Future of Brucellosis, EBL and Warble Fly surveillance
- Introduction
- Background
- History of eradication
- Reintroduction of infection in cattle since 1991
- History of Surveillance in Great Britain
- Targetted Surveillance of Imported Cattle
- Routine Surveillance of Indigenous Cattle
- Lessons Learnt and Risk Assessment
- Risk Mitigation
- Enzootic Bovine Leucosis (EBL) and Warble Fly
- Wider Implications for Disease Outbreak Diagnostics
- Impact on the Veterinary Profession
- Summary
- Annex A: Summary of Changes to Surveillance
Introduction
1. This paper sets out the background to the review of our approach to routine brucellosis, enzootic bovine leucosis (EBL) and warble fly serological surveillance in GB beef herds. This decision was part of an ongoing review of current animal disease surveillance programmes to ensure that they remain effective and deliver value for money to the taxpayer. The changes are summarized in Annex A to this paper.
2. In making these changes we have considered:
- Background and history of brucellosis control, and recent outbreaks;
- A review of the current surveillance strategy;
- Risks of stopping components of current surveillance;
- Risk mitigation measures in place and any others required;
- Potential cost savings;
- Wider implications.
Background
3. Brucellosis is a bacterial disease of cattle resulting from infection with Brucella abortus which causes reduced fertility, abortion and premature calving. The disease is spread by infected cattle after they have aborted or calved, the organism being present in the placenta, uterine discharge and in the milk of infected cows. People who work with infected cattle or drink unpasteurised milk from infected cows can become infected and suffer a persistent recurring ‘flu like disease known as ‘undulant fever’. Other species of Brucella can affect other mammals and also cause disease in humans.
History of eradication
4. A study of bovine brucellosis in Great Britain carried out in 1934 concluded that about 40% of cattle herds contained cattle infected with brucellosis; this was similar to the estimated prevalence of bovine tuberculosis in cattle at the time. Free calf vaccination was introduced in 1962. Compulsory area eradication commenced in 1971 and by 1981 all herds in Great Britain were attested and calf vaccination ended. A programme of serological testing and partial herd slaughter to remove seropositive adult cattle was also implemented. Great Britain gained formal recognition as a region of the European Union with Officially Brucellosis Free (OBF) status in 1985; although the first year with no new confirmed cases was not until 1991.
Reintroduction of infection in cattle since 1991
5. Brucellosis was confirmed in 1993 in a dairy herd in Anglesey, which had imported infected cattle from France. Infection was first identified by a positive bulk milk test; this was rapidly followed by a positive abortion investigation.
6. Brucellosis was reintroduced in 2003 following the import of heifers, which originated from a herd in the Republic of Ireland. Infection was detected following a report from Ireland that infection had been confirmed in the herd of origin. The imported cattle were traced to four beef-breeding herds; check testing identified that infected cattle were present in three of these herds all in Scotland. Later in the same year another heifer imported from Ireland was found to be infected following post-import check testing, the herd of origin in the Republic of Ireland was found to be infected.
7. In 2004 an infected beef-breeding herd was identified in Cornwall following abortion investigation. The origin of this case was never identified; but genetic typing of the isolate suggested that the case is likely to have been indirectly linked to cattle from an infected region.
History of Surveillance in Great Britain
8. Until now, GB has undertaken continuous surveillance of the national dairy and beef herds to monitor for brucellosis. This surveillance programme was introduced in the 1980s in accordance with European Commission Directive 64/432, which governs intra-Community trade in cattle and pigs, to support GB’s case for recognition by the European Commission as Officially Brucellosis Free (OBF). As a condition of the Directive, GB was required to maintain a surveillance programme for 5 years after achieving officially disease-free status. Since this period has elapsed, GB is entitled to use discretion in its application of a national brucellosis surveillance strategy with the option to cease all routine testing of indigenous cattle.
9. The basis of the current surveillance programme was established at a time when brucellosis had just been eradicated from GB so the programme was necessary, not only to satisfy EU requirements for establishing disease free status but also to ensure that any remaining pockets of disease would be picked up in order to prevent the serious economic losses and human disease risk which existed when brucellosis was endemic. In 1981 the annual blood testing of dairy herds was replaced by monthly bulk milk testing and in 1985 the annual blood testing of beef breeding herds was reduced to testing once every two years.
10. With the passage of time we can now be sure that the disease is no longer present in the indigenous national herd; but that there remains an ongoing threat of brucellosis re-entering GB through imported stock. Many countries from which we import cattle are now brucellosis free, but we remain at risk of an incursion of brucellosis from both Republic of Ireland and Northern Ireland.
11. Our current brucellosis surveillance includes:
- targeted surveillance of cattle imported from non-OBF regions; and
- routine surveillance of indigenous cattle by investigating cattle abortions and testing of milk or blood samples.
Targetted Surveillance of Imported Cattle
12. In accordance with EU rules imported cattle entering GB from non-OBF regions require pre-import blood testing and veterinary certification and immediate post-import testing is carried out under the Import of Animals and Animal Products Regulations. In practice nearly all the imported cattle from non-OBF regions come from Ireland and the majority of these are beef breeding cattle. Under our domestic controls imported breeding cattle imported from Ireland are subject to an additional 60 day post-import test (which is taken at the same time as a 60 day post-import TB test) and all herds with a regular intake of cattle from Ireland have an annual brucellosis blood test.
13. Following a risk assessment carried out by the Veterinary Laboratories Agency (VLA) in Weybridge in 2001; we considered that GB was at a higher risk of a brucellosis incursion because of post-FMD re-stocking imports, so we enhanced the post import checks on cattle imported from non-OBF regions of the EU to include post-calving checks of imported breeding cattle. This reflected the knowledge that the disease cannot always be detected in infected cattle until after the first calving following exposure to infection.
14. In addition all female cattle imported from a non-OBF region are subject to a post-calving test following their first calving in GB. This is facilitated by the use of the British Cattle Movement System (BCMS) to notify DVMs each week of imported cattle which have calved for the first time in Great Britain, or imported female cattle which require breeding history checks. Breeding history checks are required for imported heifers which reach 36 months of age without a recorded calving or adult females which do not have a recorded calving within 12 months of import.
Routine Surveillance of Indigenous Cattle
15. Until now, the national brucellosis surveillance programme in GB comprised monthly bulk milk testing of all dairy herds and blood testing of beef breeding herds every two years.
16. In addition, reporting of all abortions and premature calvings is
required under the Brucellosis
(England) Order 2000 
(67 KB) and equivalent legislation in Scotland and Wales. Abortion investigations
in dairy herds are carried out on the basis of risk assessment (for example
cases of multiple abortions occurring within thirty days or abortions
in imported cattle). In beef breeding herds and in any other herds not
subject to monthly bulk testing, all reported abortions are investigated.
17. During the year 2005 bulk milk testing was carried out on 16,862 dairy herds and herd blood testing was carried out on 30,485 beef-breeding herds (approximately 1 million blood samples from beef breeding cattle are collected and tested each year – there are nearly four times as many beef breeding herds as dairy herds). The number of abortion investigations carried out was 7,968.
Lessons Learnt and Risk Assessment
18. GB has had OBF status for 20 years, and has maintained a surveillance program that is more stringent that required under Directive 64/432. We have continued to revise our risk assessments and have enhanced post-import check testing. We have had small-scale re-introductions of infection that have been effectively identified at an early stage and controlled. Against this background, we have reviewed our current surveillance mechanisms to ensure that they remain effective and deliver value for money to the taxpayer.
19. It is clear that the following components of our brucellosis surveillance continue to be vital and have proved effective in identifying suspected and confirmed brucellosis incursions:
- Import controls and certification;
- Exporting country alerts of brucellosis breakdowns in exporting herds;
- Post-import check testing;
- Post-calving check testing;
- Abortion reporting and investigations.
20. A detailed risk analysis prepared by the VLA Weybridge in 2001 attempted
to estimate the probability of brucellosis spreading from the herd of
import should an infected animal be imported without detection through
the post-import checks. The assessment uses a notional estimate of time
for a fixed number of herds to become infected before infection is detected
by routine surveillance, the longer the time the more effective the surveillance.
Table 1 below sets out estimated times for the dairy herd.
Table 1: Dairy herds
Time to infect 5 herds |
||
| Testing Strategy | With abortion notification | Without abortion notification |
| All herds every month (current regime) | 30 years + | 30 years + |
| All herds twice a year | 31 months | 6.9 months |
50% herds twice a year |
26.1 months | 3.6 months |
| 20% herds twice a year | 25.9 months | 2.9 months |
| No milk testing | 25 months | 2.3 months |
21. The risk analysis shows that if bulk milk testing is not carried out
every month, abortion reporting is vital to minimise risks of disease
spread. Monthly bulk milk testing has played a lesser role, but did help
identify the 1993 outbreak in Anglesey. It offers extremely good value
for money (costing approximately £250,000 per year across GB), and
as tests are carried out monthly, they provide regular and quick confirmation
of disease freedom in the dairy herd. Results are also be used in assessing
risks for abortion investigations in dairy herds. We have concluded that
this component of brucellosis surveillance should remain in place.
22. The same risk analysis made similar notional estimates of time for a fixed number of beef herds to become infected before infection is detected by routine surveillance. Table 2 below sets out estimated times for the beef herd.
Table 2: Beef herds
Time to infect 5 herds |
||
| Testing Strategy | With abortion notification | Without abortion notification |
| 50% herds once a year (current regime) | 10.7 months | 6.1 months |
| 25% herds once a year | 9.8 months | 5.5 months |
| 20% herds once a year | 9.4 months | 4.9 months |
| No blood testing | 8.9 months | 4.2 months |
23. This risk analysis shows that the frequency of blood testing can reduce
the time to infect 5 herds, but not very significantly. It shows that
abortion reporting is far more important in increasing the time to spread
the disease. Routine blood testing only appears to provide evidence that
the herd remains free of the disease, but considerable resources are required
to deliver this confirmation. We have concluded that the current routine
2-yearly blood testing no longer provides a cost-effective means of retaining
freedom from this disease. The reasons are as follows:
- Experience suggests that blood tests have never identified a positive animal in GB – most cases of brucellosis are identified as a result of abortion reporting.
- If we identified a positive beef animal through the current two yearly blood testing cycle we may have spotted it too late to implement swift and effective control measures to contain it.
- Blood testing is not required under existing EU legislation, as we are now allowed discretion after a long period of freedom from the disease.
- It is also worth noting that we understand that other EU Member States have started to relax their testing regimes. It appears that Denmark and Netherlands no longer carry out routine serology or routine bulk milk testing for brucellosis. We understand that Sweden and Finland have abandoned routine serology but continue bulk milk testing of dairy herds.
24. New disease threats, such as avian influenza and bluetongue, need to be addressed and require funding. We therefore need to re-prioritise our expenditure so that existing budget allocations can be used effectively to address these new threats. It is difficult to justify the current level of expenditure for routine brucellosis sampling and testing if the risks can be effectively managed through the other more cost-effective mechanisms. There were two possible options:
- Decrease the frequency of sampling and testing beef herds to a 4-yearly cycle,
- Stop blood testing altogether (but maintain other surveillance risk mitigation measures).
25. From a risk assessment perspective there is relatively little difference in overall risk between adopting a 4 yearly-cycle (9.8 months to infect 5 herds) of testing and stopping it altogether (8.9 months to infect 5 herds). We therefore decided to scale down this blood testing to stop completely in a short period of time, certainly within April 2007.
Risk Mitigation
26. We need to identify and mitigate any residual risks arising from
stopping routine blood testing in the beef herd. Although we gain little
from the testing itself, the process of identifying herds at regular intervals
for testing helps maintain a level of awareness of brucellosis in the
minds of beef farmers. Continued freedom from brucellosis depends on all
farmers being aware of the risks and reporting abortions without delay
so that they can be investigated. There is a risk that the farmers would
gradually forget about the risks of brucellosis, and that abortion reporting
could gradually stop, with a risk that an outbreak could go undetected
at the early stages.
27. We need to mitigate against this risk by maintaining a level of awareness
in the beef industry about the risks of brucellosis and the legal requirement
to report abortions to DVMs. Ideally, the message would be tied in with
biosecurity messages as well, which would bring broader benefits. We will
seek opportunities to work with the veterinary profession and the beef
industry to achieve this.
28. In addition, we will ensure that the SVS and VLA are resourced to respond to all abortion notifications, and that investigations and testing are done promptly and properly. Thus, some of the savings we make by stopping the routine sampling of beef herds would need to be re-allocated to ensure the SVS and VLA are able to deliver this measure effectively.
Enzootic Bovine Leucosis (EBL) and Warble Fly
29. Stopping blood sampling from beef herds for brucellosis testing will have implications for surveillance for enzootic bovine leucosis (EBL) and warble fly. Some of the samples collected for brucellosis surveillance under the current regime are also tested to demonstrate freedom from EBL and warble fly, which like brucellosis, have been eradicated from GB (see costings for these activities in included in Annex A to this paper). We need to take into account that:
- currently the main sources of cattle imported into GB are Ireland (the Republic of Ireland and Northern Ireland), the Channel Islands, Denmark and some other Northern European countries. The information that we have indicates that these countries are free from EBL and warble fly.
- under Council Directive 64/432 we must continue surveillance at abattoirs for EBL. Currently, the Meat Hygiene Service submits about 60 suspect tumours for examination per year. All have been negative.
- we are seeking clarification from the European Commission regarding the requirements of Council Directive 64/432 in terms of serological testing if we have EBL disease freedom. However, we will be maintaining bulk milk serological testing, and believe we are in compliance with the requirements of this Directive.
- imported cattle are currently treated with either a pour-on or injectable insecticidal product against warble fly, required under the Animals (Post-Import Control) Order 1995. So even if the cattle are imported from a warble fly-free country, we are implementing an extra line of defence under our domestic legislation.
Wider Implications for Disease Outbreak Diagnostics
30. A wider implication of stopping blood testing is that the VLA serological diagnostics facilities, which are currently used for testing for these three diseases, would need to be used in a different way. These facilities are vital in our response to disease threats and outbreaks, and thus will continue to be maintained in a state of readiness in a cost-effective way. Consideration is currently being given to how this will be achieved.
Impact on the Veterinary Profession
31. One inevitable consequence of this change will be that the incomes of some veterinary practices that carry out brucellosis blood sampling will be reduced. However, Government clearly has a duty to ensure that its surveillance programme remains effective and delivers the best possible value for money to the taxpayer.
Summary
32. We have reviewed the routine disease surveillance arrangements we have in place as part of an on-going review of existing policy. Defra, SEERAD and the Welsh Assembly Government have concluded that there is little justification for continuing the existing routine beef herd surveillance. This is for the following reasons:
- We are no longer required to maintain this testing under EU rules;
- The testing adds little in our ability to detect brucellosis outbreaks. The other mechanisms in place will be maintained and enhanced where appropriate;
- Overall, this testing does not represent a cost effective mechanism for demonstrating freedom from this disease, or for detecting disease;
- This allows us to reprioritise activities against the allocated budgets for the State Veterinary Service and Veterinary Laboratories Agency.
33. Defra and the Devolved Administrations will therefore implement a complete withdrawal from routine blood testing of the GB beef herd starting from April this year. We will maintain the other risk management measures. It is recognised that it will be important to maintain a high level of awareness about brucellosis in the beef sector to ensure that abortions are reported, and to ensure that resources are available for prompt investigations. Defra and the Devolved Administrations will work with both the veterinary profession and the beef industry to enhance the level of awareness.
Surveillance, Zoonoses and Emerging Issues Division
Defra
March 2007
Annex A: Summary of Changes to Surveillance
Defra and the Devolved Administrations will revise the brucellosis,
EBL and warble fly surveillance policy as follows:
For brucellosis:
- Maintain, and where possible enhance abortion reporting and investigations (this remains the most effective means of identifying a disease incursion, as well as being a continuing legal requirement under the relevant EU legislation);
- Maintain existing import, post-import and post-calving check testing (including annual blood testing of beef herds that routinely import cattle form Ireland);
- Maintain links with exporting countries so that we are alerted of brucellosis breakdowns in exporting herds;
- Maintain monthly bulk milk testing, on the basis that it is very good value for money, and helps refine a risk-based approach to abortion investigations in dairy herds;
- Stop the two-yearly blood testing of the beef herd on the basis that we gain little benefit in terms of brucellosis detection, for the cost involved. The increase in risk of cutting this component of our surveillance is relatively low if we retain the monthly bulk milk testing and abortion reporting;
- Replace the routine blood testing with a mechanism to enhance awareness of the disease in the beef-sector to encourage prompt abortion reporting.
For EBL:
- Maintain examinations of suspect tumours through existing abattoir surveillance;
- Maintain bulk milk sampling and testing for EBL in a proportion of the GB dairy herd;
- Stop blood serological tests for EBL by VLA.
For warble fly:
- Maintain routine treatment of imported cattle with appropriate products for precautionary warble fly control;
- Stop blood serological tests for Warble Fly by VLA.
Page last modified:
March 22, 2007