Routes of intraspecies transmission of Mycobacterium avium subsp. paratuberculosis in rabbits (Oryctolagus cuniculus): a field study

The role of Mce proteins in Mycobacterium avium paratuberculosis infection

Mycobacterium avium subspecies paratuberculosis (MAP) is the causative agent of Johne's Disease, a chronic granulomatous enteritis of ruminants. MAP establishes an infection in the host via the small intestine. This requires the bacterium to adhere to, and be internalised by, cells of the intestinal tract. The effector molecules expressed by MAP for this purpose remain to be fully identified and understood. Mammalian cell entry (mce) proteins have been shown to enable other Mycobacterial species to attach to and invade host epithelial cells. Here, we have expressed Mce1A, Mce1D, Mce3C and Mce4A proteins derived from MAP on the surface of a non-invasive Escherichia coli to characterise their role in the initial interaction between MAP and the host. To this end, expression of mce1A was found to significantly increase the ability of the E. coli to attach and survive intracellularly in human monocyte-like THP-1 cells, whereas expression of mce1D was found to significantly increase attachment and invasion of E. coli to bovine epithelial cell-like MDBK cells, implying cell-type specificity. Furthermore, expression of Mce1A and Mce1D on the surface of a previously non-invasive E. coli enhanced the ability of the bacterium to infect 3D bovine basal-out enteroids. Together, our data contributes to our understanding of the effector molecules utilised by MAP in the initial interaction with the host, and may provide potential targets for therapeutic intervention.

Alternatives to antibiotics in veterinary medicine: considerations for the management of Johne's disease

Antibiotic resistance has become a major health concern globally, with current predictions expecting deaths related to resistant infections to surpass those of cancer by 2050. Major efforts are being undertaken to develop derivative and novel alternatives to current antibiotic therapies in human medicine. What appears to be lacking however, are similar efforts into researching the application of those alternatives, such as (bacterio)phage therapy, in veterinary contexts. Agriculture is still undoubtedly the most prominent consumer of antibiotics, with up to 70% of annual antibiotic usage attributed to this sector, despite policies to reduce their use in food animals. This not only increases the risk of resistant infections spreading from farm to community but also the risk that animals may acquire species-specific infections that subvert treatment. While these diseases may not directly affect human welfare, they greatly affect the profit margin of industries reliant on livestock due to the cost of treatments and (more frequently) the losses associated with animal death. This means actively combatting animal infection not only benefits animal welfare but also global economies. In particular, targeting recurring or chronic conditions associated with certain livestock has the potential to greatly reduce financial losses. This can be achieved by developing novel diagnostics to quickly identify ill animals alongside the design of novel therapies. To explore this concept further, this review employs Johne's disease, a chronic gastroenteritis condition that affects ruminants, as a case study to exemplify the benefits of rapid diagnostics and effective treatment of chronic disease, with particular regard to the diagnostic and therapeutic potential of phage.

Intestinal Mycobacterium avium Infection in Pet Dwarf Rabbits (Oryctolagus cuniculus)

Mycobacteriosis has been rarely described in pet rabbits (Oryctolagus cuniculus). Here we present two cases of intestinal mycobacteriosis from north-eastern Germany. The first adult rabbit was euthanized due to severe cardiovascular failure, hypothermia and chronic weight loss. Necropsy revealed cachexia and a focal, fibrinonecrotic lesion in the caecum. Histologically, severe granulomatous inflammation, with numerous multinucleated giant cells and abundant acid-fast bacilli, was detected under the fibrinonecrotic material in the abdominal wall adjacent to the caecal lesion, caecal lymph nodes, spleen, liver and lungs. Microbiological culture detected Mycobacterium avium subspecies hominissuis, Escherichia coli, Clostridium disporicum and Bacteroides ovatus. A retrospective assessment of 2,013 other pet rabbit necropsies, performed between 1995 and 2019, revealed one additional case of intestinal mycobacteriosis. This animal had been euthanized due to persistent hindlimb lameness and necropsy revealed comminuted fractures of the pelvic bones and multiple large liquefied abscess-like lesions in the caecal and colonic walls. Histology revealed granulomatous inflammation with acid-fast bacilli. Polymerase chain reaction on formalin-fixed, paraffin-embedded tissue identified the presence of M. avium spp. In contrast to European wild rabbits (Oryctolagus cuniculus) from Scotland, these findings indicate that intestinal mycobacteriosis is rare in pet rabbits from north-eastern Germany. Zoonotic potential should be considered due to the close contact between pets and their owners and the chronic course of the disease with an initial lack of clinical signs.

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.

Mycobacterial Infections in Rabbits: From the Wild to the Laboratory

Tuberculous mycobacterial diseases such as leprosy and tuberculosis are ancient diseases that currently continue threatening human health in some countries. Non-tuberculous mycobacterial (NTM) infections cause a series of well-defined pathological entities, as well as some opportunistic diseases that have also increased worldwide, being more common among immunocompromised patients but rising also in immunocompetent individuals. Reports on natural infections by mycobacteria in rabbits are scarce and mainly involve NTM such as Mycobacterium avium subsp. avium in pigmy rabbits in the United States and Mycobacterium avium subsp. paratuberculosis in wild rabbits in Europe. Rabbits have been used as laboratory animals through the years, both to generate immunological reagents and as infection models. Mycobacterial infection models have been developed in this animal species showing different susceptibility patterns to mycobacteria in laboratory conditions. The latent tuberculosis model and the cavitary tuberculosis model have been widely used to elucidate pathogenic mechanisms and to evaluate chemotherapy and vaccination strategies. Rabbits have also been used as bovine paratuberculosis infection models. This review aimed to gather both wildlife and experimental infection data on mycobacteriosis in rabbits to assess their role in the spread of these infections as well as their potential use in the experimental study of mycobacterial pathogenesis and treatment.

The potential Public Health Impact of Mycobacterium avium ssp. paratuberculosis: Global Opinion Survey of Topic Specialists

Global research knowledge has accumulated over the past few decades, and there is reasonable evidence for a positive association between Mycobacterium avium spp. paratuberculosis and Crohn's disease in humans, although its role as a human pathogen has not been entirely accepted. For this reason, management of public health risk due to M. paratuberculosis remains an important policy issue in agri-food public health arenas in many countries. Responsible authorities must decide whether existing mitigation strategies are sufficient to prevent or reduce human exposure to M. paratuberculosis. A Web-based questionnaire was administered to topic specialists to elicit empirical knowledge and opinion on the overall public health impact of M. paratuberculosis, the importance of various routes of human exposure to the pathogen, existing mitigation strategies and the need for future strategies. The questionnaire had four sections and consisted of 20 closed and five open questions. Topic specialists believed that M. paratuberculosis is likely a risk to human health (44.8%) and, given the paucity of available evidence, most frequently ranked it as a moderate public health issue (40.1%). A significant correlation was detected between topic specialists' commitment to M. paratuberculosis in terms of the number of years or proportion of work dedicated to this topic, and the likelihood of an extreme answer (high or low) to the above questions. Topic specialists identified contact with ruminants and dairy products as the most likely routes of exposure for humans. There was consensus on exposure routes for ruminants and what commodities to target in mitigation efforts. Described mandatory programmes mainly focused on culling diseased animals and voluntary on-farm prevention programmes. Despite ongoing difficulties in the identification of subclinical infections in animals, the topic specialists largely agreed that further enhancement of on-farm programmes in affected commodities by the agri-food industry (68.4%) and allocation of resources by governments to monitor the issue (92%) are most appropriate given the current state of evidence.

A systematic review of risk factors associated with the introduction of Mycobacterium avium spp. paratuberculosis (MAP) into dairy herds

The objective of this study was to systematically collect and appraise the scientific evidence related to risk factors associated with the introduction of Mycobacterium avium spp. paratuberculosis (MAP) into a herd of cattle. An electronic search was conducted to collect relevant references addressing 2 specific questions: are i) purchasing/introduction of cattle into a herd, and ii) presence of wildlife or domestic animals, risk factors for the introduction of MAP into a herd? The screening was based on titles and abstracts and selected studies were fully analyzed. Seventeen manuscripts published between 1996 and 2011 were ultimately analyzed. Unit of interest was mainly the herd (n = 17). The specific description of the risk factors studied varied between studies. The principal study design was cross-sectional (n = 15). The review indicated that purchase/introduction of animals was an important risk factor and that the importance of wildlife or other domestic species as a mechanism for transmission into a cattle herd was not measurable.

Mycobacterium avium subspecies paratuberculosis is widely distributed in British soils and waters: implications for animal and human health

In the first comprehensive geographical survey of distribution in Great Britain, Mycobacterium avium ssp. paratuberculosis (MAP) was detected in 115 of 1092 (10.5%) soil cores, in the range of 5 × 10(2) to 3 × 10(6) MAP cell equivalents (CE) g(-1) wet weight soil with the majority of the positive PCR reactions (n = 75; 65%) occurring around the limit of detection (500-5000 CE g(-1) wet weight soil). The distribution of MAP significantly increased from North to South and was significantly correlated with increasing cattle numbers over the same longitudinal axis. Similarly MAP occurrence significantly increased towards easterly latitudes although none of the parameters measured were associated. Comparisons of land use indicated that MAP was widely distributed in both farming and non-farming areas. Soil core samples taken from the rivers Wyre and Douglas catchments (Lancashire, UK) and river Tywi (South Wales) were negative for MAP. However, river monitoring showed a consistent presence of MAPs throughout those catchments over a 6-month period. We concluded that MAP is widely distributed within and outside the confines of the farming environment; its geographical distribution is wider than originally anticipated and; monitoring rivers describes the MAP status of catchment better than individual soil samples.

Wildlife and paratuberculosis: a review

Paratuberculosis (PTB) is an infectious granulomatous enteritis caused by Mycobacterium avium paratuberculosis (MAP) causing significant economic losses in livestock. However, PTB in free-living and captive wildlife has not been as extensively studied as in livestock. We reviewed the existing literature references on MAP to (i) determine the potential impact of MAP infection in wildlife species; (ii) analyze whether wildlife reservoirs are relevant regarding MAP control in domestic ruminants; (iii) assess the importance of MAP as the cause of potential interferences with tuberculosis diagnosis in wildlife. The mean MAP prevalence reported in wildlife was 2.41% (95% confidence interval 1.76-3.06). Although MAP should be considered an important disease in farmed cervids, its impact on free-ranging species is questionable. MAP reservoirs may exist locally but their significance for PTB control in livestock is quite limited. The most critical aspect derived of MAP infection in wildlife is the interference with tuberculosis diagnosis.

Mycobacteriosis in the rabbit and rodent

Spontaneous mycobacteriosis is rare in rabbits and rodents with the exception of the pygmy rabbit, and there are only a handful of reported cases involving other rodents. Mycobacterium avium complex was the most commonly identified organism in reports of spontaneous mycobacteriosis involving rabbits and rodents. The resistance of rabbits and rodents to mycobacterial disease has been useful in understanding the disease in humans and other animals. Preventing or controlling Mycobacterium sp transmission from wildlife to domestic animals will require collaboration between agriculture, wildlife, environmental, and political entities. Understanding the ecology and epidemiology of mycobacteria is needed for better worldwide management of tuberculosis.

Occurrence of Mycobacterium avium subspecies paratuberculosis across host species and European countries with evidence for transmission between wildlife and domestic ruminants

Background

Mycobacterium avium subspecies paratuberculosis (Map) causes an infectious chronic enteritis (paratuberculosis or Johne's disease) principally of ruminants. The epidemiology of Map is poorly understood, particularly with respect to the role of wildlife reservoirs and the controversial issue of zoonotic potential (Crohn's disease). Genotypic discrimination of Map isolates is pivotal to descriptive epidemiology and resolving these issues. This study was undertaken to determine the genetic diversity of Map, enhance our understanding of the host range and distribution and assess the potential for interspecies transmission.

Results

164 Map isolates from seven European countries representing 19 different host species were genotyped by standardized IS900 - restriction fragment length polymorphism (IS900-RFLP), pulsed-field gel electrophoresis (PFGE), amplified fragment length polymorphisms (AFLP) and mycobacterial interspersed repeat unit-variable number tandem repeat (MIRU-VNTR) analyses. Six PstI and 17 BstEII IS900-RFLP, 31 multiplex [SnaBI-SpeI] PFGE profiles and 23 MIRU-VNTR profiles were detected. AFLP gave insufficient discrimination of isolates for meaningful genetic analysis. Point estimates for Simpson's index of diversity calculated for the individual typing techniques were in the range of 0.636 to 0.664 but a combination of all three methods increased the discriminating power to 0.879, sufficient for investigating transmission dynamics. Two predominant strain types were detected across Europe with all three typing techniques. Evidence for interspecies transmission between wildlife and domestic ruminants on the same property was demonstrated in four cases, between wildlife species on the same property in two cases and between different species of domestic livestock on one property.

Conclusion

The results of this study showed that it is necessary to use multiple genotyping techniques targeting different sources of genetic variation to obtain the level of discrimination necessary to investigate transmission dynamics and trace the source of Map infections. Furthermore, the combination of genotyping techniques may depend on the geographical location of the population to be tested. Identical genotypes were obtained from Map isolated from different host species co-habiting on the same property strongly suggesting that interspecies transmission occurs. Interspecies transmission of Map between wildlife species and domestic livestock on the same property provides further evidence to support a role for wildlife reservoirs of infection.

Use of host population reduction to control wildlife infection: rabbits and paratuberculosis

Reduction in wildlife populations is a common method for the control of livestock infections which have wildlife hosts, but its success is dependent on the characteristics of the infection itself, as well as on the spatial and social structure of the wildlife host. Paratuberculosis (Mycobacterium avium subsp. paratuberculosis; Map) is a widespread and difficult infection to control in livestock populations and also has possible links to Crohn's disease in humans. Rabbits have recently been identified as a key wildlife species in terms of paratuberculosis persistence in the environment and risk to the wider host community, including cattle. Here we use a spatially explicit stochastic simulation model of Map dynamics in rabbit populations to quantify the effects of rabbit population control on infection persistence. The model parameters were estimated from empirical studies of rabbit population dynamics and rabbit-to-rabbit routes of Map transmission. Three rabbit control strategies were compared: single unrepeated population reductions based on removing individual animals; single unrepeated population reductions based on removal of entire social groups; and repeated annual population reductions based on removing individual animals. Unrealistically high rabbit culls (>95% population reduction) are needed if infection is to be eradicated from local rabbit populations with a single one-off population reduction event, either of individuals or social groups. Repeated annual culls are more effective at reducing the prevalence of infection in rabbit populations and eradicating infection. However, annual population reductions of >40% are required over extended periods of time (many years). Thus, using an approach which is both highly conservative and parsimonious with respect to estimating lower bounds on the time to eradicate the infection, we find that Map is extremely persistent in rabbit populations and requires significant and prolonged effort to achieve control.

Effects of host social hierarchy on disease persistence

The effects of social hierarchy on population dynamics and epidemiology are examined through a model which contains a number of fundamental features of hierarchical systems, but is simple enough to allow analytical insight. In order to allow for differences in birth rates, contact rates and movement rates among different sets of individuals the population is first divided into subgroups representing levels in the hierarchy. Movement, representing dominance challenges, is allowed between any two levels, giving a completely connected network. The model includes hierarchical effects by introducing a set of dominance parameters which affect birth rates in each social level and movement rates between social levels, dependent upon their rank. Although natural hierarchies vary greatly in form, the skewing of contact patterns, introduced here through non-uniform dominance parameters, has marked effects on the spread of disease. A simple homogeneous mixing differential equation model of a disease with SI dynamics in a population subject to simple birth and death process is presented and it is shown that the hierarchical model tends to this as certain parameter regions are approached. Outside of these parameter regions correlations within the system give rise to deviations from the simple theory. A Gaussian moment closure scheme is developed which extends the homogeneous model in order to take account of correlations arising from the hierarchical structure, and it is shown that the results are in reasonable agreement with simulations across a range of parameters. This approach helps to elucidate the origin of hierarchical effects and shows that it may be straightforward to relate the correlations in the model to measurable quantities which could be used to determine the importance of hierarchical corrections. Overall, hierarchical effects decrease the levels of disease present in a given population compared to a homogeneous unstructured model, but show higher levels of disease than structured models with no hierarchy. The separation between these three models is greatest when the rate of dominance challenges is low, reducing mixing, and when the disease prevalence is low. This suggests that these effects will often need to be considered in models being used to examine the impact of control strategies where the low disease prevalence behaviour of a model is critical.

Isolation of Mycobacterium avium subspecies paratuberculosis from non-ruminant wildlife living in the sheds and on the pastures of Greek sheep and goats

This study aimed to: (1) investigate whether non-ruminant wildlife interfacing with dairy sheep and goats of four Greek flocks endemically infected with Mycobacterium avium subspecies paratuberculosis (MAP) harboured MAP and (2) genetically compare the strains isolated from the wildlife to those isolated from the small ruminants of these flocks. We cultured and screened, by polymerase chain reaction (PCR), pooled-tissue samples from 327 wild animals of 11 species for the MAP-specific IS900 insertion sequence. We also cultured faecal samples from 100 sheep or goats from each of the four flocks. MAP was detected in samples from 11 sheep, 12 goats, two mice, two rats, a hare and a fox. Only one rat had histopathological findings. Genetic typing categorized 21 isolates as cattle-type strains and two, from a house mouse and a goat respectively, as sheep-type strains; this is the first report of a rodent harbouring a sheep-type strain. The MAP types that were most frequently isolated amongst the sheep and goats of each flock were also the ones isolated from sympatric rodents; those isolated from the fox and hare also belonged to the predominant ruminant strains.