DTD 5
Preventive Veterinary Medicine xxx (2005) xxx–xxx www.elsevier.com/locate/prevetmed
Experiences from BVDV control in Sweden L. Hult a,*, A. Lindberg b a
Swedish Dairy Association, Dairy Cattle Health Service, Box 1146, SE-631 80 Eskilstuna, Sweden b Swedish Dairy Association, Research and development, Box 7019, SE-750 07 Uppsala, Sweden Received 5 January 2005; received in revised form 15 April 2005; accepted 15 April 2005
Abstract A control scheme on BVDV was launched in Sweden in 1993 with the aim to prevent spread of the infection between herds, to eliminate virus from infected herds and, ultimately, to eradicate BVDV from Sweden. At the start it was voluntary and fully financed by the affiliated farmers. The estimated prevalence of infected herds was 40%. After 11 years there were only 205 (0.9%) herds still under clearance. Measures perceived to be of importance in concluding the scheme are subsidies on costs for analyses, gradually making regulations for contacts between herds and prevention of indirect infection stricter and also to eventually make the scheme compulsory. # 2005 Elsevier B.V. All rights reserved. Keywords: Bovine viral diarrhoea (BVD); Control scheme; Eradication; Epidemiology
1. Introduction During the 1990s, efficient methods for detecting bovine viral diarrhoea virus (BVDV) in serum, and for detecting antibodies in serum, milk and bulk milk (Niskanen et al., 1991) were developed. In Sweden, a national bulk milk screening in 1993 showed that more than 50% of the dairy herds had high antibody levels in the bulk milk, indicating an ongoing or recent infection (Niskanen, 1993). At the same time, practical experiences had shown that it was possible and profitable to clear infected herds from the disease and maintain their free * Corresponding author at: Swedish Board of Agriculture, Animal Disease Control Division, SE-55182 Jo¨nko¨ping, Sweden. Tel.: +46 36 15 62 74; fax: +46 36 16 38 28. E-mail address:
[email protected] (L. Hult). 0167-5877/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.prevetmed.2005.04.005
PREVET-2094; No of Pages 6
DTD 5
2
L. Hult, A. Lindberg / Preventive Veterinary Medicine xxx (2005) xxx–xxx
status. This resulted in a decision to control BVDV, and a scheme was started by the Swedish Dairy Association in 1993 with strong support from the farmers’ own organisations. The aim of the scheme is to prevent spread of the infection between herds, to eliminate the virus from infected herds and, ultimately, to eradicate BVDV from Sweden (Alenius et al., 1996). At the start, the scheme was voluntary and fully paid for by the farmers. Since 1996, the Board of Agriculture has granted funds that are used mainly to subsidise costs for analyses. Today most of the costs for analyses and central administration are subsidised, whereas the farmers still pay for labour and local administration. The epidemiological principles underlying the scheme have been described elsewhere (Lindberg and Alenius, 1999), but briefly the scheme is based on a non-vaccination approach, where repeated demonstration of absence of antibodies is required for certification, and a systematic test-and-cull protocol is used for eliminating PI animals from infected herds. The regulatory framework is aimed at controlling the major routes of introduction of BVDV infection into a herd, i.e. through direct contact with PI animals or through purchase of dams carrying PI foetuses. However, as the scheme has proceeded, relatively more emphasis has been put on preventing infection through indirect contacts. The purpose of this paper is to describe changes made and actions taken during the scheme in relation to the progress.
2. Materials and methods Most of the data regarding the progress of the BVD scheme were obtained from the BVD database that was set up in 1997 and which stores results from all the analyses taken within the scheme. It also contains information about all affiliated herds, as herd size, production type (dairy/beef/heifer rearer) as well as historical and present BVD status. Information from the time before April 1997 was derived from output from an older computer system, which was less detailed. Other sources of information have been personal communication with veterinarians working in the field, livestock traders and farmers. Over time, a series of actions have been taken in order to make all herds affiliate and comply with the rules, to prevent new infections, and to find and take actions in infected herds. Actions and events perceived as having had major influence on the progress are listed in Table 1.
3. Results In the spring of 1993, 52% of all the dairy herds had very high levels of antibodies to BVDV in the bulk milk, indicating a recent or ongoing infection. In November 2004, only 2% were in class 3. Also, in January 2005, 97.3% of the herds were certified free, 1.9% were awaiting their second test before certification, and 0.8% (173 herds) were still undergoing clearance. The progress of affiliation and certification of free herds (Fig. 1) was markedly higher among dairy herds than among the beef herds. While 50% of the dairy herds had affiliated after less than 2 years it took about 4.5 years to affiliate 50% of the beef
DTD 5
L. Hult, A. Lindberg / Preventive Veterinary Medicine xxx (2005) xxx–xxx
3
Table 1 Actions of importance for the Swedish BVD scheme, and their consequences Time
Actions and events of importance
Consequence
April 1993
National bulk milk screening. BVD status obtained on all dairy herds. Herds with an approved result are able to use it as a first approved result in the scheme
A population of non-infected herds was identified that could reach certification shortly after the scheme started. They created the basis for low-risk trade in compliance with the rules of the scheme
September 1993
The scheme starts. Voluntary, fully paid for by farmers Governmental funds obtained. Mainly used for subsidising costs for analyses of individual samples, initially in regions with intensified eradication (Lindberg, 1996) and later in the whole country The dairy industry demands affiliation
September 1996
July 1997 November 1997
January 1999
January 1999
June 2002
January 2004
June 2004
Continuously
Recommendations on individual testing before trading pregnant animals from free herds if not represented in the herd test method (e.g. heifers on remote pasture in herds monitored on bulk milk) The beef industry demands affiliation
Significant livestock traders put additional value on calves from BVD-free herds with an approved test not older than 3 months (in accordance with scheme rules). An increased number of dairy herds move from annual testing to 3-month subscription on bulk milk testing, in order to always have a current status BVD-control compulsory for all herds except specialized fattening herds. Makes it possible to take action in herds that have not affiliated to the voluntary scheme. Sanctions for non-compliers become available, as exclusion from the voluntary scheme implies no access to subsidies End phase project starts. Individual virus elimination plans for all infected herds Infected herds obliged to inform neighbours and others concerned. Calves sold from infected herds to fattening units must be tested and not PI Information and education of stakeholders
Affiliation increased (see Fig. 2), incidence decreased in project areas
100% coverage of dairy herd population (Fig. 2) Reduced incidence, by preventing recently infected herds from selling dams carrying PI animals
No. of affiliated beef herds increased = higher coverage of beef herd population (Fig. 2) Monitoring of dairy herds became more efficient new infections detected at an earlier stage
100% coverage of the cattle population. Decreased incidence and prevalence
Duration of the elimination period (infectious period) shortened Decrease in incidence
Decrease in incidence
DTD 5
4
L. Hult, A. Lindberg / Preventive Veterinary Medicine xxx (2005) xxx–xxx
Fig. 1. Progress and major actions/events during the course of the Swedish BVD scheme 1997–October 2004.
Fig. 2. Incidence as new herds where BVDV virus was found per 1000 herds at risk 1995–2004 and annual number of new cases.
DTD 5
L. Hult, A. Lindberg / Preventive Veterinary Medicine xxx (2005) xxx–xxx
5
herds. The incidence has decreased steadily (Fig. 2) and of the 32 new herds where PIs were found in 2004 only 6 were found during the last 6 months.
4. Discussion Running an eradication scheme is a process where a lot of factors have to be taken into account. Most problems do not have to do with the virus itself or with the analyses, but rather with human factors such as degree of support from authorities and other involved parts, resources for taking samples and so on. Many problems can be solved by informing and cooperating with the parties involved, such as farmers, the dairy and beef industry, livestock traders, insurance companies and other relevant stakeholders. The ability of a scheme to reach full coverage will be dependent on the back-up from authorities and the farmers’ own organisations (voluntary versus compulsory, subsidies, etc.), the ability to spread understanding of what will be gained by the scheme, the farmers’ knowledge about the disease, and market effects such as better prices for BVD-free cattle or no market for not BVD-free cattle. In our situation, one of the hardest tasks was to convince farmers with beef production herds to join. Possible reasons are the relatively higher cost for monitoring of beef herds (as they can not use bulk-milk testing) and the relatively higher proportion of non-professional farmers that are difficult to reach with information. Positive measures directed towards this category involved subsidies on affiliation fees and analyses, but different types of compulsion (from the industry as well as legislation) had a better effect. Many measures aimed at preventing new infection are included in the regulations of the scheme but their limitation is that they only cover affiliated farmers. Also, the general awareness of them decreases with time. Still, a critical measure in BVDV control is to change trade patterns and prevent PI animals from being put on the market. A powerful tool to achieve this is to sensitize livestock traders to a demand for BVD tested animals by informing farmers about BVD and the importance of asking for BVD status of the stock they buy. In Sweden, this gave livestock traders a strong incentive to work with the scheme rather than against it. In our opinion, this has been of major importance in reducing the incidence. A scheme’s ability to find new infections in due time is dependent on test performance and interval but also of activities aimed at finding and checking any contact herds to which the infection has been transmitted, before they manage to spread the infection further. The interval is theoretically set by the scheme rules, but in reality also by other factors such as costs and inconvenience caused by the monitoring that has an impact on the farmer’s willingness to test in time. Compared to the cost-efficient bulk-milk testing used in BVD-free dairy herds, individual blood samples taken in beef herds are more expensive and thus the frequency of testing in beef herds tends to be much lower. Also, access to beef herds may be more difficult, e.g. during pasture periods or if the owner has got farming only as a side-business. Sampling at slaughterhouses has been implemented in other Scandinavian countries and may be a solution for this category of herds in the future, also in Sweden.
DTD 5
6
L. Hult, A. Lindberg / Preventive Veterinary Medicine xxx (2005) xxx–xxx
It is crucial that farmers comply with interventions needed to eliminate virus from infected herds. In our situation this has normally not been a problem. Virus elimination by culling PI animals is one of the possible consequences the farmer has accepted in joining the scheme, and he/she understands what is to be gained from doing so. The most common arguments raised against elimination of virus shedders have been firstly the cost and secondly the fear of re-infection. Still, arguments in the other direction are the worry of transmitting the infection to neighbouring herds and in better pricing on bull calves from BVD-free herds. Today, there are specific plans for all infected herds remaining. In order to get access to the very last herds, the governmental decision to make the scheme compulsory was very helpful. However, it only applies to a handful of farmers. Farmers in the compulsory scheme do not get any subsidies, so for non-compliers already in the scheme, exclusion is an efficient sanction.
5. Conclusion The most effective way of eradicating BVDV from any region is probably a compulsory scheme with effective trade regulations and no costs for the farmers. As this was never an option in Sweden, controlling the virus has been a continuous effort to balance between the epidemiologically and economically best way on one hand, and what has been possible to do on the other. In doing so, the scheme has slowly moved towards the theoretical optimum. Our experience, largely shared by the other Nordic countries, is that – even when the scheme is not optimally designed from the start – given it is implemented in a systematic manner and with basic biosecurity, elimination of virus from infected herds and monitoring of non-infected herds, BVDV eradication is possible and profitable.
References Alenius, S., Lindberg, A., Larsson, B., 1996. A national approach to the control of bovine viral diarrhoea virus. In: Proceedings of the Third ESVV Symposium on Pestivirus Infections. pp. 162–169. Lindberg, A., 1996. Regionalised eradication of bovine viral diarrhoea virus in Sweden—an approach complementary to the current control scheme. In: Proceedings of the Society for Veterinary Epidemiology and Preventive Medicine, Glasgow, Scotland, March 27–29, 1996, pp. 146–156. Lindberg, A., Alenius, S., 1999. Principles for eradication of bovine viral diarrhoea virus (BVDV) infections in cattle populations. Vet. Microbiol. 64 (2–3), 197–222. Niskanen, R., Alenius, S., Larsson, B., Jacobsson, S.O., 1991. Determination of level of antibodies to bovine virus diarrhoea virus (BVDV) in bulk tank milk as a tool in the diagnosis and prophylaxis of BVDV infections in dairy herds. Arch. Virol. Suppl. 3, 245–251. Niskanen, R., 1993. Relationship between the levels of antibodies to bovine viral diarrhoea virus in bulk tank milk and the prevalence of cows exposed to the virus. Vet. Rec. 133 (14), 341–344.
