Biology and Epidemiology of the Rabies Virus
Rachel Radcliffe, DVM, MPH
CDC Career Epidemiology Field Officer
Division of Infectious Disease Epidemiology
Objectives
• Describe epidemiology of rabies virus• Describe transmission and pathogenesis of
rabies virus• Outline management of animals potentially
exposed to rabies• Outline management of animals that
potentially expose humans to rabies
The Rabies Virus
• Lyssavirus of the Rhabdoviridae family• Bullet-shaped, RNA virus• Infects only mammals• Various strains of rabies virus exist
Rabies Epidemiology — World
• >55,000 deaths worldwide–Mainly Africa and Asia
• 60–70% of human cases are children 5–15 years of age
• ~98% of human cases caused by dog bites
Rabies Epidemiology — United States
• Human rabies deaths relatively rare– 4 deaths in 2009
• >90% of animal rabies cases occur in wildlife– 6,690 animal rabies cases in 2009• 92% wildlife animals• 8% domestic animals
• Rabies annual prevention costs ~$300 million
Rabies Epidemiology — West Virginia
• Most animal rabies cases occur in wildlife• Cat most common domestic animal to be
rabies-positive• Raccoon-strain rabies endemic to eastern
portion of state• Bat strain found throughout state• Most cases occur during warm-weather
months
Counties with Confirmed Cases of Raccoon Strain Rabies In West Virginia, 2001–2010
HANCOCK
BROOKE
OHIO
MARSHALL
WETZEL
TYLERPLEASANTS
WOOD
JACK-SON
RITCHIE
WIRT
ROANE
CAL-HOUN
MONONGALIA
MARION
TAYLOR
2
DODD-RIDGE
LEWISGILMER
PRESTON
BARBOUR TUCKER
UP-SHUR RANDOLPH
HARRISON
MORGAN BERKELEY
JEFFERSON
MINERAL
HAMPSHIRE
GRANT HARDY
PENDLETONBRAXTON
WEBSTER
POCAHONTASNICHOLAS
GREENBRIERFAYETTE
CLAYPUTNAM
KANAWHA
BOONE
MASON
CABELL
WAYNELINCOLN
MINGO LOGAN
McDOWELL
WYOMING
RALEIGH
MERCER
SUM-MERS
MONROE
Counties with Raccoon-Strain Rabies
Rabies Transmission
• Saliva from bite of infected animal• Scratch– Theoretical risk
• Saliva or neural tissue contact with mucous membrane (mouth, nose)
• Saliva or neural tissue introduced into fresh, open wound*
* Fresh, open wound is defined as wound that has bled in past 24 hours
Rabies Pathogenesis
• Virus introduced through bite wound, open skin wound, or mucous membrane
• Travels along nerves from site of bite to brain
• Virus multiplies in brain leading to inflammation
• Virus moves from brain to salivary glands and saliva where virus is shed
Rabies Pathogenesis
• Virus introduced through bite wound, open skin wound, or mucous membrane
• Travels along nerves from site of bite to brain
• Virus multiplies in brain leading to inflammation
• Virus moves from brain to salivary glands and saliva where virus is shed
Rabies Incubation Period
• Time between bite and appearance of symptoms
• Weeks to months• No risk of rabies transmission from infected
animal during incubation period• Used to establish confinement periods for
animals exposed to potentially rabid animals
Rabies Diagnosis
• Animal diagnosis– Post-mortem testing– Direct Fluorescent Antibody (DFA) test• Antigen of virus in brain tissue
• Human diagnosis– Several tests required for ante-mortem
diagnosis– Saliva, serum, cerebrospinal fluid, hair
follicle from nape of neck
Rabies Treatment and Prevention in Humans
• No effective treatment once clinical signs appear
• Rabies post-exposure prophylaxis (PEP) given before onset of symptoms is nearly 100% effective
• Rabies PEP–Wound cleansing– Rabies Immunoglobulin (RIG)– Rabies Vaccination– No time limit to give PEP
Rabies PEP — Wound Cleansing
• Should occur as quickly as possible after wound received
• Soap and water or povidone-iodine
Rabies PEP — RIG
• Given only once with first vaccine dose • If not given with first vaccine dose, can be
given up to 7 days after first vaccine dose received
• If person has previously received PEP or pre-exposure prophylaxis, RIG should not be given
Rabies PEP — Vaccination
• Previously unvaccinated persons get 4 doses– Days 0, 3, 7, and 14– 5th dose dropped from vaccine schedule
last year– Intramuscular injections
• Previously vaccinated persons get 2 doses– Days 0 and 3– No RIG given
Rabies Pre-exposure Prophylaxis
• Recommended for certain high-risk groups– Veterinarians, wildlife biologists, animal
control personnel• 3 vaccine doses– Days 0, 7, and 21 or 28
• Does not eliminate need for medical care after an exposure
Rabies Treatment and Prevention in Animals
• No treatment for animal rabies• No post-exposure prophylaxis for animals• Routine vaccination is the only way to
prevent animal rabies• Vaccination schedule for dogs and cats– First vaccine at 3 months of age– Booster vaccine 1 year later– Vaccinate every 3 years after this
Management of Animals Potentially Exposed to Rabies
• Vaccinated cats, dogs, ferrets– Rabies booster immediately– 45 day observation• Under owner’s control
– Any sign of illness should be reported and animal evaluated by a veterinarian
Management of Animals Potentially Exposed to Rabies
• Unvaccinated dogs, cats, ferrets– Euthanasia – Strict isolation for 6 months• Confinement in an enclosure that
precludes direct contact with people or other animals• Rabies vaccine upon entry or 1 month
prior to release• Any sign of illness should be reported
and animal evaluated by a veterinarian
Management of Animals Potentially Exposed to Rabies
• Expired vaccinations in dogs, cats, ferrets– Evaluated on a case-by-case basis – Information to consider• Severity of exposure• Time lapsed between vaccinations• Number of previous vaccinations • Current health status• Rabies epidemiology
Management of Animals Potentially Exposed to Rabies
• Vaccinated livestock– Rabies booster vaccine immediately– 45 day observation–Multiple rabid animals in a single herd is
unusual• Restriction of entire herd usually not
necessary– Coordinate with WV Dept. of Agriculture
Management of Animals Potentially Exposed to Rabies
• Unvaccinated livestock– Euthanasia– Confined under close observation for 6
months• Any signs of illness should be reported
and animal euthanized and tested for rabies
– Vaccination during confinement can be done
– Coordinate with WV Dept. of Agriculture
Management of Animals Potentially Exposed to Rabies
• Other animals– Consider on case by case basis– Euthanasia generally recommended
Management of Animals that Potentially Expose Humans
• Dogs, Cats, Ferrets– Owned animals should be observed for 10
days• Rabies vaccination not recommended
during this time– Strays should be euthanized and tested• 10 day quarantine can be done if resources
allow• If not available for testing, PEP should be
considered based on rabies epidemiology of area, bite circumstances, etc.
Management of Animals that Potentially Expose Humans
• Exotic mammalian pets– No established rabies observation period
for animals except dogs, cats, ferrets– Consider on case-by-case basis– Information to consider• Type of animal• Rabies epidemiology of area• Bite circumstances
Management of Animals that Potentially Expose Humans
• Livestock– Not high risk for transmitting rabies– Healthy and available animals can be
observed for 14 days• Unknown shedding period of rabies
virus in saliva– Euthanasia and testing is other option– Coordinate with WV Dept of Agriculture
Management of Animals that Potentially Expose Humans
• Wildlife– If available, euthanize and test immediately– If unavailable, PEP should be considered
based on • Type of animal• Rabies epidemiology of area• Bite circumstances
Management of Animals that Potentially Expose Humans
• Small mammals are considered low risk for rabies– Not been found to cause human rabies in
US– PEP not usually recommended for these
exposures unless animal was sick and rabies activity is high in the area
• Groundhogs/woodchucks may pose greater risk
• Special consideration for bats
Rabies Resources
• www.cdc.gov/rabies• ACIP recommendations• Compendium of Animal Rabies Prevention
and Control, 2008• WV Rabies Surveillance, Management, and
Control Manual (DC-4)
Rabies Summary
• Human rabies rare in US and WV• Most rabies cases occur in wildlife in US and
WV• Transmission occurs through introduction of
infectious saliva or neural tissue into the body
• Human prevention based on rabies PEP• Animal prevention based on rabies
vaccination