Farm-based control measures for caseous lymphadenitis in small ruminants: Offering a choice to the producer

Final Report for ONE12-164

Project Type: Partnership
Funds awarded in 2012: $14,969.00
Projected End Date: 12/31/2013
Region: Northeast
State: Maine
Project Leader:
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Project Information

Summary:

Knowing whether your sheep are free of chronic disease is an important management and marketing tool for sheep producers. Caseous lymphadenitis (CL) is a disease that can cause abscesses in sheep that are responsible for carcass downgrades, and poor health in general. CL can’t be cured, and once in a flock, tends to spread. Therefore, farmers should avoid this problem. This project tested sheep on Maine farms, identifying those free of CL, counseled the producers on quarantine and biosecurity to avoid CL, and supported the development of the accepted standard diagnostic test for CL, a serum hemagglutinin inhibition (SHI) test, in Maine. A “Decision Tree” was devised to help producers and vets handle CL questions.

Our serosurvey of 17 Maine sheep farms revealed that 43% of farms tested had at least one CL-positive animal, and that, of 705 sheep tested at least once, 22% were CL positive. During farm visits, factors for possible introduction, or spread of CL were identified and possible solutions were discussed. Farm visits were important to building relationships for small ruminant veterinarians, although the cost for producers of having private vets visit the farm was considered prohibitive, and conversely, veterinarians did not feel that the stipend provided in the grant was enough to cover their time in the project. Therefore, most data collection was completed by the PI. Recommendations for all producers included keeping a “closed” flock, CL testing of the whole flock at intervals, and using effective quarantine and testing of new animals in order to remain CL-free. CL vaccination is available, but not completely protective, and also interferes with current testing methods.

In this project, we found that producers did not always know if animals had been vaccinated, or whether booster vaccines had been given. Thus, vaccines were not being utilized properly, and on some farms, there continued to be abscesses in the presence of vaccinations. CL-free farms should consider maintaining this status as a positive marketing strategy, and buyers of breeding stock should demand evidence of CL-free status. While biosecurity and periodic testing remains the best strategy to keep sheep flocks free of CL, we found that some farmers with CL-positive animals did not wish to cull due to investments in the genetics or other aspects of individual animals. In these cases, we suggested separating animals by CL status and using periodic testing to evaluate new positives, as well as considering vaccination for CL, with the hope of reducing abscess frequency. With the adoption of CL testing as a common practice in Maine, awareness of this contagious disease may help reduce the frequency of “buying and selling” infectious small ruminant disease.

Final Advice:
Know the CL status of your flock: retest as needed
• Maintain closed flock/herd with high biosecurity
– Notify visitors about biosecurity
– Inform shearers about biosecurity
– New or returning animals:
• Don’t immediately mix with “home” flock
– “nose to nose H quaranIne”
• CL test immediately at entry and prior to release from
quarantine (2 mo. later)
– If positive, cull or sequester positives
» Retest exposed animals at 2 months: cull if +
» Keep quarantined until all negative for CL at 2
consecutive tests 2 months apart

Simple decision tree:
Introducing new animal?> does source flock have CL?
       Yes> Don’t buy or quarantine and test at entry and 2 months
        No>Quarantine and test at entry and 2 months

CL positive at end of quarantine?
       Yes> Slaughter or Sequester (meaning no shared spaces, feed, water, equipment and AI only if a ram)
         No> Add to group. Keep CL negative using good biosecurity.

Introduction:

Sustainable farming is dependent on healthy animals. Chronic, incurable diseases can “sneak up” on producers, causing serious economic loss. Caseous lymphadenitis (CL) is a highly contagious disease affecting small ruminants, such as sheep and goats. The causative bacterium (Corynebacterium pseudotuberculosis) travels throughout the host, and eventually may cause abscesses in the skin, lymph nodes or internal organs. It can be transmitted from animal to animal, and also by shearing equipment or other environmental factors, entering the host primarily through skin or mucosal defects. Although experimental vaccines may be effective, it is still considered optimal to detect the disease before it gets onto a farm, and to maintain a disease-free herd by use of biosecurity, effective disinfection practices, and removing affected animals prior to spread of the disease. Because testing methods are not perfect, and because available vaccines may be ineffective, may be used improperly, may cause local reactions, and interfere with testing, farmers have difficult choices once CL is found in their flock.

In 2014, interest in small scale farming in New England is increasing; and small ruminants are an important part of that sector, with over $3.6 million in sales of sheep and goat products in Maine alone during 2012 (http://www.agcensus.usda.gov/). Maine is also home to over 2000 registered alpacas (USDA 2007, AOBA 2008). Caseous lymphadenitis (CL) is a highly contagious disease affecting all of them. External abscesses decrease the value of the hides, and may even render the whole carcass unacceptable at slaughter. A more dire effect is the development of internal abscesses in the lung and abdominal areas. These may rupture, releasing proteins and toxins that are likely to prove fatal. Due to the unapparent nature of the disease early in the infection process, it can “sneak up” on a producer.

CL can be transmitted easily by equipment/bedding and via contact when small skin abrasions are present, such as those caused by fencing, handling equipment or shearing. Once infected, the sheep may harbor the bacterium for prolonged periods. As well, if abscesses occur and then rupture, the exudate is a potent source of infection for other animals1.

Vaccinating for CL prior to, or in the face of active infection may be a good choice for a
farm. However, currently farmers do not have a choice of effective vaccines against CL. There is a licensed vaccine in the US, but it may not be effective, may cause tissue
reactions, may not be used as directed, and will definitely interfere with the most commonly used test for the disease. Experimental vaccines have been used effectively to reduce but not eliminate CL5, and newer vaccines have been developed in the last 10 years for use in Australia, New Zealand and the UK. These may well prove to be more efficacious than older vaccines. If newer vaccines are to be utilized in the United States, authorization for their use must be obtained. This process is likely to take time, and in the meantime, producers need support in detecting and eliminating this disease from their farms.

The ability of producers to detect and prevent CL is dependent on testing, education, and on developing their own farm biosecurity programs. Preliminary work in 2009 by Richard Brzozowski suggested that approximately 6% of Maine flocks had problems with CL in the past, and that although many were aware of biosecurity, few had a plan for their farm. During 2011, several sheep producers reported a high incidence of CL in their flocks, and due to the slow onset of this disease, the overall prevalence in Maine was predicted to be increasing. This study increased general awareness of CL and supported the development of a more economically available, rapid turnaround time test for CL in Maine, which may assist regional producers to detect and avoid this preventable disease.

Project Objectives:

1. Recognizing CL:
SARE support was utilized to support travel to collaborating farms, and for initial blood sample testing at Washington State University, using their validated SHI test for CL. We sent blood samples in groups of 250 per shipment to conserve resources and receive a reduced price per test from WSU. This extended our ability to test more samples. After the summer of 2013, our lab was converted to meet BSL2 and hazard specifications according to University of Maine standards, and we began using the SHI test in our lab, running duplicates of the samples previously tested by WSU for evaluation of our methods, along with positive and negative control sera. By the spring of 2014, we began testing goat sera as well.

2. Disseminating information:
We used Cooperative Extension and the UMAHL to disseminate information, and spoke at local, regional and national conferences on the topic of CL and our project (10 seminars given in 2013-14; Maine large animal veterinarians (2013 and ’14), Maine Sheep Breeders Assoc., 2012 and ’14), Maine Boer goat Assoc. 2014, Maine Extension Sheep and Goat Seminar 2014, Maine Extension Agents 2013, National Extension (Galaxy Conf., 2013), American Dairy Goat Association 2014, Missouri Livestock Conference 2014). Information was posted on the Maine Extension Sheep and Goat page, and links with other small ruminant pages are being created.

3. Choices in managing CL:
We succeeded in following several farms, but it was not possible to enforce complete compliance with animal management plans to isolate CL+ from CL- animals on farms. When positive animals were a rarity, and culling was done very soon after learning of a positive, we found that farmers benefitted from testing and embraced the idea of being CL-negative. However, when farms had a large number of CL+ animals, it was generally economically impossible to cull all the positives immediately. On these farms there seemed to be several alternatives. In one case, the farmer considered culling but rejected the option due to the high quality of the fiber obtained from the affected ewes, and their breeding potential for the farm. This farmer opted to separate young animals in an attempt to develop a CL-free flock, and also opted to vaccinate the CL+ animals to reduce the incidence of CL abscesses. On this farm, a large wooden feeder was central to several pens of animals, and a probable focus for spread of CL by ruptured abscesses and splintering wood. Eradication of CL from this farm had not occurred by the third visit to the farm, after approximately 6 months of effort (57% CL+ reduced to 21% CL+). A similar situation was found in another farm, where a large number of sheep were CL+, and full separation of the flocks was thought to be impossible. However, the farmer is planning a new barn, and will design it to allow creation of an effective quarantine area, and management of a CL- flock. In several farms, culling was embraced as an immediate strategy, along with quarantine and testing of new animals, and CL spread in the flock was averted.

4. Decision tree for CL:
We chose not to post each farm’s outcomes, due to the large number of farms that were followed, but instead created a generic “decision tree” model for dealing with CL.
This simplified plan has been discussed at the 10 public seminars regarding this project, and is included in the PDF material accompanying this report.

5. Farmer and veterinary interactions: 17 sheep farms (original goal was 4) and 9 goat farms have participated. Each agreed to allow blood testing of animals twice, to keep adequate records to allow animal identification, location, treatments and culling, and to allow investigators access to those records. One farm was unable to allow the second blood test, after several requests, due to lambing schedules. Two additional farms were not available for testing when offered. Vet stipends were paid to collaborators who visited farms to collect blood for the project, although veterinarians suggested after the fact that the stipend paid ($200 for each day visiting farms) was inadequate to cover their normal fees.

6. Biosecurity surveys and interviews:
A survey was developed and posted; discussions about biosecurity were held with all farms visited. One undergraduate capstone thesis was given on the topic of comparing CL- versus CL+ farm biosecurity (E. Kershner, 2012). A biosecurity guide for shearers was reviewed and posted (http://umaine.edu/sheep/biosecurity/safer-shearing/).

Cooperators

Click linked name(s) to expand
  • Dr. Meghan Flanagan
  • Becky Myers-Law

Research

Materials and methods:

Serologic testing: Initial serum testing was done by agreement with Washington State University, and duplicate samples were stored at the University of Maine. A subset of these were later tested using the same method (serum hemagglutinin inhibition) at the PI’s lab. Validation steps are in progress. All test results have been reported to the collaborating farmers and their vets.

Farm visits and communications: Maine sheep farms in the study were identified by contact with regional small-ruminant veterinarians, and in some cases, self-identified. Farmers signed a consent form, which was prepared with consultation from the University of Maine counsel. For all farms visited, discussion of either prevention or of CL management was provided by a veterinary practitioner. All farm visits and blood collection for testing was done by either the PI (Dr. Lichtenwalner) or collaborating veterinarians (Dr. Becky Myers-Law, Dr. Megan Flanagan, Dr. Don McLean, or Dr. Tammy Doughty). At each visit, the farmer cooperated with handling and identifying sheep, and also discussed biosecurity measures to avoid or contain CL on their farm. On several farms, CL abscess treatment was demonstrated and discussed. These visits also allowed discussion of other sheep health management issues, and helped to forge professional relationships with the producers. Practitioners received a stipend for visiting the farm, and for providing followup consultation with the farmer regarding the results of testing.

Research results and discussion:

Seventeen Maine sheep farms and over 700 sheep were tested for CL; sheep on all but 3 farms were tested twice; on 3 farms sheep were tested 3 times. Of 17 sheep farms evaluated, 8 (47%) were positive for CL on at least one visit. Six remained seronegative on all repeated visits. The farms fell into 3 patterns: tolerant of some positives, but making an attempt to avoid new cases; positive and not willing to do anything about it (overwhelmed); and either completely or almost negative (and determined to stay that way). In one case, previous vaccination may have occurred (unclear history), but seroconversions (low titers) appeared to be present nonetheless.

The results suggested that for intensively managed flocks, where animals are used for fiber, producers may be aware of CL as a major issue, but are not willing to make the culling decisions required to contain it. In these flocks, vaccination may be useful, if excellent records are kept, frequent boosters are given, and vaccination status is clearly communicated to buyers. Vaccine options in the US are limited at this time to Case Bac (Colorado Serum Company). Other difficulties in these flocks are lack of adequate quarantine facilities and having feeders/fencing that cannot be adequately disinfected, should abscesses occur. Given the persistence of CL in the environment and the expense of replacing infrastructure (wooden feeders/fences) it seems unlikely that complete eradication is possible without ongoing culling in these flocks.

In a flock producing a combination of meat lambs and some specialized breeding stock, sheep had been obtained from multiple sites, and were moved into a number of configurations in the year to maximize access to pasture. Thus, mixing of animals was unavoidable in this flock, and follow-up testing was not possible. High seroprevalence was found at the initial (only) blood test. The history was unclear, and may have included vaccination (without current boosters). However, low to intermediate titers in a number of animals, as well as negative titers, suggested that natural exposure to the CL organism was present in this flock. Selling animals for meat would be appropriate, but selling animals for fiber or for breeding from this flock would be inappropriate without disclosure of the CL status.

Finding either negative farms or farms with very low numbers of positives was encouraging. On two farms, sheep had recently been returned to the home flock after flock sales that did not work out. On one farm, after reintroduction of animals that were offsite at initial testing, a third visit was made to test all sheep. All sheep were still seronegative. On another large farm, a “commercial” flock had been sold, moved offsite, but then returned to the farm after failure of the sale. In this case, the “home” animals, which were breeding/show stock, were initially all seronegative. The returned flock had one seropositive, which was discovered after the flock had already been returned to the farm. On the second test of the “home” flock, one animal had a low titer. Culling and quarantine were advised, and tougher biosecurity for show animals suggested. Both farms produce breeding stock, and much discussion about the critical role of biosecurity ensued. The farmers were encouraged to use CL seronegative status as a selling point for breeding stock.

Another small fiber flock of 7 animals had 1 with a low titer at the first test; 4 were positive at the second test. In this flock, culling would be impractical, but vaccination and good biosecurity was advised. Even in very small flocks, biosecurity is the best defense against many livestock diseases and parasites.

The IACUC approval, agreement forms and schedules were developed during May to
June 2012. Visits to farms occurred during June to December 2012, with additional visits conducted during spring, summer and fall 2013 and spring and summer 2014. Lab tests were conducted from June 2012 to June 2013. Development of the SHI test took place from June to November 2013, and validation during October and November, 2013.

Final Advice:
Know the CL status of your flock: retest as needed
• Maintain closed flock/herd with high biosecurity
– Notify visitors about biosecurity
– Inform shearers about biosecurity
– New or returning animals:
• Don’t immediately mix with “home” flock
– “nose to nose H quaranIne”
• CL test immediately at entry and prior to release from
quarantine (2 mo. later)
– If positive, cull or sequester positives
» Retest exposed animals at 2 months: cull if +
» Keep quarantined until all negative for CL at 2
consecutive tests 2 months apart

Simple decision tree:
Introducing new animal?> does source flock have CL?
       Yes> Don't buy or quarantine and test at entry and 2 months
        No>Quarantine and test at entry and 2 months

CL positive at end of quarantine?
       Yes> Slaughter or Sequester (meaning no shared spaces, feed, water, equipment and AI only if a ram)
         No> Add to group. Keep CL negative using good biosecurity.

Research conclusions:

With small farming on the rise, and the median age of new farmers falling in Maine, having a chronic disease affect small ruminants could be devastating to the new farmer. The overall effects of excellent biosecurity, and of being careful to buy and sell only healthy animals, will be to improve profitability of, and satisfaction with, livestock farming.

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary:

Education/outreach description:

A shearing biosecurity fact sheet was provided to participants and posted on the Cooperative Extension site. Presentations have been given to local, regional and national audiences, including producers, extension workers and veterinarians: Maine Sheep Breeders Assoc., 2012 and ’14, Maine Boer Goat Assoc. 2014, Maine Extension Sheep and Goat Seminar 2014, Maine Extension Agents 2013, National Extension (Galaxy Conf., 2013), American Dairy Goat Association 2014, and the Missouri Livestock Conference 2014. Information was posted on the Maine Extension Sheep and Goat page, and links with other small ruminant pages are being created; a summary PDF has been included.

Project Outcomes

Project outcomes:

Economic analysis: Lamb prices currently are approximately $200 per hundredweight, so the cost of culling live animals may range from $100 to $700 (American Sheep Industry, 2013). In northern New England’s approximately 1,800 small ruminant farms, with approximately 32,000 sheep and 17,000 goats, the cost of culling could significantly reduce profits (2010 NASS statistics). At the minimum, testing was provided to producers at no cost, which conferred an average benefit to each farm of $1,232.50 and a total benefit to all farms in the study of $18,487.50. If future culling of all flocks and herds in New England were reduced by only 10% due to this study, the benefit to New England’s sheep farmers could be $1.5 million.

Farmer Adoption

Our sheep producers are proud of their flocks and, once aware of the threat of CL, wanted to eliminate it.  We found some "hotspots" of CL that may have been actively spreading the disease through sales of broodstock throughout the region, and this project raised awareness about that practice.  Although owners with valuable broodstock are not likely to cull intensively, those with negative flocks are much more aware of the increased value conferred by CL negative flock status.

Assessment of Project Approach and Areas of Further Study:

Areas needing additional study

Improved testing methods and awareness of CL at the farmer level is a continuing goal.
Our laboratory is expanding use of our testing methods to goats and camelids, and also looking for alternative testing methods. We support development of an effective vaccine that will not interfere with diagnostic methods. Evaluation of new vaccines, and efforts to allow importation of effective vaccines into the United States may be an appropriate next step.

Information Products

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.