Characterizing infectious disease progression through discrete states using hidden Markov models

Infectious disease management relies on accurate characterization of disease progression so that transmission can be prevented. Slowly progressing infectious diseases can be difficult to characterize because of a latency period between the time an individual is infected and when they show clinical signs of disease. The introduction of Mycobacterium avium ssp. paratuberculosis (MAP), the cause of Johne’s disease, onto a dairy farm could be undetected by farmers for years before any animal shows clinical signs of disease. In this time period infected animals may shed thousands of colony forming units. Parameterizing trajectories through disease states from infection to clinical disease can help farmers to develop control programs based on targeting individual disease state, potentially reducing both transmission and production losses due to disease. We suspect that there are two distinct progression pathways; one where animals progress to a high-shedding disease state, and another where animals maintain a low-level of shedding without clinical disease. We fit continuous-time hidden Markov models to multi-year longitudinal fecal sampling data from three US dairy farms, and estimated model parameters using a modified Baum-Welch expectation maximization algorithm. Using posterior decoding, we observed two distinct shedding patterns: cows that had observations associated with a high-shedding disease state, and cows that did not. This model framework can be employed prospectively to determine which cows are likely to progress to clinical disease and may be applied to characterize disease progression of other slowly progressing infectious diseases.

Modelling spread and surveillance of Mycobacterium avium subsp. paratuberculosis in the Swedish cattle trade network

To monitor a state of disease freedom and to ensure a timely detection of new introductions of disease, surveillance programmes need be evaluated prior to implementation. We present a strategy to evaluate surveillance of Mycobacterium avium subsp. paratuberculosis (MAP) using simulated testing of bulk milk in an infectious disease spread model. MAP is a globally distributed, chronic infectious disease with substantial animal health impact. Designing surveillance for this disease poses specific challenges because methods for surveillance evaluation have focused on estimating surveillance system sensitivity and probability of freedom from disease and do not account for spread of disease or complex and changing population structure over long periods. The aims of the study were to 1. define a model that describes the spread of MAP within and between Swedish herds; 2. define a method for simulation of imperfect diagnostic testing in this framework; 3. to compare surveillance strategies to support surveillance design choices. The results illustrate how this approach can be used to identify differences between the probability of detecting disease in the population based on choices of the number of herds sampled and the use of risk-based or random selection of these herds. The approach was also used to assess surveillance to detect introduction of disease and to detect a very low prevalence endemic state. The use of bulk milk sampling was determined to be an effective method to detect MAP in the population with as few as 500 herds tested per year if the herd-level prevalence was 0.2 %. However, detection of point introductions in the population was unlikely in the 13-year simulation period even if as many as 2000 herds were tested per year. Interestingly, the use of a risk-based selection strategy was found to be a disadvantage to detect MAP given the modelled disease dynamics.

Mycobacterium aviumsubsp. paratuberculosis isolated from wild red deer (Cervus elaphus) in Northern Italy

Paratuberculosis (or Johne's disease) is an infectious disease which affects mainly ruminants and it is caused by Mycobacterium avium subsp. paratuberculosis (MAP). During a culling program (years 2011-2015) aimed at controlling the red deer (Cervus elaphus) population in Stelvio National Park (Italian Alps), where paratuberculosis was already described in this species, 382 tissue samples from the Lombardy Region and 102 fecal specimens from the Autonomous Province of Bolzano were analyzed by PCR. Of these, 77 samples (20.16%) from the Lombardy area and 19 specimens (18.63%) from the Bolzano area resulted PCR positive. The cultural test was carried out on PCR positive samples (n = 96), enabling the isolation of 19 MAP field strains which were genotyped using MIRU-VNTR typing and Short Sequence repeats (SSRs). Our results suggest that all isolates share an identical VNTR profile corresponding to the INMV1 genotype. The only variation was on the locus SSR2, but the utility of this last locus has already been questioned because of its instability. Overall, these data suggest a common clonal origin and host adaptation during the diffusion of paratuberculosis in this population. Finally, this profile is the same as that which has already been described in the cattle population in Northern Italy, suggesting a possible inter-species disease transmission pattern from wildlife to domestic ruminants and vice versa.

Modeling environmental transmission of MAP infection in dairy cows

Johne's disease is caused by Mycobacterium avium subspecies paratuberculosis(MAP). It is a chronic, progressive, and inflammatory disease which has a long incubation period. One main problem with the disease is the reduction of milk production in infected dairy cows. In our study we develop a system of ordinary differential equations to describe the dynamics of MAP infection in a dairy farm. This model includes the progression of the disease and the age structure of the cows. To investigate the effect of persistence of this bacteria on the farm on transmission in our model, we include environmental compartments, representing the pathogen input in an explicit way. The effect of indirect transmission from the bacteria in the environment and the culling of high-shedding adults can be seen in the numerical simulations. Since culling usually only happens once a year, we include a novel feature in the simulations with a discrete action of removing high-shedding adults once a year. We conclude that with culling of high shedders even at a high rate, the infection will persist in the modeled farm setting.

Merging DNA typing and network analysis to assess the transmission of paratuberculosis between farms

Paratuberculosis, a chronic enteric infection caused by Mycobacterium subsp. paratuberculosis (MAP), is endemic in all farmed ruminant species in New Zealand. The use of genotyping in combination with network analysis of livestock movement events from one farm location to another has the potential to contribute to our understanding of between-farm transmission events. We studied a population of 122 farms from a corporate commercial livestock enterprise in New Zealand, trading with each other in near isolation from other commercial farms. The data consisted of longitudinal movements to and from these farms between 2006 and 2010, as well as the results of cross-sectional MAP screening and genotyping performed in 2010. We explored associations between past livestock movements and current strain type distribution in this population of farms using quadratic assignment procedure. Our results show that measures of farm clustering within the movement network were significantly associated with sharing of MAP strains. For example, farms closely related by trade were twice as likely to share the same strains of MAP (p=0.033). Other covariates were also associated with the probability of sharing the same strains of MAP, such as being located on the same island (OR=5.8 to 8.7, p<0.01), farming the same livestock species and Euclidian distance between farms. The novel approach we used supports the hypothesis that livestock movement is indeed a significant contributor to farm-to-farm transmission of MAP.

Impact of the shedding level on transmission of persistent infections in Mycobacterium avium subspecies paratuberculosis (MAP)

Super-shedders are infectious individuals that contribute a disproportionate amount of infectious pathogen load to the environment. A super-shedder host may produce up to 10,000 times more pathogens than other infectious hosts. Super-shedders have been reported for multiple human and animal diseases. If their contribution to infection dynamics was linear to the pathogen load, they would dominate infection dynamics. We here focus on quantifying the effect of super-shedders on the spread of infection in natural environments to test if such an effect actually occurs in Mycobacterium avium subspecies paratuberculosis (MAP). We study a case where the infection dynamics and the bacterial load shed by each host at every point in time are known. Using a maximum likelihood approach, we estimate the parameters of a model with multiple transmission routes, including direct contact, indirect contact and a background infection risk. We use longitudinal data from persistent infections (MAP), where infectious individuals have a wide distribution of infectious loads, ranging upward of three orders of magnitude. We show based on these parameters that the effect of super-shedders for MAP is limited and that the effect of the individual bacterial load is limited and the relationship between bacterial load and the infectiousness is highly concave. A 1000-fold increase in the bacterial contribution is equivalent to up to a 2-3 fold increase in infectiousness.

Resolution of Crohn's disease and complex regional pain syndrome following treatment of paratuberculosis

A cohort of family members with various chronic diseases including Crohn’s disease, asthma, complex regional pain syndrome, hypothyroidism, type 1 diabetes mellitus, and lymphangiomatosis and/or evidence of infection by Mycobacterium avium subsp. paratuberculosis (MAP) are described in this series of case reports. MAP was cultured from the blood of three members affected by the first five diseases and there was accompanying elevated anti-MAP IgG in two members. The patient affected by the sixth disease has a markedly elevated anti-MAP titer. The two patients affected by the first four diseases have been treated with a combination of anti-MAP antibiotics and ultraviolet blood irradiation therapy with resolution of the disease symptomatology and inability to culture MAP in post treatment blood samples. These case reports of patients with MAP infections provide supportive evidence of a pathogenic role of MAP in humans.

Back to the real world: connecting models with data

Mathematical models for infectious disease are often used to improve our understanding of infection biology or to evaluate the potential efficacy of intervention programs. Here, we develop a mathematical model that aims to describe infection dynamics of Mycobacterium avium subspecies paratuberculosis (MAP). The model was developed using current knowledge of infection biology and also includes some components of MAP infection dynamics that are currently still hypothetical. The objective was to show methods for parameter estimation of state transition models and to connect simulation models with detailed real life data. Thereby making model predictions and results of simulations more reflective and predictive of real world situations. Longitudinal field data from a large observational study are used to estimate parameter values. It is shown that precise data, including molecular diagnostics on the obtained MAP strains, results in more precise and realistic parameter estimates. It is argued that modeling of infection disease dynamics is of great value to understand the patho-biology, epidemiology and control of infectious diseases. The quality of conclusions drawn from model studies depend on two key issues; first, the quality of biology that has gone in the process of developing the model structure; second the quality of the data that go into the estimation of the parameters and the quality and quantity of the data that go into model validation. The more real world data that are used in the model building process, the more likely that modeling studies will provide novel, innovative and valid results.

Mycobacterium avium subspecies paratuberculosis causes Crohn's disease in some inflammatory bowel disease patients

Crohn’s disease (CD) is a chronic inflammatory condition that plagues millions all over the world. This debilitating bowel disease can start in early childhood and continue into late adulthood. Signs and symptoms are usually many and multiple tests are often required for the diagnosis and confirmation of this disease. However, little is still understood about the cause(s) of CD. As a result, several theories have been proposed over the years. One theory in particular is that Mycobacterium avium subspecies paratuberculosis (MAP) is intimately linked to the etiology of CD. This fastidious bacterium also known to cause Johne’s disease in cattle has infected the intestines of animals for years. It is believed that due to the thick, waxy cell wall of MAP it is able to survive the process of pasteurization as well as chemical processes seen in irrigation purification systems. Subsequently meat, dairy products and water serve as key vehicles in the transmission of MAP infection to humans (from farm to fork) who have a genetic predisposition, thus leading to the development of CD. The challenges faced in culturing this bacterium from CD are many. Examples include its extreme slow growth, lack of cell wall, low abundance, and its mycobactin dependency. In this review article, data from 60 studies showing the detection and isolation of MAP by PCR and culture techniques have been reviewed. Although this review may not be 100% comprehensive of all studies, clearly the majority of the studies overwhelmingly and definitively support the role of MAP in at least 30%-50% of CD patients. It is very possible that lack of detection of MAP from some CD patients may be due to the absence of MAP role in these patients. The latter statement is conditional on utilization of methodology appropriate for detection of human MAP strains. Ultimately, stratification of CD and inflammatory bowel disease patients for the presence or absence of MAP is necessary for appropriate and effective treatment which may lead to a cure.

Pathogens at the livestock-wildlife interface in Western Alberta: does transmission route matter?

In southwestern Alberta, interactions between beef cattle and free-ranging elk (Cervus elaphus) may provide opportunities for pathogen transmission. To assess the importance of the transmission route on the potential for interspecies transmission, we conducted a cross-sectional study on four endemic livestock pathogens with three different transmission routes: Bovine Viral Diarrhea Virus and Bovine Herpesvirus 1 (predominantly direct transmission), Mycobacterium avium subsp. paratuberculosis (MAP) (indirect fecal-oral transmission), Neospora caninum (indirect transmission with definitive host). We assessed the occurrence of these pathogens in 28 cow-calf operations exposed or non-exposed to elk, and in 10 elk herds exposed or not to cattle. We characterized the effect of species commingling as a risk factor of pathogen exposure and documented the perceived risk of pathogen transmission at this wildlife-livestock interface in the rural community. Herpesviruses found in elk were elk-specific gamma-herpesviruses unrelated to cattle viruses. Pestivirus exposure in elk could not be ascertained to be of livestock origin. Evidence of MAP circulation was found in both elk and cattle, but there was no statistical effect of the species commingling. Finally, N. caninum was more frequently detected in elk exposed to cattle and this association was still significant after adjustment for herd and sampling year clustering, and individual elk age and sex. Only indirectly transmitted pathogens co-occurred in cattle and elk, indicating the potential importance of the transmission route in assessing the risk of pathogen transmission in multi-species grazing systems.

Using vaccination to prevent the invasion of Mycobacterium avium subsp. paratuberculosis in dairy herds: a stochastic simulation study

Paratuberculosis, or Johne's disease (JD), is a chronic enteric disease of ruminants infected by Mycobacterium avium subsp. paratuberculosis (MAP) that causes a significant financial loss in dairy industry. To reduce prevalence and transmission in dairy herds infected with MAP, control programs have been implemented, including test-based culling, improved calf rearing management, and vaccination. The important issue of preventing MAP invasion into a MAP-free herd has been less investigated, however. The objective of this study was to examine whether vaccination was able to prevent MAP invasion in dairy cattle using a stochastic simulation approach. We developed a MAP vaccination model in which calves were vaccinated with a vaccine that is both imperfect in reducing the susceptibility of the host ('leaky') and that does not successfully immunize all calves ('failure in take'). Probability of MAP persistence and the number of infected animals in herds were computed for both control and vaccinated herds over a ten-year period after introduction of an initial infected heifer. Global parameter sensitivity analyses were performed to find the most influential parameters for MAP invasion. Our results show that vaccination of calves is effective in preventing MAP invasion, provided that the vaccine is of high efficacy in both reduction of susceptibility and 'take' effects; however, there is still a small chance (<0.15) that MAP can be sustained in herds over a long time (>10 years) due to vertical transmission. This study indicates that reduction in the transmission rate of high shedders (>50 CFU), the number of infected heifers initially introduced to herds, and vertical transmission are important to further decrease the probability of MAP becoming endemic and the overall number of infected animals in endemic herds. The simulation work is useful for designing vaccination programs aimed at preventing MAP invasion in MAP-free herds.

Exploring the zoonotic potential of Mycobacterium avium subspecies paratuberculosis through comparative genomics

A comparative genomics approach was utilised to compare the genomes of Mycobacterium avium subspecies paratuberculosis (MAP) isolated from early onset paediatric Crohn's disease (CD) patients as well as Johne's diseased animals. Draft genome sequences were produced for MAP isolates derived from four CD patients, one ulcerative colitis (UC) patient, and two non-inflammatory bowel disease (IBD) control individuals using Illumina sequencing, complemented by comparative genome hybridisation (CGH). MAP isolates derived from two bovine and one ovine host were also subjected to whole genome sequencing and CGH. All seven human derived MAP isolates were highly genetically similar and clustered together with one bovine type isolate following phylogenetic analysis. Three other sequenced isolates (including the reference bovine derived isolate K10) were genetically distinct. The human isolates contained two large tandem duplications, the organisations of which were confirmed by PCR. Designated vGI-17 and vGI-18 these duplications spanned 63 and 109 open reading frames, respectively. PCR screening of over 30 additional MAP isolates (3 human derived, 27 animal derived and one environmental isolate) confirmed that vGI-17 and vGI-18 are common across many isolates. Quantitative real-time PCR of vGI-17 demonstrated that the proportion of cells containing the vGI-17 duplication varied between 0.01 to 15% amongst isolates with human isolates containing a higher proportion of vGI-17 compared to most animal isolates. These findings suggest these duplications are transient genomic rearrangements. We hypothesise that the over-representation of vGI-17 in human derived MAP strains may enhance their ability to infect or persist within a human host by increasing genome redundancy and conferring crude regulation of protein expression across biologically important regions.

High prevalence of Mycobacterium avium subspecies paratuberculosis ('Indian bison type') in animal attendants suffering from gastrointestinal complaints who work with goat herds endemic for Johne's disease in India

OBJECTIVES

In this study we aimed to estimate the prevalence of Mycobacterium avium subspecies paratuberculosis (MAP) in animal attendants who were chronic colitis patients or who had inflammatory bowel disease and were suspected for Crohn's disease; these animal attendants worked with goat herds endemic for Johne's disease. Microscopic examination and culture tests were used. For comparison purposes a group of healthy human subjects (not suffering with colitis) was also screened.

METHODS

Stool samples obtained from 98 human subjects (58 animal attendants suspected for Crohn's disease and 40 healthy humans) were screened for the presence of MAP by microscopic examination and culture. Of the 58 animal attendants screened, 38 had abdominal pain, 29 had suffered episodes of diarrhea, 39 had experienced weight loss, 27 had fever, and 32 had a history of raw milk consumption. Animal attendants had had contact of variable duration with goat herds endemic for Johne's disease (1-5, 6-10, 11-15, and >15 years). Forty stool samples from healthy humans with no symptoms/history of contact with animals were also screened. IS900 PCR and IS1311 PCR restriction endonuclease analysis were used to characterize and genotype the MAP colonies.

RESULTS

MAP was recovered from 34 of the 98 human subject stool samples (34.7%). Of the 98 samples, 16.3% (n=16) were acid-fast. None of the 40 healthy human subjects were positive for MAP by microscopy, but five (12.5%) were positive for MAP by culture. Of the 58 animal attendants, 16 (27.6%) were positive by microscopy and 29 (50%) were positive by culture. MAP were recovered from 68.4% of animal attendants with abdominal pain, 72.4% of those with diarrhea, 71.8% of those with weight loss, 44.4% of those with fever, and 46.9% of those who had a history of raw milk consumption. Of the 29 culture-positive animal attendants, 48.3% had worked for >15 years, 27.6% for 11-15 years, 20.7% for 6-10 years, and 3.4% for 1-5 years with goat herds endemic for Johne's disease. Of the 34 culture isolates, 28 (82.4%) showed good quality DNA on agarose gel and were positive by IS900 PCR. Of the 28 IS900-positive DNA samples, 23 (82.1%) were genotyped as 'Indian bison type' and five (17.9%) as 'cattle type'.

CONCLUSIONS

The prevalence of MAP was higher in attendants suffering from gastrointestinal problems who worked with goat herds endemic for Johne's disease, than in humans with no history of contact with animals. The risk of developing gastrointestinal problems with clinical symptoms indistinguishable from inflammatory bowel disease was higher in humans who were in contact with goat herds endemic for Johne's disease as compared to healthy humans, and the risk was correlated with the duration of association with the endemic goat herds.

[Possible association between Mycobacterium avium subsp paratuberculosis infection and Crohn's disease]

Paratuberculosis is a chronic intestinal disease of animals caused by Mycobacterium avium subsp. paratuberculosis (MAP), which has some pathological features similar to Crohn's disease (CD) in humans. The presence of MAP in food for human consumption and in affected tissues of patients with CD has been detected. Therefore, a causal association between this microorganism and the disease in humans, has been postulated. However, several related studies have failed to confirm this hypothesis and the scientific acceptance of MAP as a zoonotic agent remains controversial. This review presents the main findings related to this issue, contrasting evidences for and against an association between MAP and CD. The need to promote national studies focusing on this area is suggested.

Evidence of Mycobacterium avium subsp. paratuberculosis infection in Dutch farmed red deer

Paratuberculosis is a chronic disease in ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). Most economic losses due to MAP occur in the dairy industry. However, the infection is not restricted to cattle, but also occurs in other ruminants, such as sheep, goat, and deer. Although deer are of minimal economic importance in The Netherlands, they may constitute a source of infection for the dairy industry. This pilot study was conducted to estimate the prevalence of Johne's disease in farmed red deer in The Netherlands. Serum and faecal samples were collected from 140 animals, originating from 8 different farms. Four of the farms had animals that tested positive for Johne's disease. The within-herd MAP seroprevalence varied between 4.8% and 21.2%. In conclusion, this pilot study provides evidence of MAP infection in the Dutch farmed deer population, and thus there might be a risk of MAP transmission between farmed red deer and dairy cattle.

Exposure of young dairy cattle to Mycobacterium avium subsp. paratuberculosis (MAP) through intensive grazing of contaminated pastures in a herd positive for Johne's disease

This study investigated the susceptibility of 1- to 2-year-old cattle to Mycobacterium avium subsp. paratuberculosis (MAP) on pasture previously grazed by infected cattle. The exposure of yearling cattle to pastures contaminated with MAP resulted in infection with MAP, showing that age resistance to infection can be overcome by pressure of infection.

Intrauterine and transmammary transmission ofMycobacterium aviumsubspparatuberculosisin sheep

OBJECTIVE

To investigate intrauterine infection of foetuses with Mycobacterium avium subsp paratuberculosis and the presence of infection in mammary secretions of sheep.

DESIGN

A study of 142 late-pregnant ewes and their foetuses from two heavily infected flocks.

PROCEDURE

Infection of ewes was determined at necropsy by histopathology and culture of tissues and mammary secretions. Antemortem tests (clinical assessment, faecal culture and serology) were also applied. Foetuses from 59 infected ewes and 47 apparently uninfected ewes were examined by culture and histopathology.

RESULTS

Five of five ewes with clinical ovine Johne's disease had infected foetuses. Only one of 54 subclinically affected ewes, and none of 47 uninfected ewes had an infected foetus. M a paratuberculosis was cultured from mammary secretions or mammary glands of only two of 76 ewes, both of which were clinical cases and had infected foetuses.

CONCLUSION

Although intrauterine or transmammary transmission of Mycobacterium avium subsp paratuberculosis may occur frequently in clinically affected sheep, these are less common in subclinically infected ewes. Therefore these modes of transmission are unlikely to compromise existing control programs for ovine Johne's disease on most farms, especially if programs include the immediate culling of clinically affected sheep.

Transmission parameters of Mycobacterium avium subspecies paratuberculosis infections in a dairy herd going through a control program

A Johne's disease control program, including stringent management practices and a test-and-cull program (whole-herd fecal-samples taken twice a year), was implemented on a medium-sized Pennsylvania dairy farm that was suffering losses from clinical Johne's disease. The data that emerged from the control program, combined with birthdates, culling dates, lactation information and pedigrees, yielded an extensive longitudinal dataset. The dataset was processed through SAS 9.1 for statistical analysis; herd-level disease dynamics and dam-to-daughter transmission parameters were calculated. After the implementation of the program in 1984, prevalence dropped dramatically from 60% to less than 20% in 1989. After an apparent prevalence peak (25%) in 1991 due to improved test sensitivity, prevalence maintained a plateau of 10% from 1996 to 2000. After the implementation of the program, 9.5% of the offspring from test-negative dams and 26.8% of the offspring from known-infected dams became infected with Mycobacterium avium subspecies paratuberculosis (Map) (chi(2)=14.7; p=0.0001). Calves born shortly following the calving of an infected dam and calves growing up with a future high shedder were more likely to be infected compared to calves without this risk profile. It was concluded that, after the implementation of the control program, the most important causes of infections of susceptible calves were their own dams or infected animals which had calved recently.

Mycobacterium avium subsp. paratuberculosis in scavenging mammals in Wisconsin

The presence of Mycobacterium avium subsp. paratuberculosis (MAP) in non-ruminant wildlife has raised questions regarding the role of these species in Johne's disease transmission. In this study we tested 472 tissues from 212 animals of six different species of scavenging mammals. All animals were taken from within a 210-square-mile area in Dane and Iowa counties of south central Wisconsin from September to May in 2003-04 and tested for the presence of MAP. We detected MAP-specific DNA in 81 of 212 (38%) scavenging mammals, in 98 of the 472 (21%) tissues; viable MAP was cultured from one coyote's ileum and lymph node tissue. Despite the low numbers of viable MAP isolated in this study, our data adds to the increasing evidence demonstrating the potential for transmission and infection of MAP in nonruminant species and provides possible evidence of interspecies transmission. The apparently high exposure of nonruminant wildlife provides potential evidence of a spill-over of MAP to wildlife species and raises the question of spillback to domestic and wild ruminants. These results demonstrate the importance of understanding the role of wildlife species in developing management strategies for Johne's disease in domestic livestock.

Immune response to and faecal shedding of Mycobacterium avium ssp. paratuberculosis in young dairy calves, and the association between test results in the calves and the infection status of their dams

The objectives of this study were to: (i) evaluate the results of an intradermal skin test, a modified IFN-gamma test, and a commercial ELISA in commercially raised dairy calves at 2, 4, 6 and 8 months of age relative to faecal shedding of Mycobacterium avium ssp. paratuberculosis (MAP); (ii) determine the proportion of 8-month-old calves shedding MAP in faeces as detected by culture and One Tube Nested Polymerase Chain Reaction (OTSN-PCR) and (iii) explore the association between results of tests described above in the calves and the Paratuberculosis (PTB) status of their dams as determined by faecal culture and/or serology. The study calves belonged to two dairy herds with different risk of exposure to MAP (high and low) and were enrolled based on their dam's ELISA results prior to calving. Approximately 3% of the calves were shedding MAP in faeces at 8 months of age. No agreement was observed among the evaluated immunity-based tests or between the immunity-based tests and the detection of MAP in faeces. Although no association was observed between the infection status of the dam and the results from the IFN-gamma and skin tests on the calves, there is an indication that calves born from dams that were faecal shedders might be at a higher risk of testing positive to the IFN-gamma test at 8 months of age. The disagreement among all tests evaluated in this calf cohort suggests that the detection of MAP infection in young stock requires the use of combined multiple tests. The early detection of PTB in calves is a challenge that requires further exploration of new methods to confirm infection status. These new testing methods should be both affordable and compatible with regular husbandry practices.

Horizontal transmission of Mycobacterium avium subsp. paratuberculosis in cattle in an experimental setting: Calves can transmit the infection to other calves

In September 2001, two subsequent transmission experiments both lasting 3 months were carried out to study cow-calf transmission of Mycobacterium avium subsp. paratuberculosis (Map) (Period 1), followed by calf-calf transmission of the infection (Period 2). Every 2 weeks, serum, heparinised blood and faecal samples were collected from all animals. After these experiments, the 20 calves were housed individually for more than 3 years to be able to detect the infection status and excretion pattern of each animal. In autumn 2004, the animals were inseminated, to observe a possible increase in faecal excretion of Map shortly before expected calving. One month before the expected calving date in 2005, animals were slaughtered and several tissues per cow and unborn calf were sampled for culture. The results indicate that horizontal cow-calf transmission is readily achieved (Period 1). At the highest infection pressure (six shedding cows of which three high shedders in Period 1) all five calves excreted Map in their faeces during Period 1 (shortly after infection), and four of these calves during Period 2 (when the shedding cows were absent). After that, excretion became less frequently. Horizontal calf-calf transmission did take place (Period 2), as the four donor-calves infected two receiver-calves. Transmission rates during the 3 months periods were quantified as a reproduction ratio R. The R [95% CI] of cow-calf and calf-calf transmission were estimated as 2.7 [1.1, 6.6] and 0.9 [0.1, 3.2] new infections per infectious animal during 3 months.

Application of Different Methods for the Diagnosis of Experimental Paratuberculosis in Goats

The diagnosis of subclinical paratuberculosis is still considered a major problem worldwide. As part of investigating diagnostic strategies for the paratuberculosis infection, sequential results of various diagnostic methods in a progressive experimental infection in goats were evaluated. Twenty-three goat kids were divided into three groups: the infected, contact and control, comprising 10, five and eight goats respectively. Animals of the infected group were orally inoculated on seven occasions with 5 ml of inoculum containing 2 x 10(9)Mycobacterium avium ssp. paratuberculosis per ml. Lymphoycte proliferation test using johnin PPD detected paratuberculosis infection from 60 days post-infection (DPI) onwards. The johnin PPD was found to be a better antigen for the proliferative assays as compared with the sonicated antigen. The faecal smear examination with acid-fast staining detected more goats as positive than bacterial culture and polymerase chain reaction (PCR). Lipoarabinomannan enzyme-linked immunosorbent assay (ELISA) started detecting infected goats from 150 DPI onwards followed by indirect ELISA and agar gel immunodiffusion from 180 DPI onwards. Histological examination was confirmatory and detected five infected goats as positive.

A case-control study of drinking water and dairy products in Crohn's Disease--further investigation of the possible role of Mycobacterium avium paratuberculosis

Similarities between Johne's disease in ruminants and Crohn's disease in humans have led to speculation that Mycobacterium avium paratuberculosis (MAP) might be a causative agent in Crohn's disease. However, evidence remains inconsistent. In this case-control study (1999-2004), the authors assessed the possible role of drinking water and dairy products potentially contaminated with MAP in the etiology of Crohn's disease. A total of 218 patients with Crohn's disease recruited from nine hospitals in England and 812 controls recruited from the community completed a short questionnaire for evaluation of proxy measures of potential exposure to MAP. Logistic regression showed no significant association with measures of potential contamination of water sources with MAP, water intake, or water treatment. Multivariate analysis showed that consumption of pasteurized milk (per kg/month: odds ratio (OR) = 0.82, 95% confidence interval (CI): 0.69, 0.97) was associated with a reduced risk of Crohn's disease. Meat intake (per kg/month: OR = 1.40, 95% CI: 1.17, 1.67) was associated with a significantly increased risk of Crohn's disease, whereas fruit consumption (per kg/month: OR = 0.78, 95% CI: 0.67, 0.92) was associated with reduced risk. This study does not support a role for water or dairy products potentially contaminated with MAP in the etiology of Crohn's disease. The observed association with meat and the negative association with pasteurized milk need further study.

Survey of Ground Beef for The Detection of Mycobacterium avium paratuberculosis

Mycobacterium avium paratuberculosis (MAP) is thought to be associated with Crohn's disease in humans. Since Johne's disease affects dairy and beef cattle, meat may be a possible route of transmission of MAP to humans. In this study, we compared a rapid multiplex real time PCR assay and conventional culture to detect MAP in ground beef. The real time PCR assay amplifies both an internal sequence of the IS900 gene and an internal control targeting the ruminant-specific mt-cyt-b gene, in order to control for any false negative results. The sensitivity of this multiplex real time PCR assay on ground beef is 10(1) CFU/g and the sensitivity of conventional culture at 10(3) CFU/g. Furthermore, we conducted a survey of 200 retail ground beef samples using this system and did not detect the presence of MAP.

Monensin might protect Ontario, Canada dairy cows from paratuberculosis milk-ELISA positivity

Our objective was to define the role of monensin sodium in protecting cows from being milk-ELISA positive for paratuberculosis in Ontario, Canada dairy herds. In total, 4933 dairy cows from 94 herds were enrolled in this cross-sectional study. Forty-four of the enrolled herds were selected purposively by their herd veterinarian and another 50 herds were randomly selected from a local milk production-recording agency. A herd-management survey was completed on each farm during the months of May through August 2003. During this same time-period, composite milk samples were collected from all lactating cows and tested with a milk-ELISA for antibodies to Mycobacterium avium subspecies paratuberculosis. Analyses were stratified according to the paratuberculosis history of the herds. In the 48 herds in which paratuberculosis had not been diagnosed before, the use of calf hutches and monensin in milking cows were both associated with reduced odds of a cow testing positive (OR=0.19 and 0.21, respectively). In the 46 herds with a prior history of paratuberculosis, feeding monensin to the breeding-age heifers was associated with decreased odds of a cow testing positive (OR=0.54). Monensin use might be associated with milk-ELISA positivity, but its impact on the transmission of paratuberculosis remains unknown.

No evidence of Mycobacterium avium subsp. paratuberculosis in in vitro produced cryopreserved embryos derived from subclinically infected cows

The aim of the project was to ascertain if Mycobacterium avium subsp. paratuberculosis (Map) could be cultured from frozen-thawed in vitro produced (IVP) embryos derived from cows with subclinical Johne's disease (JD). Straws of 109 IVP embryos were obtained from 267 cumulus-oocyte-complexes (COCs) collected from 12 clinically normal cows in which antibodies against Map were detected in blood by an enzyme-linked immunosorbent assay (ELISA). These embryos were processed, washed using the standard protocol as described by the International Embryo Transfer Society (IETS) and frozen in a commercial IVP embryo laboratory. Of the 12 donor cows, 11 had histopathological or bacteriological evidence of infection at post-mortem inspection. The frozen embryos were thawed and the contents of the straws were cultured using the radiometric mycobacterial culture method. No Map was detected in any of the 109 embryos or freezing media. This suggests that the use of in vitro produced and cryopreserved embryos derived from cows with subclinical JD poses very low, if any, risk of spreading infection to susceptible animals.

Efficacy of monensin sodium for the reduction of fecal shedding of Mycobacterium avium subsp. paratuberculosis in infected dairy cattle

Reducing the quantity of Mycobacterium avium subsp. paratuberculosis (MAP) being shed by cows with Johne's disease should decrease the risk of spread of this disease to young stock. Previous work has suggested that monensin sodium decreases the pathologic lesions associated with Johne's disease, but the impact on shedding of viable MAP remains unknown. After serologic screening of 32 dairy herds in southwestern Ontario, 228 cows from 13 of these herds were enrolled into a randomized clinical trial. Fecal culture and PCR were used to identify 114 cows as potential fecal shedders, while another 114 cows were enrolled as ELISA negative, herd and parity matched controls. All cows were randomized to receive either a monensin controlled release capsule (CRC) or a placebo capsule. Serial fecal and blood samples were collected for fecal culture and serum ELISA testing over a 98-day period. On day 98 of the study, treatments were switched for all cows continuing in the trial. These remaining cows were followed for another 98 days with a similar sampling protocol. Mixed effect models were used to measure the impact of treatment on the number of colony forming units identified on fecal cultures over time. During the first 98 days of the study, cows treated with a monensin CRC were found to shed 3.4cfu per tube less than placebo treated cows (P=0.05). The serum ELISA S/P ratio was reduced by 1.39 units in cows given monensin (P=0.06). However, treatment with monensin did not reduce the odds of testing positive on serology. Only the cows shedding MAP on day 0 were found to have a reduced odds of testing positive on fecal culture when treated with monensin (OR=0.27; P=0.03). Monensin sodium administered to infected animals at 335mg/day marginally reduced fecal shedding of MAP in mature dairy cattle, but the biological significance of this reduction is unknown.

Comparative evaluation of two decontamination methods for the isolation of Mycobacterium avium subspecies paratuberculosis from faecal slurry and sewage

Faecal slurry of animal origin from sale yards and raw sewage from a sewage treatment plant were sampled for the radiometric culture over 5 months at approximately weekly intervals. Before the radiometric culture, samples were decontaminated using the double incubation method. One set of triplicate samples of slurry and sewage was decontaminated at 37 degrees C and the other set was decontaminated at 42 degrees C. M. a. paratuberculosis or its DNA was detected in seven of 45 cultures (15.6%) of slurry decontaminated at 37 degrees C and in 14 of 39 cultures (35.9%) of slurry decontaminated at 42 degrees C. The contamination rates in cultures of slurry processed at 37 degrees C and 42 degrees C were 82.2% and 69.2%, respectively. M. a. paratuberculosis DNA was also detected in one of 45 cultures (2.2%) of sewage decontaminated at 42 degrees C. The contamination rates in samples of sewage processed at 37 degrees C and 42 degrees C were 84.4% and 4.4%, respectively. Results of this study warrant further investigations to evaluate the suitability of a decontamination method at 42 degrees C for the isolation of M. a. paratuberculosis from faeces, tissues and milk.

Risk of transmission of Mycobacterium avium ssp. paratuberculosis by embryo transfer of in vivo and in vitro fertilized bovine embryos

Over a 5-year interval, experiments were conducted to determine if Mycobacterium avium ssp. paratuberculosis (Map) is associated with in vivo and in vitro fertilized (IVF) embryos and whether it can be transmitted by embryo transfer. The present studies included: collection of embryos from five asymptomatic, naturally infected donors and transfer to uninfected recipients; collection of oocytes from two naturally infected donors with overt clinical signs; exposure of in vivo and IVF embryos to Map and transfer to uninfected recipients; and the inoculation (transfer) of "clean" IVF embryos to the uterine lumen of infected cows. The presence of Map was confirmed in the uterine horns of all asymptomatic, infected donors. None of the tested embryos, which were not used for embryo transfer, or unfertilized ova (two per batch), were positive for Map, as determined by culture (n = 19) or by PCR (n = 13). However, all in vivo fertilized embryos exposed to Map in vitro (and subsequently sequentially washed) tested positive for Map, by both culture (12 batches) and PCR (15 batches), whereas IVF embryos treated in the same manner tested positive on culture (51%, 18/35 batches) and by PCR (28%, 20/71 batches). Transferring both in vivo embryos and IVF embryos potentially contaminated with Map into 28 recipients resulted in 13 pregnancies and eight calves born without evidence of disease transmission to either the recipients or the offspring over the following 5-year period. In samples collected from one of the clinically infected animals, two of seven (28%) cumulus oocyte complexes (COC) and follicular fluid tested positive by PCR and 10/10 cumulus oocyte complexes on culture for Map. From the second clinically infected cow, three of five batches of IVF embryos (n = 20) were positive on PCR and two of four batches containing unfertilized oocytes and embryos were positive on culture. Only 10% of embryos reached the morula and blastocyst stage 10 days after fertilization. In conclusion, Map is unlikely to be transmitted by embryo transfer when the embryos have been washed as recommended by the International Embryo Transfer Society.

Detection of Mycobacterium avium subsp. paratuberculosis in Two Brown Bears in the Central European Carpathians

The incidence of mycobacterial infections was monitored in brown bears (Ursus arctos) in the National Park Low Tatras in the central European Carpathians in Slovakia. Tissue samples of 20 brown bears were examined microscopically and by culture for the presence of mycobacteria. Acid-fast rods were detected by Ziehl-Neelsen staining in a smear from the kidney of one brown bear, although the culture was negative for mycobacteria. Mycobacterium avium subsp. paratuberculosis, the causative agent of paratuberculosis in ruminants, was isolated from the intestinal mucosa of another two brown bears. The isolates were identified by polymerase chain reaction for the specific insertion sequence IS900. Using standardized IS900 restriction fragment length polymorphism (RFLP) analysis, the M. a. paratuberculosis isolates were classified as RFLP type B-C1, which also were detected in the infected cattle in surrounding area. This study describes the first isolation of M. a. paratuberculosis from a brown bear. Our results confirm that animal species other than ruminants can become infected with M. a. paratuberculosis and can act as potential vectors and/or reservoirs of the infection.

Cattle transfers between herds under paratuberculosis surveillance in The Netherlands are not random

The rate and structure of cattle transfers between 206 Dutch cattle herds with a 'Mycobacterium avium subsp. paratuberculosis (Map)-free' status by November 2002, were analyzed over a 3-year period (November 1999-November 2002). Of the 206 'Map-free' herds, 184 were closed herds during the period studied. In total, 280 cattle had been introduced into 22 herds at an average rate of 0.33 animals per year per 100 cattle present in the 206 herds. Assuming a random herd-contact structure, the observed rate of cattle transfers between certified 'Map-free' herds was sufficiently low to relax the surveillance scheme to biennial herd examinations by pooled fecal culture of all cattle > or =2 years of age. The cattle transfers were not randomly distributed over the herds. Forty-four of the 280 cattle originated from 12 other 'Map-free' herds. The other 236 cattle did not originate from a 'Map-free' herd and were introduced into a herd before it obtained the 'Map-free' status. No cattle were introduced into any of the 'Map-free' herds from which cattle were transferred to other 'Map-free' herds. Thus, continued propagation of the infection by cattle transfers was impossible in the group of herds studied during the study period. Therefore the surveillance scheme may be further relaxed, and may be differentiated regarding the risk herds pose to other herds.

Intra-uterine transmission of paratuberculosis (Johne's disease) in farmed red deer

AIM

To determine whether intra-uterine transmission of paratuberculosis (Johne's disease) occurs in farmed red deer (Cervus elaphus) in New Zealand.

METHODS

On four different farms, nine late-stage pregnant hinds with Johne's disease were slaughtered and samples were taken from them and their 10 fetuses. Samples of the hepatic, ileocaecal and mesenteric lymph nodes and the posterior ileum were collected from the hinds. The lung, liver, spleen, jejunum and ileum from the fetuses were sampled, as were the placentomes. Blood samples were tested using the 'Paralisa' test, a modified immunoglobulin G1 (IgG1) enzyme-linked immunosorbent assay (ELISA). Tissue samples were cultured using the BACTEC system, and fixed samples were sectioned and histological slides examined.

RESULTS

All nine hinds and 9/10 fetuses (one hind had twins) were culture-positive for Mycobacterium avium subsp paratuberculosis (M. ptb). Six hinds had gross lesions of Johne's disease, while all hinds had characteristic histopathological lesions affecting the ileum, ileocaecal valve and associated lymph nodes. The only histopathological change observed in the fetuses was some mild inflammation in the lungs of one individual. Acid fast organisms (AFOs) were seen in histological sections of the lymph nodes and ileum of six hinds, and none were seen in tissues from the fetuses. These six hinds were Paralisa-positive, whereas the remaining hinds and fetuses were serologically-negative.

CONCLUSIONS

These results confirm that there is a high risk of transmission of M. ptb from clinically affected hinds to their fetuses during pregnancy.

CLINICAL RELEVANCE

Johne's disease is an increasingly important disease responsible for deaths in young red deer. Recognising the influence of intra-uterine transmission on the spread of this disease may be an important step towards improved control of Johne's disease.

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

Rabbits have been increasingly linked to the persistence of paratuberculosis (Johne's disease) in domestic ruminants in the United Kingdom. The aims of this study were to determine the routes of intraspecies transmission of Mycobacterium avium subspecies paratuberculosis (MAP) in rabbits and to estimate the probability of transmission via each route, in order to gain understanding of the dynamics of MAP in this host. Rabbits were sampled from two sites where MAP had previously been isolated from the livestock and rabbit populations. No pathology was noted in any animals, but the overall prevalence of MAP in rabbits was high at both sites studied, 39.7% and 23.0%, respectively. MAP was isolated from the testes, uterus, placenta, fetuses, and milk. This is the first time that the bacterium has been isolated from any of these tissues in a nonruminant wildlife species. These results suggest that transmission may occur vertically, pseudovertically, and horizontally. Vertical, i.e., transplacental, and/or pseudo-vertical, i.e., through the ingestion of contaminated milk and/or feces, transmission occurred in 14% of offspring entering the population at 1 month of age. As infection via these routes is only possible from infected adult females, this equates to a probability of infection via this route of 0.326. Probability of infection via horizontal transmission (including interspecies transmission) occurred at up to 0.037 per month. The presence of these routes of transmission within natural rabbit populations will contribute to the maintenance of MAP infections within such populations and, therefore, the environment.

Clustering of Mycobacterium avium subsp. paratuberculosis in rabbits and the environment: how hot is a hot spot?

Clustering of pathogens in the environment leads to hot spots of diseases at local, regional, national, and international levels. Scotland contains regional hot spots of Johne's disease (caused by Mycobacterium avium subsp. paratuberculosis) in rabbits, and there is increasing evidence of a link between paratuberculosis infections in rabbits and cattle. The spatial and temporal dynamics of paratuberculosis in rabbits within a hot spot region were studied with the overall aim of determining environmental patterns of infection and thus the risk of interspecies transmission to livestock. The specific aims were to determine if prevalence of paratuberculosis in rabbits varies temporally between seasons and whether the heterogeneous spatial environmental distribution of M. avium subsp. paratuberculosis on a large scale (i.e., regional hot spots) is replicated at finer resolutions within a hot spot. The overall prevalence of M. avium subsp. paratuberculosis in rabbits was 39.7%; the temporal distribution of infection in rabbits followed a cyclical pattern, with a peak in spring of 55.4% and a low in summer of 19.4%. Spatially, M. avium subsp. paratuberculosis-infected rabbits and, thus, the risk of interspecies transmission were highly clustered in the environment. However, this is mostly due to the clustered distribution of rabbits. The patterns of M. avium subsp. paratuberculosis infection in rabbits are discussed in relation to the host's socioecology and risk to livestock.

Evaluation of Mycobacterium avium subsp paratuberculosis infection of dairy cows attributable to infection status of the dam

OBJECTIVE

To estimate the extent to which infection with Mycobacterium avium subsp paratuberculosis (MAP) of cows in a large dairy was attributable to the infection status of their dams.

DESIGN

Retrospective longitudinal study.

ANIMALS

625 dam-daughter pairs of Holstein cows.

PROCEDURE

Serologic test results were compared between cows and their dams. Logistic regression was used to assess whether a cow's serologic status was associated with its dam's serologic status. Infection with MAP attributable to being born to a seropositive dam was estimated for individual cows and for the herd.

RESULTS

Cows with seropositive dams were 6.6 times as likely to be seropositive, compared with cows of seronegative dams. For seropositive cows born to seropositive dams, 84.6% of seropositivity was attributable to being born to a seropositive dam and 15.4% to other exposures, including exposure as calves to flush water that contained feces of adult cattle. For the herd as a whole, the seropositive status in 34% of seropositive cows was attributable to being born to a seropositive dam.

CONCLUSIONS AND CLINICAL RELEVANCE

For dairy herds that breed seropositive cows, subsequent transmission of MAP to their daughters, either congenitally or via exposure to feces and colostrum of the dam shortly after birth, can contribute substantially to maintaining prevalence of MAP in a herd. Removal of seropositive, clinically unaffected cows and their daughters would be necessary to reduce infection with MAP attributable to congenital or peri-parturient transmission from dam to daughter.

[From farm to fork--Mycobacterium avium ssp. paratuberculosis (MAP) as zoonotic agent?]

Mycobacterium avium ssp. paratuberculosis (MAP) is the causative agent of the paratuberculosis (Para Tb) in ruminants. In addition, this pathogen has been suspected to be implicated in the pathogenesis of Morbus Crohn disease (MC), causing chronic inflammatory intestine changes of humans. The participation of MAP in this illness is discussed intensively and has very contradictory opinions. On the one hand several times succeeded in proving MAP DNA in changed human tissues as well as, in recent time, the bacteria has been isolated from patient's blood. On the other hand there are many publications which support the opposite opinion. In critical evaluation of already available data, therefore the hypothesis can be formulated that MAP could possibly take part in the MC of humans. The reliable verification of this hypothesis will only be possible, if the diagnostic procedures can be refined upon the substantial deficit concerning the sensitivity and/or specificity of the diagnostic methods. In addition, till now there is lack of optimized statistically case control studies. The conceivable transmission of the bacteria to humans by the direct animal contact has been considered as possible vector, furthermore, MAP has been detected in pasteurised milk and other food of animal origin. The prevalence data, usually estimated by ELISA for milk cattle stock show over 80% prevalence in many counties of the Federal Republic of Germany with an individual case prevalence ranging between 1% and 17% in different stocks. Comparable data are present also from other countries as well as for small ruminants. MAP has been concerned as a global problem, moreover the high spreading rate of MAP in wild animal populations as well as the considerable ability of the bacteria to survive in different stages of the infectious- and contamination-cycle, which might hardly be broken through. Thus it requires intensive research efforts for the development of the methodical diagnostic process as basis for valid epidemiological investigations of animals, humans and food.

Isolation of Mycobacterium avium subsp paratuberculosis (Map) from Feral Cats on a Dairy Farm with Map-infected Cattle

Paratuberculosis is an economically important disease of dairy cattle caused by Mycobacterium avium subsp. paratuberculosis (Map). The role of nonruminant, nondomestic animals in the epidemiology of paratuberculosis in cattle is unclear. To examine nonruminant, nondomestic animals for the presence of Map, 25 feral cats, nine mice (species unknown), eight rabbits (Sylvilagus floridanus), six raccoons (Procyon lotor), and three opossums (Didelphis virginiana) were collected from a mid-western dairy with known Map-infected cattle. Mycobacterium avium subsp. paratuberculosis was isolated from the mesenteric lymph node from seven of 25 (28%) feral cats. Ileum was culture-positive for three of these seven cats, and an isolation of Map was also made from the ileum of one of nine (11%) mice. Tissue samples from other species were negative as determined by Map culture; microscopic lesions consistent with paratuberculosis were not seen in any animal. Restriction fragment polymorphism analysis of isolates from cats and dairy cattle suggest interspecies transmission. The means by which interspecies transmission occurred may be through ingestion of Map-contaminated feces or waste milk or through ingestion of Map-infected prey. Shedding of Map from infected cats was not evaluated. The epidemiologic role of Map-infected feral cats on dairy farms requires further investigation.

Longitudinal study of the spread of ovine Johne's disease in a sheep flock in southeastern New South Wales

OBJECTIVE

The aim of this study was to apply whole flock testing over time to determine the prevalence, distribution and spread of infection in a recently infected flock, with a view to planning intervention strategies for disease control.

PROCEDURE

Serology, pooled faecal culture (PFC) and histology were used to determine the distribution and persistence of infection in a sheep flock in south east New South Wales between 1997 and 2002. Partial flock testing was done up to June 2000, after which annual whole flock testing, using PFC was performed.

RESULTS

Faecal shedding of M a paratuberculosis was not detected in home-bred sheep until 7 years after the introduction of infected sheep in 1993. For at least 7 years there was clustering of infection and shedding within two age groups only. The infected groups appeared to have been exposed to infection (mycobacterial contamination) at an early age (<12 months) and commenced shedding at 5 years of age or older. Groups that were exposed to contamination as adults did not shed detectable amounts of M a paratuberculosis during the study period.

CONCLUSION

Clustering of detectable infection in age groups of sheep that were exposed as lambs was a feature on this farm, providing indirect evidence of finite duration of survival of M a paratuberculosis on pasture and the influence of age on the susceptibility of sheep to develop detectable M a paratuberculosis infection. Spread of infection occurred very slowly and was probably related to the long incubation period (exposure to shedding interval) of 5 years observed on this farm. The findings suggest that partial flock culling, selective grazing management and vaccination could lead to a reduction in mycobacterial contamination on farm to a level at which patent infection no longer occurs. Better understanding of disease spread within flocks over time through flock profiling using PFC will help in devising surveillance strategies (including testing protocols for market assurance testing) to detect infected flocks where there has been clustering and slow spread of infection.

Distribution of Mycobacterium avium subsp. paratuberculosis in organs of naturally infected bull-calves and breeding bulls

Paratuberculosis, caused by Mycobacterium avium subsp. paratuberculosis, has particular importance in cattle due to the resulting chronic diarrhoea, weight loss, decreased production, infertility and eventual death. While faecal oral route of infection is generally recognised, reports about semen-derived infection are rare. The objective of this work was to assess whether M.a. paratuberculosis may disseminate from the gastrointestinal tract to reproductive organs, and compare this event between naturally infected bull-calves and breeding bulls. Ten bull-calves, aged 6-28 weeks and four breeding bulls were tested by serology, faecal and tissue culture, IS900 PCR and RFLP. In seven bull-calves M.a. paratuberculosis was isolated predominantly from mesenteric lymph nodes (75%); isolates from mucosa of the intestine constituted 25%. In three breeding bulls, M.a. paratuberculosis was isolated both from intestinal mucosa and mesenteric lymph nodes. Head and mediastinal lymph nodes, liver, spleen and semen of bull no. 1 (Holstein-Friesian); testes and epididymis of bull no. 2 (Piemonte); testes, epididymides and seminal vesicle of bull No. 3 (Hereford); and seminal vesicle of bull No. 4 (Simmental) tested positive by culture. Hot-start PCR revealed M.a. paratuberculosis in semen, seminal vesicle and intestinal tissue where culture isolation was difficult. Isolates from bull-calves and breeding bulls were of RFLP types B-C9 and B-C1, respectively. Bull-calves born in infected herd can be sources of infection when later used for natural mating or artificial insemination. Sub-clinically infected bulls release M.a. paratuberculosis into semen, consequently infecting the uterine environment of cows.

Mycobacterium avium subsp. paratuberculosis from free-ranging deer and rabbits surrounding Minnesota dairy herds

The objectives of this study were to estimate the prevalence of Mycobacterium avium subsp. paratuberculosis (MAP) among deer and rabbits surrounding infected and noninfected Minnesota dairy farms using fecal culture, and to describe the frequency that farm management practices were used that could potentially lead to transmission of infection between these species. Fecal samples from cows and the cow environment were collected from 108 Minnesota dairy herds, and fecal pellets from free-ranging white-tailed deer and eastern cottontail rabbits were collected from locations surrounding 114 farms; all samples were tested using bacterial culture. In addition, a questionnaire was administered to 114 herd owners. Sixty-two percent of the dairy herds had at least 1 positive fecal pool or environmental sample. A total of 218 rabbit samples were collected from 90% of the herds, and 309 deer samples were collected from 47% of the herds. On 2 (4%) of the farms sampled, 1 deer fecal sample was MAP positive. Both farms had samples from the cow fecal pool and cow environment that were positive by culture. On 2 (2%) other farms, 1 rabbit fecal sample was positive by culture to MAP, with one of these farms having positive cow fecal pools and cow environmental samples. Pasture was used on 79% of the study farms as a grazing area for cattle, mainly for dry cows (75%) and bred or prebred heifers (87%). Of the 114 farms, 88 (77%) provided access to drylot for their cattle, mainly for milking cows (77/88; 88%) and bred heifers (87%). Of all study farms, 90 (79%) used some solid manure broadcasting on their crop fields. Of all 114 farms, the estimated probability of daily physical contact between cattle manure and deer or rabbits was 20% and 25%, respectively. Possible contact between cattle manure and deer or rabbits was estimated to occur primarily from March through December. The frequency of pasture or drylot use and manure spreading on crop fields may be important risk factors for transmission of MAP among dairy cattle, deer, and rabbits. Although the MAP prevalence among rabbits and deer is low, their role as MAP reservoirs should be considered.

[Paratuberculosis in cattle. Reflections on the interactions with Crohn disease in humans. A literature review]

Based on more than 30 literature references, the author tries to explain the phenomena of paratuberculosis in cattle. He gives a short description of the origin of the infection, the disease categories, the diagnostic problems and eradication. Also the human infection with the Mycobacterium known as Mycobacterium avium supspecies paratuberculosis (MAP)--a recognized pathogen in animals causing some or possibly all cases of Crohn's disease will be discussed. The conclusion is that until now no study gives evidence that MAP may be transmitted to humans through foods derived from cattle with MAP infection.

[A study of the epidemiological behaviour of bovine paratuberculosis using time series in Tandil in the province of Buenos Aires, Argentina]

The authors present the results of a study conducted using time series data from the 1993--2001 period in order to characterise the clinical behaviour of bovine paratuberculosis. The case data, confirmed by macroscopic examination, enzyme-linked immunosorbent assay (ELISA) and comparative tuberculin test, came from the herd health register, located in Tandil in the province of Buenos Aires, Argentina. The upper limit of customary variation was observed in April, with an incidence of 2.5%. In 1997, 1999, 2000 and 2001 the disease was epidemic and a peak of 5.6% occurred in March 1999. Over the long term a rise in the total annual incidence was observed, from 0.7% in 1993 to 10.2% in 2001. Knowledge about the epidemiology of paratuberculosis will help to control the disease and minimise its impact on the national economy, and will also provide new information for use in public health.

A deterministic and stochastic simulation model for intra-herd paratuberculosis transmission

In France, the considerable economic losses due to paratuberculosis introduction in cattle herds may justify the development of a herd-level certification procedure. For a cost/benefit analysis purpose, a simple deterministic and stochastic simulation model for intra-herd paratuberculosis transmission has been developed to evaluate the economic consequences of the purchase of a single infected heifer in a French average herd. The values of the epidemiological parameters were provided by a panel of French paratuberculosis experts. The results were in adequacy with field observations. A sensitivity analysis was conducted. The model was however difficult to validate rigorously, since few data on the intra-herd paratuberculosis true prevalence level are currently available.

A cost/benefit study of paratuberculosis certification in French cattle herds

Paratuberculosis has received increasing attention in France because of the important losses this disease may provoke. The use of certification schemes has proven its effectiveness for the protection of healthy herds against diseases transmitted mainly by trade. The economic justification of such schemes in the particular case of paratuberculosis is studied, for French cattle herds, using a cost/benefit approach. The basic economical hypotheses and estimates have been proposed and carefully examined by a working group composed of paratuberculosis experts and field specialists. By adopting the point of view of a breeder that buys animals, we first estimated the benefits resulting from the non-introduction of the disease. They were then compared with the costs resulting from the fact that the vendor reports its own certification costs on the price of the animals he sells. Two average herds (the mean French beef herd and the mean French dairy herd), and two certification levels were studied. The results show that, currently, the use of the certification is not very economically profitable in French cattle herds. This conclusion, however should be reappraised if the certification costs decrease, for example with the commercialization of diagnostic tests on mixtures.