Preventing the

Westward Spread of

Rabies

During the 1990s, the number of reported cases of

rabies among wild animals in the United States

increased dramatically. This surge in the number of

rabies cases is especially evident in the eastern

United States where raccoons account for about 40

percent of all documented cases.

While the raccoon strain of rabies is already

enzootic (endemic) in much of the eastern United

States, U.S. Department of Agriculture, Animal and

Plant Health Inspection Service, Wildlife Services

(WS) biologists in cooperation with State, Federal,

university, and other partners are working to stop the

westward spread of this deadly disease.

Since 1997, a coalition of cooperators has distributed more than 9 million units of oral rabies vaccination (ORV) bait in Maryland, New York, Ohio,

Pennsylvania, Vermont, and West Virginia to create a

barrier of immune raccoons to prevent spread of the

virus. Initially, WS entered into cooperative programs

with Ohio, New York, and Vermont. The need to

lengthen the barrier to close off corridors where 

raccoon rabies could spread to the West led to the

involvement of other cooperating States. This summer, Tennessee and Virginia are joining the program.

Pennsylvania will be greatly expanding its involvement to include the western portion of the State.

Distributing the Vaccine

The ORV bait, developed and manufactured by

Merial Inc. in Athens, GA, consists of a hollow fishmeal polymer cube (1 1/4 inches x 3/4 inch). A

sachet or plastic packet containing the Raboral 

V-RG® rabies vaccine is inserted into the hollow area

of the bait and then sealed with wax. Fishmeal is

attractive to raccoons and the bait is strong enough

to withstand distribution from airplanes flying at an

altitude of about 500 feet. When a raccoon finds the

bait and bites into it, the sachet ruptures, allowing the

vaccine to bathe the lymphatic tissue in the raccoon’s

throat as it swallows. Raccoons that swallow an 

adequate dose of vaccine develop immunity to rabies

and, as the number of vaccinated raccoons in the

population increases, they act as a barrier to stop the

spread of the disease to other wildlife, domestic 

animals, and humans.

In an effort to establish the immune barrier, WS

has provided funding to purchase ORV baits and

assisted in the coordination of aerial and ground 

distribution of baits in strategic areas to prevent the

spread of raccoon rabies. WS uses the latest mapping technology and rabies surveillance to determine

which areas to target in the campaign against rabies.

Fixed-wing aircraft are the most effective means

for distributing large numbers of the ORV baits

throughout the targeted ORV zones. Hand baiting is

also important for reaching urban areas where there

may be safety risks associated with distributing baits

by air.

Determining the Effectiveness of the

Program

After the baits have been distributed and the 

raccoons have had a chance to ingest the baits, WS

works with its cooperators to measure the success of

the ORV campaign. Live traps are set throughout

ORV zones and marshmallows, vanilla, cat food, and

other attractants are used to lure raccoons into the

traps.

Live traps are checked regularly and affixed with

labels to inform the public about WS’ trap and release

program. All captured raccoons are temporarily

anesthetized so that blood samples can be taken and

their first premolar, a small tooth, can be removed.

The raccoons do not experience pain during this 

procedure, and they are not released back into the

wild until the effects of the anesthetic have worn off.

The animals are then monitored until they have fully

recovered.

Raccoon
All samples are sent to cooperating laboratories

such as the rabies lab at the Department of Health

and Human Services’ Centers for Disease Control and

Prevention in Atlanta, GA, where the antibody level for

each raccoon sample is determined. Tooth samples

are sent to laboratories for sectioning to determine if

they contain a biomarker that indicates whether one

or more baits were ingested.

In Ohio, where the cooperative ORV program has

been in place since 1997, approximately 34 percent of

all raccoons tested have protective antibodies to

rabies. This vaccination rate appears to be sufficient

to prevent the spread of rabies across the barrier.

Ohio has seen a dramatic drop in the number of

cases of raccoon rabies since the program began. In

1997, Ohio reported 59 rabies-positive raccoons, but

in 2000 none were reported. In 2001, Ohio documented only one case of raccoon rabies along its

eastern border with Pennsylvania.

The Future

WS is committed to the principle that an educated

public is better able to understand the risks imposed

by rabies and therefore better equipped to participate

in, and benefit from, rabies prevention efforts.

Because rabies is a fatal disease in wildlife, domestic

animals, and untreated humans, WS’ goal is to prevent exposure to rabies. Education is the first step in

achieving this goal.

Expertise from a variety of sources, including public health, wildlife, and agricultural agencies, is integral

to the overall team-centered approach to rabies prevention. For many years, WS has provided a variety

of technical and operational services for rabies management, including assistance with effective disease

and wildlife population surveillance, a continued commitment to the development of effective oral vaccines,

and improved methodology to modify site-specific

habitats to prevent human exposure to rabies.

Preliminary successes of ORV campaigns in

Europe and Canada, along with recent cooperative

efforts in the United States, have advanced our understanding of rabies management methods. The development and implementation of effective ORV programs promises to change the future approach to

rabies management.

Additional information

For more information about rabies and other WS

programs call WS Operational Support Staff at (301)

734–5175. You can also visit WS’ Website at

http://www.aphis.usda.gov/ws.

The U.S. Department of Agriculture (USDA) prohibits discrimination

in all its programs and activities on the basis of race, color, national

origin, sex, religion, age, disability, political beliefs, sexual orientation, or marital or family status. (Not all prohibited bases apply to

all programs.) Persons with disabilities who require alternative

means for communication of program information (Braille, large

print, audiotape, etc.) should contact USDA’s TARGET Center at

(202) 720–2600 (voice and TDD).

To file a complaint of discrimination, write USDA, Director, Office of

Civil Rights, Room 326–W, Whitten Building, 1400 Independence

Avenue, SW, Washington, DC 20250–9410 or call (202) 720–5964

(voice and TDD). USDA is an equal opportunity provider and

employer.