The scrapie agent is thought to be spread most commonly from the ewe to her offspring and to other lambs in contemporary lambing groups through contact with the placenta and placental fluids and through milk and colostrum. Signs or effects of the disease usually appear 2 to 5 years after the animal is infected but may take longer to appear. Sheep usually live 1 to 6 months after the onset of clinical signs and in some cases longer, but death is inevitable. Signs of scrapie vary widely among individual animals and develop very slowly.
As the result of nerve cell damage, affected animals usually show behavioral changes, tremor especially of the head and neck , pruritus, and locomotor incoordination, which 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, 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. The official test currently used for scrapie diagnosis in the United States is immunohistochemistry. Histopathology is used to identify pathological changes in the brain following necropsy.
Pathological changes of scrapie are confined to the central nervous system. The lesions are characteristically found in the grey matter of the brainstem.
They include neuronal vacuolation, other forms of neuronal degeneration, astrocytosis, and a vacuolar or spongy alteration called status spongiosis. Third-eyelid and rectal lymphoid tissue biopsy are APHIS-approved tests for scrapie detection in live animals. The tests use a biopsy of lymphoid tissue from the third eyelid or rectum and IHC. Rectal biopsies are preferred over third-eyelid biopsies because they typically have more follicles so fewer samples are read out as invalid test due to insufficient follicles.
Most collectors also find it easier to collect rectal biopsies compared to third eyelid biopsies. A single rectal biopsy or two third eyelid biopsies done at the same time have a sensitivity of approximately 87 percent when compared to the result of IHC testing on lymph node and brain.
When animals over 14 months are tested, held and necropsied upon death the sensitivity of the third eyelid is reduced to about 70 percent as would be expected due to the long incubation period of the disease. Classical scrapie is transmitted through exposure to scrapie-infected animals e. Scientific evidence suggests that Atypical scrapie, the second variant, is spontaneous and non-contagious. In this opinion EFSA experts have considered both variants, with a particular focus on Classical scrapie, which is the topic of the study under review.
E-mail: press [at] efsa. Contact our Ask a Question service! English en Select your language. Search Search. Governance Management board members Executive director Operational Management. Documents Corporate publications. Israel has also reported outbreaks of scrapie, with the most recent being in early There have been isolated reports of scrapie from a number of countries including New Zealand and the Republic of South Africa In these instances, the disease was confined to imported sheep and was eradicated by destruction of the affected group.
Australia is free of scrapie and is recognised as meeting the World Organisation for Animal Health OIE requirements for a scrapie historically free country. Australia has had one isolated case of scrapie, on a single property in Victoria in Four of a group of 10 Suffolk sheep imported from the United Kingdom were affected. The disease was eradicated by slaughter of affected and in-contact sheep, ploughing paddocks on which they had grazed and leaving them fallow for a year, and quarantine of the property for a year.
Atypical scrapie is a non-contagious, sporadic, degenerative brain condition which can arise spontaneously in older sheep and, less commonly, in goats. Atypical scrapie is a separate disease to classical scrapie. Atypical scrapie has been diagnosed in more than 20 countries worldwide.
Most countries that test large numbers of sheep for classical scrapie have found cases of atypical scrapie. Sheep that develop atypical scrapie show neurological signs such as lack of coordination, head pressing and circling.
Sheep and goats are susceptible to scrapie. Breeds of sheep vary in their susceptibility to scrapie but all goat breeds appear susceptible. The main mode of transmission of scrapie is from mother to offspring immediately after birth and to other susceptible newborns exposed to the birth fluids and tissues of an infected animal.
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