Investigative Guidelines: Animal Bites and Rabies

December 2018

PUBLIC HEALTH DIVISION

Acute and Communicable Disease Prevention

Animal Bites and Rabies

Investigative Guidelines

December 2018

1. DISEASE REPORTING

1.1 Purpose of Reporting and Surveillance

1. To assess the risk of rabies in persons bitten or otherwise possibly exposed

to recommend rabies post-exposure prophylaxis (RPEP) to those who need

it, and to provide counseling and reassurance to those who don’t.

2. As necessary to arrange for the capture and either confinement (10-day

observation) of a live dog, cat or ferret, or the laboratory examination of an

animal head. This may involve coordination with other agencies, e.g., the

Humane Society, county sanitarians, animal control and local law enforcement.

3. To identify zoonotic sources of infection.

1.2 Reporting Requirements

1. Anyone with knowledge of humans being bitten by potentially rabid animals

(e.g., physicians, veterinarians, animal control personnel, law-enforcement

officials, or animal owners), is required to report such incidents to the Local

Health Department (LHD) within one working day.

2. Laboratories: Any confirmed case of rabies in an animal and any suspected

or confirmed case of human rabies must be reported immediately (day or

night) to the LHD. If the LHD cannot be reached, the Acute and

Communicable Disease Prevention (ACDP) Section of Oregon Health

Authority (OHA) should be contacted at 971-673-1111.

1.3 Local Health Department Reporting and Follow-Up Responsibilities

1. Investigate all reports of animal bites, on the day of the report whenever

possible.

2. Determine, in consultation with OHA on-call staff as necessary, whether the

exposure constitutes a significant risk for rabies, in which either empiric

RPEP or testing of the animal is to be recommended. (N.B., a

recommendation to test the animal should be made if, and only if, RPEP

would be recommended if the animal proves to be rabid.) If testing is to be

recommended, solicit approval from OHA staff for testing at OHA expense.

3. Enter into Orpheus any exposure, associated details, and ultimate

disposition in which

• empiric RPEP is recommended; or

• testing of the animal is recommended.

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Note: entry into Orpheus of any other instances of animals biting humans is

encouraged for general surveillance purposes, but not required.

4. When feasible, recommend quarantine of dogs, cats, or ferrets that bite

humans. See §4.1.

5. Assist relevant parties in the shipment, at OHA expense, of animals

recommended to be tested following significant exposure of humans, to the

Oregon State University Veterinary Diagnostic Laboratory (OSU VDL, 541-

737-3261), with prior approval from OHA’s on-call epidemiologist. In the

absence of OHA approval, the sender will be responsible for the cost of

rabies testing.

6. Investigate immediately any suspected case of human rabies, in close

collaboration with OHA epidemiologists.

2. THE DISEASE AND ITS EPIDEMIOLOGY

2.1 Etiologic Agent

The rabies virus, a bullet-shaped RNA virus of the Rhabdovirus family, genus

Lyssavirus.

2.2 Description of Illness

Rabid animals can show a range of symptoms, often described as either “dumb”

or “furious” rabies; they may progress from one state to the other. Dumb rabies

— the most common form in dogs — is characterized by reclusive behavior,

drooling, anorexia, a startle response to sudden noise or light exposure and

irritation around the site of the bite resulting in frequent licking and biting of the

area. Furious rabies is marked by excitation and aggressiveness, notably biting

of objects, animals, humans, or even self. They may manifest an apparently

disordered appetite, eating and chewing stones, earth and rubbish (pica).

Salivation is profuse, and there is usually a change in voice. Central nervous

system (CNS) signs of rabies may include ascending paralysis, incoordination,

convulsions and blindness. Rabid wild animals often seem to lose their fear of

people; nocturnal and crepuscular creatures may disport themselves during

daylight hours. Infected bats may act strangely—crawling around, hissing, etc.

Paralysis eventually sets in and the rabid animal may be unable to eat and drink

(hydrophobia — “fear of water”).

It is important to remember that these signs and behaviors are not

pathognomonic for rabies. Behavioral changes and clinical signs caused by a

variety of infectious and non-infectious processes (e.g., pesticide exposure,

heavy-metal poisoning, trauma) can mimic those associated with rabies.

2.3 Reservoirs

Almost all terrestrial mammals can be infected in theory, but in practice only one

or two species tend to be significant reservoirs in endemic areas. In Oregon,

Washington, and Idaho, bats are the only reservoir species, and other animals

— notably bat predators such as foxes, coyotes or cats — are rarely infected as

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“spill-over” from rabid bat populations. In other parts of the U.S., skunks,

raccoons and foxes are (in addition to bats) important reservoirs. In some parts

of the world, dogs and other carnivores may be important reservoirs.

2.4 Modes of Transmission

Rabies is spread by the inoculation of virus-containing saliva into broken tissue

or onto mucous membranes — almost exclusively via animal bite. Person-to-

person transmission of rabies has never been confirmed, other than via corneal

and other organ transplants. During 2008–2017, 23 cases of human rabies were

reported in the U.S., and of those, 15 were acquired within the U.S.

2.5 Incubation Period

Typically, 3–8 weeks, but highly variable. Reports as short as 5 days and >1

year have been reported for non-human animals, and an incubation period of 7

years was inferred for one human. This variation may depend on the species

exposed, the size of the viral inoculum, and other factors. The proximity of the

bite to the brain may also be a factor; virus inoculation into the head has a

relatively short distance to travel through the nerves before reaching the brain.

2.6 Period of Communicability

Infected animals can transmit rabies only after the infection has spread to the

salivary glands, which typically occurs close to or after the time that CNS signs

develop. In fact, many animals will die of rabies before they begin to shed the

virus. Rabies virus is shed in the saliva of infected dogs, cats and ferrets

generally no more than a few days before clinical signs appear. (This is the

rationale for observation of dogs, cats and ferrets for 10 days following a bite.

Little or nothing is known about salivary viral shedding in other species.)

Shedding may persist until, inevitably, the animal dies — typically in a few days.

2.7 Treatment

Treatment for rabies is essentially palliative. Once symptoms attributed to

infection occur (both in humans and other animals), the chance of survival is

virtually nil.

3. CASE DEFINITIONS, DIAGNOSIS AND LABORATORY SERVICES

With respect to concern for rabies, animal bites can be classified into three

categories: high-risk, low-risk and no risk. Risk assessment hinges on the

answer to two questions:

1. Was there a significant exposure to live animal saliva, such as via a bite?

2. Is there a significant risk that the animal in question was shedding rabies

virus in saliva at the time of the bite?

3.1 Was there a Significant Human Exposure?

Rabies virus does not penetrate skin or clothing. Thus, unless there is a history of

a bite that broke the skin, or saliva contact with broken skin or mucous

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membranes (including the eyes) there was no exposure. For example, those who

merely pet a dog or pick up a bat later found to be rabid have not had a

significant exposure. If there was no exposure, then there is no risk.

1. The Species of the Biting Animal

As noted above, only bats or mammals that might have been exposed to

infected bats are potential sources of transmission in Oregon (absent

evidence that a biting animal has recently come from out-of-state). Bats are

less active in Oregon during cold weather, so there is relatively little risk of

animals being bitten by bats between, say, November and March. By the

same token, indoor pets cannot be exposed unless a bat flies into the house,

bites them, and escapes unnoticed — a scenario that is not very plausible.

While almost all mammals can be experimentally infected with the rabies

virus, in real life, many species are essentially rabies-free, due to both

behavior and dietary characteristics as well as innate resistance to the virus.

Lagomorphs (e.g., rabbits, hares), small rodents (e.g., mice, rats, squirrels,

gerbils, hamsters), opossums, and cervids (e.g., deer, elk) all fall into this

category. Absent extraordinary circumstances, bites by these animals do not

merit follow-up for rabies.

2. Circumstances of the Bite

Talk to the person bitten and other witnesses to get a first-hand account of

what was happening when the bite occurred. You would need to distinguish

between bites that represent typical and atypical, or normal and abnormal,

behavior for that animal.

Bites representing typical animal behavior (carrying low risk for rabies)

include:

• Bite by an unfamiliar or non-domesticated animal with which the

person interacted (e.g., petting a stray cat, feeding squirrels, breaking

up a fight between animals, cornering a raccoon on the porch, etc.);

• Bite by an injured animal (e.g., a dog or cat hit by a car);

• Bite by a dog protecting “its space” (e.g., a front yard or its food).

3. Knowledge of the Offending Animal

Previous history: Bites by animals with a history of menacing or biting are

less likely to reflect changes in behavior that might be attributable to rabies.

Vaccination history: Considered an animal to be either vaccinated (up-to-

date) or not vaccinated (incompletely vaccinated, overdue for booster or no

history of vaccination). Although vaccine failure is possible, dogs, cats, and

ferrets with a documentable history of up-to-date rabies vaccination(s) are

unlikely to be rabid. Vaccines given to other species, including hybrids such

Because of the prevalence of rabies in bats, all bat bites are

considered high risk, regardless of circumstances.

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as wolf-dog crosses, are of unknown efficacy and should be disregarded as

mitigating factors; they have no legal standing in Oregon.

4. Laboratory Testing

Animals can only be tested postmortem for rabies by assaying brain tissue

for the presence of virus. As of December 2018, rabies testing is available in

Oregon only at the Oregon State University Veterinary Diagnostics

Laboratory (OSU VDL).

Antemortem specimens from humans suspected to have rabies can be

tested at the Centers for Disease Control and Prevention after consultation

with an OHA epidemiologist. Required specimens will include serum,

cerebrospinal fluid, saliva, and a skin biopsy from the nape of the neck that

contains one or more hair follicles. Contact the OHA on-call epidemiologist

for instruction on collection, handling, and shipping of human specimens

3.3 Making A Decision

OHA epidemiologists are available 24/365 for consultation. LHD personnel are

strongly encouraged to consult about all high-risk bites other than bat bites. Bat

bites are always high-risk and should always be investigated as potential rabies

exposures — i.e., the bat tested if possible, and if not, RPEP recommended.

4. ROUTINE CASE INVESTIGATION

4.1 Confinement

To avoid needless euthanasia of pets — and to minimize the considerable

expense of animal testing — confinement and observation (sometimes

misleadingly referred to as “quarantine”) is the preferred follow-up for dogs, cats

and ferrets that have bitten people. Such animals should never be euthanized if

they can be held under observation, preferably at the owner’s expense. Without

the approval of local health officials, veterinarians and others are prohibited by

law from euthanizing any mammal that has bitten a human without public health

authorization (OAR 333-019-0024 and -0027).

If a dog, cat, or ferret was rabid and infectious at the time of biting, it would die

from the disease within 10 days. So, if the animal is alive after 10 days, it was

not rabid at the time of the bite. Should an animal that has been confined

following a bite develop any signs of CNS disease, it should be euthanized

immediately, and the head submitted for testing. Such symptoms include: hind

leg paralysis, aimless movement, seizures, unusual voice sounds, blindness,

inability to swallow, and persistent dilation of pupils.

The mechanics of animal confinement are left to the discretion of the LHD.

Confinement may be at a county animal shelter or some local humane society.

At the discretion of the LHD, responsible owners may be allowed to confine low-

risk dogs or cats on their own premises.

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4.2 Animal Rabies Testing

OSU VDL must be notified in advance (541-737-3261) of all heads being

submitted for testing. After consultation and approval by the OHA epidemiologist

or the state public health veterinarian, costs of shipping and testing of animals

following significant exposures of humans will be borne by OHA. In the absence

of consultation and approval by OHA, the sender will be responsible for all

charges related to rabies shipping and testing. Please review shipping

instructions in the attached appendix from OSU VDL. Upon approval from OHA,

OSU VDL will provide an electronic UPS shipping label by email to transport the

specimen to the laboratory. Please ship specimens only Monday through

Thursday for next-day arrival. The specimen should be accompanied by a OSU

VDL submission form. See Rabies Testing Information (Appendix 1) at the end of

this document.

Laboratory Schedule

Coordinating the transportation of heads to OSU VDL is often the most

important step in assuring a satisfactory and timely result. Transportation

alternatives include air freight, drive-in to the lab (by the person bitten, the

animal owner, or a county employee), bus service, or same- or next-day

courier service (FedEx, UPS, Express Mail, etc.). Each LHD outside the

Corvallis area should investigate these alternatives and establish a means of

transport before the need arises. Collect the relevant information (route

schedules, fees, payment options, phone numbers, etc.), and keep it current

and available to the appropriate personnel.

OSU VDL will process and test all specimens received before 11 A.M. on the

same day. Specimens received after 11 A.M. will be processed and tested the

following day. Please do not ship samples on Friday, as OSU VDL is closed on

weekends

A need for RPEP is generally urgent, but rarely emergent; usually

one can wait until after a weekend. In the rare circumstance where weekend

testing might be desired, RPEP should be commenced empirically, then

discontinued when test results become available.

Specimen Handling and Shipping

Animals should preferably be euthanized by lethal injection or other means that

will not damage the brain and that do not place people at risk of further

exposure. Heads received in poor condition often cannot be satisfactorily

tested. Caution should be exercised when decapitating animals; remember, the

working assumption should be that the animal is rabid. For your protection,

wear heavy gloves and use goggles or a face shield to avoid splashing central

nervous system tissue into the eyes or mouth.

Pack the head in a leak-proof container, and seal it with tape. If plastic bags

are used, use at least two, and make sure they are sealed. The sealed head

should

go into another leak-proof container with enough cold packs to maintain

refrigerator temperatures until the specimen reaches the lab.

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Please Do Not Freeze Animal Heads To Be Tested for Rabies.

Dry ice is not recommended, as it may freeze the head. Label the outside of

the container with “REFRIGERATED SPECIMEN.” Containers must be

addressed to:

Oregon State University

Veterinary Diagnostic Laboratory

134 Magruder Hall

Corvallis, OR 97331-8555

541-737-3261

Reporting or Results

OSU VDL will notify OHA epidemiologists of all test results. The OHA

epidemiologist will notify the LHD promptly. It is the responsibility of the LHD to

communicate results to the person bitten and to other relevant parties (medical

providers, veterinarians, etc.). For high-risk situations, make sure you know

how to contact these persons promptly

5. PROPHYLAXIS

5.1 Wound Treatment

All bite wounds should be thoroughly and immediately washed with soap and

water, with copious flushing. Chlorohexidine solution or similar disinfectants can

be also applied. If possible, the wound should be left open to heal. Animal-bite

(especially cat-bite) wounds often become infected and may require antibiotic

therapy. Check tetanus immunization status and provide a booster to persons

who are not up-to-date. Patients should be encouraged to seek medical attention

promptly should signs of wound infection occur.

5.2 Rabies Post-Exposure Prophylaxis (RPEP)

LHD and OHA staff can only make recommendations to patients and physicians

about the advisability of RPEP. Rabies immune globulin (RIG) and rabies

vaccine are available by prescription, and physicians are at liberty to take or

leave our advice. N.B.: RPEP is quite expensive — several thousand dollars per

course — and OHA has no funds with which to pay for it.

Although expensive, modern RPEP is simple, highly effective, and not terribly

painful. The course consists of passive immunization with rabies immune

globulin (RIG, Imogam®; 20 IU/kg), given as soon as possible after exposure,

combined with active immunization with human diploid cell vaccine (HDCV),

purified chick embryo cell vaccine (PCECV) or rabies vaccine absorbed (RVA)

administered intramuscularly (IM) into the deltoid in 1-mL doses on four days

(days 0, 3, 7, 14). Although RIG will need to be administered by a nurse or

physician, rabies vaccine can be given by either pharmacists or medical

personnel.

Rabies biologics are stocked at hospital pharmacies and several emergency

departments in Oregon; they can be ordered for next-day delivery at most other

locations. As many as 50% of vaccinees may experience local reactions

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including pain, erythema, and swelling or itching at the injection site, or systemic

reactions such as headache, nausea, abdominal pain, myalgias, and dizziness.

RPEP should not be interrupted or discontinued because of side effects short of

anaphylactic reaction. Pregnancy is not a contraindication.

5.3 Pre-Exposure (Human)

Persons who live in an area with a high rate of terrestrial rabies and are at risk of

being bitten or exposed to infected tissues (e.g., veterinarians, wildlife workers,

laboratory personnel, animal control officers) may benefit from pre-exposure

rabies prophylaxis. This regimen consists of three IM doses of HDCV on days 0,

7, and 21 or 28. Should immunized persons subsequently be bitten by a possibly

rabid animal, they will need only two 1-mL boosters of HDCV, three days apart.

6. FOLLOW-UP TO ANIMAL RABIES CASES; BAT-PROOFING

6.1 Education

Publicity surrounding the identification of a rabid animal often provides an

opportunity to educate people about the importance of ongoing animal-control

measures, including the following recommendations.

1. Avoid physical contact with bats (and other wild animals, for that matter) —

healthy, sick, alive, or dead. Bats are an important and interesting part of the

natural world, providing many benefits (such as insect control). But a high

percentage of those tested have rabies.

2. Do not hand feed or otherwise handle stray animals or wildlife.

3. Report all animal bites promptly to the local health department or animal-

control agency.

4. Make every effort to capture stray or wild animals that have bitten people, if it

can be done safely, so that the animals can be tested for rabies if indicated.

5. Vaccinate all dogs and cats to create an immune barrier between these

frequently handled animals and wildlife.

6. Control populations of stray or unwanted animals.

6.2 Animals Exposed to Known or Suspected Rabid Animals

Unimmunized dogs or cats with known contact with a rabid animal should be

humanely euthanized. If the owner will not permit this, the animal must undergo

a supervised quarantine for 4 months, with rabies vaccine administered at the

time of entry into quarantine to bring the animal up to current rabies vaccination

status. Administration of vaccine should be done as soon as possible. It is

recommended that the period from exposure to vaccination not exceed 96 hours.

If vaccination is delayed, public health officials may consider increasing the

quarantine period for dogs and cats from 4 to 6 months. Unimmunized ferrets

should be quarantined for 6 months.

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A dog, cat or ferret with a current rabies vaccination that has had a known

contact with a rabid animal should be revaccinated and confined at home for 45

days (indoors, in a fenced yard, or on a leash at all times).

For other situations, see the National Association of State Public Health

Veterinarians (NASPHV) Compendium of Animals and Rabies Control.

6.3 Bat Control

Houses and out buildings can be bat-proofed by covering large openings with

screen wire and caulking or closing holes to less than 1 cm (3/8 in.) in diameter.

Doors and windows should be screened. Fireplace dampers should be closed

during warm months.

For those interested in encouraging bat colonies, bat boxes are easily

constructed (plans are available from various sources). They should be located

away from human habitations.

With care, bats can be removed safely from a dwelling. Wait for the bat to settle

on a reasonably flat surface, then trap it under a wide-mouthed jar or can. Use a

piece of cardboard as a temporary cover. When the bat settles to the bottom of

the jar, slide the cardboard off and immediately put the jar lid in place. Sick or

injured animals should be euthanized humanely using gas anesthesia, 4% CO,

or CO

(see AVMA euthanasia guidelines). Please note that putting the jar or

can in the freezer is not considered to be humane euthanasia.

7. MANAGING SPECIAL SITUATIONS

7.1 Curious Animal Behavior

Rabies is only one of many conditions that can affect animal behavior. Trauma,

pesticide and other poisons, and infectious diseases can all trigger rabies-like

signs. Unless humans are bitten by these animals, there should be no public

health concern about rabies.

Canine distemper, for example, often affects Oregon raccoons, causing muscle

twitching, convulsions with salivation and chewing movements, and ascending

paralysis with ataxia. Foxes, coyotes, mink, and skunks are also susceptible to

canine distemper, but outbreaks in these species have not been reported in

Oregon. Infected animals may come out during the day and may approach

humans or domestic pets without fear. A definitive diagnosis of distemper can be

made by sending the animal to OSU VDL (541-737-3261) for necropsy and

histopathology studies. Call to find out the cost per animal.

7.2 Wildlife Die-offs

Local Health Departments are often called because of animal die-offs. These

reports are best handled by contacting the nearest area office of the Department

of Fish and Wildlife; their staff is well versed on the ecology of the area and are

trained in these investigations

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7.3 Suspected Human Rabies

Contact OHA immediately at 971-673-1111.

Humans suspected of having rabies can be tested antemortem; nuchal-skin

biopsies, corneal-impression smears, neutralizing antibody titers and other tests

must by performed at CDC after consultation by OHA.

UPDATE LOG

December 2018: Changes in testing procedures; clarification of Orpheus data-entry

requirements; OSPHL no longer testing for rabies (Paul Cieslak)

July 2017: Updated Section 6.2 Quarantine and link to Compendium (Emilio

DeBess)

Jan 2015: Animal bites and rabies positive animals and human are reportable

condition and should be entered into the Orpheus database. (Emilio DeBess)

June 2014: Updated human vaccine information. (Emilio DeBess)

March 2011: Clarified language (overall). Updated ACIP recommendation on the

number of rabies vaccines required for post exposure prophylaxis and updated

time of vaccination when animals are quarantined for 6 months (animal to

animal rabies exposure). (Emilio DeBess)