Effectiveness of Gudair™ vaccine for the control of ovine Johne's disease in flocks vaccinating for at least 5 years

Adjuvants influence the immune cell populations present at the injection site granuloma induced by whole-cell inactivated paratuberculosis vaccines in sheep

Vaccination is the most effective tool for paratuberculosis control. Currently, available vaccines prevent the progression of clinical disease in most animals but do not fully protect them against infection and induce the formation of an injection site granuloma. The precise mechanisms that operate in response to vaccination and granuloma development, as well as the effect that adjuvants could trigger, have not been fully investigated. Therefore, this study aimed to investigate the injection site granulomas induced by two inactivated paratuberculosis vaccines, which differ in the adjuvant employed. Two groups of 45-day-old lambs were immunized with two commercially available vaccines-one (n = 4) with Gudair® and the other (n = 4) with Silirum®. A third group (n = 4) was not vaccinated and served as control. The peripheral humoral response was assessed throughout the study by a commercial anti-Mycobacterium avium subspecies paratuberculosis (Map) antibody indirect ELISA, and the cellular immune response was assessed similarly by the IFN-γ release and comparative intradermal tests. The injection site granulomas were measured during the experiment and sampled at 75 days post-vaccination (dpv) when the animals were euthanized. The tissue damage, antigen and adjuvant distribution, and the presence and amount of immune cells were then determined and assessed by immunohistochemical methods. Antibodies against Map antigens; a general macrophage marker (Iba1), M1 (iNOS), and M2 (CD204) macrophages; T (CD3), B (CD20), and γδ T lymphocytes, proteins MHC-II and NRAMP1, and cytokines IL-4, IL-10, TNF, and IFN-γ were employed. Silirum® elicited a stronger peripheral cellular immune response than Gudair®, while the latter induced larger granulomas and more tissue damage at the site of injection. Additionally, adjuvant and Map antigen distribution throughout the granulomatous inflammatory infiltrate, as well as the NRAMP1 cell expression, which is linked to antigen phagocytosis, were highly irregular. In Silirum® induced granulomas, a higher number of MHC-II and TNF-expressing cells and a lower number of M2 macrophages suggested an improved antigen presentation, which could be due to the better antigen distribution and reduced tissue damage induced by this vaccine.

Characterization of early immune responses elicited by live and inactivated vaccines against Johne's disease in goats

Mycobacterium avium subspecies paratuberculosis (M. paratuberculosis) is the causative agent of Johne's disease, a chronic debilitating condition affecting ruminants causing significant economic losses to the dairy industry. Available inactivated vaccines are not effective in controlling the disease and vaccinated animals can continue to infect newly born calves. Recently, we have shown that a live-attenuated vaccine candidate (pgsN) is protective in goats and calves following challenge with virulent strains of M. paratuberculosis. To decipher the dynamics of the immune responses elicited by both live-attenuated and inactivated vaccines, we analyzed key immunological parameters of goats immunized through different routes when a marker-less pgsN vaccine was used. Within a few weeks, the inactivated vaccine triggered the formation of granulomas both at the site of inoculation and in regional lymph nodes, that increased in size over time and persisted until the end of the experiment. In contrast, granulomas induced by the pgsN vaccine were small and subsided during the study. Interestingly, in this vaccine group, histology demonstrated an initial abundance of intra-histiocytic mycobacterial bacilli at the site of inoculation, with recruitment of very minimal T lymphocytes to poorly organized granulomas. Over time, granulomas became more organized, with recruitment of greater numbers of T and B lymphocytes, which coincided with a lack of mycobacteria. For the inactivated vaccine group, mycobacterial bacilli were identified extracellularly within the center of caseating granulomas, with relatively equal proportions of B- and T-lymphocytes maintained across both early and late times. Despite the differences in granuloma-specific lymphocyte recruitment, markers for cell-mediated immunity (e.g., IFN-γ release) were robust in both injected pgsN and inactivated vaccine groups. In contrast, the intranasal live-attenuated vaccine did not elicit any reaction at site of inoculation, nor cell-mediated immune responses. Finally, 80% of animals in the inactivated vaccine group significantly reacted to purified protein derivatives from M. bovis, while reactivity was detected in only 20% of animals receiving pgsN vaccine, suggesting a higher level of cross reactivity for bovine tuberculosis when inactivated vaccine is used. Overall, these results depict the cellular recruitment strategies driving immune responses elicited by both live-attenuated and inactivated vaccines that target Johne's disease.

Correlates of vaccine protection against Mycobacterium avium sub-species paratuberculosis infection revealed in a transcriptomic study of responses in Gudair® vaccinated sheep

A critical hindrance in the development of effective vaccine strategies to combat infectious disease is lack of knowledge about correlates of protection and of the host responses necessary for successful adaptive immunity. Often vaccine formulations are developed by stepwise experimentation, with incomplete investigation of the fundamental mechanisms of protection. Gudair^® is a commercially available vaccine registered for use in sheep and goats for controlling spread of Mycobacterium avium sub-species paratuberculosis (MAP) infections and reduces mortality by up to 90%. Here, using an experimental infection model in sheep, we have utilized a transcriptomics approach to identify white blood cell gene expression changes in vaccinated, MAP-exposed Merino sheep with a protective response in comparison to those vaccinated animals that failed to develop immunity to MAP infection. This methodology facilitated an overview of gene-associated functional pathway adaptations using an in-silico analysis approach. We identified a group of genes that were activated in the vaccine-protected animals and confirmed stability of expression in samples obtained from naturally exposed commercially maintained sheep. We propose these genes as correlates of vaccine induced protection.

Effects of Paratuberculosis Vaccination at Different Ages in a Dairy Goat Herd: A 2-Year Follow-Up

Vaccination could be considered as an effective method for paratuberculosis control, although controversial, with a need for investigation in some aspects. The objective of this study was to evaluate the effect of vaccination, depending on the age of the animals, on their immune response, the reduction of paratuberculosis cases, mortality and culled animals in a commercial dairy herd. Goats from three different ages were immunized with the inactivated Gudair^® vaccine. Peripheral antibody and IFN-γ output were evaluated for 21 months post-vaccination (mpv) and intradermal skin tests (IDSTs) for tuberculosis, with avian- and bovine-purified protein derivatives (PPD), were carried out at 6 and at 18 mpv to evaluate the humoral and cellular immune peripheral responses, respectively. The number of dead or culled animals, regardless of the reason, was also monitored and the causes of death determined by pathological examination. A significant increase in the production of IFN-γ was observed in all the vaccinated groups when the blood samples were stimulated with avian PPD, from 3 mpv to 18 mpv, and with bovine PPD, between 3 and 21 mpv. Moreover, serum antibody levels increased between 3 and 21 mpv in all vaccinated groups. The highest levels were found in animals vaccinated at 5 months, and the lowest in adult individuals. No positive reactants to tuberculosis were found by intradermal skin test. No animal losses associated with clinical paratuberculosis were detected in any of the groups. The number of total culled animals was significantly lower in the vaccinated than in the unvaccinated groups, especially on 1.5-month-old vaccinated kids. These results suggest that vaccination of paratuberculosis, especially in young animals, could induce heterologous protection.

Effect of heat-inactivated Mycobacterium avium subspecies paratuberculosis (MAP) vaccine on the lesions and immunopathology developed in target tissues of naturally MAP-infected goats

Paratuberculosis (PTB) is a disease caused by Mycobacterium avium subspecies paratuberculosis (MAP), which affects a broad range of hosts, including domestic and wild animals. PTB is a chronic granulomatous enteritis and lymphadenitis that compromises animal welfare and causes economic losses. The objective of this study was to evaluate the effect of a commercial heat-inactivated MAP vaccine on lesions and immunopathology developed in the target tissues of goats naturally infected with MAP. Lesions compatible with PTB in the intestine and regional lymph nodes (LNs), as well as local immune response to MAP, were evaluated and compared in Gudair®-vaccinated (n = 14) and unvaccinated (n = 11) goats from a MAP-infected farm. The percentage of animals with multifocal granulomatous lesions in the jejunal (p = 0.05) and ileocecal (p = 0.02) LNs was higher in unvaccinated animals, while a lesion score reduction of 50% was found in the LNs of vaccinated animals. Unvaccinated animals showed increased numbers and wider distribution of macrophages (MΦs, CD68 +) in histiocytic infiltrate (p = 0.0003), associated with increased numbers of mycobacteria. Increased inducible nitric oxide synthase (iNOS) expression was also reported in these animals, while M2 MΦs (CD163 +) were scarce in both groups. Vaccinated animals showed an increase in CD3 + lymphocytes, although differences in interferon gamma (IFNγ) were negligible. These results support the hypothesis that heat-inactivated MAP vaccination could reduce the severity of PTB lesions and mycobacterial load in target tissues in vaccinated adult goats.

Evaluation of a virulent strain of Mycobacterium avium subsp. Paratuberculosis used as a heat-killed vaccine

Bovine paratuberculosis is one of the most important chronic infectious diseases in livestock. This disease is difficult to control because of its inefficient management (test and cull strategy and inadequate biosecurity). Thus, the development of an effective vaccine is essential. In this study, we evaluated a local virulent strain (6611) of Mycobacterium avium subsp. paratuberculosis as an inactivated vaccine in comparison with the Silirum vaccine in mouse model and cattle. Regarding the mice model, only the groups vaccinated with 6611 showed lower colony forming unit (CFU) counts with a lower lesion score in the liver in comparison to the control group at 6 and 12 weeks post-challenge (wpc). The immune response was predominantly humoral (IgG1), although both vaccinated groups presented a cellular response with IFNγ production as well, but the 6611 group had also significant production of IL-2, IL-6, IL-17a, TNF, and IL-10. In cattle, the 6611 vaccinated group was the only one that maintained significant antibody values at the end of the trial, with significant production of IgG2 and IFNγ. No PPDb reactor was detected in the vaccinated animals, according to the intradermal caudal fold tuberculin test. Our results indicate that the 6611 local strain protected mice from challenge with a virulent strain, by inducing a humoral and cellular immune response. In the bovine, the natural host, the evaluated vaccine also induced humoral and cellular immune responses, with higher levels of CD4 + CD25+ and CD8 + CD25+ T cells populations than the commercial vaccine. Despite the encouraging results obtained in this study, an experimental challenge trial in cattle is mandatory to evaluate the efficacy of our candidate vaccine in the main host.

Is vaccination a viable method to control Johne's disease caused by Mycobacterium avium subsp. paratuberculosis? Data from 12 million ovine vaccinations and 7.6 million carcass examinations in New South Wales, Australia from 1999-2009

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.

Continuity in ovine Johne's disease vaccination practices despite a decline in clinical disease

The Gudair® vaccine has been commercially available in Australia for almost two decades for the control of ovine Johne's disease, but concerns have been raised about potential discontinuation of vaccination by producers after a decline in the incidence of clinical disease. An online questionnaire was distributed to Australian sheep producers to identify the proportion of respondents discontinuing the Gudair vaccine and reasons for discontinuation. Results revealed that 88% of sheep producers surveyed have continued to vaccinate their sheep with Gudair, with continuation greater for predominantly Merino sheep flocks. Reasons for discontinuing vaccination stemmed from management, economic or health concerns. These results suggest that Gudair is still widely used by Australian sheep producers and concerns about large-scale discontinuation are unfounded. These findings have implications for ovine Johne's disease control programs in Australia.

Factors influencing the effectiveness of the Gudair vaccine for controlling Johne's disease in sheep flocks in Australia

Ovine Johne's disease is a chronic debilitating disease of sheep caused by Mycobacterium avium subsp. paratuberculosis (Mptb) which results in diarrhoea, emaciation and mortalities in infected animals. Vaccination with Gudair® has been a key strategy for controlling the disease in Australia since its approval in 2002. Previous research conducted in Australia has demonstrated that the vaccine is quite effective in reducing sheep mortalities. While some farms have also been successful in reducing the prevalence of the disease in their flocks to undetectable levels, sheep in other flocks continue to shed Mptb in faeces even after an ongoing vaccination program . This study was conducted to investigate management, husbandry and biosecurity factors associated with paratuberculosis infection in Gudair® vaccinated sheep flocks in Australia. We enrolled 64 sheep farmers and interviewed them to obtain information about their management and biosecurity practices. Pooled faecal samples were collected from sheep at each farm and cultured to create two outcome variables: Mptb positive (yes/no) and disease prevalence level (nil, < 1 %, ≥ 1 %). Binary and ordinal logistic regression analyses were conducted to evaluate the association of management, husbandry and biosecurity factors with these outcome variables. Farms were more likely to have Mptb positive sheep and a higher disease prevalence in their flocks if they: (a) provided supplementary feed on the ground (instead of in a trough); (b) had a greater number of neighbours with sheep; and (c) had introduced rams from a greater number of sources. The results suggest the effectiveness of Gudair® vaccination to control OJD can be improved if sheep producers maintain other risk management strategies and biosecurity practices. Extension agencies should advise farmers not to relax their biosecurity practices and to purchase rams from only low-risk sources, even if they are continuing to vaccinate their flocks.

Ovine Paratuberculosis Control in Australia Revisited

Simple Summary

Ovine Johne’s Disease (OJD) is caused by Mycobacterium avium subspecies paratuberculosis (MAP) and is a less serious animal health issue in Australia than it was 10–20 years ago, with abattoir surveillance confirming declining prevalence. Control strategies for paratuberculosis potentially include (i) test and cull programs; (ii) management interventions to reduce faecal–oral transmission; and/or (iii) vaccination to limit and suppress infection, with the decline in OJD concern in Australia mostly attributable to vaccination programs providing effective disease suppression. However, as disease spread has continued, control program extension renewal to encourage the safe and wider use of vaccination, plus address misinformation promulgated by some disaffected producers, is required. As vaccination for OJD has contributed significantly to the welfare of Australian sheep, the livelihoods of producers, and reduced risk of MAP entering the human food chain, it should be more widely adopted globally.

Abstract

OJD is no longer the serious animal health issue that it was for many Australian rural communities a decade and a half ago. Despite declining OJD prevalence as determined by abattoir surveillance, the disease continues to spread, with OJD extension programs required to continually address the misinformation promulgated by some disaffected producers as new areas have become affected. Improved regional and on-farm biosecurity, including the introduction of a risk-based trading system, may have contributed to improved attitudes to OJD control, although attitudinal differences between OJD endemic areas and where the disease is not well established remain. Declines in on-farm OJD prevalence are almost certainly attributable to the widespread uptake of vaccination programs, although encouraging the ongoing use of vaccination to prevent recrudescence and improved biosecurity when mortalities disappear, remains challenging. Vaccination has provided a robust strategy for managing OJD and contributed significantly to the health of Australian sheep and the lives of producers with affected properties. As vaccination offers a pathway to reduce the risk of MAP infection entering the human food chain from small ruminant products, it should be more widely adopted globally, accompanied by research efforts to improve efficacy and importantly, the safety of vaccination to both operators and livestock.

Vaccine approaches for the 'therapeutic management' of Mycobacterium avium subspecies paratuberculosis infection in domestic livestock

High endemicity of Johne’s disease (JD) in herds adversely affects heavy milk yielding breeds by reducing the per animal productivity and ‘productive life-span’. This review evaluates different vaccines used for its control and summarizes the benefits of ‘global vaccine’ in the four major domestic livestock species, namely goat, sheep, buffalo and cattle. Vaccines developed by using ‘native strains’ revealed both 'therapeutic' and preventive effects in domestic livestock. The 'therapeutic' role of vaccine in animals suffering from clinical JD turned out to be valuable in some cases by reversing the disease process and animals returning back to health and production. Good herd management, improved hygiene, ‘test and cull’ methodology, proper disposal of animal excreta and monitoring of MAP bio-load were also regarded as crucial in the 'therapeutic' management of JD. Vaccine approaches have been widely adopted in JD control programs and may be considered as a valuable adjunct in order to utilize huge populations of otherwise un-productive livestock. It has been shown that vaccination was the preeminent strategy to control JD, because it yielded approximately 3–4 times better benefit-to-cost ratios than other strategies. Internationally, 146 vaccine trials/studies have been conducted in different countries for the control of JD and have shown remarkable reduction in its national prevalence. It is concluded that for JD, there cannot be global vaccines or diagnostic kits as solutions have to come from locally prevalent strains of MAP. Despite some limitations, vaccines might still be an effective strategy to reduce or eradicate JD.

A Novel Approach to Deliver a Mycobacterium avium subsp. paratuberculosis Antigen in Eukaryotic Cells

This study was aimed to express and deliver a Mycobacterium avium subsp. paratuberculosis antigen to macrophages using salmonella as carrier. The coding sequence of a fibronectin attachment protein which is expressed by Mycobacterium avium subsp. paratuberculosis was cloned into pcDNA3.1 (+) plasmid. The construct was introduced into the attenuated Salmonella typhimurium strain SL7207 (ΔhisG, ΔaroA) as carrier. In order to evaluate the delivery capacity of Salmonella and gene expression by antigen-presenting cells, the THP-1 derived macrophages were infected with the salmonella carrier. SDS-PAGE and western blot analysis showed the successful delivery and expression of targeted gene in THP-1 cell line. Although, in vitro stimulation of peripheral blood mononuclear cells with Salmonella containing plasmid did not trigger IFNγ production significantly. But it seems that this carrier can increase plasmid uptake and antigen expression by host intestinal antigen-presenting cells after mucosal administration. So, the construct can be used for further in vivo studies on the Salmonella carrier's efficiency in mycobacterial DNA vaccines.

Protection efficacy of Argentinian isolates of Mycobacterium avium subsp. paratuberculosis with different genotypes and virulence in a murine model

Paratuberculosis is a chronic disease caused by Mycobacterium avium subsp. paratuberculosis (Map). The disease causes economic losses and, therefore, it is imperative to follow proper control strategies, which should include an effective vaccine. Several strategies have assessed the virulence and immune response of Map strains that could be used as a vaccine. This study evaluates the degree of virulence, immune response, and protection of Argentinian strains of Map with different genotype in a murine model. Four local isolates (Cattle type) with different genotypes (analyzed by MIRU-VNTR and SSRs) were selected and evaluated in a virulence assay in BALB/c mice. This assay allowed us to differentiate virulent and low-virulence Map strains. The less virulent strains (1543/481 and A162) failed to induce a significant production of the proinflammatory cytokine IFNg, whereas the virulent strain 6611 established infection along with a proinflammatory immune response. On the other hand, the virulent strain 1347/498 was efficient in establishing a persistent infection, but failed to promote an important Th1 response compared with 6611 at the evaluated time. We selected the low-virulence strain 1543/498 as a live vaccine and the virulent strain 6611 as a live and inactivated vaccine in a protection assay in mice. Strain 1543/481 failed to protect the animals from challenge, whereas strain 6611, in its live and inactivated form, significantly reduced the CFUs count in the infected mice, although they had different immunological response profiles. The inactivated virulent strain 6611 is a potential vaccine candidate against paratuberculosis to be tested in cattle.

Knowledge gaps that hamper prevention and control of Mycobacterium avium subspecies paratuberculosis infection

In the last decades, many regional and country-wide control programmes for Johne's disease (JD) were developed due to associated economic losses, or because of a possible association with Crohn's disease. These control programmes were often not successful, partly because management protocols were not followed, including the introduction of infected replacement cattle, because tests to identify infected animals were unreliable, and uptake by farmers was not high enough because of a perceived low return on investment. In the absence of a cure or effective commercial vaccines, control of JD is currently primarily based on herd management strategies to avoid infection of cattle and restrict within-farm and farm-to-farm transmission. Although JD control programmes have been implemented in most developed countries, lessons learned from JD prevention and control programmes are underreported. Also, JD control programmes are typically evaluated in a limited number of herds and the duration of the study is less than 5 year, making it difficult to adequately assess the efficacy of control programmes. In this manuscript, we identify the most important gaps in knowledge hampering JD prevention and control programmes, including vaccination and diagnostics. Secondly, we discuss directions that research should take to address those knowledge gaps.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): paratuberculosis

Paratuberculosis has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on the eligibility of paratuberculosis to be listed, Article 9 for the categorisation of paratuberculosis according to disease prevention and control rules as in Annex IV and Article 8 on the list of animal species related to paratuberculosis. The assessment has been performed following a methodology composed of information collection and compilation, expert judgement on each criterion at individual and, if no consensus was reached before, also at collective level. The output is composed of the categorical answer, and for the questions where no consensus was reached, the different supporting views are reported. Details on the methodology used for this assessment are explained in a separate opinion. According to the assessment performed, paratuberculosis can be considered eligible to be listed for Union intervention as laid down in Article 5(3) of the AHL. The disease would comply with the criteria in Sections 3, 4 and 5 of Annex IV of the AHL, for the application of the disease prevention and control rules referred to in points (c), (d) and (e) of Article 9(1). The animal species to be listed for paratuberculosis according to Article 8(3) criteria are several species of mammals and birds as susceptible species and some species of the families Bovidae, Cervidae and Leporidae as reservoirs.

Superior Protection from Live-Attenuated Vaccines Directed against Johne's Disease

Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) is the etiological agent of Johne's disease in ruminants. Johne's disease is an important enteric infection causing large economic losses associated with infected herds. In an attempt to fight this infection, we created two novel live-attenuated vaccine candidates with mutations in sigH and lipN (pgsH and pgsN, respectively). Earlier reports in mice suggested these vaccines are promising candidates to fight Johne's disease in ruminants. In this study, we tested the performances of the two constructs as vaccine candidates using the goat model of Johne's disease. Both vaccines appeared to provide significant immunity to goats against challenge from wild-type M. paratuberculosis The pgsH and pgsN constructs showed a significant reduction in histopathological lesions and tissue colonization compared to nonvaccinated goats and those vaccinated with an inactivated vaccine. Unlike the inactivated vaccine, the pgsN construct was able to eliminate fecal shedding from challenged animals, a feature that is highly desirable to control Johne's disease in infected herds. Furthermore, strong initial cell-mediated immune responses were elicited in goats vaccinated with pgsN that were not demonstrated in other vaccine groups. Overall, the results indicate the potential use of live-attenuated vaccines to control intracellular pathogens, including M. paratuberculosis, and warrant further testing in cattle, the main target for Johne's disease control programs.

Changes in prevalence of ovine paratuberculosis following vaccination with Gudair®: Results of a longitudinal study conducted over a decade

Since its registration in 2002, Gudair® vaccine has become the key tool for managing paratuberculosis in sheep in Australia. This study was conducted to evaluate its effectiveness in reducing paratuberculosis prevalence in 12 flocks over more than one decade. Flocks with variable initial prevalence (5, 4 and 3 with low, medium, and high prevalence, respectively) were enrolled in the study in 2003-04. Six biennial faecal samplings were conducted in these flocks over a 10year period. At each sampling, faeces from four age groups (3, 4, 5 and 6year-old sheep) were collected from each flock. The aim was to select 7 or 14 pools of faeces constituted with pellets from 50 or 25 sheep from each age group, respectively, but the numbers and sizes of pools did vary due to logistical issues. Samples were cultured using pooled faecal culture approach and sheep level paratuberculosis prevalence was estimated. Changes in probability of a pool being positive and in paratuberculosis prevalence over time were evaluated by fitting generalised-linear and linear mixed models. The proportion of positive faecal pools significantly declined over time from 50.3% at the first sampling in 2003-04 to only 3.1% at the last sampling in 2013-14, suggestive of a 30-fold reduction in the odds of a pooled faecal sample to be positive (p<0.001). Similarly, the average animal level prevalence in flocks dropped from 7.64% at the first sampling to 0.12% at the last sampling. However, faecal shedding persisted and was still present in 3 of the 8 flocks (37.5%) that remained in the study at the last sampling conducted in 2013-14. This is the longest study ever conducted to evaluate paratuberculosis vaccine effectiveness. The results will enable sheep producers to make informed decisions on managing paratuberculosis, and in evaluating the risks of purchasing and trading vaccinated sheep.

Development of vaccines to Mycobacterium avium subsp. paratuberculosis infection

Johne's disease or paratuberculosis is a chronic debilitating disease in ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). The disease causes significant economic losses in livestock industries worldwide. There are no effective control measures to eradicate the disease because there are no appropriate diagnostic methods to detect subclinically infected animals. Therefore, it is very difficult to control the disease using only test and cull strategies. Vaccination against paratuberculosis has been considered as an alternative strategy to control the disease when combined with management interventions. Understanding host-pathogen interactions is extremely important to development of vaccines. It has long been known that Th1-mediated cellular immune responses are play a crucial role in protection against MAP infection. However, recent studies suggested that innate immune responses are more closely related to protective effects than adaptive immunity. Based on this understanding, several attempts have been made to develop vaccines against paratuberculosis. A variety of ideas for designing novel vaccines have emerged, and the tests of the efficacy of these vaccines are conducted constantly. However, no effective vaccines are commercially available. In this study, studies of the development of vaccines for MAP were reviewed and summarized.

Paratuberculosis in sheep and goats

Paratuberculosis is a chronic insidious, often serious, disease of the global small ruminant industries, mainly causing losses from mortalities and reduced productivity on-farm, interference in trading and, in Australia, profound socio-economic impacts that have periodically compromised harmony of rural communities. The pathogenesis, diagnosis, impacts and disease management options for ovine and caprine paratuberculosis are reviewed, comparing current controls in the extensive management system for sheep in wool flocks in Australia with the semi-intensive system of dairy flocks/herds in Greece. Improved understanding of the immune and cellular profiles of sheep with varying paratuberculosis outcomes and the recognition of the need for prolonged vaccination and biosecurity is considered of relevance to future control strategies. Paratuberculosis in goats is also of global distribution although the prevalence, economic impact and strategic control options are less well recognized, possibly due to the relatively meagre resources available for goat industry research. Although there have been some recent advances, more work is required on developing control strategies for goats, particularly in dairy situations where there is an important need for validation of improved diagnostic assays and the recognition of the potential impacts for vaccination. For all species, a research priority remains the identification of tests that can detect latent and subclinical infections to enhance removal of future sources of infectious material from flocks/herds and the food chain, plus predict the likely outcomes of animals exposed to the organism at an early age. Improving national paratuberculosis control programs should also be a priority to manage disease risk from trade. The importance of strong leadership and communication, building trust within rural communities confused by the difficulties in managing this insidious disease, reflects the importance of change management considerations for animal health authorities. Although concerns of vaccine efficacy, safety and issues with diagnosis and administration persist, vaccination is increasingly recognized as providing a robust strategy for managing paratuberculosis, having made important contributions to the health of Australian sheep and the lives of producers with affected properties, and offering a mechanism to reduce risk of infection entering the food chain in ovine and caprine products.