NEWS

Eighty-nine 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 but is more difficult to access. Photo from Wikipedia.

For history buffs, you can read more about the life of B.B. Crohn in an editorial by F. Guilherme published in 2013.

COMMENT

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 concluded 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? Paratuberculosis (pTB), also called Johne’s disease, is regional ileitis in animals and MAP is the cause.

Fast forward to today……..

The tide of medical opinion maybe gradually changing. An editorial by Dr. Giles R.G. Monif, published in the journal Gastrointestinal Disorders, states that Crohn’s disease, caused by MAP, is both preventable and curable if treated appropriately in its early stages. I urge you to read Dr. Monif’s article.

For an overview of research linking MAP with Crohn’s disease see the page on this site called Zoonotic Potential.

Today’s news is about observations I have made when communicating with goat owners seeking advice through the Ask and Expert feature of this website. These observations have led me to hypothesize that chickens harbor microbes, probably members of the mycobacteria family, that trigger false-positive ELISA results. Here’s a real-world case using a fictitious owner name but with diagnostic test results that are real, with all owner and goat details removed.

Recently Sally wrote to me saying:

After years of negative tests, I just had 5 out of 11 goats (all goats here that are at least a year old) test positive for Johne’s and many of the others not being far away from the 0.800 threshold to consider them positive as well. All of them are easy keepers and fat and sleek with no sign of Johne’s.

These are the ELISA results Sally provided to me with S/P values and the laboratory’s interpretation (S/P values >0.800 being positive).

Goat #1, S/P value 0.491, negative

Goat #2, S/P value 1.459, POSITIVE

Goat #3, S/P value 0.851, POSITIVE

Goat #4, S/P value 0.610, negative

Goat # 5, S/P value 0.250, negative

Goat #6, S/P value 0.887, POSITIVE

Goat #7, S/P value 0.516, negative

Goat #8, S/P value 0.318, negative

Goat #9, S/P value 0.959, POSITIVE

Goat #10, S/P value 1.290, POSITIVE

Goat #11, S/P value 0.656, negative

This report shows an apparent prevalence of 5/11 (45%) equating to 100% true prevalence and the positive predictive value of 100% for the positive tests. These values assume an ELISA sensitivity of 25% and specificity of 98%. The estimated true prevalence and positive predictive value were calculated using Epitools.

https://epitools.ausvet.com.au/trueprevalence

I explained to Sally that the Johne’s disease ELISA is a rapid, low-cost screening test for Johne’s disease but to confirm a diagnosis I recommended she have a fecal PCR done on the ELISA-positive goats. Sally sent fecal samples to a USDA-approved laboratory and all 5 results came back “negative”; MAP not detected.

Sally’s story is not unique. In fact, I have encountered at least a dozen such similar stories of a surprising number of ELISA-positive goats with 100% negative fecal PCR results. The common denominator has always been goats that share an environment with chickens. This is purely an observation, but I speculate that backyard poultry harbor microbes that infect goats sufficiently to trigger antibody that reacts in the Johne’s disease ELISA but is not MAP and does not cause the goats to get sick.

Like Sally, most of the goat owners in this situation are breeders, meaning they sell live animals for breeding purposes. Because of the low sensitivity of the ELISA and the significant chances of false-positive results on farms where there are poultry, I strongly urge all breeders to avoid using the ELISA and instead use the fecal PCR. I also urge them to test all adult animals in their herd annually. It is vital that breeders do not sell MAP-infected goats for the sake of their business and the sake of their particular goat breed. Thus, they should invest in the best diagnostic test for Johne’s disease available and test their herd annually, always using USDA-approved labs.

To limit the cost of this diagnostic testing, owners should use laboratories that offer to do sample pooling. The owner or his/her veterinarian submits individual fecal samples. The laboratory then pools equal amounts of feces from 5 goats, ideally based on age (5 oldest goats in the first pool, etc.) and does a single PCR on the fecal pool. If the PCR is negative, then all the goats contributing to that pool are declared negative, i.e., no MAP detected in feces.

Prices for these laboratory tests vary but using WVDL rates for 2021 I made cost some cost comparisons. The cost of pooled PCR for Sally’s 11 goats would be $70.04 for 2 pooled PCRs for the first 10 goats (5/pool) and $30.89 for the individual PCR on the 11^th goat for a total of $100.93 (plus a $10 accession fee). This equates to a cost of $10.08/goat. The cost of doing an ELISA on these goats at the WVDL would be $6 x 11 plus $10 = $76 or $6.91/goat. Note: had Sally’s herd been only 10 goats the per goat cost for pooled PCR would have been only $7.28.

In sum, pooled fecal PCR is the test of choice for goat breeders. It is roughly 3 times more sensitive (better able to detect MAP-infected goats), has higher specificity (rare false-positives) and is comparable in cost to the ELISA when sample pooling is done by the lab.

My “chicken theory” is just that, a theory based on observations when working with goat owners who have unexpected positive ELISA results. I hope that some talented young researcher will explore this further. Perhaps the microbe triggering these false-positive ELISAs would be a candidate for a live avirulent vaccine for Johne’s disease.

An international team of investigators reported on MAP infections in domestic sheep and guanaco in Patagonia. Their work was published in the journal Transboundary and Emerging Diseases.

ABSTRACT

Natural herbivore populations have experienced uninterrupted pressures from direct and evident domestic-wildlife interactions and competition, to indirect or less obvious ones such as pathogen transmission. Thus, pathogen spillover between wild and domestic animals is a constant concern because the domestic–wildlife interface represents the ecological frontier in which pathogen transmission takes place in both directions. In Patagonian steppe communities, extensive sheep ranching and guanaco (Lama guanicoe) populations coexist, and guanaco have shown to be infected by pathogens such as Mycobacterium avium subspecies paratuberculosis (MAP) likely transmitted from livestock. MAP causes chronic enteritis and affects mostly domestic ruminants. We evaluated MAP prevalence and pathogen shedding in both species’ faeces collected in non-shared and shared sites according to presence/absence of sheep and guanaco along a year, in four different seasons (autumn, winter, and spring 2018, and summer 2019). Our results indicate that MAP circulates in both sheep and guanaco populations with self-sustained transmission; however, both species differ in their levels of competence. We detected higher pathogen shedding in sites occupied by sheep, suggesting that sheep populations may be the main source of infection for susceptible animals due to their large numbers which drive MAP dynamics.

COMMENT

As the global MAP epidemic continues unabated the infection is increasingly spreading to wildlife. This article about sheep sharing pastures and also MAP with guanaco. Many captive and free-ranging wild ruminants and camelids, like the guanaco, are at risk of MAP infection spillover from domestic livestock.

[caption id="attachment_3675" align="aligncenter" width="2560"]
From Wikipedia: Although the species is still considered wild, around 300 guanacos are in U.S. zoos, and around 200 are registered in private herds. Guanacos have long been thought to be the parent species of the domesticated llama, which was confirmed via molecular phylogenetic analysis in 2001, although the analysis also found that domestic llamas had experienced considerable cross-hybridization with alpacas, which are descended from the wild vicuña. This Wikipedia page tells you more about guanaco.[/caption]

Lawrence Gavey and colleagues from Animal Health Ireland and the Centre for Veterinary Epidemiology and Risk Analysis, UCD School of Veterinary Medicine, University College Dublin published an article describing the Irish Johne’s disease (JD) control program. Their Open Access article appeared August 27, 2021, in the journal Frontiers in Veterinary Science.

ABSTRACT

The Irish Johne's Control Programme (IJCP) provides a long-term approach to the voluntary control of Johne's disease (JD) in Ireland, strongly supported by Irish cattle industry leadership. It leverages the establishment of Animal Health Ireland for control of animal diseases not regulated by the European Union. The IJCP has four objectives: facilitate protection against spread of JD to uninfected farms; reduce the level of infection when present; assure markets of JD control in Ireland; and improve calf health and farm biosecurity. Key IJCP elements are an annual veterinary risk assessment and management plan (VRAMP), annual whole herd test (WHT) by ELISA on blood or milk samples with ancillary faecal PCR testing of ELISA reactors, and Targeted Advisory Service on Animal Health (TASAH) investigations of infected herds. There are pathways for assurance of herds with continuing negative tests and for management of test-positive herds. Herdowners are responsible for on-farm activities, and specifically-trained (approved) veterinary practitioners have a pivotal role as technical advisors and service providers. The programme is supported by training of veterinarians, performance of testing in designated laboratories, documentation of policies and procedures, innovative data management for herd and test activities and for programme administration, training, and broad communication and awareness activities. Tools and systems are refined to address emerging issues and enhance the value of the programme. An Implementation Group comprising industry, government and technical leaders sets strategic direction and policy, advised by a Technical Working Group. Shared funding responsibilities are agreed by key stakeholders until 2022 to support herds in the programme to complete requirements. Herd registrations have increased steadily to exceed 1,800. National bulk tank milk surveillance is also being deployed to identify and recruit test-positive herds with the expectation that they have a relatively high proportion of seropositive animals. The programme will continue to innovate and improve to meet farmer and industry needs.

Website editor’s note: According to the Irish Cooperative Organisation Society’s website, “There are 18,000 dairy farmers in Ireland, producing milk of an outstanding quality from over 1.2 million dairy cows. Irish dairy farms are family run enterprises, supplying 6.4 billion litres of milk in 2015.” This means that the Irish Johne’s Control Programme has enrolled roughly 10% of Irish dairy herds this far.

COMMENT

The Irish JD program has all the same elements found in most national Johne’s disease programs:
1. Education of producers and veterinarians.
2. Herd risk assessments to identify when and where MAP transmission occurs on the farm.
3. Changes to animal husbandry methods to limit MAP transmission.
4. Regular application of diagnostic tests to all adults in the herd for many years.
5. Consistent actions based on the diagnostic test results.
6. Monitoring progress.

The program is also available for beef cattle producers.

The authors of this publication discuss the challenges for sustaining and growing the program stating: “The judgement of insufficient reward for the risk, inconvenience and expense of participation, especially for low-risk herds, remains a constant limitation and is recognised as an inhibitor to uptake of programmes internationally”.

This impediment could be addressed by paying farmers more for milk from herds that are test-negative or deemed to be low-risk. Currently, according to the Animal Health Ireland (AHI) website, Irish milk processors pay dairy farmers a set amount per cow each year depending on whether they are in the test-negative pathway or the test-positive pathway and the number of years in the program, as shown below (copied from the AHI website).

Funding Support per Eligible Animal by Year of Registration 

Test-negative pathway

1. €2.75 ($3.25)**
2. €2.06 ($2.43)
3. €1.38 ($1.63)
4. Nil*

Test-positive pathway

1. €2.75 ($3.25)
2. €2.75 ($3.25)
3. €2.75 ($3.25)
4. €2.75 ($3.25)

*It is anticipated that after four consecutive years of test-negative results, herds in the text-negative pathway will move to a lower-intensity maintenance testing programme – details of which are to be announced in the near future.
** Currency conversion based on values on 11-SEP-2021.

There are two problems with this. First, while I am sure the financial support is welcome, it represents a very small portion of the actual costs that dairy producers incur when trying to control JD. For more on the costs of a JD control program see Table 6 in Roch, et al. Journal of Dairy Science, 2020 (Open Access).

Secondly, in this plan for test-negative herds there appears to be a financial disincentive to remain in the program. It seems to me that test-negative herds should be paid an increasing amount for each year they remain in the program and the test-positive herds that do not show progress in the program after 3 years should have a decreasing rate of financial support. Farmers must spend money not only on annual diagnostic testing of their herd but also the management changes necessary to limit MAP transmission. They do this for the health and welfare of their animals but also for the health and safety of the public and the profitability of the Irish dairy industry as a whole.

In 2019, according to the Irish Dairy Board website, Irish dairy exports reached €4.4 billion, making it the largest food and drink export category. This was the third consecutive year in which the value of dairy exports exceeded the €4bn mark. Protection and expansion of export markets are a major driver for the Irish dairy industry as the graphic below shows.

Profits from the export of dairy products, that rely on the eco-friendly, wholesome and healthy image of Irish dairy products with a zero or very low MAP infection rate, need to be equitably shared with the people who make this possible, the Irish dairy producers.

In 2009 Dairy UK, milk processor body set up an industry initiative with stakeholders from the dairy industry called Action Johne's. All UK dairy farms have a single supply contract with a designated buyer, who has control over the standards to which the milk is produced. This has progressed over the years from a Johne's Disease (JD) education and engagement program to a more structured framework for the control and management of Johne's Disease in the UK dairy herd called the National Johne's Management Plan (NJMP).

In 2017 the scheme structure involved the training or more than 1000 veterinarians to be Approved JD Advisors through the British Cattle Vet Association and a campaign through the milk buyers to ensure their farmers had undertaken an annual risk assessment in conjunction with a trained and accredited Johne's Veterinary Adviser and selected an appropriate control strategy from six possible options. The UK national farm assurance program (Red Tractor) incorporated the NJMP into the dairy farm standards in 2020, effectively making it mandatory to be part of the NJMP, resulting in 95% of all UK dairy farmers now being included in the scheme.

Dr. Pete Orpin, Chair of the Johne’s Technical Action Group has provided the document updating the UK National Johne's Management Plan and a link to videos describing the UK program and the progress it has made to date.

COMMENT

The UK program has all the same elements found in most national Johne’s disease programs:

1. Education of producers and veterinarians.
2. Herd risk assessments to identify when and where MAP transmission occurs on the farm.
3. Changes to animal husbandry methods to limit MAP transmission.
4. Regular application of diagnostic tests to all adults in the herd for many years.
5. Consistent actions based on the diagnostic test results.
6. Monitoring progress.

What is special about the UK program is that the main costs of implementing the program have been born by the farmers and milk processors, and indirectly by the milk market. There has not been any State involvement.

Pamela Steuer, working on the laboratory of Miguel Salgado at the Universidad Austral de Chile, published a series of three articles on the effects of copper ions on Mycobacterium avium subsp. paratuberculosis (MAP). This news story summarizes those three articles.

The first study, published in2018 in BMC Microbiology, showed that copper ions resulted in a significant reduction of MAP in suspended in saline (PBS), although some MAP survival on some occasions was observed.

The second study, published in 2020 in the Journal of Applied Microbiology, showed that copper ions have a significant inactivating effect on MAP as well as certain other bacterial communities found in naturally contaminated cow’s milk. However, there were some copper-tolerant MAP strains.

The third study, published in the July 2021 issue of Animals (Open Access), attempted to use copper treatment of milk to prevent infection of calves on farm. Below is the full abstract of that publication.

ABSTRACT

One of the important routes of Mycobacterium avium subsp. paratuberculosis (MAP) transmission in dairy calves is milk. The aim of the present study was to assess the efficacy of milk treatments to prevent MAP infection transmission to calves. A one-year longitudinal study was carried out. Newborn calves were assigned to one of four experimental groups: 5 calves received naturally MAP-contaminated milk, 5 calves received copper treated milk, 4 calves were fed calf milk replacer, and 3 were fed UHT pasteurized milk. MAP load in milk was estimated. Infection progression was monitored monthly. After one year, calves were euthanized, and tissue samples were cultured and visually examined. MAP was undetectable in milk replacer and UHT milk. Copper ion treatment significantly reduced the number of viable MAP in naturally contaminated milk. Fecal shedding of MAP was observed in all study groups but began earlier in calves fed naturally contaminated milk. Paratuberculosis control programs must place multiple hurdles between the infection source, MAP-infected adult cows, and the most susceptible animals on the farm, young calves. As our study shows, strict dependence on a single intervention to block infection transmission, no matter how important, fails to control this insidious infection on dairy farms.

COMMENT

This series of studies opens new avenues of investigation on use of copper to control of MAP. There are many applications of copper to kill MAP in settings other than the farm that can be explored. However, as the on-farm study showed, controlling MAP in dairy cattle requires multiple complimentary strategies to be effective.

The fact that a Chilean institution studied the effect of copper on MAP is no surprise. Chile produces more than one quarter of the world's copper and is also by far the country with the largest copper reserves.

Dr. C.T. Dow has published a thought-provoking article (11 pages with 169 references) proposing that the inflammatory response to a MAP infection of humans could lead to Alzheimer’s disease. The article appears in the August issue of Frontiers in Immunology.

ABSTRACT

This article prosecutes a case against the zoonotic pathogen Mycobacterium avium ss. paratuberculosis (MAP) as a precipitant of Alzheimer’s disease (AD). Like the other major neurodegenerative diseases AD is, at its core, a proteinopathy. Aggregated extracellular amyloid protein plaques and intracellular tau protein tangles are the recognized protein pathologies of AD. Autophagy is the cellular housekeeping process that manages protein quality control and recycling, cellular metabolism, and pathogen elimination. Impaired autophagy and cerebral insulin resistance are invariant features of AD. With a backdrop of age-related low-grade inflammation (inflammaging) and heightened immune risk (immunosenescence), infection with MAP subverts glucose metabolism and further exhausts an already exhausted autophagic capacity. Increasingly, a variety of agents have been found to favorably impact AD; they are agents that promote autophagy and reduce insulin resistance. The potpourri of these therapeutic agents: mTOR inhibitors, SIRT1 activators and vaccines are seemingly random until one recognizes that all these agents also suppress intracellular mycobacterial infection. The zoonotic mycobacterial MAP causes a common fatal enteritis in ruminant animals. Humans are exposed to MAP from contaminated food products and from the environment. The enteritis in animals is called paratuberculosis or Johne’s disease; in humans, it is the putative cause of Crohn’s disease. Beyond Crohn’s, MAP is associated with an increasing number of inflammatory and autoimmune diseases: sarcoidosis, Blau syndrome, autoimmune diabetes, autoimmune thyroiditis, multiple sclerosis, and rheumatoid arthritis. Moreover, MAP has been associated with Parkinson’s disease. India is one county that has extensively studied the human bio-load of MAP; 30% of more than 28,000 tested individuals were found to harbor, or to have harbored, MAP. This article asserts an unfolding realization that MAP infection of humans 1) is widespread in its presence, 2) is wide-ranging in its zoonosis and 3) provides a plausible link connecting MAP to AD.

COMMENT

(excerpt from the discussion section of the article)

This article suggests steps to further investigate this potentially fertile line of inquiry: 1) determine population-based MAP “bio-load”, 2) use optimized blood-based biomarkers to determine AD risk, 3) test for MAP in those with elevated AD risk vs. healthy controls. Concurrently, interventions could be initiated to 1) eliminate MAP from animals, the environment, and the food chain, 2) initiate clinical trials to test iterations of anti-mycobacterial agents shown to have benefit for AD. Parsimoniously, when searching for new directions in the efforts against AD, look at the MAP.

Lauren and John Todd Kuenstner have published an article titled: Mycobacterium avium ssp. paratuberculosis in the Food Supply: A Public Health Issue which appears in the most current issue of Frontiers in Public Health.

Article Description

This article examines the policy implications of Mycobacterium avium subspecies paratuberculosis (MAP) as a zoonotic pathogen and the public health risks posed by the presence of MAP in food, particularly milk products. Viable MAP has been cultured from commercially pasteurized milk in the US. Dairy pasteurization standards and regulations are examined in light of this finding. On the basis of the precautionary principle, the authors suggest options to reduce exposure to MAP, including (1) increased federal authority to regulate pasteurization of all dairy products, (2) modification of pasteurization standards in order to more effectively kill MAP, (3) removal of the Pasteurized Milk Ordinance (PMO) provision that allows states to override federal policy in intrastate dairy sales, and (4) creation of a mandatory Johne's Disease Control Program. These measures would reduce human exposure to MAP and may reduce the risk of diseases associated with MAP.

Comment

The Precautionary Principle is used in EU countries but less so in the US.  Wikipedia does an excellent job describing this principle that guides development of many governmental regulations.  It is worth reading the entire article, including criticisms are the very end.

Researchers in Mexico surveyed sheep flocks in the state of Aguascalientes in Mexico. Their findings were published in Abanico Veterinario.

ABSTRACT

With the objective of identifying the presence of Paratuberculosis (PTB), an infectious disease caused by Mycobacterium avium ssp paratuberculosis (MAP), in sheep, through pathological studies, bacterial culture and IS900 PCR, as well as estimating seroprevalence to MAP. The present cross-sectional study, was conducted in 16 different flocks, with the serum of 2415 adult sheep, and analyzed by Enzyme-Linked ImmunoSorbent Assay (ELISA); nine sheep were used with clinical signs suggestive of PTB, from which samples were obtained for the identification studies; obtaining 51.3% of animals seropositive to MAP (1239/2415), in 100% of the herds (16/16); Bacterial isolation and its identification by PCR IS900 were founded in five of the nine cases (5/9) corresponding to 31.25% of the herds (5/16). Confirming the presence of Mycobacterium avium ssp paratuberculosis, and a high frequency of seropositive animals to MAP in flocks of Aguascalientes.

RESUMEN

Con el objetivo de identificar la presencia de Paratuberculosis (PTB), enfermedad infecciosa causada por el Mycobacterium avium subsp paratuberculosis (MAP), en ovinos, a través de estudios anatomopatológicos, cultivo bacteriano y PCR IS900, así como estimar la seroprevalencia a MAP. El presente estudio, de tipo transversal, se realizó en 16 diferentes rebaños con el suero de 2415 animales adultos y analizados por Ensayo por Inmunoabsorción Ligado a Enzimas (ELISA); se emplearon nueve ovinos con signos clínicos sugerentes a PTB, de los cuales se obtuvieron muestras para la realización de los estudios de identificación; obteniendo un 51.3 % de animales seropositivos a MAP (1239/2415), en el 100% de los rebaños (16/16); el aislamiento bacteriano y su identificación por PCR IS900 en cinco de los nueve casos hallados (5/9) correspondiendo al 31.25% de los rebaños (5/16). Conformando la presencia del Mycobacterium avium subsp paratuberculosis, así como una elevada frecuencia de animales seropositivos a MAP en rebaños de Aguascalientes.

COMMENT

Johne’s disease is far more common than most sheep owners realize. Biosecurity regarding animal purchasing is critical to prevention of this economically important disease. This is especially true for sheep breeders. MAP infection prevention is far less costly than MAP infection control. In other words: PREVENTION PAYS. Sheep breeders should only buy animals from flocks that are 100% negative by fecal PCR. Breeders that don’t follow this practice will eventually have sheep that look like the one shown above from publication and then spend years and a lot of money trying to eradicate the infection.

Australian researchers have published the results of a large scale 10-year effort to control Johne’s disease in sheep, also known as ovine JD (OJD). The study was published in PLOS ONE (38 pages with 106 references). It is one of the most comprehensive and extensive field studies on JD vaccination and the publication is comprehensive in its discussion of OJD and the role of vaccination; highly recommended reading.

ABSTRACT

Background

Mycobacterium avium subsp. paratuberculosis (MAP) causes Johne’s disease (or paratuberculosis), a chronic wasting disease of ruminants and other animals resulting from granulomatous enteritis. There are increasing concerns that MAP is zoonotic. The prevalence of Johne’s disease is increasing worldwide. In an attempt to control an epidemic of ovine Johne’s disease (OJD) in New South Wales (NSW), a government/industry sponsored voluntary vaccination/on-farm management program commenced in 2000. We report herein an observational study of changes in disease prevalence as vaccination progressed, based on abattoir surveillance data for OJD from 1999 to 2009. We also discuss the epidemiological, policy, regulatory, research, economic and sociological elements that contributed to the development of a mature control program, whose aim was to halt the epidemic spread of OJD in a naïve sheep population.

Methods

NSW was divided into areas of “High” (HPA), “Medium” (MPA) and “Low” (LPA) OJD prevalence. A killed whole cell vaccine (Gudair®) was administered to sheep from 2000 to 2009. Trained examiners evaluated the viscera of adult sheep carcasses at slaughter for gross evidence of OJD. MAP infection was confirmed by histopathology.

Principal findings

From 2000–2009, 12 million vaccine doses were administered in NSW (91%; 10.9 million in the HPA). Many of the vaccinated flocks were suffering > 5% annual mortality in adult sheep, with some individual flocks with 10–15% losses attributable to OJD. A total of 7.6 million carcasses were examined (38%; 2.9 million from the HPA). Overall, 16% of slaughter consignments (sheep consigned to the abattoir from a single vendor) were positive for OJD, of which 94% were from the HPA. In the HPA, the percentage of animals with lesions attributable to OJD at slaughter fell progressively from 2.4% (10,406/432,860) at commencement of vaccination in 2000 to 0.8% (1,573/189,564) by 2009. Herd immunity from vaccination in the HPA was estimated at 70% by 2009, the target commonly espoused for an effective control program based on vaccination. This coincided with a progressive decrease in reports of clinical disease and mortalities in vaccinated flocks.

Significance

We show a decrease in the prevalence of lesions attributable to OJD in NSW concomitant with initiation of voluntary vaccination, on-farm management plans, abattoir monitoring and feedback of animal prevalence data to sheep producers. We conclude that a target of ≤ 1% regional prevalence of OJD affected sheep at slaughter is achievable using these interventions.

COMMENTS

As the authors noted, the decline in OJD animal-level prevalence was achieved “by the combination of voluntary vaccination, abattoir monitoring, feedback of surveillance data to sheep producers and the implementation of appropriate disease management strategies on farm”. The study was not designed to define the extent to which each of these practices contributed to OJD control, although there is a tendency to give the vaccine most of the credit.

Only 7 countries (31.8% of 22 countries with JD control programs) use vaccination as part of their JD control program (Whittington, 2019). This is due in part to conflicting data on the efficacy of vaccination, interference with TB testing and eradication programs, and the hazards of using the current vaccines. Presently, the widest use of JD vaccines is in countries with a significant small ruminant animal agriculture and then primarily in commercial production systems, as opposed to breeder flocks. This is largely due to economics, i.e., other JD control methods are deemed not affordable.

This important publication shows the economic value of vaccination as part of a comprehensive JD control effort at a regional or national level. Having lost the opportunity in most countries to eradicate JD before it became endemic, vaccination may become necessary for protection of both animal and human health. However, there is significant room for improvement in the safety and efficacy of current JD vaccines.