NR APPZ
AU Hörnlimann,B.
TI Scrapie occurrence and BSE risk factors among European countries
IA http://www.priondata.org/data/A_scrapieex.html#European
VT
Keywords Bovine spongiform encephalopathy, Scrapie, Risk factor, evaluation, Importation, Live cattle, Meat and bone meal, Feed, concentrates, Offal rendering, Scrapie-like agent, Prion Diseases
Introduction
Bovine spongiform encephalopathy (BSE), a sub-acute degenerative disease affecting the central nervous system of cattle, belongs to a group of related diseases known as the transmissible spongiform encephalopathies. They are caused by poorly characterized scrapie-like agents (prions) that produce spongiform changes in the brain (1). Sheep scrapie is thought to be the origin of BSE which was first diagnosed in the United Kingdom (UK) in 1986. The disease was confirmed a few years later in domestic cattle in France, the Republic of Ireland, Portugal and Switzerland (2) as well as in cattle exported from the UK to Denmark, Canada, the Falkland Islands, Germany, Italy, the Sultanate of Oman and, to Portugal and the Republic of Ireland beside the occurrence in domestic cattle. Surveillance of BSE and/or scrapie is carried out in some countries. However, there is no test to detect the disease in live animals and the screening for the disease is rather difficult since it is based on the detection of clinically suspect cases (3). An additional approach to ascertain if BSE risk factors are likely to be present in a country is to conduct a qualitative or quantitative risk assessment. This paper evaluates qualitatively some of the BSE risk factors in Europe.
Material and methods
Questions
For all European countries, the following questions were asked:
1. What was the cattle feeding practice concerning the use of animal waste-derived by-products such as meat and bone meal (MBM) and meat meal (MM): was it permitted and until when?
2. What was the quantity of MBM and MM imported from the UK through direct routes from 1985 to 1989?
3. What was the number of live cattle imported from the UK through direct routes to other European countries beginning in 1980?
4. What was the ratio of the sheep population versus the cattle population from 1985 to 1993?
5. What was the scrapie status since 1980: (i) endemic, (ii) sporadic, (iii) rare or (iv) no occurrence?
The main data sources were FAO (4), OIE (5, 6) and FAO-OIE-WHO (7) publications. Additional data was obtained from proceedings of the European Union's scientific BSE committee (8) and from national veterinary authorities (written communications) such as the British export statistics (9).
Using the OIE classification, countries were grouped into high-BSE incidence countries, low-BSE incidence countries and countries with no BSE cases. Countries with a low BSE incidence were subdivided into (i) countries with a low BSE incidence in domestic cattle, and (ii) countries with a low BSE incidence only due to the importation of live cattle from the UK. Furthermore, countries with officially no BSE cases were subdivided into (i) countries with BSE notification, and (ii) countries without BSE notification. Concerning the occurrence of scrapie, countries were, similarly to the BSE status, distinguished between countries with a high scrapie incidence (disease endemic), a low scrapie incidence (disease sporadic), and very low scrapie incidence (disease rare). Countries in which scrapie had never been recorded were subdivided into (i) countries with or (ii) without scrapie notification.
Results
To date, BSE was diagnosed in domestic animals in five out of 26 European countries: In the UK, Ireland, Portugal, Switzerland and France. Furthermore, Denmark, Germany and Italy reported BSE cases in imported UK cattle and so did Portugal and Ireland beside the occurrence in domestic cattle (Table 1). Data currently available on the following BSE risk factors are summarized in Tables 1, 2 and 3.
Risk factor 'feeding of meat and bone meal (MBM), and/or meat meal (MM) to cattle'
The potential BSE risk of feeding MBM and MM from insufficiently heated offal contaminated by scrapie-like agents, was first identified in 1988 (10, 11). Furthermore, in 1994 it was suggested that only a relative low dose exposure of MBM or MM is necessary for oral infection of cattle (12). Since it was difficult to separate abattoir waste from different species slaughtered, MBM and MM from the UK was generally considered as potentially contaminated in this study.
Sixteen out of 26 countries, including those countries that recorded BSE cases in domestic cattle, permitted the use of MBM or MM in cattle feed concentrates at some time. No data on the former or current use of MBM and MM was available for ten or eight countries, respectively (Table 1).
Iceland (in 1973); the UK (in 1988); the Republic of Ireland, Switzerland and Denmark (in 1990); France, Norway and Sweden (in 1991); and the EU (in 1994) prohibited the use of MBM and MM in cattle feeding (13).
Risk factor 'animal waste-derived protein imported from the UK'
The importation of UK animal waste-derived protein, i.e. MBM and MM, is considered as a BSE risk factor (14). Assuming a homogenous distribution of scrapie-like particles in British MBM or MM between 1985 and 1989, this potential BSE risk has increased proportionally per weight or volume unit imported. Furthermore, taking into consideration the long BSE incubation period (15), cattle exposed to British MBM imported from 1985 to 1989 must still be regarded as a part of the population at risk.
Out of 25 countries, 14 had imported MBM and/or MM from the UK. Belgium and Luxembourg, the Netherlands, France and the Republic of Ireland imported large quantities of MBM and MM. Out of these five countries only France and the Republic of Ireland recorded BSE cases in domestic cattle, together with Switzerland and Portugal. The latter two countries, however, imported only minor quantities of MBM and MM (Table 1).
Risk factor 'live cattle importation from the UK'
Since five European countries experienced BSE cases in imported animals from the UK, importation of cattle from this country is considered as a BSE risk factor. In the Republic of Ireland, for example, out of 78 BSE cases (as of 5/1994) ten involved animals imported from the UK (16). It was previously suggested that British cattle were infected with the scrapie-like agent starting in 1981 (11), and ending not before 1991, when still some cattle in the UK seem to have been exposed to BSE-contaminated MBM, despite the 'feed ban' of 1988 (17).
At least nine European countries imported live animals from the UK within the indicated periods (Table 1). The list includes only four of five countries where BSE occurred in imported UK animals since no data was available on Italy. The largest numbers were imported from the UK by the Republic of Ireland (7,138 UK cattle from 1986 to 1989), (16); and Portugal (12,000 UK cattle during the period from 1981 to 1989), (18). These two countries recorded ten and six BSE cases, respectively, in imported animals. In comparison, Germany (7,107 UK cattle imported from 1985 to 1992), (oral communication); and Denmark (150 animals imported in 1990), (written communication) reported four BSE cases and 1 case, respectively. Data from Italy (two BSE cases due to importation), and from 13 other countries were not available. Iceland and Switzerland imported no UK live cattle imports in the periods indicated (Table 1).
Risk factor 'sheep to cattle ratio'
The larger a scrapie-affected-sheep population is in relation to the size of a cattle population, the more likely it is that offal from domestic sheep could become the source of an indigenous BSE infection (15). In 1985 and in 1993, the sheep population was larger relative to the cattle population in 11 out of 26 countries. Among BSE-affected countries, this ratio was > 1 in the UK, Portugal and Italy in 1985 and 1993, respectively (Table 2).
In countries where the sheep population was outgrowing the cattle population, it could become even more likely for the latter species to be exposed to offal-derived meal originating from domestic sheep than in the other countries. From 1985 to 1993, in 12 out of 26 countries this ratio was clearly increasing from approximately 10% to 140%; the UK, France, Ireland and Switzerland, but not Portugal, i.e. countries with BSE cases occurred in domestic animals, are included in the 12 countries (Table 2).
Moreover, movement of live sheep is more likely to increase due to market activities, if a country's sheep population is growing. From 1985 to 1993 this was the case in 15 out of 26 countries, including seven of eight countries where BSE occurred (excluding Germany), (Table 2).
Risk factor 'scrapie'
Scrapie is thought to be the origin disease of BSE (11, 15). Out of 26 countries, 15 reported in 1980 and in 1985 that they did not diagnose scrapie. Seventeen countries stated this in 1990, whereas in 1991 and 1993, only 11 and 12 countries, repectively, stated that scrapie has not been recorded (Table 3).
Over the examined 14-year period, in one country (the UK) scrapie was endemic, in six countries there were sporadic outbreaks (in France, Iceland, the Republic of Ireland, Norway, the Netherlands and Former-Yugoslavia) and in seven countries scrapie occurred rarely: in Belgium, the Czech/Slovak Republic, Germany, Italy, Spain, Sweden and Switzerland. In all other countries the disease was not diagnosed; however, in Albania, Bulgaria, Malta and Poland scrapie is not notifiable. In 1984, Spain (19); Former-Yugoslavia and Norway (in 1985); Sweden (in 1986), Germany (in 1990), Switzerland and the Czech/Slovak Republic (in 1991) and Belgium (in 1992) began to report scrapie cases. Some of these countries, including Switzerland, confirmed the disease for the first time in history (Table 3).
Of all eight European countries that experienced BSE outbreaks, only Portugal and Denmark never recorded scrapie cases during the 14-year period, whereas the other countries had at least a single scrapie outbreak from 1980 to 1993 (Table 3).
Risk factor 'minimum offal rendering requirements'
Ruminant-derived offal contaminated by scrapie-like agents which was rendered under insufficient conditions in regard to temperature and duration of the heating process, was identified as a BSE risk factor in 1988 and confirmed in 1991 (10, 11). The recommended autoclaving conditions for inactivation of Creutzfeldt-Jakob Disease is a porous-load cycle at a minimum of 134deg.C for 18 minutes. The condition of 133deg.C for 20 minutes, approximately the equivalent of 134deg.C for 18 minutes, has now been largely adopted as an appropriate decontamination standard for scrapie-like agents generally (20).
Discussion
Summary
In this study, data on risk factors in BSE affected and BSE free European countries were analyzed. Reliable data was not available for all 26 countries or on all risk factors, respectively. However of the 10 countries of whom data on all parameters were available (Denmark, Finland, France, Germany, Iceland, Ireland, the Netherlands, Spain, Sweden, Switzerland and the UK) none had the same combination of risk factors found in the UK, i.e. (i) feeding cattle with MBM or MM, (ii) a large sheep to cattle population ratio, (iii) a high scrapie prevalence, and (iv) insufficient heating of high-risk abattoir-waste (20).
Importation and cattle feeding
For other countries than the UK the importation of British live cattle or the risk factor combination of (i) importation of ruminant-derived protein from the UK and (ii) feeding of ruminants with such material seemed to be most important. For France, the Republic of Ireland and Switzerland this is a confirmation of previous studies (14, 16). The data obtained on importation of animal waste-derived protein from the UK were limited to direct importations only. However, the scrapie-like agent might also have entered a country via indirect routes (14). Any country with considerable importations of MBM and MM from the UK might have been an intermediate trading station re-exporting the material to further countries. MBM could have been passed on undiluted or diluted with domestic animal waste-derived protein originating from the intermediate country. This additional risk factor could have been of major importance for some countries and should be examined in more details in the future.
The importation-related BSE risk factors are currently decreasing due to control measures enforced by risk management of many importing countries. In addition, live cattle importation-related risks are markedly decreasing due to declining infection rate of UK cattle since 1988 (17): Implementation of the feed ban of ruminant-derived proteins seems to be an efficient disease control element since interruption of the BSE infection chain leads to a decrease of the epidemic curve as it has been shown in the UK (21). Therefore veterinary officials of the EU (13) and of some non-member countries have enforced a BSE control and prevention program that prohibits the use of ruminant-derived proteins in ruminant feeds.
Consequently, the feeding-related risk factor becomes also less important.
Scrapie and sheep population
Sheep populations are growing in many countries and movement of live sheep is likely to increase, particularly within the EU (free trade). Consequently, and in contrast to the risk factors discussed above, the the potential risk of disease spread from a scrapie affected to a yet scrapie-free country is potentially increasing. In the examined period, eight countries reported new or even the first scrapie outbreaks in history.
In this context, a large and increasing sheep population may remain a risk factor, that is if it occurs in combination with scrapie (15). However, and in contrast to the UK, where the scrapie prevalence is high (22) and the incidence seems to be increasing (23), scrapie prevalence appears to be low in other European countries, e.g. in the Netherlands (24), Spain (25) and Italy or Switzerland (2). Nonetheless, we support previous suggestions (26), that scrapie eradication should be pursued as a long term goal by the international community to prevent new scrapie-related transmissible spongiform encephalopathies in other species. So far, scrapie has become a notifiable disease in the EU, as of January 1993 (27), and in some non-member states.
Acknowledgments
The author is grateful to Andrea Vicari, Dagmar Heim, Christian Griot for their critical comments on the manuscript.
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Kommentare und Fragen an bse-info@ivi.ch bzw. Tel. 031 323 03 03 Bern-Liebefeld, 28.3.96
IN Bisher wurde BSE in 5 von 26 EU-Ländern bei einheimischen Rindern diagnostiziert. Dies waren England, Irland, die Schweiz, Portugal und Frankreich. In Dänemark, Deutschland und Italien wurde BSE nur, in Portugal und Irland auch bei aus England importierten Tieren beobachtet. Eine Hauptursache sieht der Autor in der zumindest in 16 der 26 EU-Länder zeitweise erlaubten Verwendung von Fleischmehl und Fleisch-Knochenmehl in Kraftfutter für Rinder. Für die restlichen Länder hat er keine Daten. Die Verwendung von Fleischmehl und Fleisch-Knochenmehl in Kraftfutter für Rinder wurden in Island 1973, in England 1988, in der Republik Irland, der Schweiz und Dänemark 1990, in Frankreich, Norwegen und Schweden 1991 und EU-weit 1994 verboten. Der Autor unterscheidet allerdings nicht zwischen den gesetzlichen Regelungen und der Praxis der Tierfutterherstellung. Insbesondere bei britischen Mehlen sieht er ein hohes Infektionsrisiko. 14 der 26 EU-Länder haben britisches Fleischmehl und Fleisch-Knochenmehl importiert. Dies waren besonders Frankreich mit 42.196, Holland mit 12.945, Belgien und Luxembourg mit 10.797 und Irland mit 8.367 Tonnen in den Jahren 1985 bis 1989. Aber Deutschland importierte in diesem Zeitraum ebenfalls 1.899 Tonnen. Dabei korrelieren jedoch die Direktimportmengen nicht mit der BSE-Häufigkeit, weil diese nicht mit den an Rinder verfütterten Mengen korrelieren. Die Verwendung von aus nicht für den menschlichen Verzehr zugelassenen Tieren hergestellten Tiermehlen und den Einsatz von Schlachtfetten in Milchaustauschern läßt der Autor allerdings unerwähnt. Einen weiteren Risikofaktor stellen aus England importierte Rinder dar. Der Autor weiß von 7.138 in den Jahren 1986-1989 in die Republik Irland, 12.000 von 1981-1989 nach Portugal, 7.107 von 1985-1992 nach Deutschland und 150 im Jahr 1990 nach Dänemark exportierten britischen Rindern. Die Schweiz importierte keine britischen Rinder, von den anderen Ländern lagen dem Autor keine Daten vor. Scrapie als Risikofaktor scheint nur in England wirklich eine Rolle als Auslöser der BSE-Epidemie gespielt zu haben. Der Autor scheint allerdings nichts von den zahlreichen deutschen Scrapiefällen in den 80er Jahren zu wissen. Auf zu niedrige Temperaturen bei der Herstellung von Tiermehl, Fleischmehl und Fleisch-Knochenmehl geht der Autor nur flüchtig ein. Er beschreibt fälschlich 133° für 18 Min. als ausreichend sicheren Standard und übersieht, das dieser Standard garnicht für Fleischmehl und Fleisch-Knochenmehl gilt. Etwas naiv ist auch die Vorstellung, das der Rückgang der britischen BSE-Zahlen auf eine geringere Infektionsrate zurückzuführen sei. Der Autor unterscheidet nicht ausreichend zwischen letalen und subletalen Infektionen.
AD
Dr. med. vet. Beat Hörnlimann, Projektleiter TSE, Institut für Viruskrankheiten und Immunprophylaxe, Forschungsanstalt des Bundesamtes für Veterinärwesen in Bern, Schweiz, 3147 Mittelhäusern, Fax 0041/318489222
SP deutsch
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OR Prion-Krankheiten H