www.efsa.europa.eu/publications EFSA Supporting publication 2021:EN-6949
Annual Report of the Scientific Network on BSE-TSE 2021
European Food Safety Authority (EFSA)
Abstract
Establishing a system of Networks of organisations operating in the fields within EFSA’s mission is among the tasks of EFSA, according to Regulation (EC) No 178/2002, in order to facilitate a scientific cooperation framework by the coordination of activities, the exchange of information, the development and implementation of joint projects, the exchange of expertise and best practices. The EFSA Scientific Network on bovine spongiform encephalopathies and other transmissible spongiform encephalopathies (BSE-TSE) was established in 2006 and held its 16 th annual meeting on 18-19 October 2021, as a web meeting. The meeting served as an opportunity to exchange scientific information on BSE-TSE related issues among EU Member States, countries from the European Free Trade Association, EU candidate countries, EFSA, the European Commission (EC) and ad hoc participants [in the 2021 meeting, represented by the World Organisation for Animal Health (OIE)]. The topics discussed included: update on the VKM opinion on zoonotic potential of CWD, update on the situation and surveillance of CWD in Sweden, review of the control measures of CWD in Norway in the last five years (lessons learnt), the outputs of a risk assessment on the lift of the feed ban by ANSES, the prevalence in Britain of abnormal prion protein in human appendices (historical perspective and latest results), the new mandate of EFSA Scientific Networks 2021-2023 and joint activities of the BSE/TSE Network, recent and ongoing activities on TSE of EFSA, OIE and EC, as well as the preliminary results of the 2020 EU TSE summary report.
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2.4.2 EU TSE annual report 2020: preliminary results
EFSA Staff (BIOCONTAM Unit) presented the main findings that will be included in the EU Summary Report on TSE for year 2020.
The report presents the results of surveillance of TSE in animals and is expected to be published towards the end of November 2021 by EFSA.
It includes data from 27 Member States (MS, EU27), Bosnia and Herzegovina, Iceland, Montenegro, North Macedonia, Norway, Serbia, Switzerland and the United Kingdom (UK).
Full data set was submitted by UK (non-EU country from 1 February 2020), therefore totals were presented as EU27 plus UK to allow comparison with previous years.
In total, 1,222,671 cattle were tested by EU27 plus UK, showing a 2.4% decrease from 2019.
Four atypical BSE cases were reported in 2020 in the EU: 3 H-type reported by France, Ireland and Spain and 1 L-type reported by France.
Switzerland reported also 1 L-BSE case.
Over the year, a total of 332,513 sheep and 120,615 goats were tested in the EU27 plus UK, a decrease of 1.7% and 16% respectively, compared with 2019.
In sheep, 688 cases of scrapie were reported by 16 MS plus UK: 589 classical, 98 atypical, 1 CH1641-like.
12 additional inconclusive cases were reported by Italy.
In addition, Iceland reported 53 classical scrapie (CS) cases and Norway 12 AS cases.
Random genotyping was reported by nine MS and, after excluding Cyprus, showed that 8.8% of the genotyped sheep carried genotypes of the susceptible groups.
In goats, 328 cases of scrapie were reported by 9 MS plus UK: 319 classical and 9 atypical.
12 MS plus UK reported 9,171 tested cervids, of which more than 75% reported by the six MS (Estonia, Finland, Latvia, Lithuania, Poland, Sweden) implementing mandatory surveillance for CWD.
Two cases of CWD in moose were reported in 2020 in EU: one by Finland and one by Sweden.
In addition, Norway reported two CWD cases: in moose and in reindeer.
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2.1. Chronic wasting disease (CWD)
2.1.1 Update on VKM opinions and genetics in Norwegian cervids
The participant representing Norway presented the results of one of the two VKM (Norwegian Food Safety Authority) opinions published this year: "Zoonotic potential of chronic wasting disease (CWD) associated with animal slaughter and consumption of meat" (VKM, 2021a), following the request of the Norwegian Food Safety Authority to provide a statement with updated knowledge.
In 2016, the VKM report concluded that the zoonotic potential of CWD is very low (VKM, 2016) and this conclusion was confirmed in the 2017 CWD - update statement from VKM (VKM, 2017a). It was clarified that the expression ‘very low’ should be interpreted as ‘very rare, but cannot be excluded’ (according to OIE, 2004).
The zoonotic risk is assessed by combining data from three sources: a) surveillance, diagnostics and epidemiology; b) in vivo challenge experiments, and c) in vitro conversion assays.
Latest scientific evidence suggests that there is a unique strain of unknown origin in reindeer, unique strain(s) pleiotropic in moose and a unique strain in red deer. Therefore, distinct CWD prion strains must be evaluated separately, and information cannot be derived from North American strains. It was highlighted that accurate data on the incidence of sporadic prion diseases in humans in Norway is lacking. He also presented new data on the unsuccessful transmission of reindeer and moose CWD into human PrP-expressing transgenic mice (Wadsworth et al., 2021) and the preliminary interpretation of the ongoing inoculation study of CWD into macaques (research in progress). According to the new principal investigator, the zoonotic potential of CWD is real because the species barrier is not absolute and even if this does not prove that CWD can infect or has infected humans, it is prudent to continue to be very concerned about the risk of human exposition.
According to the VKM report (VKM, 2021a) ‘Our conclusion, based on the available information, is that the zoonotic potential of the Norwegian CWD variants, associated with animal slaughter and consumption of meat, is very low’.
Annual report of the Scientific Network on BSE-TSE 2021
www.efsa.europa.eu/publications 6 EFSA Supporting publication 2021:EN-6949
2.1.2 CWD in Sweden: update and surveillance in 2021
The participant representing Sweden presented the cases of CWD identified so far in Sweden, the intensified surveillance around the positive cases, the ongoing general surveillance and the extension beyond the legal requirement in 2021. The positive cases detected (three moose in 2019, one moose in 2021) are all female, with more than 10 years old, and all with positive brainstem/brain but negative lymph node. The intensified surveillance was designed to investigate CWD-prevalence in the area with detected case (design prevalence 0.7%) and the target animals tested were hunted/slaughtered animal for human consumption, in addition to risk animals. Results from the intensified surveillance and age distribution within the sampled animals were presented. Sweden decided to continue the general surveillance in order to reach the expected target, and it is ongoing with focus on risk animals (taking into account the difficulties due to impossibility to include road killed animals, due to national legislation measures). Finally, it was highlighted that there was high compliance and participation by hunters in area with intensified surveillance.
2.1.3 Control measures of CWD in Norway in the last 5 years: Lessons learnt
Bjørnar Ytrehus, Professor of veterinary pathology at the Swedish University of Agricultural Sciences, provided a presentation on the control measures applied after 5 years from the confirmation of the first case and on the lessons learnt (VKM, 2016, 2017, 2018, 2021a, 2021b). The key points to define the approach followed for the control measures were summarised in the following six points:
1) surveillance, providing an overview on the cases, the geographical location and the rapid response and the Nordfjella. Following the 2017 cases, the surveillance increased in areas surrounding the locations where the moose and red deer caseshad been found;
2) confinement, increased patrolling/herding at known crossing points, ceasing connectivity and closing roads, fencing and using GPS-collaring in Nordfjella area;
3) preventing congregations, reducing artificial points of host concentration (i.e. use of salt licks intended for cervids banned, from 2020 allowed use of mobile saltlicks for sheep);
4) hygiene, avoiding spread and human exposure;
5) population management, with increase hunting of wild reindeer and moose, depopulation of the reindeer herd in Nordfjella zone 1 as rapid response with the collaboration of well-trained hunters;
6) communication, putting in place a constant respectful dialogue with society.
In conclusion, the lessons learnt were that: i) communication is difficult but extremely important to allow a common understanding, ii) inaccessible area are difficult to control, iii) there is a cost of mitigation efforts to farmers, hunters, citizens in rural societies, iv) there is a need of respectful dialogue, common understanding and compromises; v) competition between authorities and researchers might be present.
2.1.4 Additional topics discussed
To reply to the questions by Italy, the prevalence of CWD in old moose in Sweden was unknown. On the origin of the reindeer in Hardangervidda, it was commented the different genetic profile compared to the reindeer in Nordfjella. The EC asked about the scientific basis for the use of the term ‘atypical CWD’ as opposed to ‘typical CWD’. Norway explained the different profile of CWD in reindeer (like that of North America) compared to moose, that affects old animals and has a different localization and tissue distribution of PrPSc, only in the brain. There was a discussion on the need to clarify the denomination of CWD in European cervids and get a consensus on whether the use of the term ‘atypical CWD’ is scientifically justified according to the current knowledge, as well as on the need to differentiate from North America CWD, and on whether the terminology should be applied at strain, species or phenotypical presentation level. This was followed by a discussion triggered by the question posed by the external presenter for point 2.1.3 on whether the reduction of density in Hardangervidda should be done fast or not. The role of environmental contamination was also pointed out.
2.2 TSE and public health
2.2.1 Risk Assessment on the lift of the feed ban (ANSES)
The participant representing France presented the risk assessment on the lift of the feed ban, published in June 2021 by ANSES (National Agency for Food, Environmental and Occupational Health & Safety) (ANSES, 2021).
Firstly, the use of pig processed animal protein (PAP) for poultry feed and poultry PAP for pig feed was discussed: starting from 1) the review and update of the interest of processed animal protein (PAP) in feed, followed by 2) the review of the risk of spreading TSE agents in the context of the introduction of PAP in animal feed.
The main risk associated with incorporating poultry and pig protein into animal feed is the transmission and amplification of TSE. The working group followed a semi-quantitative approach (Prion Risk Prioritization Method, HRPrion) with scenario-analysis, highlighting the importance of avoiding the occurrence of cross-contamination throughout the chain. Apart from any cross-contamination, the risk of recycling a possible sporadic/spontaneous TSE in pigs through the food chain can be limited: in case PAP of pigs are produced by the pressure sterilization method (method 1); in view of the presumed low susceptibility of poultry to TSEs, a Method 1 treatment (pressure sterilization) of poultry PAP is not proportionate to the risk. Effective separation by species of all the sites in the production chain, associated with control measures and traceability, would limit possible TSE amplification (ANSES, 2021).
Secondly, the use of insect PAP for pig and poultry feed was discussed. The report covers the seven species of insects authorized for feeding fish and Bombyx mori. Potential biological and chemical hazards are associated with insects therefore it was underlined that the substrate, on which insects are raised, should comply with the regulatory requirements on animal feed, since the risks associated with insect PAP could vary according to the nature of the substrate.
Finally, other conclusions were that it is important not to base management measures solely on the existence of an interspecies transmission barrier for prions, as this is not absolute, and that it is needed to maintain active surveillance of TSE.
2.2.2 Prevalence in Britain of abnormal prion protein in human
appendices: historical perspective and latest results
Simon Mead, consultant neurologist and TSE researcher, provided a historical perspective of the longstanding project on the prevalence in Britain of abnormal prion protein in human appendices, focusing on the latest result published in 2020, of which he is co-author: : ‘Prevalence in Britain of abnormal prion protein in human appendices before and after exposure to the cattle BSE epizootic’ (Gill et al., 2020). Two previous appendectomy sample surveys (Appendix-1 and -2) estimated the prevalence of abnormal prion protein (PrP) in the British population exposed to BSE. The Appendix-3 survey was aimed at measuring the prevalence of abnormal PrP in population groups thought to have been unexposed to BSE. Results, limitations of the Appendix studies and future studies were presented.
2.2.3 Additional topics discussed
Norway asked to the external speaker of agenda item 5.2 whether the presence of immunostaining in the appendices was unequivocally due to variant Creutzfeldt–Jakob disease (vCJD). The speaker answered that it is not possible to conclude that the signal is due to a prion disease, and that further tests like Protein misfolding cyclic amplification (PMCA) would be advisable to perform on these samples, which is the case in the next phase of the project. The speaker confirmed the suspicion that the only case of vCJD of 129MV genotype could be due to longer incubation period and that there is concern of a possible second wave in semi-resistant genotypes; also the incidence of sporadic Creutzfeldt–Jakob disease (sCJD) in the UK should reach a plateau but it has not done yet, although no signal of unusual cases due to other possible origin has been identified. Germany asked if the presence of immunostaining was also observed in other tissues (small intestine for example) but it was confirmed that there were no other tissues available from these patients for comparison.
2.3 New mandate of EFSA Scientific Networks 2021-2023. Joint activities of the BSE/TSE Network
EFSA staff (Engagement and Cooperation Unit) presented the modifications on the New EFSA Management Board Decision on Scientific Networks and the consideration when setting the Terms of Reference. EFSA Management Board will receive regular activity reports of the EFSA networks and decide on their continuation on a basis of at least every 3 years. MS network representatives and alternate representatives are now referred to as network participants and alternate participants. The mandate of the BSE-TSE network has been renewed for the period 2021-2023.
2.4 General session
2.4.1 EFSA activities on TSE 2020-2021
EFSA staff (Biological hazards and contaminants Unit, BIOCONTAM) updated the Network on the TSErelated risk assessment activities that took place in EFSA since the 2020 annual Network meeting. In particular, he presented the scientific opinion on the evaluation of an alternative method for the production of biodiesel using rendered fat of Category 1 (BDI-RepCat) (EFSA BIOHAZ Panel, 2021) and the scientific report on the request for scientific and technical assistance to examine the data collected by the Member States in the framework of the 2-years compulsory intensified surveillance in case of atypical scrapie (AS), published in July (EFSA, 2021).
EFSA published in April 2021 the assessment of a new alternative method for the production of biodiesel from rendered fat, including animal by-product (ABP) Category 1 tallow (BDI-RepCat). The method consists of a conversion phase (single step esterification and transesterification at temperature ≥ 200°C, pressure ≥ 70 bar with a retention time ≥ 15 min), using MgO as a catalyst and in the presence of methanol (10–15%), followed by vacuum distillation (at ≥ 150°C, ≤ 10 mbar) of the end-product, biodiesel and the co-product, glycerine. The proposed alternative method was considered able to achieve a reduction in prion infectivity, or detectable PrPSc, of at least 6 log10 therefore it was considered equivalent to the processing method laid down in the Regulation (EU) No 142/20114 for the production of biodiesel from raw materials including Category 1 ABP (EFSA BIOHAZ Panel, 2021).
The EC asked EFSA whether the scientific data on the 2-year intensified monitoring in AS outbreaks (2013–2020) provide any evidence on the contagiousness of AS, and whether they added any new knowledge on the epidemiology of AS. An ad hoc data set from intensified monitoring in 22 countries with index case/s of AS in sheep and/or goats was analysed. The results of the calculated design prevalence and of a model simulation indicated that the intensified monitoring had limited ability to detect AS, with no difference between countries with or without secondary cases. A simulation model of within-flock transmission, comparing a contagious (i.e. transmissible between animals under natural conditions) with a non-contagious scenario, produced a better fit of the observed data with the noncontagious scenario, in which each sheep in a flock had the same probability of developing AS in the first year of life. Based on the analyses performed, and considering uncertainties and data limitations, it was concluded that there is no new evidence that AS can be transmitted between animals under natural conditions, and it is considered more likely (subjective probability range 50–66%) that AS is a non-contagious, rather than a contagious disease. The results of the analysis confirmed some of the known epidemiological features of AS but identified that major knowledge gaps still remain (EFSA, 2021).
2.4.3 Update on the activities of the OIE in the TSE field
The representative of the OIE (World Organisation for Animal Health), updated the Network on the TSErelated activities ongoing in the OIE since the previous Network meeting. Currently there are 56 countries and five zones with an official BSE risk status; two new members were recognized as having a negligible BSE risk status (Canada and Ireland) in May 2021. The 2021 campaign for the maintenance of the officially recognised statuses, including BSE risk status, is due to start in November 2021. During 2020 there have been many activities in OIE linked to the revision of the BSE chapters in the Terrestrial Animal Health Code and the Manual of Diagnostic Tests and Vaccines for Terrestrial Animals. September 2021 Code Commission report and September 2021 Scientific Commission report to be published online soon; report of the June 2021 BSE ad hoc Group will be annexed to the September 2021 Scientific Commission report.
2.4.4 Update on the activities of the EC in the TSE field The representative of the European Commission (EC) provided updates on the activities of the EC since the last Network meeting. Two horizontal topics were presented: 1) Feed ban and 2) Trade related issues (with focus on the interaction with OIE and the consequences of BREXIT).
More in detail, the Regulation (EU) 2021/13725 adopted on 17 August authorises the following uses:
• processed animal protein derived from pigs and insects in poultry feed;
• processed animal protein derived from poultry and insect in pig feed;
• gelatine and collagen of ruminant origin in the feed of non-ruminant farmed animals.
Three disease-specific topics were also discussed:
1) on BSE, short-term and long-term solutions were presented for the critically low stockpile of reference material of atypical BSE (H and L- types);
2) about Scrapie, regulatory updates concerning genetic resistance to CS in goats and the intensified surveillance of AS obligation were presented;
3) the 3-years surveillance programme (2018-2020) for CWD in cervids was informally prolonged upon request of Sweden and a mandate is going to be sent to EFSA to analyse the results and provide scientific basis for a revision of the surveillance provisions in Regulation (EC) 999/20016 ; in addition, it was mentioned the need to transfer the CWD safeguard measures into the permanent framework of Regulation (EC) 999/2001.
2.4.5 Additional topics discussed
Netherlands presented a paper on the risk to implement the lift of the feed ban on the context of a circular economy (BuRO, 2020). In particular, the risk of transmission of prions due to the ruminant origin of the substrate used to feed insects, allowing the propagation and amplification in farmed animal,
5 Commission Regulation (EU) 2021/1372 of 17 August 2021 amending Annex IV to Regulation (EC) No 999/2001 of the European Parliament and of the Council as regards the prohibition to feed non-ruminant farmed animals, other than fur animals, with protein derived from animals. OJ L 295, 18.8.2021, p. 1–17.
6 Regulation (EC) No 999/2001 of the European Parliament and of the Council of 22 May 2001 laying down rules for the prevention, control and eradication of certain transmissible spongiform encephalopathies. OJ L 147, 31.5.2001, p. 1–40. Annual report of the Scientific Network on BSE-TSE 2021
www.efsa.europa.eu/publications 10 EFSA Supporting publication 2021:EN-6949
and due to the use of former foodstuff as substrate as well. This could result on indirect cannibalism. The EC explained that this is a topic under discussion internally in the EC and highlighted the complexity of the controls for the feed ban. Sweden stressed out the difference in the great efforts to conduct surveillance in live animals compared to the limited ones for surveillance of the ban in feed. Italy agreed and pointed out the lack of centralised systematic collection of data on monitoring of the feed ban in the EU.
References
© European Food Safety Authority, 2021
Key words: BSE, CWD, feed ban, meeting, network, TSE
Surveillance of Chronic Wasting Disease (CWD) in Norway 2020
Kartlegging og overvåking av skrantesjuke (Chronic Wasting Disease - CWD) 2020 Rolandsen, Christer Moe; Våge, Jørn; Hopp, Petter; Benestad, Sylvie L.; Viljugrein, Hildegunn; Solberg, Erling J.; Andersen, Roy; Strand, Olav; Vikøren, Turid; Madslien, Knut; Tarpai, Attila; Fremstad, Jørn; Veiberg, Vebjørn; Heim, Morten; Holmstrøm, Frode; Mysterud, Atle
Sammendrag
Rolandsen, C.M., Våge, J., Hopp, P., Benestad, S.L., Viljugrein, H., Solberg, E.J., Andersen, R., Strand, O., Vikøren, T., Madslien, K., Tarpai, A., Fremstad, J., Veiberg, V., Heim, M., Holmstrøm, F., Mysterud, A. 2021. Kartlegging og overvåking av skrantesjuke (CWD) 2020. NINA Rapport 1983 / Veterinærinstituttet rapport 42, 2021. 38 s.
Denne rapporten oppsummerer arbeidet som er gjennomført i 2020 for å kartlegge forekomsten av CWD, etter at sykdommen ble påvist hos villrein og elg i 2016. Den oppsummerer også totalt antall hjortedyr som er testet i perioden 2016-2020.
I 2020 ble 22 527 hjortedyr testet for CWD, og myndighetenes mål om testing av 22 000 hjortedyr ble dermed nådd. I løpet av året ble det påvist ett tilfelle av klassisk CWD hos en 8 år gammel villreinbukk på Hardangervidda og ett nytt tilfelle av atypisk CWD hos en 17 år gammel elgku i Steinkjer kommune. Totalt er det i perioden 2016-2020 påvist klassisk CWD hos 20 villrein, og atypisk CWD hos sju elgkyr og ei hjortekolle.
Prøvetakingen i 2020 omfattet som tidligere både hjerneprøve og lymfeknuter (primært svelglymfeknuter). Av de innsamlede prøvene inneholdt 72 % begge vevstypene. Dette er noe lavere enn i 2019 og 2018 med henholdsvis 78 % og 80 %.
Selv om det har vært god oppslutning om prøveinnsamlingen og det er et høyt antall testede dyr, er det utfordringer med dårlig kvalitet på en god del prøver og det er problemer med mangelfull registrering. For eksempel var 3 % av prøvene ikke merket med kommune eller område, 2 % manglet informasjon om art, og for 9 % av ville hjortedyr manglet informasjon om prøven kom fra jakt eller fallvilt.
I 2020 ble det testet i overkant av 20 % av registrerte fallvilt av viltlevende hjortedyr, noe som er en lavere andel enn ønsket. I gjennomsnitt ble over 80 % av felte villrein i de ulike villreinområdene testet, men bare for 67 % av disse ble det sendt inn både hjerne og lymfeknute. Med prøver fra både lymfeknute og hjerne vil det ta kortere tid å få kunnskap om forekomst og prevalens i områder med smitte og vi kan raskere sannsynliggjøre fravær av CWD i områder uten smitte.
Fremover er det viktig å avklare om klassisk CWD forekommer i andre områder, og særlig i områder nær Nordfjella og Hardangervidda. Et stort antall prøver er dessuten viktig for å øke kunnskapen om forekomsten av atypisk CWD hos hjortedyr.
Kunnskapen som er ervervet så langt viser at det er viktig å kjenne alder på dyrene. Dette gjelder både for klassisk og atypisk CWD. Hjorter og elger fra Fennoskandia med påvist atypisk CWD har vært gamle dyr. Det er derfor fortsatt ønskelig å aldersbestemme hjortevilt i utvalgte områder de neste årene, både fallvilt og dyr som felles under jakta. Med bedre kunnskap om aldersfordelingen kan vi med større sikkerhet beregne forekomst av atypisk CWD, og eventuelt også klassisk CWD, i ulike bestander. Rolandsen, C.M., Våge, J., Hopp, P., Benestad, S.L., Viljugrein, H., Solberg, E.J., Andersen, R., Strand, O., Vikøren, T., Madslien, K., Tarpai, A., Fremstad, J., Veiberg, V., Heim, M., Holmstrøm, F., Mysterud, A. 2021.
Surveillance of Chronic Wasting Disease (CWD) in Norway 2020.
NINA Report 1983 / Norwegian Veterinary Institute Report 42, 2021. 38 pp.
This report summarizes the efforts related to Norwegian surveillance of Chronic wasting disease (CWD) in 2020 and the total number of deer tested in the period 2016-2020.
In 2020, 22,527 cervids were tested for CWD, and the authorities' goal of testing 22,000 was thus reached. During the year, one case of classic CWD was detected in an 8-year-old wild reindeer (Rangifer tarandus) male at Hardangervidda in Vinje municipality, and a new case of atypical CWD in a 17-year-old female moose (Alces alces) in Steinkjer municipality. In total, the period 2016-2020 has revealed classic CWD in 20 wild reindeer, and atypical CWD in seven moose and one red deer (Cervus elaphus).
The sampling was intended to include both brain and lymph nodes and 72 % of the collected samples contained both types of tissue. This is somewhat lower than in 2019 (78 %) and 2018 (80 %).
Although it is satisfactory that a high number of animals was tested, there are challenges with poor tissue quality and with data registered for some samples. Thus, 3% of the samples were not labeled with municipality or area, 2% lacked information about species, and for 9% of samples from free-ranging deer, information was lacking whether it was from an individual shot during hunting or from animals that died from other causes.
An important goal for further surveillance is to collect data that can help clarify whether classical CWD is present in other areas, and especially in the areas near Hardangervidda and Nordfjella where classical CWD was found in wild reindeer. For Hardangervidda, it is also important to gain more knowledge about prevalence, as only one wild reindeer with CWD has been diagnosed so far. Moreover, a large number of samples is important to clarify the prevailing assumption that atypical CWD in moose and red deer is less contagious, if contagious at all, compared to classical CWD.
The knowledge gained over the past four years shows the importance of knowing the age of the animals, both for classic and atypical CWD. Moose and red deer with atypical CWD have all been 12-20 years old, while wild reindeer with classical CWD has been 1-8 years old. In 2020 systematic age determination of reindeer, moose and red deer has been done in some areas, both from animals shot during hunting, from those found dead for other reasons or culled. In the coming years, it is desirable to continue this data collection in selected areas. Information about the age distribution of both hunted deer and deer found dead from other causes would contribute to better knowledge regarding the prevalence of both atypical and classical CWD. Utgiver Norsk institutt for naturforskning (NINA) Serie NINA Rapport;1983 Opphavsrett © Norsk institutt for naturforskning © Veterinærinstituttet Publikasjonen kan siteres fritt med kildeangivelse
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