Scrapie

Scrapie is a fatal, degenerative disease affecting the

central nervous system of sheep and goats. It is

among a number of diseases classified as transmissible spongiform encephalopathies (TSE). Infected

flocks that contain a high percentage of susceptible

animals can experience significant production losses.

Over a period of several years the number of infected

animals increases, and the age at onset of clinical

signs decreases making these flocks economically

unviable. Female animals sold from infected flocks

spread scrapie to other flocks. The presence of

scrapie in the United States also prevents the export

of breeding stock, semen, and embryos to many

other countries. TSEs are the subject of increased

attention and concern because of the discovery of

bovine spongiform encephalopathy (BSE) in cattle,

the link between BSE and variant Creutzfeldt-Jakob

disease (vCJD) in people, and feline spongiform

encephalopathy (FSE) in cats in Europe. This

increased concern has led to the following:

• Packers and producers have had difficulty finding

options for disposal of sheep offal and dead 

sheep causing packers and producers to incur 

significant increases in disposal costs,

• Other countries have expressed concerns and 

have indicated that they may prohibit or restrict 

certain ruminant products because the United 

States has scrapie, and 

• Domestic and international markets for U.S.

sheep–derived meat and bone meal have been 

adversely affected.

The combination of all of these factors has led to

the decision to develop a strong scrapie eradication

program in the United States.

Epidemiology and Transmission

The agent responsible for scrapie and other

TSEs is smaller than the smallest known virus and

has not been completely characterized. There are

three main theories on the nature of the scrapie

agent: (1) the agent is a prion, which is an abnormal

form of a normal cellular protein, 2)the agent is a

virus with unusual characteristics, and (3) the agent

is a virino, a very small piece of DNA that acts like a

virus. The scrapie agent is extremely resistant to

heat and to normal sterilization processes. It does

not evoke any detectable immune response or inflammatory reaction in sheep and goats.

The scrapie agent is thought to be spread most

commonly from the ewe to her offspring and to other

lambs through contact with the placenta and placental fluids. Signs or effects of the disease usually

appear 2 to 5 years after the animal is infected but

may not appear until much later. Sheep may live 1 to

6 months or longer after the onset of clinical signs,

but death is inevitable. The genetics of the sheep

affects their susceptibility to scrapie.

In the laboratory, the scrapie agent has been

transmitted to hamsters, mice, rats, voles, gerbils,

mink, cattle, and some species of monkeys by inoculation. There is no scientific evidence to indicate that

scrapie poses a risk to human health. There is no

epidemiologic evidence that scrapie of sheep and

goats is transmitted to humans, such as through contact on the farm, at slaughter plants, or butcher

shops.

Clinical Signs 

Signs of scrapie vary widely among individual

animals and develop very slowly. Due to damage to

nerve cells, affected animals usually show behavioral

changes, tremor (especially of head and neck), rubbing, and locomotor incoordination that progresses to

recumbency and death.

Early signs include subtle changes in behavior or

temperament. These changes may be followed by

scratching and rubbing against fixed objects, apparently to relieve itching. Other signs are loss of coordination, weakness, weight loss despite retention of

appetite, biting of feet and limbs, lip smacking, and

gait abnormalities, including high–stepping of the

forelegs, hopping like a rabbit, and swaying of the

back end.

An infected animal may appear normal if left

undisturbed at rest. However, when stimulated by a

sudden noise, excessive movement, or the stress of

handling, the animal may tremble or fall down in a

convulsive–like state.

Several other problems can cause clinical signs

similar to scrapie in sheep, including the diseases

ovine progressive pneumonia, listeriosis, and rabies;

the presence of external parasites (lice and mites);

pregnancy toxemia; and toxins.

On the farm, veterinarians diagnose scrapie

based on the appearance of its signs combined with

knowledge of the animal's history. Scrapie can be

diagnosed in the live animal by biopsy of the lymphoid tissues on the inside of the third eyelid. This

test is used by the U.S. Department of Agriculture’s

(USDA) Animal and Plant Health Inspection Service

Factsheet

Veterinary Services August 2004

APHIS
(APHIS) to determine whether exposed flocks are

infected. Scrapie is most often diagnosed by microscopic examinations of brain tissue at necropsy or by

procedures that detect the presence of the abnormal

prion protein in brain tissue.

Research

Scrapie research efforts are currently focused on

developing more practical live–animal tests to diagnose infected sheep before they show signs, investigating transmissibility of the agent, identifying the

scrapie agent and its different strains, identifying

genes that influence scrapie infection and evaluating

genetic selection as a tool for scrapie eradication.

Substantial evidence has accrued to show that the

risk of scrapie transmission by embryo’s is negligible

provided that the embryos are properly handled

between collection and transfer, but additional experimental data are needed to support existing evidence.

Related Diseases 

The TSE family of diseases includes BSE: transmissible mink encephalopathy; FSE; chronic wasting

disease of deer and elk; kuru; both classical and variant Creutzfeldt-Jakob disease; Gerstmann–StrausslerScheinker syndrome; and fatal familial insomnia.

TSEs have also been reported in Europe in captive

wild ruminants in the bovid family, cats, and monkeys.

The occurrence of TSEs in captive wild animals is

believed to have resulted from BSE–contaminated

feed.

Eradication Program 

USDA has initiated an accelerated scrapie eradication program. The program is based on the following key concepts:

• Identification of preclinical infected sheep through 

live animal testing and active slaughter surveil

lance,

• Effective tracing of infected animals to their 

flock/herd of origin made possible as a result of 

the identification requirements, and 

• Providing effective genetic based flock cleanup 

strategies that will allow producers to stay in 

business, preserve breeding stock, and remain 

economically viable. APHIS provide the following 

to exposed and infected flocks/herds that 

participate in cleanup or monitoring plans:

1. Indemnity for high–risk, suspect, and scrapie 

positive sheep and goats, which owners agree to 

destroy,

2. Scrapie live-animal testing,

3. Genetic testing, and

4. Testing of exposed animals that have been 

sold out of infected and source flocks/herds.

Operating an effective program to deal with this

insidious disease requires cooperation among producer organizations, allied industries, and governmental

agencies.

History

First recognized as a disease of sheep in Great

Britain and other countries of Western Europe more

than 250 years ago, scrapie has been reported

throughout the world. Only two countries are recognized by the United States as being free of scrapie:

Australia and New Zealand.

The first case of scrapie in the United States was

diagnosed in 1947 in a Michigan flock. The flock

owner had imported sheep of British origin through

Canada for several years. APHIS conducted a

slaughter surveillance study from April 1, 2002, to

March 31, 2003, which determined the prevalence of

scrapie in mature U.S. cull sheep to be 0.2 percent or

one positive out of 500 cull sheep.

In the United States, scrapie has primarily been

reported in the Suffolk breed. It also has been diagnosed in a Border Leicester, Cheviots, Corriedales, a

Cotswold, Dorsets, Finn sheep, Hampshires, Merinos,

Montadales, Rambouillets, Shropshires, Southdowns,

and a number of crossbreeds. Through October

2003, approximately 2,350 cases in sheep and 12

cases in goats have been reported.

Additional Information 

For more information about scrapie, contact your

local APHIS, Veterinary Services, area office or 

contact:

USDA, APHIS, Veterinary Services 

National Animal Health Programs 

4700 River Road, Unit 43 

Riverdale, MD 20737-1231 

Telephone (301) 734-6954 

Fax (301) 734-7964 

Current information on animal diseases and suspected outbreaks is also available on the Internet.

Point your Web browser to

http://www.aphis.usda.gov/vs/nahps/scrapie/ to reach

the APHIS scrapie home page.

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United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture