming at the mouth.) Classic hydrophobia and aerophobia. Coma and death from respiratory failure ensue.
  • Note that all mammals go through the same sequence, so they can be under your observation for months after a bite, but still be rabid. They will not be a threat until they enter the terminal phase
  • Not contagious from person to person except from possible transplant (even corneal) or to healthcare workers delivering hospital care (saliva)
  • Diagnostic methods are not highly sensitive yet, and most likely cannot offer help to the victim. One teenage girl survived rabies in Wisconsin in 2004 associated with use of antiviral antibiotics and protracted supportive care. Use of this “Milwaukee Protocol” subsequently has proven to be disappointing. Of interest, since there is little tissue damage, CT/MRI of brain show little
  • Treatment is well-established: extensive lavage/debridement of the wound, leaving it open to drain (the Plastic surgeon can fix it later); HRIG, a pooled rabies immunoglobulin, infiltrated into the wound and given distantly IM; plus simultaneously initiating vaccine series. CDC recommends this in high risk cases even if they had pre-exposure vaccine
  • If possible, analysis of offending animal. Brain biopsy can give a quick answer. Or quarantine animal for 10 days if unwilling to sacrifice it. One must use judgment if it’s an unvaccinated domestic dog
  • In underdeveloped countries, it should be assumed that such timely and sophisticated care CANNOT be delivered
  • Pre-exposure vaccination is mandatory for those working with the virus in the lab, or with wild animals, or exposed to wild animals in remote settings for prolonged periods. Spelunkers should strongly consider vaccination
  • Protect children! They are at greatest risk for bites, especially in head area.
  • Don’t mess around with wild or unfamiliar animals. Don’t handle sick/dead animals, especially bats. Avoid bat-infested caves/mines. Don’t sleep outdoors exposed. Bat-proof your house
  • Remember: A HIGH RISK BITE IS A REAL MEDICAL EMERGENCY.