Roland Heynkes, 17 October 2001 (last update 31.10.2001)
Solely responsible for the English translation:
Ingrid Schütt-Abraham
Lecture given on the 18.10.2001 at the Ostrich World Conference 2001.
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Birds are most probably resistant to BSE and scrapie infections. | |
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Cannibalism nevertheless would bear a high TSE risk also in birds. | |
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Even resistant species could transmit prion diseases. | |
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Animal meal cannot be produced BSE-safe. | |
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Even animal fat can probably not been produced BSE-safe. | |
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The safety of commercial feed also depends on the prevention of cross contaminations. | |
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Literature | |
In a female ostrich which had been emergency killed because of central nervous and movement disorders histopathologically a spongiforme encephalopathy was found in the brain stem and the medulla oblongata [AKOB]. Totally 3 cases of spongiforme encephalopathies of unknown origin have been detected in North African ostriches (Struthio camelus) from 2 zoos in North West Germany [ANTX,CBF], which had been investigated in 1986, 1988 and 1989 respectively[ANTX]. These animals had besides vegetarian feed also been fed commercial poultry feed and raw meat which originated in part from emergency killed animals[AKOB,ANTX]. Allegedly this feed contained also ruminant protein [CBF]. Perhaps for this reason and also because of an appearance of the brain which reminded of scrapie and BSE especially with reference to the spread of holes[ANTX] some authors concluded and published prematurely that in these animals TSE had been diagnosed [APRY,FVE,JLI]. But microscopically no amyloid had been found [ANTX] and Prof. Diringer told me years ago by phone that he could not confirm the suspicion immunologically. On the other hand for this purpose only years old slices with a tiny amount of fixated material were available to him. Also the authors of the study did not receive fresh material and could therefore neither carry out transmission experiments nor look for scrapie associated fibrils by electron microscopy [AKOB,ANTX]. As there are many possible reasons for holes in the brain and no protease resistant prion protein typical for the disease had been found these cases cannot be considered proof for the existence of prion diseases in birds and not at all as proof for the transmissibility of BSE to birds, and the authors of the original study did not do this, either [AKOB,ANTX].
Actually it is extremely improbable that birds could be infected with BSE or scrapie, as the differences between the prion proteins of birds and mammals are just too great [AFDX,HEY1]. One cannot totally exclude it, however. Also another fact points at an alternative cause: one of the 3 ostriches had not been yet adult. This would have been very unusual for TSE and nearly impossible after oral infection, especially if it had to cross a species barrier [ANTX].
Even if birds most probably cannot be infected with BSE or scrapie, they possess a prion protein [AFDX]. Like we know from the hereditary forms of Creutzfeldt-Jakob-Disease, very probably also birds could develop their own species specific TSE by mutations in the prion protein gene. Certainly this happens only very rarely. However, if in one of millions of birds spontaneously a TSE were to develop it would be very unwise to render this bird into birds' feed. The British Food Standards Agency joins in para 58 of their Review of BSE controls the view of the SEAC that feeding animal products to animals of the same species has to be rejected for all species used for human food or animal feed.
Normal mice ar known to be clinically resistant to infections with the most used hamster scrapie strain 263K in so far as they do not develop the disease [AUI,HSM]. But obviously they can become latently infected, amplify the hamster infectivity and thereby become highly infectious themselves while appearing absolutely healthy [HSM,JHF]. Interestingly the hamster infectivity was sustained for more than 200 days even in mice lacking prion protein of their own [HSM]. Hay mites from icelandic sheep farms where only months before sheep had to be killed because of scrapie transmitted scrapie to mice [AMQV,JHZ]. Maggots which had been fed infectious hamster brain were still infectious 2 days later [JCN]. If the maggots died, however, during this period they stayed infectious even for weeks[JCN].
This shows that even animals that become only latently infected or cannot be infected at all may harbour infectivity derived from contaminated feed for some time and become by this means infectious themselves. This might become a problem if those apparently healthy but infectious animals were eaten by humans or animals which are themselves susceptible to this stored infectivity. In their Review of BSE controls the British Food Standards Agency therefore strongly advised in para 59 against feeding animal meal derived from pigs to poultry. As so far there is no proof whatsoever for any TSE resistivity of man agriculturally exploited animals should principally not been fed with products derived from mammals or their own species.
In 1995 the British working group around Taylor published a study which investigated and compared the efficiency of 12 rendering processes with regard to the inactivation of BSE infectivity [FUL]. The study was unable to detect remainders of infectivity only with the method which had been used in Germany for decades for the production of animal meal and has since July 2000 been obligatory also for sterilisation of regular slaughter offal applying 133°C at a pressure of 3 bar for at least 20 minutes. However, in their discussion of the data the authors pointed out themselves that due to the comparatively low sensitivity of their test method a reduction of the original infectivity by only the factor 100 would already have sufficed to prevent detection of infectivity. Therefore they declared expressively that their study could not prove the ability for total inactivation of the BSE agent even for the German steam pressure sterilisation method. Whoever had not read the Taylor study by himself could since spring 1998 also read in an opinion of the Scientific Steering Committee that the German rendering method for animal meal did not guarantee a completely safe product.
A simulation of the 133°C-steam sterilisation process (which by now is also used in both Dutch animal meal production plants) on laboratory scale showed reductions of BSE and Scrapie infectivity by 2-3 orders of magnitude [JHQ]. Accordingly animal meal produced by the German steam sterilisation process from BSE-infectious raw material proved to be fatal for some of the mice into which it was inoculated [JHQ].
Therefore we have to take into account that even animal meal and meat-and-bone meal produced in compliance with German legislation could harbour BSE infectivity if it were produced from BSE infected cattle. This must even be assumed where - like in the EU - tissues with the highest infectivity are destroyed separately. From scrapie infected sheep it is known that not only the specified risk materials are infectious. But even with BSE infected cattle the infectious agent has to pass through "non-risk-material" on its way from the risk material intestines to the risk material spinal cord. Thus infectivity in cattle even if present below the detection limit could be transported by nerves or blood to any part of the body. And even if this were not the case following application of the captive bolt shot one would have to take into account a contamination of the entire body [HEY2].
Even the BSE safety of tallow was doubted by the Scientific Steering Committee of the EU as early as September 1997. Then it was recommended even for countries with low BSE risk not to use BSE risk material for the production of tallow and to heat the tallow for at least 20 minutes to 133°C. In this context it is important to know that although the pithing rod was banned by Commission Decision 2000/418/EC brain tissue destroyed by the captive bolt shot might enter the blood circulation and thus contaminate the organs [HEY2]. Most crucial, however, is the fact that prions are much more resistant to heat in fat than in water [JKN] In their Review of BSE controls the British Food Standards Agency in para 66 urgently advises against recycling tallow within a species.
Based on the Commission Decision 94/381/EC feeding mammal protein to ruminants has been banned since 1994. Although Commission Decision 95/60/EC lifted this ban in 1995 following a recommendation of the Scientific Veterinary Committee dated 12 December 1994 at least the ban on feeding animal meal and meat-and-bone meal to cattle remained. However, cattle feed could become contaminated during production or transport of commercial feed or on the farm by meat-and-bone meal sticking to the metal walls or by pig feed containing meat-and-bone meal. The detection of animal meal in German cattle feed was publicly admitted only after the first German BSE case demonstrated how real this risk had been. Thorough investigations in Switzerland and Great Britain showed that so-called cross contamination is a serious problem [AFOP]. In September 1998 the Scientific Steering Committee of the EU stated these cross contamination to be inavoidable because of the tendency of meat-and-bone meal particles to stick to metal walls and because of the traditional EU production of cattle and pig feed in the same production premises. The data available to the Scientific Steering Committee of the EU showed that 4 production cycles without meat-and-bone meal were required to guarantee contamination free production of cattle feed. Because of the detection limits for animal meal in cattle feed and because of the possibility that feed of purely plant origin might be contaminated by dead rodents and cast feed controls may likewise produce false negative (contamination below the detection limit) as well as false positive (unavoidable contamination with remainders of indigenous wildlife) test results. This renders controls on a selective ban on animal meal in cattle feed practically impossible.
JKN . Appel,T.; Wolff,M.; von Rheinbaben,F.; Heinzel,M.; Riesner,D. - Heat stability of prion rods and recombinant prion protein in water, lipid and lipid-water mixtures - Journal of General Virology 2001 Feb; 82(2): 465-73
JHZ . Carp,R.I.; Meeker,H.C.; Rubenstein,R.; Sigurdarson,S.; Papini,M.; Kascsak,R.J.; Kozlowski,P.B.; Wisniewski,H.M. - Characteristics of scrapie isolates derived from hay mites - Journal of Neurovirology 2000 Apr; 6(2): 137-44
APRY . Davis,J. - It's a Mad, Mad, Mad, Maff World - The Vegetarian Society UK Autumn 1993 - http://www.veg.org/veg/Orgs/VegSocUK/Campaign/madmaff.html
JLI . Fatzer,R.; Vandevelde,M. - Transmissible spongiforme Enzephalopathien (TSE) bei Tieren - Wiener Medizinische Wochenschrift 1998; 148(4): 78-85
FVE . Greger,M. - Mad Cow Disease - "Much More Serious Than AIDS" - http://envirolink.org/arrs/AnimaLife/spring94/madcow.html
AFDX . Harris,D.A.; Falls,D.L.; Johnson,F.A.; Fischbach,G.D. - A prion-like protein from chicken brain copurifies with an acetylcholine receptor-inducing activity - Proceedings of the National Academy of Sciences of the United States of America 1991 Sep 1; 88(17): 7664-8
HEY1 . Heynkes,R. - Ein Aminosäuresequenzvergleich der Prionproteine von Mensch, Rind und Huhn - www.heynkes.de/huhn.htm
HEY2 . Heynkes,R. - Beim Schlachten BSE-infizierter Rinder kann hochinfektiöses Hirngewebe in Muskeln und Organe gelangen - www.heynkes.de/emboli.htm
JHF . Hill,A.F.; Joiner,S.; Linehan,J.; Desbruslais,M.; Lantos,P.L.; Collinge,J. - Species-barrier-independent prion replication in apparently resistant species - Proceedings of the National Academy of Sciences of the United States of America 2000 Aug 29; 97(18): 10248-53
AFOP . Hörnlimann,B.; Guidon,D.; Griot,C. - Risikoeinschätzung für die Einschleppung von BSE - Deutsche tierärztliche Wochenschrift. DTW 1994; 101(7): 295-8
AUI . Kimberlin,R.H.; Walker,C.A.; Fraser,H. - The genomic identity of different strains of mouse scrapie is expressed in hamsters and preserved on reisolation in mice - Journal of General Virology 1989 Aug; 70(8): 2017-25
CBF . Kirkwood,J.K.; Cunningham,A.A. - Epidemiologic observations on spongiform encephalopathies in captive wild animals in the british-isles - The Veterinary Record 1994 Sep 24; 135(13): 296-303
JCN . Post,K.; Riesner,D.; Walldorf,V. Mehlhorn,H. - Fly larvae and pupae as vectors for scrapie - Lancet 1999 Dec 4; 354(9194):1969-70
HSM . Race,R.; Chesebro,B. - Scrapie infectivity found in resistant species - Nature 1998 Apr 23; 392(6678): 770
AKOB . Schoon,H.A.; Brunckhorst,D.; Pohlenz,J. - Spongiforme Enzephalopathie beim Rothalsstrauss (Struthio camelus). Ein kasuistischer Beitrag. - Tierärztliche Praxis 1991 Jun; 19(3): 263-5 - http://www.bseinquiry.gov.uk/files/sc/Seac10/tab07.pdf
ANTX . Schoon,H.A.; Brunckhorst,D.; Pohlenz,J. - A contribution to the neuropathology of the red-necked ostrich (Struthio camelus) - spongiform encephalopathy - Verh. ber. Erkrg. Zootiere; 33: 309-14 - http://www.bseinquiry.gov.uk/files/sc/Seac10/tab06.pdf
JHQ . Schreuder,B.E.; Geertsma,R.E.; van Keulen,L.J.; van Asten,J.A.; Enthoven,P.; Oberthur,R.C.; de Koeijer,A.A.; Osterhaus,A.D. - Studies on the efficacy of hyperbaric rendering procedures in inactivating bovine spongiform encephalopathy (BSE) and scrapie agents - Veterinary Record 1998 May 2; 142(18): 474-80
FUL . Taylor,D.M.; Woodgate,S.L.; Atkinson,M.J. - Inactivation of the bovine spongiform encephalopathy agent by rendering procedures - The Veterinary Record 1995; 137(N24): 605-10
AMQV . Wisniewski,H.M.; Sigurdarson,S.; Rubenstein,R.; Kascsak,R.J.; Carp,R.I. - Mites as vectors for scrapie - Lancet 1996; 347(N9008): 1114
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