SAMPLE POOLING SAVES MONEY2021-03-26 16:58:46
Surveillance of cattle herds for MAP infections can be costly if individual cows are tested by fecal PCR. Some countries, such as the U.S., have adopted methods allowing pooling of fecal samples from 5 cattle before doing culture of PCR testing. If the pooled fecal sample tests PCR-negative, then all cattle contributing to that pooled sample are considered PCR-negative.
Australian researchers published a simulation modelling study indicating that the pool size can be increased to 10. Their study was published in the journal Preventive Veterinary Medicine.
Johne’s disease is a chronic intestinal disease affecting livestock. It leads to the shedding of Mycobacterium avium subspecies paratuberculosis (MAP) in the faeces, wasting and eventually death, with animal welfare, economic, and trade implications. The Johne’s Beef Assurance Scheme, used in Australia to determine the risk of Johne’s disease on beef properties and facilitate trade, is based on testing a subset of the herd with pooled faecal quantitative PCR. This study aimed to model the herd-sensitivity of pooled faecal testing under different Australian farming scenarios. Animals from simulated herds were randomly sampled and allocated into their respective pools. Each tested pool was provided a test outcome, with herd-sensitivity estimated as the probability of detecting a truly infected herd. The models simulated the test performance for the ‘Sample’ and ‘Check’ tests used in the assurance schemes (recommended sample sizes of 300 and 50, respectively) for a range of herd sizes, infection prevalence and MAP faecal shedding levels for the pool sizes of 5, 10, 15 and 20. Sensitivity and specificity input values of each pool size were obtained from a previous laboratory investigation. The herd-sensitivity estimate increased with herd size and infection prevalence levels, regardless of the pool size. Higher herd-sensitivity was also achieved for testing scenarios involving larger sample sizes. A pool size of 10 achieved similar herd-sensitivity to that of the current pool size for the majority of the Sample test and Check test scenarios. This was particularly evident when pool-specificity was assumed to be perfect. The overall herd-sensitivity of the Check test was very low for all infection prevalence levels and pool sizes, but it more than doubled, when the sample size increased from 50 to 100 animals (11% versus 26% for a herd size of 500 cattle with a 2% infection prevalence). The results show that the majority of beef producers participating in the assurance scheme can benefit from using a larger pool size for the pooled faecal quantitative PCR testing of their herd, in comparison to the pool size currently used.
Kalis et al. (2000) first demonstrated that fecal sample pooling (5/pool) was effective at detecting MAP-infected dairy herds. Importantly, he showed that samples should be pooled based on animal age. He called this “strategic pooling”. The importance of this cannot be stressed enough. Animals born around the same time experience similar risks of acquiring a MAP infection. Therefore age-based (strategic) pooling helps insure that the least number of sample pools test positive and thus the fewest number of individual cattle require follow-up PCR testing.
Wells et al. (2002) compared dairy cattle fecal pools of 5 and 10 and concluded that pools of 5 were slightly more sensitive than pools of 10 when using fecal culture as the diagnostic test. This was a small study that used feces from only 10 cows to construct various fecal combinations in pools.
Van Schaik et al. (2007) collected 50 fecal samples from each of 12 Chilean dairy herds and compared pools of 5 and 10 samples finding that pools of 10 were as good or better than pools of 5 at detecting MAP-infected dairy herds.
It is challenging for veterinary diagnostic laboratories to change protocols but perhaps the time has come to consider using age-based pooling of 10 fecal samples in cattle herds that have a very low or zero rate of MAP-infections. Unless a herd is trying to meet US. or other Johne's disease program standards for herd classification, there is no mandate to test fecal samples in pools of 5. Standards may differ in other countries.
Below are cost calculations for a herd of 100 cattle tested by fecal PCR using pools of 5 or 10 cattle/pool. Only laboratory fees are calculated, and prices are based on the rates posted on the Wisconsin Veterinary Diagnostic Laboratory (WVDL) website 26-MAR-2021 (individual feal PCR @ $30.89 and pooled PCR @ $35.02). It does not include the $10 accession fee, veterinary costs, or sample shipping. Costs are rounded to the nearest U.S. dollar. Note: The WVDL has no extra cost for Johne’s disease tests for samples originating from states or than Wisconsin.
For comparison, the cost of testing 100 cattle individually by fecal PCR would be $3,502.
This table illustrates that:
- Sample pooling can save money. Even if 5 fecal pools test PCR-positive the total cost for testing a herd of 100 cows would be less than testing each cow individually by fecal PCR.
- Sample pooling is most advantageous for herds with a low MAP infection prevalence, i.e., few PCR-positive pools.
It is important to stress that to have the fewest number of positive pools, samples should be pooled based on animal age. This will tend to group fecal samples from MAP-infected cows into the same sample pool results in in fewer pools requiring individual fecal sample testing.
How does this compare to testing by ELISA (blood sample testing)?
The cost for testing a herd of 100 cows by ELISA would be $600 at current WVDL prices. In most instances, cows testing ELISA-positive would have to be retested by individual fecal PCR to confirm the diagnosis. This makes the per head cost of doing pooled fecal PCR equal to or less than that of testing by ELISA for low prevalence herds. This is especially true if pools of 10 are tested. Given that the fecal PCR is roughly 2 to 3 times more sensitive than the ELISA, herd owners get a better return on their investment in Johne’s disease diagnostics by using fecal PCR on pooled samples; no need to resample and test ELISA-positive cows by fecal PCR and greater confidence in that the PCR-negative cattle are truly not MAP-infected.
Not all laboratories offer pooled fecal PCR testing and prices vary considerably among veterinary diagnostic laboratories. Talk to your herd veterinarians and consult with testing laboratories before sending samples. This website provides a list of laboratories that are USDA-approved to perform pooled fecal testing: scroll down to the PDF file named “Johne’s Disease-pooling methods”.
What about sheep and goats?
Sample pooling studies have not been reported for goats, but cattle-based studies are a good guide. In Australia, fecal samples from 50 sheep are pooled before PCR testing.
WHY JD CONTROL FAILS2021-03-19 01:00:02
Swiss veterinarians followed Johne’s disease (JD) control programs in 7 beef cattle and 10 dairy herds over a 3-year period. They documented the degree to which owners adopted JD control recommendations and monitored the level of MAP infection in the herds primarily by fecal culture with some supplemental testing by ELISA and fecal PCR. This study was reported in the journal PLOS ONE and is Open Access.
Various measures have been advocated for the control of Johne’s disease (caused by Mycobacterium avium subsp. paratuberculosis, MAP) in different countries. Farmers’ compliance has been reported to be variable depending on disease prevalence and incentives to participate in control programs. After the prevalence of MAP shedding and risk factors for within-herd spread of MAP were assessed in 17 Swiss cattle herds (10 dairy and 7 beef), general and herd-specific recommendations were given to the farmers to reduce MAP transmission within the herd. Participation in the study and implementation of control measures were voluntary, no financial incentives were provided for the realization of control measures. After a 3-year period of monitored observation including biannual farm visits and discussion of the situation, the implementation of the recommended control measures and their effect on prevalence of MAP shedding were evaluated. Implementation of recommended general and farm-specific control measures was only partially realized. Neither the number of animals tested positive (before or during the study) nor the farmers’ knowledge about paratuberculosis were significantly associated with their compliance for the implementation of management changes. The apparent within-herd prevalence remained constant despite limited implementation of control measures, and no particular group of control measures was found to be associated with changes in prevalence. Farmers’ compliance for the implementation of control measures to reduce the impact of Johne’s disease in infected farms was very limited under Swiss farming conditions in the frame of voluntary participation in a research project. These results indicate that the losses associated with paratuberculosis in Swiss dairy and beef operations are not estimated to be high enough by the farmers to justify important efforts for control measures, and that incentives may be necessary to achieve efficient implementation of such measures.
CONCLUSIONS (from the publication)
The managers of infected Swiss dairy and beef herds were reluctant to implement control measures to minimize MAP spread in the frame of their voluntary participation in a research project conducted over a period of three years. Except for culling test-positive animals, implementation rates were low for most proposed measures, and some of those that were implemented at the beginning of the period of observation were discontinued in the course of the study. The farmers mostly implemented cheap and easy measures, while changes impacting farm structure or their routines more deeply, e.g. improving hygiene in the calving area or minimizing animal purchase, were rarely realized. The farmers did not observe relevant economic losses due to PTB in their herds and therefore did not expect an immediate reward for expenditures in time, efforts and money. These observations suggest that incentives for a consequent implementation of control measures should be included in future programs to increase the compliance of the managers of herds infected with PTB and thus improve the chances of successfully controlling the disease.
Despite many studies documenting the cost of Johne’s disease to both dairy and beef cattle operations, these costs are not readily apparent to producers. And, if these producers are expected to shoulder 100% of the cost of controlling Johne’s disease but perceive little financial benefit, programs will not likely succeed, as the Swiss study shows. When programs have broad industry support, and the meat and milk processors who buy raw products from producers pay a premium for products from herds that are successfully controlling Johne’s disease, control program costs are shared equitably, and programs are more likely to succeed. This is the basis of the most recent national programs underway in the UK and the Republic of Ireland. JD control program costs may be passed along to consumers in the form of slightly higher retail product prices, but consumers will benefit because JD control programs result in less MAP entering the food chain making the finished products safer to consume.
As a reminder:
- MAP is found in raw milk and meat.
- MAP survives pasteurization and is found in retail milk.
- MAP survives cooking unless the meat is cooked until it is “well-done”.
- MAP is routinely found in people with Crohn’s disease (a human disease resembling JD).
- People with Crohn’s disease clinically improve when treated with anti-MAP antibiotics; some have been fully cured.
MAP is likely a food-borne zoonotic pathogen affecting people worldwide. Just as for other zoonotic pathogens found in domestic animals, such as tuberculosis and brucellosis, control programs that benefit both animal and human health begin on the farm. This is fundamental to the One Health philosophy.
- Read more about MAP in food here.
- Read more about the zoonotic potential of MAP here or watch the video on this page.
JD IN BEEF CATTLE LECTURE2021-03-12 13:10:55
Beef cattle producers and their herd veterinarians commonly ask:
- What is the best test to help control JD in beef cattle?
- What should I do with cattle that test ELISA-positive
- How can I avoid buying MAP-infected cattle?
- Which test should I use to certify my herd is free of Johne’s disease?
- What are my first steps in controlling Johne’s disease?
- Should I use the ELISA for JD on blood samples of PCR on fecal samples?
- Will JD control improve my farm profitability - what's the evidence?
- How common are national JD control programs and how to they work?
These and many more questions are addressed in a new 60-minute lecture titled “Johne’s Disease in Beef Cattle” now available on the Johnes.org website. This lecture is based on a a recent continuing education program for veterinarians. You will also find on this same web page lectures titled Johne’s disease in dairy cattle, parts-1 and 2” “Johne’s Disease in Goats” and “MAP is a Zoonotic Pathogen”.
NEW ASSAY FINDS MORE MAP IN MILK2021-03-05 01:00:01
Antonio Foddai and colleagues have developed a novel assay for detection of viable MAP in milk. The assay uses bacteriophages (viruses that attack bacterial cells) attached to magnetic beads to capture MAP in milk samples and then detect the presence of MAP by PCR. While these phages bind to both living and MAP cells, they only then infect and lyse live MAP. Thus, this assay only detects live MAP, just as do conventional culture methods. This new assay has higher diagnostic sensitivity and specificity than the most commonly used assay on milk today, the milk ELISA.
The article, published in the Journal of Dairy Science, is not Open Access, but is available for the next 40 days.
Bulk tank milk samples from 392 Northern Ireland dairy farms and individual milk from animals (n = 293) on 4 of these farms were tested by a novel phagomagnetic separation (PhMS)-quantitative (q)PCR assay able to detect and quantify viable Mycobacterium avium ssp. paratuberculosis (MAP), to demonstrate its potential utility as a milk surveillance tool. Viable MAP were detected in 26.5% of the bulk tank milks, with MAP contamination levels ranging from 1 to 8,432 MAP/50 mL of milk; less than 2% of farms had MAP contamination levels >100 MAP/50 mL in their bulk tank milk. Follow-up PhMS-qPCR testing of milk from individual animals on 4 farms that had the highest numbers of MAP in their bulk tank milks indicated that 17 to 24% of animals in each herd were shedding viable MAP in their milk. Mean MAP numbers detected ranged between 6.7 and 42.1 MAP/50 mL of milk. No significant correlation was observed between the detection of viable MAP in bulk or individual milks by PhMS-qPCR and parallel milk ELISA results, or between PhMS-qPCR results and any other milk recording results (somatic cell count, total bacterial count, % butterfat, or % protein). Viable MAP was detected by IS900 qPCR in 52 (85.2%) Pozzato broth cultures of 61 PhMS-qPCR-positive individual milks after 12 wk of incubation, suggesting few PhMS-qPCR results were false positives. The mean sensitivities of the PhMS-qPCR assay and milk ELISA applied to individual milks were estimated by Bayesian latent class analysis to be 0.7096 and 0.2665, respectively, and mean specificities were similar (0.9626 and 0.9509). Our findings clearly demonstrate that the novel PhMS-qPCR assay could be a useful milk surveillance tool for dairy processors, or a milk monitoring tool for Johne's disease control or milk quality assurance programs.
Phage-based assays for MAP have been described previously. This is the first time, however, that the phage has been linked to a magnetic bead allowing retrieval and concentration of MAP using magnets. In addition to binding to MAP, the phage then infects and lyses the live MAP bacterial cell, releasing its DNA allowing detection by qPCR technology. My schematic of the process appears below.
The head of the phage is linked to a magnetic bead. The tail of the phage binds to live mycobacteria. A magnet then pulls all of the beads+phage+MAP out of the sample.
After collecting the beads on a magnet, the phage then infects and lysis the live mycobacterial cells releasing their DNA. A qPCR specific for MAP then detects the pathogen. The phage-bead-magnet combination makes the assay very sensitive and the qPCR part of the assay makes it very MAP-specific.
Phage amplification assays for detection of mycobacterial infections were recently reviewed in the journal Microorganisms. This excellent 28 page Open Access article with 97 references provides a deeper understanding of phage-based mycobacterial detection technology but does not address this new twist: the use of phages to both capture and lyse the mycobacteria.
Actiphage is a commercial test, based on phage technology, for diagnosis of bovine tuberculosis and Johne's disease. Dr. Cath Rees (University of Nottingham) will be presenting a talk “Use of Actiphage to improve our understanding of mycobacterial diseases” on the 23rd March at 2pm as part of a virtual virology conference. Registration for the event is free.
The Wisconsin Connection
Fun factoid: Dr. Tom Brock, University of Wisconsin-Madison Professor, discovered a bacterium he named Thermus aquaticus, which grows at temperatures over 70 degrees C (158 degrees Fahrenheit) . Parts of its metabolic machinery, including the enzyme Taq polymerase, needed to assemble strands of DNA, tolerates boiling. In 1989, Science named Taq polymerase its first “molecule of the year,” because it enabled polymerase chain reaction (PCR), an essential tool for molecular biologists. Today's #1 test for COVID also depends on PCR.
The world owes a big "thank you" to Dr. Tom Brock.
DETECTION OF MAP-INFECTED DAIRY HERDS2021-02-25 01:00:58
Vera Fichtelova and colleagues from the Veterinary Research Institute, Brno, Czech Republic published a study on the optimal method for detecting MAP-infected dairy herds using environmental fecal sampling. They found that fecal samples collected from the floor of the milking alleys (paths for cows to come into the milking area close to the entrance into the milking parlor holding pens) tested by qPCR (also known as real-time PCR) was a simple and effective method for detection of dairy herds with a significant MAP infection rate.
The objective of the present study was to evaluate the suitability of environmental sampling to screen Czech dairy herds to detect Mycobacterium avium ssp. paratuberculosis (MAP) and to find the most convenient location for the MAP detection in the lactating cow area. Environmental samples (ES, n = 72) from milking parlour holding pens (n = 19), milking alleyways (n = 19) and free-stall alleyways (n = 34) from 19 herds were simultaneously tested to detect MAP by a quantitative PCR (qPCR) and bacterial culture. Eight and thirteen samples from the milking parlour holding pens, twelve and eleven samples from the milking alleyways and eleven and eighteen samples from the free-stall alleyways were qPCR and culture positive, respectively. A 4.6 times higher probability of being culture positive than qPCR positive was detected for the assessable MAP detection results from the free-stall alleyways [P = 0.008 6, odds ratio (OR) = 4.572 8)] and no association was found between the results from the milking parlour holding pens (P = 0.191 4) and the milking alleyways (P > 0.999 9) and the diagnostic method used. The percentage of qPCR-positive samples in the tested locations was detected for the milking alleyways (63.2%), free-stall alleyways and milking parlour holding pens. The herd infectious status was in agreement with 16 (84.2%), 14 (73.7%) and 12 (63.2%) qPCR results from the milking alleyways, free-stall alleyways (32.4%) and milking parlour holding pens (42.1%), respectively. No statistically significant differences were detected for these results (P = 0.396 1). MAP was detected by the qPCR and bacterial culture in all three locations where the ES were collected. We suggest an environmental sampling followed by MAP detection by qPCR as an easy-to-perform time-saving protocol for MAP screening in Czech dairy herds. Although the milking alleyways seem to be the most convenient location for the environmental sampling, this assumption was not statistically supported.
The first step toward Johne’s disease control in commercial dairy herds (herds in the business of selling milk, not breeding animals) is to establish which herds have a significant MAP infection rate. Environmental fecal samples tested by qPCR provides a rapid, low-cost methods for testing the whole dairy herd.
The environmental fecal sample methods described in the U.S. Uniform Program Standards for the Voluntary Bovine Johne’s Disease Control Program are much more difficult to perform. Page 33 of that document states: “From each dairy farm, collect two composite environmental fecal samples tested by an MAPDT (MAP detection test meaning culture of PCR) from each of the following locations on the farm: manure concentration areas (cow housing alleyways or gutters), manure storage areas (lagoons, piles, pits, or manure spreader), and another manure concentration area (sick cow pens or other cow alleyways and travel-ways). A total of six samples should be collected for submission to the diagnostic laboratory.”
The Czech system may allow more herds to be tested at less cost and therefore may be preferable to the U.S. system. However, the critical question is whether the herd-level sensitivity is comparable between the U.S. method and the newly described Czech system and also the comparative utility of the two methods. A testing system that is too onerous and therefore not used is not useful.
COST OF JD TO THE DAIRY INDUSTRY2021-02-18 16:10:38
Philip Rasmussen from the Department of Ecosystem and Public Health, University of Calgary, Calgary, AB, Canada, and colleagues have published a study on the economic losses due to Johne’s disease in dairy cattle. Their Open Access article was published online in the Journal of Dairy Science January 14, 2021.
Johne's disease (JD), or paratuberculosis, is an infectious inflammatory disorder of the intestines primarily associated with domestic and wild ruminants including dairy cattle. The disease, caused by an infection with Mycobacterium avium subspecies paratuberculosis (MAP) bacteria, burdens both animals and producers through reduced milk production, premature culling, and reduced salvage values among MAP-infected animals. The economic losses associated with these burdens have been measured before, but not across a comprehensive selection of major dairy-producing regions within a single methodological framework. This study uses a Markov chain Monte Carlo approach to estimate the annual losses per cow within MAP-infected herds and the total regional losses due to JD by simulating the spread and economic impact of the disease with region-specific economic variables. It was estimated that approximately 1% of gross milk revenue, equivalent to US$33 per cow, is lost annually in MAP-infected dairy herds, with those losses primarily driven by reduced production and being higher in regions characterized by above-average farm-gate milk prices and production per cow. An estimated US$198 million is lost due to JD in dairy cattle in the United States annually, US$75 million in Germany, US$56 million in France, US$54 million in New Zealand, and between US$17 million and US$28 million in Canada, one of the smallest dairy-producing regions modeled.
This paper is informative, international in scope, and has an excellent list of references that backup the cost estimates used in this economic modelling exercise.
JD IN DAIRY CATTLE LECTURES2021-02-12 01:00:52
Dairy producers and their herd veterinarians commonly ask:
- What is the best test to help control JD in dairy cattle?
- What should I do with cattle that test ELISA-positive?
- How can I avoid buying MAP-infected cattle?
- Which test should I use to certify my herd is free of Johne’s disease?
- What are my first steps in controlling Johne’s disease?
- Should I use the ELISA for JD on blood (serum) or milk samples?
- Will JD control improve my farm profitability - what's the evidence?
- How common are national JD control programs and how to they work?
These and many more questions are addressed in a new two-part lecture series titled “Johne’s Disease in Dairy Cattle part 1 and part 2” (40 minutes each) now available on this website. You will also find on this same web page lectures titled “Johne’s Disease in Goats” and “MAP is a Zoonotic Pathogen”.
JOHNE’S DISEASE IN SAUDI ARABIA2021-02-06 01:00:06
An international team of researchers, led by Ibrahim Elsohaby, tested 31 herds of animals with prior histories of Johne’s disease in the Eastern Province in Saudi Arabia. The Eastern Province is the third most populous province in Saudi Arabia, with varying climatic conditions from semi-desert to desert. The Eastern Province shares the borders with five countries (Iraq, Kuwait, Oman, Qatar, and the United Arab Emirates), which may increase the risk of pathogen introduction to the country.
A total of 649 sheep, goats, cattle, and camels were tested by ELISA on serum samples and IS900 PCR on fecal samples. The study was reported this month in the journal Animals. The pie charts below were created to summarize the study findings. They reveal high infection rates among all four animals species and the higher diagnostic sensitivity of fecal PCR as compared to serum ELISAs. Interestingly, the S (sheep)-strain of MAP was more prevalent than the C (cattle)-strain.
The objectives of the present study were to characterize Mycobacterium avium subsp. paratuberculosis (MAP) infection using serological and molecular tools and investigate the distribution and molecular characterization of MAP strains (cattle (C) and sheep (S) types) in sheep, goat, cattle, and camel herds in Eastern Province, Saudi Arabia. Serum and fecal samples were collected from all animals aged >2 years old in 31 herds (sheep = 8, goats = 6, cattle = 8 and camels = 9) from January to December 2019. Serum samples were tested by ELISA for the detection of MAP antibodies. Fecal samples were tested by PCR for the detection of MAP IS900 gene and the identification of MAP strains. MAP antibodies were detected in 19 (61.3%) herds. At the animal level, antibodies against MAP were detected in 43 (19.5%) sheep, 21 (17.1%) goats, 13 (19.7%) cattle and 22 (9.1%) camels. The IS900 gene of MAP was detected in 23 (74.2%) herds and was directly amplified from fecal samples of 59 (26.8%) sheep, 34 (27.6%) goats, 20 (30.3%) cattle and 36 (15.0%) camels. The S-type was the most prevalent MAP type identified in 15 herds, and all were identified as type-I, while the C-type was identified in only 8 herds. The IS900 sequences revealed genetic differences among the MAP isolates recovered from sheep, goats, cattle and camels. Results from the present study show that MAP was prevalent and confirm the distribution of different MAP strains in sheep, goat, cattle and camel herds in Eastern Province, Saudi Arabia.
This graphic from the publication shows an example of Johne's disease in goats.
Few reports on paratuberculosis in Saudi Arabia are available making this an important addition to the body of evidence that Johne’s disease is a global problem.
JOHNE’S DISEASE IN GOATS2021-01-28 01:00:46
João Paulo de Lacerda Roberto and 8 colleagues from the Federal University of Campina Grande, Post-Graduate Program in Animal Science and Health, Patos, PB, Brazil conducted a systematic review and meta-analysis on scientific articles concerning MAP in goats. They specifically examined reports on detection of antibody to MAP in goat milk and detection of MAP in goat milk by PCR methods. They found wide ranging herd-level prevalence estimates among countries as shown in their table below.
Paratuberculosis is an incurable infectious disease that affects several species, including goat (Capra hircus). The etiologic agent is Mycobacterium avium subspecies paratuberculosis (MAP) that has tropism for the intestine, causing anorexia, progressive weight loss and death. In goats, the main transmission route is the ingestion of water and food contaminated by infected feces. Affected animals also eliminate the agent through milk, with a potential biological risk to public health. Thus, the aim of this study was to conduct a research of the literature available in electronic media for a systematic review, followed by a meta-analysis of the results found on prevalence and diagnostic tests adopted in the detection of MAP antibodies and DNA in goat milk. The following search parameters were used: “Mycobacterium avium subsp. paratuberculosis” AND (goat OR small ruminant) AND (milk OR pasteurized milk). Strictly obeying pre-established criteria, 437 articles were selected from the respective electronic databases of scientific content: ScienceDirect (285), PubMed (68), Web of Science (60) and Scopus (24), of which nine papers were elected to the construction of the systematic review and meta-analysis. The prevalence of MAP antibodies in milk detected by milk-ELISA ranged from 1.1 to 67.7% and the prevalence of MAP DNA in goat milk detected by MAP-specific polymerase chain reaction (PCR) ranged from 1.94 to 37.74%. A meta-analysis indicated a combined MAP infection prevalence of 8.24%, but with high heterogeneity among study findings (I2 = 98.7%). The identification of the MAP in goat milk implies the need for surveillance of the agent in order to prevent economic losses and impact on public health.
The problem of Johne’s disease in goats has been overlooked for far too long. In Wisconsin, as in many places in the world, the goat industry is growing, particularly for dairy goats. Data from the United States Department of Agriculture, which counts livestock across the United States every 5 years, show just how much Wisconsin dominates the nation's dairy goat industry. In 2017, the most recent year the USDA surveyed producers, the size of Wisconsin's dairy goat herd easily topped the nation at more than 83,000-head. California came in a distant second, with some 43,000 dairy goats, while Iowa, Texas and Missouri rounded out the top five.
It's not only the sheer size of Wisconsin's dairy goat herd that stands out: The state also leads the nation in the value of sales from dairy goat operations and is the epicenter of national growth in goat dairy. The problem is that rapid goat herd expansion brings with it a high risk of introducing Johne’s disease and once this chronic infection takes root in a herd it becomes a financial drain on the business and a major risk to product sales should MAP become widely recognized as a food-borne zoonotic pathogen.
JD CONTROL ON GRAZING DAIRY FARMS2021-01-21 17:59:21
F. Biemans from the Centre for Veterinary Epidemiology and Risk Analysis, UCD School of Veterinary Medicine, University College Dublin, Ireland together with colleagues from INRAE, Oniris, BIOEPAR, Nantes, France and Teagasc, Oak Park, Carlow, Ireland, published a study titled: Modelling transmission and control of Mycobacterium avium subspecies paratuberculosis within Irish dairy herds with compact spring calving. Their article appears in the January 2021 issue of Preventive Veterinary Medicine.
This graphic from their publication shows the spread of Johne's disease in grazing dairy herds with and without appropriate control measures. Annual testing by serum ELISA, prompt culling of the high (strong) ELISA-positive cows and separation of the calf from the cow soon after birth were critically important control measures.
Paratuberculosis is a chronic bacterial infection of the intestine in cattle caused by Mycobacterium avium subspecies paratuberculosis (Map). To better understand Map transmission in Irish dairy herds, we adapted the French stochastic individual-based epidemiological simulation model to account for seasonal herd demographics. We investigated the probability of Map persistence over time, the within-herd prevalence over time, and the relative importance of transmission pathways, and assessed the relative effectiveness of test-and-cull control strategies.
We investigated the impact on model outputs of calf separation from cows (calves grazed on pasture adjacent to cows vs. were completely separated from cows) and test-and-cull. Test-and-cull scenarios consisted of highly test-positive cows culled within 13 or 4 weeks after detection, and calf born to highly test-positive cows kept vs removed. We simulated a typical Irish dairy herd with on average 82 lactating cows, 112 animals in total. Each scenario was iterated 1000 times to adjust variation caused by stochasticity. Map was introduced in the fully naive herd through the purchase of a moderately infectious primiparous cow. Infection was considered to persist when at least one infected animal remained in the herd or when Map was present in the environment.
The probability of Map persistence 15 years after introduction ranged between 32.2–42.7% when calves and cows had contact on pasture, and between 18.9–29.4% when calves and cows were separated on pasture. The most effective control strategy was to cull highly test-positive cows within four weeks of detection (absolute 10% lower persistence compared to scenarios without control). Removing the offspring of highly test-positive dams did not affect either Map persistence or within-herd prevalence of Map.
Mean prevalence 15 years after Map introduction was highest (63.5 %) when calves and cows had contact on pasture. Mean prevalence was 15 % lower (absolute decrease) when cows were culled within 13 weeks of a high test-positive result, and 28 % lower when culled within 4 weeks. Around calving, the infection rate was high, with calves being infected in utero or via the general indoor environment (most important transmission routes). For the remainder of the year, the incidence rate was relatively low with most calves being infected on pasture when in contact with cows. Testing and culling was an effective control strategy when it was used prior to the calving period to minimize the number of highly infectious cows present when calves were born.
Animal husbandry systems heavily influence the options for Johne’s disease control measures. This excellent publication is focus on the type of pastoral or gazing type of dairy herd management prevalent in Ireland. It reinforces the importance of culling the cows with high-positive serum ELISA results and prompt separation of calves from cows after birth. Very interested readers should read the section on model assumptions (section 3.7 on page 8) to judge whether they model fits dairy herd management systems in other their country. In the book Empirical Model-Building and Response Surfaces by Box and Draper (1987) they state: “Essentially, all models are wrong, but some are useful.” I would rank this model as very useful.
ELISAs measure the quantity of antibody in the clinical sample which can be either serum (from blood) or milk (for dairy cows). The ELISA reports numerical results called S/P or S/P% values and values above a certain cut-off are classified as positive. However, much more useful information, beyond positive or negative interpretations, can be had when you examine the magnitude of the ELISA result. Animals in the high range, typically with S/P values over 1.0 or S/P% values over 100 are consider “high-positive”, also called “strong-positive”. Multiple studies have shown that this is important information as cows with high-positive ELISA results are the ones most likely to be shedding the most MAP in their feces and milk and most likely to have infected their unborn fetus. Thus, these are the first cows among all of the ELISA-positive animals that should be culled.
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