Transmission of paratuberculosis

Infection of the calf soon after birth by oral ingestion of M. paratuberculosis organisms from feces of infected cows is the most important method of transmission of paratuberculosis. The severity and rate of progression of the disease are dependent on the quantity of organisms in the exposure and the age of the animal. Only a small dose of organisms may be required to establish infection in a newborn calf, and overwhelming age-related resistance by introduction of a large dose of organisms to an adult cow is probably possible. Other means of transmission such as transplacental and direct excretion in the milk and colostrum should not be ignored and should be a particular concern primarily in advanced stages of infection when heavy fecal shedding is detected.

Progress towards understanding the spread, detection and control of Mycobacterium avium subsp paratuberculosis in animal populations

OBJECTIVE

To review and interpret aspects of the pathogenesis and epidemiology of paratuberculosis (Johne's disease) for veterinarians involved in current Johne's disease control programs.

PROCEDURE

An electronic and manual search was undertaken to identify published information which, together with limited unpublished data, was interpreted and summarised.

CONCLUSIONS

Paratuberculosis, a chronic enteropathy of ruminants, is caused by Mycobacterium avium subsp paratuberculosis and is transmitted mainly in faeces to young animals by infected adults, some of which may not have clinical signs. The incubation period is inversely related to the size of the challenge dose but can be extremely prolonged. Clinical cases may not be seen within the economic lifespan of farm animals, particularly when stocking rates are low, pasture is spelled, or when animals are culled at a relatively young age. Other as yet unknown influences may determine the rate of progression or recovery from infection. Paratuberculosis appears in a range of forms from a disease with high prevalence and significant mortality through to one with very low prevalence and little obvious morbidity or mortality. Detection of infected flocks and herds relies on use of laboratory tests. Bacteriological culture of faeces is the most sensitive herd-level test. The passage of time and repeated testing are the greatest allies in detecting paratuberculosis because infected animals progress in the disease process and most tests are more effective in the later stages of the disease. These factors generally cause the prevalence of paratuberculosis to be underestimated at both herd or flock and regional level. Greater understanding of the epidemiology and pathogenesis of M a paratuberculosis infection is critical in order to design improved diagnostic strategies, assess the feasibility of eradication and develop control options, particularly in small ruminants.

Epidemiological study of paratuberculosis in wild rabbits in Scotland

A survey of 22 farms confirmed the presence of paratuberculosis in wild rabbits in Scotland. Regional differences were apparent in the prevalence of the disease in rabbits, with a significantly higher incidence occurring in the Tayside region. Statistical analysis showed a significant relationship between a previous history or current problem of paratuberculosis in cattle and the presence of paratuberculosis in rabbits on the farms. Molecular genetic typing techniques could not discriminate between selected rabbit and cattle isolates from the same or different farms, suggesting that the same strain may infect and cause disease in both species and that interspecies transmission may occur. The possibility of interspecies transmission and the involvement of wildlife in the epidemiology of paratuberculosis have important implications for the control of the disease.

Control of Mycobacterium avium subsp. paratuberculosis infection in agricultural species

Paratuberculosis or Johne's disease is a chronic intestinal disease caused by Mycobacterium avium subsp. paratuberculosis, which continues to spread in agricultural species. Control of paratuberculosis is challenging and should not be underestimated. Due to the long incubation period of the infection, disease is largely subclinical in domesticated livestock. Hence, direct effects on animal productivity and welfare are often masked and may appear insufficient to justify large investments in control programmes by individual farmers, livestock industries or governments. Furthermore, in some countries the main effects of the disease are indirect, resulting from the impact of market discrimination against herds and flocks known to be infected, or from the control measures enforced to reduce transmission. In such circumstances, producers may be unwilling to co-operate with surveillance that may detect infection in herds or flocks. As control programmes are rarely successful in eliminating the infection from a herd or flock in the short term without an aggressive and costly programme, financial and community support assists producers to deal with the challenge. Successful prevention and control depends on animal health authorities and livestock industries acquiring a good understanding of the nature and epidemiology of infection, and of the application of tools for diagnosis and control. Building support for control programmes under the leadership of the affected livestock industries is critical, as programmes are unlikely to be successful without ongoing political will, supported by funding for research, surveillance and control.

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.

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.

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.

Paratuberculosis: a potential zoonosis?

Available literature on the controversial role of Mycobacterium paratuberculosis as an etiologic agent in human Crohn's disease is reviewed. Despite almost 15 years of investigation, the question of causal or consequential association between Johne's disease and Crohn's disease continues to linger.

Detection of Mycobacterium avium subspecies paratuberculosis specific IS900 insertion sequences in bulk-tank milk samples obtained from different regions throughout Switzerland

BACKGROUND

Since Mycobacterium avium subspecies paratuberculosis (MAP) was isolated from intestinal tissue of a human patient suffering Crohn's disease, a controversial discussion exists whether MAP have a role in the etiology of Crohn's disease or not. Raw milk may be a potential vehicle for the transmission of MAP to human population. In a previous paper, we have demonstrated that MAP are found in raw milk samples obtained from a defined region in Switzerland. The aim of this work is to collect data about the prevalence of MAP specific IS900 insertion sequence in bulk-tank milk samples in different regions of Switzerland. Furthermore, we examined eventual correlation between the presence of MAP and the somatic cell counts, the total colony counts and the presence of Enterobacteriaceae.

RESULTS

273 (19.7%) of the 1384 examined bulk-tank milk samples tested IS900 PCR-positive. The prevalence, however, in the different regions of Switzerland shows significant differences and ranged from 1.7% to 49.2%. Furthermore, there were no statistically significant (p >> 0.05) differences between the somatic cell counts and the total colony counts of PCR-positive and PCR-negative milk samples. Enterobacteriaceae occur as often in IS900 PCR-positive as in PCR-negative milk samples.

CONCLUSION

This is the first study, which investigates the prevalence of MAP in bulk-tank milk samples all over Switzerland and infers the herd-level prevalence of MAP infection in dairy herds. The prevalence of 19.7% IS900 PCR-positive bulk-milk samples shows a wide distribution of subclinical MAP-infections in dairy stock in Switzerland. MAP can therefore often be transmitted to humans by raw milk consumption.

Mycobacterium paratuberculosis: a potential food-borne pathogen?

Mycobacterium paratuberculosis commonly infects dairy cattle, leading to Johne's disease, which is also known as paratuberculosis. The infection is chronic progressive, and incurable. As the infection progresses, excretion of M. paratuberculosis in feces and milk occurs, and the bacterium spreads through the blood to multiple internal organs. Consequently, raw products originating from cattle may harbor M. paratuberculosis. Thermal treatments, such as pasteurization, are commonly relied on to kill food-borne bacterial pathogens that can infect humans. The small number of studies conducted to determine the thermal resistance of M. paratuberculosis suggest that it is less susceptible to destruction by heat killing than are milkborne zoonotic bacterial pathogens such as Listeria spp. or Mycobacterium bovis. Published reports concerning the thermal resistance of M. paratuberculosis in milk are reviewed herein, and key issues concerning the efficacy of pasteurization for elimination of M. paratuberculosis from milk are summarized.

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.

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.

Do non-ruminant wildlife pose a risk of paratuberculosis to domestic livestock and vice versa in Scotland?

Paratuberculosis (Johne's disease) was long considered only a disease of ruminants. Recently non-ruminant wildlife species have been shown to harbor Mycobacterium avium subsp. paratuberculosis, the causative organism of paratuberculosis. We review the known non-ruminant wildlife host range of M. avium subsp. paratuberculosis and consider their role in the epidemiology of paratuberculosis in domestic ruminant livestock. Mycobacterium avium subsp. paratuberculosis has been isolated from lagomorph, canid, mustelid, corvid, and murid species. In agricultural environments domestic ruminants may contact wildlife and/or their excreta when grazing or feeding on farm-stored feed contaminated with wildlife feces, opening up the possibility of inter-species transmission. Of the wildlife species known to harbor M. avium subsp. paratuberculosis in Scotland, the rabbit is likely to pose the greatest risk to grazing livestock. Paratuberculosis in domestic ruminants is a notoriously difficult disease to control; the participation of non-ruminant wildlife in the epidemiology of the disease may partially account for this difficulty.

Paratuberculosis in farmed and free-living wild ruminants in the Czech Republic (1999-2001)

Due to the occurrence of the infection of Mycobacterium avium subspecies paratuberculosis among domestic ruminants and the rapid development of farmed deer industry and the market of cloven-hoofed game we have carried surveys of paratuberculosis, beginning in 1997, in the most common four species of wild ruminants in the Czech Republic [Pavlik et al., Vet. Microbiol. 77 (2000) 231-251]. From 1999 the prevalence of paratuberculosis has been slightly reduced in all three types of husbandry of wild ruminants. Nevertheless paratuberculosis has been diagnosed in wild ruminants in three districts, in four game parks and in five farms. M. a. paratuberculosis was isolated from 128 (5.3%) out of 2,403 wild ruminants of four animal species: 106 red deer, 2 roe deer, 4 fallow deer and 16 mouflons. In red deer farms, the highest number of clinical paratuberculosis cases was in yearling deer. RFLP type B-C1 of M. a. paratuberculosis predominated during the second period (1999-2001) in all types of husbandry with no relationship to wild ruminant species. New "cattle" RFLP types B-C5 and B-C16 of M. a. paratuberculosis were described in infected farmed red deer and one "intermediate" RFLP type R-I4 in fallow deer from one game park. The survival of M. a. paratuberculosis was found to be 4 months during winter in the pasture after destocking of all cattle infected with paratuberculosis. We found that non-vertebrates, wild ruminants or non-ruminant wildlife can be vectors and potentially become a risk factor in the spread of M. a. paratuberculosis infection.

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.

Pasteurization of milk and the heat resistance of Mycobacterium avium subsp. paratuberculosis: a critical review of the data

Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) causes Johne's disease in ruminants (including cattle, sheep and goats) and other animals, and may contribute to Crohn's disease in humans. This possibility, and the fact that M. paratuberculosis may be present in raw milk, make it important to ensure that the heat treatment specified for pasteurization of milk will give acceptable inactivation of this bacterium, with an adequate margin of safety. Published studies of the heat resistance of this bacterium in milk have given widely differing results. Possible reasons for these differences, and the technical problems involved in the work, are reviewed. It is concluded that there is a need (i) for the adoption of an agreed Performance Criterion for pasteurization of milk in relation to this bacterium, (ii) a need for definitive laboratory experiments to understand and determine the heat resistance of M. paratuberculosis, and (iii) a need for an assessment of whether the minimum heat treatments specified at present for pasteurization of milk (Process Criteria) will meet the Performance Criterion for M. paratuberculosis. Measures are also required to ensure that commercial processes deliver continually the specified heat treatment, and to ensure that post-pasteurization contamination is avoided.

Mycobacterium avium ssp. paratuberculosis detection in animals, food, water and other sources or vehicles of human exposure: A scoping review of the existing evidence

Mycobacterium avium ssp. paratuberculosis is the etiologic agent of Johne's disease in ruminants and is hypothesized to be an infectious cause of Crohn's disease, as well as some other human diseases. Due to key knowledge gaps, the potential public health impact of M. paratuberculosis is unknown. This scoping review aims to identify and characterised the evidence on potential sources and vehicles of M. paratuberculosis exposure for humans to better understand how exposure is likely to occur. Evidence from 255 primary research papers is summarized; most examined the prevalence or concentration of M. paratuberculosis in animals (farmed domestic, pets and wildlife) (n=148), food for human consumption (62) (milk, dairy, meat, infant formula) or water (drinking and recreational) and the environment (farm, pasture and areas affected by runoff water) (20). The majority of this research has been published since 2000 (Figure- abstract). Nine case-control studies examining risk factors for Crohn's disease highlighted significant associations with the consumption of processed meats and cheese, while direct contact with ruminants, high risk occupations (farmer, veterinarian), milk consumption and water source were factors not associated with the disease and/or M. paratuberculosis exposure status. Molecular epidemiology studies demonstrated strain-sharing between species. Produce and seafood were the only previously suggested sources of human exposure for which there was no supporting evidence identified in this scoping review. The results of this review indicate that ruminant populations from around the globe are infected with M. paratuberculosis and many non-ruminant species have also been found to carry or be infected with M. paratuberculosis. Several potential sources for human exposure to M. paratuberculosis were identified; however there remain important gaps in quantitative information on the prevalence and concentration of M. paratuberculosis in contaminated sources of exposure. This information is critical to understanding the risk of exposure, opportunities for risk mitigation interventions and modelling exposures to distill the importance of various sources of human exposure to M. paratuberculosis including direct contact with animals and the environment as well as consumption of contaminated foods and water. Results of this study may be used to prioritize future research and to support evidence-informed decision-making on the M. paratuberculosis issue.

Farm-specific approach to paratuberculosis (Johne's disease) control

Uncertainties in the understanding of Johne's disease make the pursuit of disease control confusing for producers and veterinarians. Genetic control recommendations have limited adoption or success because they fail to account for the unique circumstances of individual farms. A systematic and pragmatic approach for developing farm control plans is presented. It targets the development of plans that are adapted to individual farm circumstances and are thus more likely to be implemented and effective.

On-farm batch pasteurization destroys Mycobacterium paratuberculosis in waste milk

A recent dairy survey conducted in 1996 by the National Animal Health Monitoring System suggests between 20 and 40% of dairy herds in the United States have some level of Johne's disease. This figure will continue to increase unless producers implement management regimes that will help control the spread of this disease within their herds. The neonatal calf is the target for infection with Mycobacterium paratuberculosis, the causative agent of Johne's disease. Calves become infected via exposure to the bacterium through contaminated feces, bedding, colostrum, and milk. Shedding of viable M. paratuberculosis has been documented in the colostrum and milk of infected dams. This study evaluated the efficacy of on-farm pasteurization to destroy M. paratuberculosis in waste milk fed to calves to circumvent this mode of transmission. In three replicate experiments, waste milk was experimentally inoculated with M. paratuberculosis and heated at 65.5 degrees C for 30 min. No viable bacteria were recovered after 28 wk of incubation. These results suggest that batch pasteurization of waste milk contaminated with M. paratuberculosis was effective at generating a clean product to feed to young calves.

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.

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.

Biosecurity on dairy operations: hazards and risks

The objective here was to present a model for considering biosecurity related to infectious diseases on US dairy operations using a risk assessment framework. With the example of an important dairy cattle pathogen (Mycobacterium paratuberculosis), I followed risk assessment steps to characterize risks related to the use of certain management practices and possible risk reduction within an infectious disease biosecurity program. Biosecurity practices focus on the prevention of introduction of these pathogens to the dairy, and estimates of the risks associated with introduction of different sources of cattle are presented. In addition, biosecurity practices also limit the transmission of these pathogens within an infected dairy operation, especially those focused on sick cow management, calving area management, and manure management. Recent information from the National Animal Health Monitoring System (NAHMS) Dairy 96 Study indicates that many of these practices have not been adopted on US dairy operations, indicating both risk of disease and opportunity for animal health improvement.