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

Animal Management Summary

• Management of animals potentially exposed to rabies depends on vaccination status and type of animal exposed

• Management of animals that expose humans to rabies depends on type of animal, ownership status of animal, and other factors