NEWS

Two Related Research Publications

Two excellent articles about use of the ELISA diagnostic test on milk samples (milk ELISA) appeared in the past few weeks. The first, by Ozsvari and colleagues uses the milk ELISA to evaluate the impact of paratuberculosis on milk production, fertility, and culling in large commercial dairy herds in Hungary.  This article published in Frontiers in Veterinary Science is Open Access.

Abstract

Paratuberculosis (PTBC) is a chronic disease caused by Mycobacterium avium subsp. paratuberculosis (MAP), which is common in dairy herds worldwide, although the scale of its impact on herd productivity is unclear. The aim of our study was to determine the differences between MAP ELISA positive vs. negative cows in terms of milk production and quality, reproductive parameters, and culling. The data of five large dairy herds that participated in the voluntary PTBC testing program in Hungary were analyzed. Cows were tested by ELISA (IDEXX Paratuberculosis Screening Ab Test, IDEXX Laboratories, Inc., Westbrook, ME, USA) using milk samples collected during official performance testing. The outcome of the initial screening test involving all milking cows in the herds was used for the classification of the cows. The 305-day milk production, reproduction and culling data of 4,341 dairy cows, and their monthly performance testing results (n = 87,818) were analyzed. Multivariate linear and logistic models, and right censored tobit model were used for the statistical analysis. Test-day and 305-day milk production of ELISA positive cows decreased by 4.6 kg [95% CI: 3.5–5.6 kg, P < 0.0001 (−13.2%)] and 1,030 kg [95% CI: 708–1,352 kg, P < 0.0001 (−9.4%)], compared to their ELISA negative herdmates, respectively. Milk ELISA positive cows had 35.8% higher [95% CI: 17.9–56.4%, P < 0.0001] somatic cell count, on average. Test positive cows conceived 23.2 days later [95% CI: 9.2–37.3 days, P = 0.0012 (+16.5%)] and their calving interval was 33.8 days longer [95% CI: 13.2–54.4 days, P = 0.0013, (+9.7%)], compared to the negative cows, on average. Milk ELISA positive cows were less likely to conceive to first insemination (odds ratio: 0.49, 95% CI: 0.31–0.75, P = 0.0013), and required 0.42 more inseminations to conceive [95% CI: 0.07–0.77, P = 0.0192 (+13.7%)], on average. Milk ELISA positive cows were culled 160.5 days earlier after testing compared to their ELISA negative herdmates (95% CI: 117.5–203.5 days, P < 0.0001). Our results suggest that MAP ELISA positive cows experience decreased milk production, milk quality, fertility, and longevity, which supports the need to control the prevalence of PTBC in dairy herds.

______________

The second publication is by Barden and colleagues from the U.K. describes the effect of skin testing for bovine tuberculosis (TB) on milk ELISA results.  This article published in the journal Preventive Veterinary Medicine is available online only until November 29.

Abstract

Background: In the UK, quarterly Johne’s disease milk antibody ELISAs (JD-mELISAs) are commonly used to classify animals which are likely to be infectious, termed “red cows”. “Red cows” are classified following two positive results from the previous four tests (e.g. + - - +). All cattle are also regularly screened for bovine tuberculosis using intradermal avian and bovine tuberculin, and it is advised to maintain a 60 day interval between a tuberculosis test and JD-mELISA. Aims: To evaluate the impact of bovine tuberculosis testing on JD-mELISAs, and to quantify the impact of test specificity and “red cow” classification test pattern on the probability of infection.

Methods: Four years of individual cow milk records with JD-mELISA results were collated from 735 dairy farms and matched to tuberculosis testing records. A two-level multivariable logistic regression model quantified the effect of tuberculosis testing on JD-mELISA result. The specificity and age-dependent sensitivity of a single JD-mELISA were estimated and used to calculate likelihood ratios following each test. Using Bayes’ theorem, the posterior probability of infection with Johne’s disease was calculated for different specificities, ages of cow, and patterns of test results.

Results: There were increased odds of a positive JD-mELISA if it was ≤30 days (OR: 2.1) or 31− 60 days (OR: 1.2) after a tuberculosis test, compared to >90 days. A larger avian skin reaction at the tuberculosis test was also associated with increased odds of a positive JD-mELISA. The proportion of cows which tested exclusively negative after their first positive JD-mELISA was higher if that JD-mELISA was ≤30 days after a tuberculosis test compared to >90 days. The posterior probability of infection reduced substantially when the test specificity was slightly reduced. In “red cows” classified following two consecutive positive tests, if the test specificity was reduced to 0.95, then the posterior probability of infection was only >95 % if the prior probability was >13 %. If the “red cow” classification was due to two non-consecutive positive tests (+ - - +), the posterior probability of infection was only >95 % if the prior probability was >43 %.

Conclusions: Testing for Johne’s disease within 60 days of a tuberculosis test is associated with a higher chance of a positive JD-mELISA and this may reflect a reduction in the ELISA specificity. Relatively small reductions in JD-mELISA specificity can markedly reduce the posterior probability of infection which also depends on the pattern of test results which classifies “red cows”. [Red cows are those with 2 consecutive positive milk ELISA tests.]

____________

Comment: The milk ELISA is the most affordable testing option for commercial dairy cattle herds. It primarily identifies cows in the more advanced stages of a MAP infection. As the Ozsvari study shows, milk ELISA-positive cows are those that are less productive and likely to be culled sooner (160.5 days earlier) that their milk ELISA-negative herdmates. In countries with endemic bovine TB, where TB testing of cattle happens regularly, it is important to avoid use of the milk ELISA for at least 60 days after a whole herd TB skin test. TB skin testing seems to increase the rate of false-positive test results (decreases assay specificity).

Milk ELISA testing importantly makes JD control more affordable and thus increases producer participation in national programs like the one in the U.K. However, limitations in diagnostic sensitivity mean that while it is a useful tool for controlling MAP-infections in dairy cattle herds it is not sufficiently sensitive to drive eradication of the infection from herds. For that purpose, more sensitive tests, such as the fecal PCR, are required.

Medical gastroenterologists commonly raise five concerns that seem to argue against a role for MAP in Crohn’s disease.

They are:

1. Why is there variability in studies which aim to detect MAP in Crohn’s patients?
2. Has MAP fulfilled Koch’s postulates?
3. Why does immunosuppressive therapy not worsen Crohn’s Disease if it is caused by MAP, as is seen with MTB (the cause of tuberculosis)?
4. Why is the incidence of Crohn’s not higher in at‑risk subgroups, such as veterinarians or farmers?
5. If MAP causes Crohn’s, why doesn’t atypical mycobacterial antibiotic therapy (AMAT) cure Crohn’s, and related to that, have RCTs (randomized controlled clinical trials) shown that AMAT is ineffective?

Dr. Gurav Agrawal and colleagues (myself included) published and invited review in the journal Digestive Diseases and Sciences addressing these 5 questions. The article is Open Access (11 pages with 86 references).

Abstract

For decades, Mycobacterium avium subspecies paratuberculosis (MAP) has been linked to the pathogenesis of Crohn’s disease. Despite many investigations and research efforts, there remains no clear unifying explanation of its pathogenicity to humans. Proponents argue Crohn’s disease shares many identical features with a granulomatous infection in ruminants termed Johne’s disease and similarities with ileocecal tuberculosis. Both are caused by species within the Mycobacterium genus. Sceptics assert that since MAP is found in individuals diagnosed with Crohn’s disease as well as in healthy population controls, any association with CD is coincidental. This view is supported by the uncertain response of patients to antimicrobial therapy. This report aims to address the controversial aspects of this proposition with information and knowledge gathered from several disciplines, including microbiology and veterinary medicine. The authors hope that this discussion will stimulate further research aimed at confirming or refuting the contribution of MAP to the pathogenesis of Crohn’s disease and ultimately lead to advanced targeted clinical therapies.

Worth noting:

As evidence that some gastroenterologists think MAP is a cause of Crohn's disease, in the UK, a phase I clinical trial has started to investigate the safety and efficacy of two candidate MAP vaccines in patients with active Crohn's disease (ISRCTN - ISRCTN36126048).

Mary Garvey, Lecturer at the Institute of Technology Sligo, Sligo, Ireland published a review article titled:  Mycobacterium Avium Paratuberculosis: A Disease Burden on the Dairy Industry in the journal Animals (11 pages with 58 references).

Abstract

Mycobacterium avium paratuberculosis is responsible for paratuberculosis or Johne’s disease in cows, having economic impacts on the dairy industry and a prevalence rate exceeding 50% in dairy herds. The economic burden of Johne’s disease relates to decreased milk production and costs of disease prevention, treatment, and management, while having an economic impact on dairy producers, processors, consumers, and stakeholders of the dairy industry. Determining the true economic impact of the disease is difficult at regional and farm level as symptoms are not evident in subclinically infected animals. At present, the virulence, pathogenicity, persistence, and infectious dose of M. avium paratuberculosis are poorly understood, consequently effective paratuberculosis control measures remain obscure. M. avium paratuberculosis is potentially zoonotic with foodborne transmission a public health risk due to a possible causative link with inflammatory bowel disease in humans. A preventive approach is necessary to reduce the presence of this drug-resistant pathogen in dairy herds and subsequently dairy food. The use of inefficient diagnostic tests coupled with the long latency period of infection results in delayed animal culling and trade of asymptomatic animals, leading to regional transmission and increased disease prevalence. To date, there has been limited success at controlling and treating this terminal endemic disease, leading to significant prevalence rates. This study aims to outline the key factors associated with Johne’s disease while outlining its significant impact on the dairy sector.

Comment: The direct financial costs of Johne’s disease (JD) to dairy producers is small relative to diseases such as mastitis. Hence, without financial incentives most dairy producers conclude that the cost of JD control exceeds the cost of the disease. Therefore, few producers implement JD control programs allowing this chronic, infectious disease to continue spreading within and among dairy herds globally. For more on the epidemiology of JD in dairy cattle read this page of our site.

If, however, MAP is recognized as a zoonotic, food-borne pathogen, causing Crohn’s disease and triggering other so-called autoimmune disease like Type I Diabetes Mellitus, the impact on the dairy industry would be huge.

For more on the MAP as a zoonotic pathogen see this page of our website or for patients, visit the Human Para Foundation website.

Related News

Today, October 15, is the publication anniversary of the landmark paper defining Crohn’s disease (1932). As I do annually, I acknowledge this event in Johnes.org news.

Eighty-eight years ago, Burrill B. Crohn, Leon Ginzburg, and Gordon D. Oppenheimer published a paper titled Regional Ileitis – A Pathologic and Clinical Entity in the Journal of the American Medical Association (vol. 99, no. 16, pp 1323-1329, October 15, 1932).  Honoring the importance of this report, the article was later reprinted as a Landmark Article in The Mount Sinai Journal of Medicine (vol 67, no. 3, pp 263-268, May 2006).  We provide the original JAMA article here for users interested in reading this influential publication in its original form.  Note: the reprinted version in the Mount Sinai Journal of Medicine has better print quality.

Comment:  I appreciate history as I grow older.  Also, it is important to read original published reports to avoid misquoting or perpetuating misunderstandings.  Interesting note: As described in Wikipedia, Crohn always preferred the medically descriptive terms "regional ileitis" and "regional enteritis" to "Crohn's disease", but he was not able to prevent the appropriation of his name for the disease. It’s worth noting that Johne's disease is also a regional ileitis affecting ruminants.

Without providing much detail, B.B. Crohn’s article mentions efforts to determine if Mycobacterium tuberculosis was involved in the regional ileitis cases he described including culture for M. tuberculosis, inoculation of lymph node homogenates from five patients into guinea pigs, rabbits, and chickens, and acid-fast staining of tissue sections.  He concludes that M. tuberculosis was not a cause of these cases of regional ileitis.  However, he never mentions the 1913 report by Dalziel or makes any mention of Mycobacterium paratuberculosis or the similarities of regional ileitis in humans to that of cattle, as described by H.A. Johne in 1895. Clearly, Dr. Crohn recognized how the pathology in his afflicted patients resembled that caused by a mycobacterial infection. How might history be different had Dr. Crohn considered the possibility M. a. paratuberculosis (MAP) was the cause?

The picture of B.B. Crohn is credited to Wikipedia.

The second edition of the book titled Paratuberculosis: Organism, Disease, Control has just been published. The editors, Behr, Stevenson and Kapur, have produced a timely follow up to the first book on Paratuberculosis (2010), this new edition is still the only comprehensive text providing both historical context and the latest developments in the field. Examining the epidemiology of paratuberculosis, the organism that causes the disease, and practical aspects of its diagnosis and control, it also addresses the link between paratuberculosis in the food chain and human health implications, including Crohn's disease. The 438 page book contains 23 chapters written by the leading world experts in paratuberculosis (Johne's disease). It is available from Amazon for e-readers for US$147.25 or from Google for US$124.00. The hard cover version has not yet been released for sale but can be pre-ordered from Amazon for US$155.00

Antonio Foddai and Irene Grant from the Institute for Global Food Security, School of Biological Sciences, Queen’s University Belfast, Belfast, Northern Ireland have created a novel assay to quantify viable MAP in milk (patent pending).  Their report, titled “A novel one-day phage-based test for rapid detection and enumeration of viable Mycobacterium avium subsp. paratuberculosis in cows’ milk” appeared September 24 in the journal Applied Microbiology and Biotechnology [Open Access].

In this assay phages (viruses that infect bacteria) are used to both concentrate MAP and to then infect and lyse MAP, allowing for final detection and quantification by qPCR. The total assay time is roughly 7 hours, faster than other phage-based assay systems. The key to the assay is the binding orientation of the phage. The head is bound to the paramagnetic bead allowing the tail to bind to MAP. After binding, the phage then lyses the MAP organism making its DNA available for detection by qPCR.

Diagram of a similar phage from ViralZone.

Abstract

Bacteriophage-based methods for the rapid detection of viable Mycobacterium avium subsp. paratuberculosis (MAP) in veterinary specimens are a recent addition to the Johne’s disease diagnostic toolbox. Here, we report the use of D29 mycobacteriophage-coated tosylactivated paramagnetic beads to capture and concentrate MAP cells from samples (termed phagomagnetic separation, PhMS) and then naturally lyse viable MAP cells (from the inside out) to provide DNA for IS900 qPCR purposes. Transmission electron microscopy confirmed that D29 phages had bound to beads in the correct orientation and that the phage-coated beads captured MAP cells from a suspension. During test optimization, conventional IS900 PCR results were used to subjectively assess the effect of different phage:bead coating ratios, differing amounts of coated beads during PhMS, optimal incubation time post-PhMS to obtain maximal MAP DNA, and the potential benefit of a brief heat shock (55 °C/1 min) prior to IS900 TaqMan qPCR. The limit of detection 50% (LOD50%) of the optimised PhMS-qPCR assay was 10.00MAP cells/50 ml milk (95% CI 1.20–82.83). Finally, in order to demonstrate the new assay’s ability to detect viable MAP in naturally contaminated milk, bulk tank milk samples from 100 dairy farms were tested. Forty-nine (49%) of these tested PhMS-qPCRpositive, with viable MAP numbers detected ranging from 3–126 MAP/50 ml. The novel PhMS-qPCR assay is a sensitive, specific and easy-to-apply phage-based assay for viable MAP, with potential application for milk surveillance or diagnosis of Johne’s disease.

Comment: No other assay system can claim the ability to quantify such low numbers of viable MAP in milk in such a short time. I predict that this assay will reveal that there is far more MAP in raw milk than previously recognized. Hopefully this novel technology also can be applied to other types of clinical samples, e.g. blood samples from Crohn’s disease patients. For more about D29 phages see this Wikipedia page.

In the second of two JD articles, veterinarians Pete Orpin, Dick Sibley and Karen Bond provide an excellent overview of UK’s national program to control Johne’s disease. The principles apply to all nationally coordinated efforts facilitated by specially qualified veterinarians.

The article appears in the UK magazine In Practice. The magazine publishers have generously provided readers of Johnes.org news exclusive free access to the full article.

As stated in the summary of their article:
Any JD management plan should meet the principles of any good herd health plan, in accordance with the VESPA acronym used in the British Cattle Veterinary Association’s health planning training:

• Valued – it must engage the farmer and all the staff;
• Effective – it must be robust and cover all components of the strategy;
• Specific – it has to be detailed to fit with the specific management and husbandry of the farm;
• Practical – it has to be deliverable by the farm and the staff, within the resource limitations;
• Agreed – it has to be agreed by all involved as a practical and deliverable plan.

Here's an example of the messaging in this important article:

About the authors:

Pete Orpin qualified from the University of Bristol in 1983 and worked as a farm vet within the Park Vet Group in Leicestershire for 35 years before retiring. He is a founding member of Action Group Johne’s and chair of its technical group, and is a director of Myhealthyherd.

Dick Sibley qualified from the University of Bristol in 1977 and is currently a practicing vet in Witheridge, Devon. A founding member of Action Group Johne’s and director of Myhealthyherd, he has had a long interest in the practical management and control of infectious diseases, including bovine viral diarrhea, tuberculosis and Johne’s disease.

Karen Bond qualified from the University of Glasgow in 2000 and works as a veterinary adviser for National Milk Records, where she has a special interest in the testing and management of infectious disease. She is currently undertaking a PhD in Johne’s disease transmission on dairy farms.

Comment: I wish to thank the publisher, BMJ, for granting access to these excellent articles on Johne’s disease published in In Practice, a publication of the British Cattle Veterinary Association.

Veterinarians Dr. Pete Orpin and Dr. Dick Sibley and Dr. Karen Bond (PhD student) provide an excellent overview of Johne’s disease, targeted at dairy farmers and veterinarians. The article appears in the UK magazine In Practice. The magazine publishers have generously provided readers of Johnes.org news free access to the full article. The article nicely describes the disease, its importance, and measures to control it with lovely graphics. It also briefly describes UK’s national Johne’s control program, which has many similarities to that of the US.

The second article of the series goes into more depth about on-farm control measures and the UK’s National Johne’s Management Plan. It will be featured in coming news stories on this website.

About the authors:

Dr. Pete Orpin qualified from the University of Bristol in 1983 and worked as a farm vet within the Park Vet Group in Leicestershire for 35 years before retiring. He is a founding member of Action Group Johne’s and chair of its technical group, and is a director of Myhealthyherd.

Dr. Dick Sibley qualified from the University of Bristol in 1977 and is currently a practicing vet in Witheridge, Devon. A founding member of Action Group Johne’s and director of Myhealthyherd, he has had a long interest in the practical management and control of infectious diseases, including bovine viral diarrhea, tuberculosis and Johne’s disease.

Dr. Karen Bond qualified from the University of Glasgow in 2000 and works as a veterinary adviser for National Milk Records, where she has a special interest in the testing and management of infectious disease. She is currently undertaking a PhD in Johne’s disease transmission on dairy farms.

Comment: I wish to thank the publisher, BMJ, for granting access to these excellent articles on Johne’s disease published in In Practice, a publication of the British Veterinary Association.

This year the laboratory of Dr. Adel Talaat, School of Veterinary Medicine, University of Wisconsin-Madison, has reported on two unique vaccines to combat Johne’s disease. The first, a nanovaccine, was reported in npj Vaccines February 14, 2020. The second, a live attenuated (avirulent) vaccine (LAV) was reported in the journal Microorganisms September 17, 2020. Both  publications describing these vaccines are Open Access.

A single dose polyanhydride-based nanovaccine against paratuberculosis infection

Abstract

 Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) causes Johne’s disease in ruminants and is characterized by chronic gastroenteritis leading to heavy economic losses to the dairy industry worldwide. The currently available vaccine (inactivated bacterin in oil base) is not effective in preventing pathogen shedding and is rarely used to control Johne’s disease in dairy herds. To develop a better vaccine that can prevent the spread of Johne’s disease, we utilized polyanhydride nanoparticles (PAN) to encapsulate mycobacterial antigens composed of whole cell lysate (PAN-Lysate) and culture filtrate (PAN-Cf) of M. paratuberculosis. These nanoparticle-based vaccines (i.e., nanovaccines) were well tolerated in mice causing no inflammatory lesions at the site of injection. Immunological assays demonstrated a substantial increase in the levels of antigen-specific T cell responses post-vaccination in the PAN-Cf vaccinated group as indicated by high percentages of triple cytokine (IFN-γ, IL-2, TNF-α) producing CD8+ T cells. Following challenge, animals vaccinated with PAN-Cf continued to produce significant levels of double (IFN-γ, TNF-α) and single cytokine (IFN-γ) secreting CD8+ T cells compared with animals vaccinated with an inactivated vaccine. A significant reduction in bacterial load was observed in multiple organs of animals vaccinated with PAN-Cf, which is a clear indication of protection. Overall, the use of polyanhydride nanovaccines resulted in development of protective and sustained immunity against Johne’s disease, an approach that could be applied to counter other intracellular pathogens.

A protective vaccine against Johne’s disease in cattle

Abstract

Johne’s disease (JD) caused by Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) is a chronic infection characterized by the development of granulomatous enteritis in wild and domesticated ruminants. It is one of the most significant livestock diseases not only in the USA but also globally, accounting for USD 200–500 million losses annually for the USA alone with potential link to cases of Crohn’s disease in humans. Developing safe and protective vaccines is of a paramount importance for JD control in dairy cows. The current study evaluated the safety, immunity and protective efficacy of a novel live attenuated vaccine (LAV) candidate with and without an adjuvant in comparison to an inactivated vaccine. Results indicated that the LAV, irrespective of the adjuvant presence, induced robust T cell immune responses indicated by proinflammatory cytokine production such as IFN-, IFN-_, TNF-_ and IL-17 as well as strong response to intradermal skin test against paratuberculosis antigens. Furthermore, the LAV was safe with minimal tissue pathology. Finally, calves vaccinated with adjuvanted LAV did not shed M. paratuberculosis post-challenge, a much-desired characteristic of an effective vaccine against JD. Together, this data suggests a strong potential of testing LAV in field trials to curb JD in dairy herds.

Comments:

The LAV is among the first live vaccine to be tested in mice, then goats and now finally in this report, cattle. The early evidence suggests it will be a useful tool in the global effort to control Johne’s disease. However, assuming a company licenses one of the vaccines it will take several years to bring it to market.

The LAV did not produce the unsightly granulomas of traditional killed vaccines like Mycopar™. Below is the lesion score data from the LAV publication followed by a photo of a cow in Wisconsin vaccinated with Mycopar™ when she was just a calf. Regulations require that the Mycopar™ vaccine be administered in the brisket before the animal is 35 days old. The Mycopar™ vaccine is no longer being produced in the U.S.

In countries with bovine tuberculosis (TB), caused by Mycobacterium bovis, it is vital that animals that are vaccinated against JD can be discriminated from those with bovine TB. In the study on the LAV, the authors reported:

Mycopar™ vaccinated calves displayed significant skin indurations after the injection of M. bovis PPD clearly showing cross-reactivity to bovine TB. On the other hand, none of the LAV vaccinated calves developed significant skin indurations against M. bovis PPD at 12 MPC, despite mounting a robust reaction to Johnin. In fact, pgsNQ vaccinated calves did not respond to the M. bovis PPD at the 2 MPV time point, as well. This lack of reactivity to bovine PPD feature, could be crucial for further developing the LAVs used here as DIVA compliant vaccines (vaccines with a simple assay to differentiate infected from vaccinated animals). The DIVA-compliant vaccines would be very useful to implement to control paratuberculosis in countries where bovine tuberculosis is prevalent and farmers hesitate to use the current JD vaccine. The observed cross reactivity to M. avium PPD by calves from all vaccine groups is expected because of the close similarity between M. avium and M. paratuberculosis but could be employed as a further confirmation of developing immunity against paratuberculosis.

Manju Singh and 8 colleagues from universities in India reported on tests for MAP in a variety of dairy products purchased from retail stores. Their publication (16 pages with 55 references) appears in the August 2020 issue of the Journal of Experimental Biology and Agriculture Science (JEBS). All the articles published by JEBAS Open Access.

Abstract

Twelve types of milk products belonging to 22 market brands were purchased from local shops in South Uttar Pradesh and were screened for the presence of Mycobacterium avium subspecies paratuberculosis (MAP) as major contaminant using six tests (microscopy, Indirect Fluorescent Antibody Test, IS900 PCR, Indigenous Enzyme linked Immuno Sorbent Assay, dot_ELISA, and Latex agglutination Test). Sample positive in any one of the six tests was considered as positive. Of 276 milk products screened, the cumulative bio-presence of MAP was, 52.8% (146) and was highest in butter (75.0%), followed by curd (66.0%), buttermilk (52.9%), lassi (50.0%), cheese (40.0%) and ice-cream (28.5%). Bio-typing of MAP DNA from milk products using IS1311 PCR_REA revealed presence of ‘Indian Bison Type’ as a major biotype. Kappa (0.700 – 0.815) and two-tailed p (<0.0001–1.0) values for six tests were significant for all six tests. This study for the first time revealed large scale contamination of ‘milk products’ marketed by leading commercial brands in India, with MAP bacilli and therefore not safe for human consumption.

Comment: Some of the assays used in this study measured the presence of antibodies against MAP, not the organism. However, by IS900 PCR, samples of curd, butter, ice cream, butter, and cheese were all found positive at rates ranging from 6.0% to 13.8%. None of the assays used could determine if the MAP that was detected was alive. Regardless, it indicates that MAP is spilling over from domestic animals into the food supply. This Wikipedia link describes Indian dairy products.

In 1915 the Wisconsin Experiment Station began a study of Johne’s disease. This tradition continues at the University of Wisconsin to this day. Today’s news post looks at studies in the U.S. that have tried to estimate the herd-level prevalence of this infection for dairy herds, i.e. percentage of MAP-infected herds. Also, because this literature is often hard to access, the original publications from which the graphics below originate, are also provided.

In 1927 Hastings et al. published a 44-page report on Johne’s disease (Wisconsin Research Bulletin 81) with 121 references. In that report, the authors provided a graphic illustrating where Johne’s disease had been reported (below).

In 1976, at a meeting of the American Association of Bovine Practitioners, Dr. Aubrey Larsen reviewed developments in research on paratuberculosis and provided the results of two U.S. surveys, one in 1949 and one in 1971 (Proceedings of the 1976 AABP meeting).

In 1996 the USDA surveyed U.S. dairy herds using an ELISA for serum antibodies against MAP. They used 3 definitions for a “positive”, i.e. MAP-infected herd: 1) herds with 1 or more ELISA-positive cows (40.6% of all herds), 2) herds with 2 or more ELISA-positive cows (16.8% of all herds), and 3) herds with 1 or more ELISA-positive cows and reports of clinical signs of Johne’s disease by herd owners (21.6% of all cows. The 21.6% figure is the one most often cited as herd-level MAP infection prevalence for U.S. dairy herds in 1996. Significant regional differences were only found for the second case definition.

In 2002 the USDA did another study for the purposes of comparing Johne’s disease diagnostic test accuracy and evaluating within-herd infection prevalence but did not attempt to estimate the herd-level prevalence of Johne’s disease in the U.S. After testing 7,238 dairy cows, they reported that the ELISA done on serum detected only 27.4% of fecal culture-positive cows, showing that any survey done using ELISA methods underestimates the number of cows that are truly MAP-infected and shedding MAP in their feces, i.e. infectious. However, the ELISA was good at detecting the cows shedding the highest amounts of MAP in their feces.

In 2007 the USDA repeated the national survey of U.S. dairy herds but used environmental fecal culture on 6 samples per farm as the diagnostic test. That survey found that MAP was isolated from at least one environmental sample on 68.1% of operations, and herd-level prevalence was higher for larger herds. They reported: “About one-fourth of operations had six culture positive environmental samples.  Operations with one to five culture-positive samples were less common. These results suggest that at least one-fourth of U.S. dairy operations may have a relatively high percentage of infected cows in their herds." A clear relationship between herd size and frequency of finding MAP was shown.

The rate of detection of MAP-infected herds is called the apparent prevalence (percentage of test-positive herds). Using this data, Dr. Jason Lombard et al. (Preventive Veterinary Medicine 108:234, 2013) used epidemiological methods to estimate the true herd-level prevalence or paratuberculosis in U.S. dairy herds at 91.1% of U.S. dairy herds (95% probability interval, 81.6 to 99.3%).

Comment: Chronic infectious diseases cause by slow-growing pathogens like MAP spread insidiously as herd owners buy and sell animals without considering the MAP infection status of the source herds. Although researchers have repeatedly tried to call attention to this problem, more acute or immediate challenges for dairy herd owners divert attention away from this growing problem. Early in the start of this epidemic clear warnings were issued:

“The aim of this bulletin is to call the attention of veterinarians and breeders to Johne’s disease, which, it is felt, is not recognized by many, in order that steps may be taken to prevent its introduction into still healthy herds, and to gradually eliminate it from affected herds.”  (Beach & Hastings, 1922)

 "Dr. V.A. Moore has compared the  present position of Johne's disease with  that of bovine tuberculosis 60 years ago and has prophesied that, if not controlled, it may become a more troublesome scourge for future generations than tuberculosis is for the present generation of cattle-owners." (Larson, et al., 1924).

Their warnings remain true today and their aim, to raise awareness, is the same aim as that of this website.

 Below is my view of the global epidemic curve. If MAP is a zoonotic pathogen, the prevalence of this infection in food-producing animals does not bode well for the health of humanity.

Explanatory note: Chilean reports of Johne’s disease are used as an example of how MAP is spreading to developing countries. The photo is that of Dr. H.A. Johne. For more on the history of Johne’s disease check out the history timeline.