NR AJGV
AU Pattison,I.H.; Hoare,M.N.; Jebbett,J.N.; Watson,W.A.
TI Spread of scrapie to sheep and goats by oral dosing with foetal membranes from scrapie-affected sheep
QU The Veterinary Record 1972 Apr 22; 90(17): 465-8
PT journal article
AB
Foetal membranes were obtained in late pregnancy from six scrapie-affected Swaledale ewes. The membranes from each ewe were used for the experimental inoculation of four sheep and six goats. Two sheep and three goats were injected intracerebrally with an inoculum prepared from a small portion of the membranes ; two other sheep and three other goats were fed a suspension of the remainder which ranged in weight from 165 g. to 650 g.
To date (30 months after beginning the experiment) foetal membranes from four donor ewes have proved infective. Scrapie has occurred in five sheep and three goats dosed orally, and in four sheep and one goat inoculated intra-cerebrally.
Because sheep will eat foetal membranes voided by other sheep at lambing time, and because the transmissible agent of scrapie is very resistant to adverse physical and chemical treatments and is active in high dilution, it is suggested that scrapie may be spread by the ingestion of foetal membranes from affected sheep, or material contaminated by such membranes.
VT
The Veterinary Record
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Saturday, April 22nd, 1972
Spread of Scrapie to Sheep and Goats by Oral Dosing with Foetal Membranes from Scrapie-affected Sheep
I. H. PATTISON, B.Sc., F.R.C.V.S., MARGARET N. HOARE, F.R.C.V.S. and JEAN N. JEBBETT
A.R.C. Institute for Research on Animal Diseases, Compton, Newbury, Berks.
and W. A. WATSON,* B.V.Sc., F.R.C.V.S.
M.A.F.F. Veterinary Investigation Centre, Merrythought, Calthwaite Penrith, Cumberland
*Present address: State Veterinary Service, A.D.A.S. East Midland Region, Chalfont Drive, Nottingham.
Vet. Rec. (1972). 90. 465-468
Introduction
THE MECHANISM of spread of scrapie disease within a flock, or between flocks, is still not known in spite of much observational and experimental work carried out over many years. Literature concerned with the problem was reviewed by Pattison (1964), who concluded that although hereditary or congenital transmission was important in sheep there was also strong evidence that, in certain rare circumstances, transfer of the agent could occur by contact. He suggested that contact transmission might be by ingestion of material containing the agent, because the disease is readily transmissible experimentally by the oral route (Pattison & Millson, 1961a). However, he was unable to say what ingested material might produce the disease because the agent had not been detected in milk, urine, faeces or saliva of scrapie-affected animals.
Chelle (1942), Stamp (1962), and Hourrigan, Klingsporn, McDaniel & Riemenschneider (1969) described the occurrence of scrapie in goats held in close contact for long periods with scrapie-affected sheep, either at pasture or indoors. These observations supported strongly the hypothesis of spread by contact, because the possibility of spread by breeding - the aspect most difficult to eliminate in sheep - could be ignored. Brotherston, Renwick. Stamp, Zlotnik & Pattison (1968), working at Moredun Institute, Edinburgh, and at the Institute for Research on Animal Diseases, Compton, described transmission of scrapie to sheep and goats maintained indoors for several years at Moredun Institute in direct contact with a succession of sheep affected with natural scrapie. However, the actual method of spread of the disease was not determined, and it could not be explained why the disease failed to spread during the same period among goats held at Compton in direct contact with a succession of sheep clinically affected with experimentally-produced scrapie. It was suggested that the natural and experimental diseases might differ in that only the former would transmit by contagion.
Some three years ago it occurred to us that foetal membranes of scrapie-affected sheep had not been examined for the presence of the transmissible agent. As sheep will eat membranes voided by other sheep after lambing, and as sheep are usually concentrated in a restricted area at lambing time, it seemed that this might be a method of spreading the disease by contact if the agent were present in the membranes. Furthermore, as the agent is active in high dilution and is extremely resistant to adverse physical and chemical treatments, the surroundings of scrapie-affected ewes might remain contaminated for a considerable period after lambing.
This paper describes an experiment started in March, 1969, and still in progress, to examine the foetal membranes of scrapie-affected sheep for the presence of the transmissible agent.
Materials and Methods
Scrapie-affected Sheep
These six animals were of the Swaledale breed and were in the second half of pregnancy when transferred to Compton from Cumberland. They were held under observation for up to six weeks before being killed. Clinical signs of scrapie were unequivocal in all cases, including incoordination of movement, trembling, staring expression, grinding of teeth and compulsive rubbing. Histological examination of the brains showed typical lesions of scrapie.
Foetal Membranes
When pregnancy was judged to be well advanced the scrapie-affected animal was destroyed and the gravid uterus was removed immediately. After about 10 minutes it was possible to strip the membranes from their cotyledonary attachments. A few grammes of membrane were used to prepare a 10 per cent. w/v suspension in physiological saline. After centrifugation for 20 min. at 800 g, 1.0 ml of the supernatant was inoculated intracerebrally into each of two sheep and three goats. The remainder of the membranes (ranging in weight from 165 g. to 650 g.) was homogenised in an Atomix at full speed for five min. ; equal parts of distilled water and milk substitute were added to a concentration of 50 per cent. w/v, and this was again homogenised. The homogenate was divided into five approximately equal portions for dosing two sheep and three goats by mouth. The calculated dose per animal of membranes from the six scrapie-affected donor sheep ranged from about 30 g to about 130 g.
Recipient Animals
(a) Goats purchased from various sources were brought to Compton when about one week old, and they were about 10 months old when used for experiment. The expected susceptibility of the goat to scrapie is greater than 95 per cent.
(b) Sheep were from the Herdwick flock at Compton that is being selectively bred to increase suspectibility to scrapie (Gordon, 1966). The expected susceptibility to scrapie of the animals used was greater than 80 per cent. (Henderson, Nussbaum & Pattison, 1971).
Goats and sheep were housed separately, each species being held in groups in loose-boxes.
Diagnosis of Scrapie
Diagnosis of scrapie in recipient animals was in all cases based on the occurrence of typical clinical signs and characteristic histological lesions in the brain.
Results
The results to date (30 months after the beginning of the experiment) are given in Fig. 1. Four goats died of intercurrent disease, and histological examination of their brains did not show evidence of scrapie. The first case of scrapie in a recipient animal occurred in a sheep 21 months after oral dosing with membranes from Donor D. No scrapie has yet been produced by Donors C and E. and only one case by Donor B. Scrapie has occurred in a larger proportion of sheep than of goats, thus : -
FIG. 1. Oral dosing and intracerebral inoculation of sheep and goats with foetal membranes from six cases of natural
scrapie in Swaledale sheep (A-F).
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No. of Cases of
Group animals scrapie
Sheep dosed orally 12 5
Goats dosed orally 14* 3
Sheep inoculated intracerebrally 12 4
Goats inoculated intracerebrally 18 1
*Four died not scrapie
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It was recorded in Materials and Methods that size of the oral dose of membranes available from the different donors ranged from about 30 g. per animal to about 130 g., but there was no relationsnip between the size of this dose and the number of cases of scrapie produced, nor between dose and length of the incubation period; e.g., Donors C and E from which there have been no cases gave the fourth and second largest doses respectively.
The clinical signs of scrapie varied somewhat among individual sheep, but there was no obvious clinical difference between animals dosed orally and those inoculated intracerebrally from the same donor. Most animals showed rubbing, but notable exceptions were the sheep dosed or inoculated with membranes from Donor F. These were typical cases of "nervous " scrapie (Stockman, 1926), with marked hypersensitivity and without rubbing, and clinical signs developed so rapidly that they had to be destroyed within 10 days of first-observed abnormalities. Clinical signs in all goats were of the "mixed" type (neither truly "nervous" nor "scratching", as described by Pattison and Millson, 1961b) that occurs typically in goats inoculated with tissue from scrapie-affected sheep.
Discussion
Pattison (1964) stated, " It has long been known by shepherds that the disease can be controlled within a flock, if not entirely eliminated, by slaughter of affected animals and their parents and progeny." The disappointing features of such attempts to eliminate scrapie are the uncertainty of success, and the absence of any clue as to why the disease sometimes persists in a flock without, apparently, any hereditary or congenital mechanism being involved. Spread of the disease through ingestion of foetal membranes from scrapie-affected animals, or of material contaminated by such membranes, would appear to offer an explanation for the perpetuation of scrapie within a flock. Also, it could explain hitherto inexplicable episodes (e.g. Stockman, 1913; M'Fadyean, 1918; Greig, 1940; Sigurdsson, 1954) in which there was spread of scrapie between groups of sheep without mating and apparently through exposure to contaminated pasture or other surroundings. Again, it offers a possible explanation for our experience at Compton that contact spread of scrapie has never been observed during 18 years of experimentation with scrapie in sheep and goats, because only males or non-pregnant females have been used as scrapie-affected donor animals. By contrast, in experiments conducted elsewhere in which scrapie has been found to spread by contact from scrapie-affected sheep to sheep and goats (e.g. Brotherston et al., 1968) the animals at risk were exposed for years to a constant succession of naturally-occurring cases of scrapie in sheep some of which, especially in the spring of the year, would almost certainly have been pregnant ewes.
The well recognised resistance of the transmissible agent of scrapie to adverse chemical and physical treatments, and its activity in high dilution, might well lead to contamination of herbage and other foodstuffs for long periods. Further, it would appear that membranes containing the scrapie agent could be voided from apparently normal sheep in the pre-clinical stages of scrapie, because it is well known that the agent is widely distributed in the body tissues before clinical signs appear. Once a sheep has eaten contammated material, there would appear to be a possibility that the disease might be per-petuated in its offspring, because it is known (Gordon, 1960) that some lambs born of experimentally-inoculated parents will themselves develop scrapie.
It is of interest, and may be relevant to scrapic, that changes have been noted in the epidemiological pattern of kuru (a disease closely similar to scrapie, occurring in the primitive Fore people of New Guinea), since the suppression about 1957 of ritualistic cannibalism in which brains of kuru victims were eaten by women and children. The total incidence of the disease has fallen dramatically, and children under 12 years of age are now rarely affected (Alpers, 1970). If transmission of scrapie by ingestion of foetal membranes, or of food contaminated by this tissue, is a method by which the disease can spread under field conditions, prevention of this possibility might make a significant contribution to controlling the disease.
The experiment described in this paper is still in progress and further cases of scrapie may well occur, because incubation periods for the emergence of clinical scrapie in sheep and goats can exceed four years. It would appear, however, that the general pattern of results is unlikely to change significantly, and that the fact has already been established that scrapie can be passed from scrapie-affected sheep to sheep and goats by oral dosing with foetal membranes.
References
ALPERS, M. (1970). Am. J. trop. Med. Hyg. 19.133.
BROTHERSTON, J. G., RENWIcK, C. C., STAMP, J. T., ZLOTNIK, I., & PATTISON, I. H. (1968). J. comp. Fat/i. 78.9. CRELLE, P. L. (1942). BulL Acad. vet. Fr. 15.294.
GORDON, W. S. (1960). Proc. 63rd. Ann Meet. U.S. Livestock San. Assoc. p.286.
GORDON, W. S. (1966). ARS 91-53. "Report of Scrapie Seminar. Washington, D.C. 1964." Paper No. 5, 53.
GREIG, J. R. (1940). Vet. J. 96.203.
HENDERSON, W. M., NUSSBAUM, R. F., & PATTISON, I. H. (1972). In preparation.
HOURRIGAN, J. L., KLINGSPORN, A. L., MCDANIEL, H. A., & RIEMENSCHNEIDER, M. N. (1969). J. Am. vet. med. Ass. 154.538.
M'FADYEAN, J. (1918). J. comp. Path. 31.102.
PATTISON, I. H. (1964). Vet. Rec. 76. 333.
PATTISON, I. H.& MILLSON, G. C. (1961a).J. comp.Path. 71. 171.
PATTISON, I. H.& MILLSON, G. C. (1961b). Ibid.71. 101.
SIGURDSSON, B. (1954). Vet. J. 110. 341.
STAMP, J. T. (1962). Trans. roy. high. agric. Soc. 7.19.
STOCKMAN, S. (1913). J. comp. Path. 26. 317.
STOCKMAN, S. (1926). Ibid. 39. 42.
(Concluded at foot of page 468)
IN Jeweils wenige Gramm fötaler Membranen von 6 hochschwangeren Schafen mit eindeutigen Scrapie-Symptomen wurden jeweils in der neunfachen Menge physiologischer Kochsalzlösung homogenisiert und 20 Minuten mit der 800-fachen Erdbeschleunigung zentrifugiert. Mit jeweils 1 ml des klaren Überstandes wurden je 2 Schafe und 3 Ziegen intrazerebral inokuliert. Die restlichen 165-650 Gramm der fötalen Membranen wurden ebenfalls homogenisiert, mit Wasser und Milchpulver gemischt und an je 2 Schafe sowie 3 Ziegen verfüttert, sodass jedes Empfängertier 33-130 g der fötalen Membranen erhalten haben sollte. Vermutlich aufgrund einer massiven Überdosierung war kein Einfluß der Dosis auf die Infektiosität erkennbar. Die Empfängertiere waren alle auf besondere Empfänglichkeit für Scrapie gezüchtet worden. 30 Monate danach haben sich die fötalen Membranen von 4 Mutterschafen als infektiös erwiesen. 5 Schafe und 3 Ziegen erkrankten nach oraler, 4 Schafe und 1 Ziege erkrankten nach intrazerebraler Infektion. Die oralen Infektionen mit mindestens um 2 Größenordnungen höheren Dosen führten bei mehr Tieren zum Tode, die Inkubationszeiten waren aber etwas länger. Es gab keine Unterschiede zwischen oraler und intrazerebraler Infektion hinsichtlich der Symptome. Allerdings wurden die mit Material des Spenderschafes F infizierten Schafe nervös ohne sich zu kratzen und mussten bereits nach 10 Tagen getötet werden. Alle Ziegen zeigten Symptome zwischen dem nervösen und dem Kratztyp.
MH Animal; Female; Fetal Membranes/*microbiology; *Goats; Injections; Pregnancy; Pregnancy Complications, Infectious/veterinary; Prions/*pathogenicity; *Scrapie/pathology; Sheep
AD Agricultural Research Council, Institute for Research on Animal Disease (Field Station), Compton, Newbury, Berkshire
SP englisch
PO England
OR Prion-Krankheiten 6
ZF kritische Zusammenfassung von Dr. Ingrid Schütt-Abraham