Calves shedding Mycobacterium avium subspecies paratuberculosis are common on infected dairy farms

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

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

Performance of immunohistochemistry versus real-time PCR method for detecting mycobacterial infections of cattle ‎ screened by comparative tuberculin test

In addition to the fifty years since the test-and-slaughter program began in Iran and despite a significant reduction in the disease prevalence, positive tuberculosis cases are still being isolated from livestock farms across the country. Tests with 100% sensitivity and specificity are essential features for bovine tuberculosis diagnosis. The relationship between real-time PCR and immunohistochemistry (IHC) as two essential laboratory methods in the diagnosis of bacterial infections were aimed to evaluate single intradermal comparative tuberculin test (SICTT) results. One hundred thirty-eight cows in two groups were examined: Reactors (108 cows) and clean (as a control group; 30 cows). In the reactor group, 58(54.00%) cows were Mycobacterium bovis positive, 46(43.00%) were Mycobacterium avium subsp. paratuberculosis (MAP) positive, and 11(10.00%) were Mycobacterium tuberculosis positive. 32(55.00%) cows were co-infected with M. bovis and MAP and 5(4.55%) cows were co-infected with Mycobacterium tuberculosis and MAP in this group. Of 50 M. bovis negative cows of reactor group were 14(28.00%) MAP positive and 36(72.00%) negative, as well. Concurrent infection with all was observed in one reactor case. Comparing IHC and real-time PCR for the detection of bovine tuberculosis and Johne's disease showed very good agreement (Kappa values 0.81 - 1.00). The results also provided further confirmation on IHC and real-time PCR as a sensitive and reliable diagnostic screening approach for detection of bovine tuberculosis. The use of one laboratory method to detect bovine tuberculosis is not sufficient alone.

Predicting Positive ELISA Results in Dairy Herds with a Preferred Status in a Paratuberculosis Control Program

Dairy herds participating in the Dutch milk quality assurance program for paratuberculosis are assigned a herd status on the basis of herd examinations by ELISA of individual serum or milk samples, followed by an optional confirmatory fecal PCR. Test-negative herds are assigned Status A; the surveillance of these herds consists of biennial herd examinations. Farmers falsely believing that their Status A herds are Map-free may inadvertently refrain from preventive measures. Therefore, we aimed to develop a predictive model to alert Status A farmers at increased risk of future positive ELISA results. Using data of 8566 dairy herds with Status A in January 2016, two logistic regression models were built, with the probabilities of ≥1 or ≥2 positive samples from January 2017–June 2019 as dependent variables, and province, soil type, herd size, proportion of cattle born elsewhere, time since previous positive ELISA results, and the 95th percentile of the S/P ratios in 2015–2016, as explanatory variables. As internal validation, both models were applied to predict positive ELISA results from January 2019–June 2021, in 8026 herds with Status A in January 2019. The model predicting ≥1 positive sample had an area under the receiver-operating-characteristics curve of 0.76 (95% CI: 0.75, 0.77). At a cut-off predicted probability πc = 0.40, 25% of Status A herds would be alerted with positive and negative predictive values of 0.52 and 0.83, respectively. The model predicting ≥2 positive samples had lower positive, but higher negative, predictive values. This study indicates that discrimination of Status A herds with high and low risks of future positive ELISA results is feasible. This might stimulate farmers with the highest risks to take additional measures to control any undetected Map infections.

Economic losses due to Johne's disease (paratuberculosis) in dairy cattle

Johne's disease (JD), or paratuberculosis, is an infectious inflammatory disorder of the intestines primarily associated with domestic and wild ruminants including dairy cattle. The disease, caused by an infection with Mycobacterium avium subspecies paratuberculosis (MAP) bacteria, burdens both animals and producers through reduced milk production, premature culling, and reduced salvage values among MAP-infected animals. The economic losses associated with these burdens have been measured before, but not across a comprehensive selection of major dairy-producing regions within a single methodological framework. This study uses a Markov chain Monte Carlo approach to estimate the annual losses per cow within MAP-infected herds and the total regional losses due to JD by simulating the spread and economic impact of the disease with region-specific economic variables. It was estimated that approximately 1% of gross milk revenue, equivalent to US$33 per cow, is lost annually in MAP-infected dairy herds, with those losses primarily driven by reduced production and being higher in regions characterized by above-average farm-gate milk prices and production per cow. An estimated US$198 million is lost due to JD in dairy cattle in the United States annually, US$75 million in Germany, US$56 million in France, US$54 million in New Zealand, and between US$17 million and US$28 million in Canada, one of the smallest dairy-producing regions modeled.

A Novel Real-Time PCR-Based Screening Test with Pooled Fecal Samples for Bovine Johne's Disease

Johne's disease (JD) is an economically important infectious disease in livestock farming caused by Mycobacterium avium subsp. paratuberculosis As an alternative to serological tests, which are used mainly for the screening of whole herds, we developed a novel ResoLight-based real-time PCR (RL-PCR) assay with pooled fecal samples for the detection of fecal shedders in cattle herds. The RL-PCR assay included an internal amplification control (IC) which was amplified using the same primer pair as the target molecule M. avium subsp. paratuberculosis IS900 and differentiated based on melting temperatures. Individual fecal suspensions were pooled and concentrated by centrifugation to avoid a loss of sensitivity by the dilution effect. Combined with a DNA extraction kit (Johne-PureSpin; FASMAC), no inhibition of PCR amplification was observed with up to 15 fecal samples in a pool. The detection limit of RL-PCR at a pool size of 10 was 10 M. avium subsp. paratuberculosis organisms per gram of feces, which was comparable to that of individual testing. A total of 2,654 animals in 12 infected herds were screened by individual antibody-enzyme-linked immunosorbent assay (ELISA) and the RL-PCR assay using pooled feces. Fifty animals were diagnosed with JD through the screening by RL-PCR, compared with only 5 by ELISA (which were also positive in RL-PCR). In 7 JD-free herds, the results of 4 out of 327 pools (1.2%) were invalid due to the lack of IC amplification, and then animals were confirmed negative individually. Our results suggest that implementation of herd screening by pooled RL-PCR would advance the monitoring and control of JD in cattle herds.

Regional Dichotomy in Enteric Mucosal Immune Responses to a Persistent Mycobacterium avium ssp. paratuberculosis Infection

Chronic enteric Mycobacterium avium ssp. paratuberculosis (MAP) infections are endemic in ruminants globally resulting in significant production losses. The mucosal immune responses occurring at the site of infection, specifically in Peyer's patches (PP), are not well-understood. The ruminant small intestine possesses two functionally distinct PPs. Discrete PPs function as mucosal immune induction sites and a single continuous PP, in the terminal small intestine, functions as a primary lymphoid tissue for B cell repertoire diversification. We investigated whether MAP infection of discrete vs. continuous PPs resulted in the induction of significantly different pathogen-specific immune responses and persistence of MAP infection. Surgically isolated intestinal segments in neonatal calves were used to target MAP infection to individual PPs. At 12 months post-infection, MAP persisted in continuous PP (n = 4), but was significantly reduced (p = 0.046) in discrete PP (n = 5). RNA-seq analysis revealed control of MAP infection in discrete PP was associated with extensive transcriptomic changes (1,707 differentially expressed genes) but MAP persistent in continuous PP elicited few host responses (4 differentially expressed genes). Cytokine gene expression in tissue and MAP-specific recall responses by mucosal immune cells isolated from PP, lamina propria and mesenteric lymph node revealed interleukin (IL)22 and IL27 as unique correlates of protection associated with decreased MAP infection in discrete PP. This study provides the first description of mucosal immune responses occurring in bovine discrete jejunal PPs and reveals that a significant reduction in MAP infection is associated with specific cytokine responses. Conversely, MAP infection persists in the continuous ileal PP with minimal perturbation of host immune responses. These data reveal a marked dichotomy in host-MAP interactions within the two functionally distinct PPs of the small intestine and identifies mucosal immune responses associated with the control of a mycobacterial infection in the natural host.

Quantifying transmission of Mycobacterium avium subsp. paratuberculosis among group-housed dairy calves

Johne’s disease (JD) is a chronic enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP), with control primarily aimed at preventing new infections among calves. The aim of the current study was to quantify calf-to-calf transmission of MAP among penmates in an experimental trial. Newborn Holstein bull calves (n = 32) were allocated into pens of 4, with 2 inoculated (IN) calves and 2 calves that were contact exposed (CE). Calves were group-housed for 3 months, with frequent collection of fecal and blood samples and tissue collection after euthanasia. The basic reproduction ratio (R₀) was estimated using a final size (FS) model with a susceptible-infected model, based on INF-γ ELISA and tissue culture followed by qPCR. In addition, the transmission rate parameter (β) for new shedding events was estimated using a general linearized method (GLM) model with a susceptible-infected-susceptible model based on culture, followed by qPCR, of fecal samples collected during group housing. The R₀ was derived for IN and CE calves separately, due to a difference in susceptibility, as well as differences in duration of shedding events. Based on the FS model, interferon-γ results from blood samples resulted in a R₀^IG of 0.90 (0.24, 2.59) and tissue culture resulted in a R₀^T of 1.36 (0.45, 3.94). Based on the GLM model, the R₀ for CE calves to begin shedding (R₀^CE) was 3.24 (1.14, 7.41). We concluded that transmission of MAP infection between penmates occurred and that transmission among calves may be an important cause of persistent MAP infection on dairy farms that is currently uncontrolled for in current JD control programs.

Is the transmission of Mycobacterium avium subspecies paratuberculosis (MAP) infection through milk intended to feed calves an overlooked item in paratuberculosis control programs?

As in many parts of the world, Chile shows a high Mycobacterium avium subsp. paratuberculosis (MAP) infection rate. Evidently, the control recommendations have been inefficient. In the author's opinion, the potential risk of MAP transmission to susceptible calves through milk consumption is largely overlooked. Two observational studies were performed, one to confirm MAP shedding in young stock in a high MAP-infected dairy herd and MAP load in milk intended to feed these calves was estimated. In parallel, in a second study, we estimated the relationship between MAP herd seroprevalence and the cow MAP shedding level as well as the presence of this pathogen in milk used to feed dairy calves. In the first study, 53.7% of cows and 22.5% of calves showed positive culture results. Among all cows tested, 9 (2.19%) animals had a positive serum ELISA, and MAP load in milk reached 10⁶ bacteria/mL. In the second study, three seroprevalence categories were established as follows: high (≥ 9%), medium (> 5% and ≤ 9%), and low (≤ 5%). Statistical significant differences among these categories were observed. Animals from the high seroprevalence category shed significantly more MAP than the others. However, in the low category, heavy shedder animals were also observed. Finally, in all study herds, MAP presence in milk intended to feed calves was reported, even from herds without ELISA-positive animals.

Prevalence of Mycobacterium avium ssp. paratuberculosis infections in Canadian dairy herds

Johne's disease is a progressive, chronic disease with inflammation of the small intestine of ruminants caused by Mycobacterium avium ssp. paratuberculosis (MAP). Accurately estimating prevalence of MAP infections is important when controlling spread of infection or monitoring effectiveness of control programs. In the absence of a consistent test method used in prevalence studies across Canada, prevalence estimates among regions and programs cannot be compared. The aim of the current study was to estimate and compare prevalence of MAP infection in Western Canada, Ontario, Québec, and the Atlantic provinces, as well as among varying herd sizes and housing types. On 362 dairy farms located in all 10 provinces of Canada, environmental samples were collected and cultured for detection of MAP. For each herd, 1 sample was collected from the lactating cow area and manure storage. An additional environmental sample was collected from the area where breeding-age heifers were housed. Using prior distributions from previous research, diagnostic sensitivity and specificity were calculated to assess the ability of only 2 environmental samples (manure storage and lactating cow area) to identify MAP-positive farms, resulting in a sensitivity and specificity of 38 and 100%, respectively. We found no difference in sensitivity and specificity when including breeding-age heifers environmental samples. Test characteristics were applied to environmental culture results from the 362 participating farms in all 4 regions, resulting in true prevalence estimates of 66% for farms in Western Canada, 54% in Ontario, 24% in Québec, and 47% in Atlantic Canada. Herds housed in tiestalls had lower prevalence than freestall-housed herds, and herds with 101-150 and >151 cows had higher prevalence than herds with ≤100 cows. This was the first time MAP prevalence was determined using 1 detection method, performed in 1 laboratory, and within a single year across Canada, enabling direct comparisons of prevalence among regions, housing types, and herd sizes.

ISMap02 element targeted nested polymerase chain in the detection of Mycobacterium avium subsp. paratuberculosis in fecal samples of cattle and buffaloes

Background and Aim

Johne's disease is chronic granulomatous enteritis which affects ruminants. There are many diagnostic approaches for the detection of Mycobacterium avium subsp. paratuberculosis (MAP) of which molecular detection methods using various elements are less time consuming and more accurate. The present study was conducted using ISMap02 element for nested polymerase chain reaction (nPCR) based detection of MAP in fecal samples. The aim was to test the sensitivity and specificity of the ISMap02 element and also to use this element for the detection of MAP in fecal samples of cattle and buffaloes.

Materials and Methods

A total of 211 fecal samples of cattle and buffaloes from different herds around Ludhiana aged between 2 and 13 years were collected, and DNA extraction was done from these samples. The nPCR was carried out for the detection of MAP in fecal samples.

Results

The ISMap02 element was specific for the detection of MAP only and showed a sensitivity of detection of 7.6 fg/µL of the standard genomic DNA. Among the 211 fecal samples of cattle and buffaloes tested for the ISMap02 element, 18 samples (8.5%) were positive for MAP.

Conclusion

The ISMap02 element is specific and sensitive for the detection of MAP in various samples, and when used in nPCR format, it can increase the sensitivity of detection.

Quantifying fecal shedding of Mycobacterium avium ssp. paratuberculosis from calves after experimental infection and exposure

Johne's disease, a chronic enteritis caused by Mycobacterium avium ssp. paratuberculosis (MAP), causes large economic losses to the dairy industry worldwide. Fecal shedding of MAP contaminates the environment, feed, and water and contributes to new infections on farm, yet there is limited knowledge regarding mechanisms of shedding, extent of intermittent shedding, and numbers of MAP bacteria shed. The objectives were to (1) compare (in an experimental setting) the frequency at which intermittent shedding occurred and the quantity of MAP shed among pen mates that were inoculated or contact-exposed (CE); and (2) determine whether an association existed between inoculation dose and quantity of MAP shed. In the first experiment, 32 newborn Holstein-Friesian bull calves were allocated to pens in groups of 4, whereby 2 calves were inoculated with a moderate dose (MD; 5 × 10⁸ cfu) of MAP and 2 calves acted as CE. Calves were group-housed for 3 mo, fecal samples were collected and cultured, and culture-positive samples were quantified. In the second experiment, 6 calves were inoculated with either a low (LD) or high (HD) dose of MAP (1 × 10⁸ or 1 × 10¹⁰ cfu, respectively), and fecal samples were collected for 3 mo and cultured for detection of MAP. The amount of MAP was quantified using direct extraction (DE) of DNA from fecal samples and F57-specific quantitative PCR. In experiment 1, the average amount of MAP in all culture-positive samples did not differ between MD and CE calves. In experiment 2, when comparing inoculation doses, LD calves had the lowest proportion of MAP-positive culture samples and HD had the highest, but no difference was detected in the average quantity of MAP shed. This study provided new information in regards to Johne's disease research and control regarding shedding from various inoculation doses and from CE animals; these data should inform future trials and control programs.

Evaluation of fecal shedding and antibody response in dairy cattle infected with paratuberculosis using national surveillance data in Japan

Paratuberculosis or Johne's disease (JD), is a chronic infectious disease causing intractable diarrhea in cattle, which leads to less productivity, such as decreased milk yield, and lower daily weight gain. As a control measure against JD in cattle, national serological surveillance has been conducted in Japan since 1998. To conduct modeling studies that are useful to evaluate the effectiveness of control measures against JD, reliable parameter values, such as length of time from infection to the start of fecal shedding or antibody expression, are especially important. These parameters in the Japanese cattle population are assumed to be different from those in other countries with a higher prevalence of JD or in experimental infection settings; therefore, they must be estimated for the cattle population in Japan. Data from national surveillance conducted in Tokachi District, Hokkaido Prefecture, were used for this study. Using data from JD diagnostic tests for all cattle in Tokachi District between 1998 and 2014, all testing histories for infected animals were estimated as the number of tested cattle and positive cattle at each age of month for both fecal and antibody tests. A deterministic mathematical model for JD development, from infection to fecal shedding and antibody expression in infected cattle, was constructed to obtain the probability of testing positive when applied to both fecal and antibody tests at a given age. Likelihood was obtained from these estimated test results and best values for parameters were obtained using the Markov Chain Monte-Carlo method. Fifty-five percent of infected cattle were projected to have a transient shedding period, which was estimated to start 12 months after infection and last for 4 months. Persistent shedding was projected to occur in all infected cattle, and estimated to begin 7-84 months from infection. Following persistent shedding, antibody expression was estimated to start 7 months later. These values are useful for developing models to evaluate the status of JD infection and the effectiveness of control measures in the Japanese cattle population.

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

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

Management of the calving pen is a crucial factor for paratuberculosis control in large dairy herds

Improvement of hygiene and herd management to reduce the contact of calves with adult cow feces to prevent new infections is one of the basic strategies to manage paratuberculosis-affected dairy herds. Control programs should recommend an evidence-based selection of factors that demonstrably reduce the transmission of the infectious agent and decrease the prevalence of infected cattle to improve acceptance and implementation of the recommended measures among farmers. This study aimed to assess the influence of several management measures on control success in a longitudinal study in 28 large dairy herds with a median size of 415 cows in Thuringia, Germany. The cumulative incidence of cows shedding Mycobacterium avium ssp. paratuberculosis (MAP) per year was determined by individual fecal culture of all cows during 5 consecutive years. Relevant management practices as well as herd size, milk yield, and purchase of cattle were recorded by on-farm risk assessment. Mean holding time of MAP shedders within the herd was calculated from individual data of each shedding cow. Using multiple regression models, separate calving pens for shedders and disinfection of the pen after use were identified as significant risk factors that reduced the cumulative incidence of MAP shedders per year on the herd level. The results provide evidence that, in addition to other factors, calving hygiene and management of the calving pens are crucial for paratuberculosis control, particularly in large dairy herds. Considered together with the outcome from other studies, these results might be important to weight various risk factors and to avoid overburdening and overwhelming farmers and keeping them committed.

Fecal shedding and tissue infections demonstrate transmission of Mycobacterium avium subsp. paratuberculosis in group-housed dairy calves

Current Johne’s disease control programs primarily focus on decreasing transmission of Mycobacterium avium subsp. paratuberculosis (MAP) from infectious adult cows to susceptible calves. However, potential transmission between calves is largely overlooked. The objective was to determine the extent of MAP infection in calves contact-exposed to infectious penmates. Thirty-two newborn Holstein–Friesian calves were grouped into 7 experimental groups of 4, consisting of 2 inoculated (IN) calves, and 2 contact-exposed (CE) calves, and 1 control pen with 4 non-exposed calves. Calves were group housed for 3 months, with fecal samples were collected 3 times per week, blood and environmental samples weekly, and tissue samples at the end of the trial. The IN calves exited the trial after 3 months of group housing, whereas CE calves were individually housed for an additional 3 months before euthanasia. Control calves were group-housed for the entire trial. All CE and IN calves had MAP-positive fecal samples during the period of group housing; however, fecal shedding had ceased at time of individual housing. All IN calves had MAP-positive tissue samples at necropsy, and 7 (50%) of the CE had positive tissue samples. None of the calves had a humoral immune response, whereas INF-γ responses were detected in all IN calves and 5 (36%) CE calves. In conclusion, new MAP infections occurred due to exposure of infectious penmates to contact calves. Therefore, calf-to-calf transmission is a potential route of uncontrolled transmission on cattle farms.

Experimental infection with Mycobacterium avium subspecies paratuberculosis resulting in decreased body weight in Holstein-Friesian calves

Fifty calves inoculated at either 2 weeks or at 3, 6, 9, or 12 months of age with either a low or high dose of Mycobacterium avium subspecies paratuberculosis (MAP) were on average 32 and 39 kg lower in body weight, respectively, compared to negative controls at 17 months of age.

Detection of Mycobacterium avium subspecies paratuberculosis in tie-stall dairy herds using a standardized environmental sampling technique and targeted pooled samples

Mycobacterium avium ssp. paratuberculosis (MAP) is the etiologic agent of Johne's disease, a chronic contagious enteritis of ruminants that causes major economic losses. Several studies, most involving large free-stall herds, have found environmental sampling to be a suitable method for detecting MAP-infected herds. In eastern Canada, where small tie-stall herds are predominant, certain conditions and management practices may influence the survival and transmission of MAP and recovery (isolation). Our objective was to estimate the performance of a standardized environmental and targeted pooled sampling technique for the detection of MAP-infected tie-stall dairy herds. Twenty-four farms (19 MAP-infected and 5 non-infected) were enrolled, but only 20 were visited twice in the same year, to collect 7 environmental samples and 2 pooled samples (sick cows and cows with poor body condition). Concurrent individual sampling of all adult cows in the herds was also carried out. Isolation of MAP was achieved using the MGIT Para TB culture media and the BACTEC 960 detection system. Overall, MAP was isolated in 7% of the environmental cultures. The sensitivity of the environmental culture was 44% [95% confidence interval (CI): 20% to 70%] when combining results from 2 different herd visits and 32% (95% CI: 13% to 57%) when results from only 1 random herd visit were used. The best sampling strategy was to combine samples from the manure pit, gutter, sick cows, and cows with poor body condition. The standardized environmental sampling technique and the targeted pooled samples presented in this study is an alternative sampling strategy to costly individual cultures for detecting MAP-infected tie-stall dairies. Repeated samplings may improve the detection of MAP-infected herds.

Paratuberculosis in buffaloes in Northeast Brazil

Several farms in the Northeast of Brazil were investigated for Mycobacterium avium subsp. paratuberculosis infection in order to identify the occurrence of paratuberculosis in buffaloes. Samples were obtained from 17 farms, two slaughter houses, and a quarantine area in the Northeast. About 15,000 buffaloes of the Murrah, Mediterranean, and Jafarabadi breed as well as their crossbreeds were evaluated for meat, dairy, and mixed farms with semi-intensive or extensive breeding practices. For diagnostic purposes, postmortem and histopathological examination, including Ziehl-Neelsen test of fecal smears and scraped intestinal mucosa were performed. PCR was applied for fecal samples, mesenteric lymph nodes, and intestines. Six Johne's disease-positive farms, which together with those previously identified, indicate that the disease is spread through the Brazilian Northeast, similar to what occurs in cattle herds in other regions of the country. The increase in prevalence of paratuberculosis is a consequence of introduction of animals from other regions without adequate veterinary assistance and due to the little official attention paid to this initially silent and chronic disease.

The isolation and molecular characterization of Mycobacterium avium subsp. paratuberculosis in Shandong province, China

BACKGROUND

Mycobacterium avium subspecies paratuberculosis (Map) causes Johne's disease in domestic and wild ruminants. It has been a debate that whether Map can cause Crohn's disease in human. To our knowledge there is no report about molecular characterization of Map in China, although several Map strains have been reported in other country. The objectives of this study was to know the recent prevalence of Johne's disease in dairy farms in Shandong province, and have a better understanding of genotypic distribution of Map in China.

METHODS

Johne's disease was detected from 1038 individuals in 19 dairy farms by ELISA. Map in fecal and milk specimens was identified by Ziehl-Neelsen staining and confirmed using PCR-REA. In addition, frozen sections of ileum and mesenteric lymph nodes from two Map shedding cows were performed to observe the histopathological changes. Next-generation sequencing technology was performed to get whole genome sequences.

RESULT

A total of 121 (11.7 %) animals were positive for Map antibody from 1038 sera tested, and 11 (57.9 %) dairy herds were positive for Map antibody. Typically histopathologic changes were observed in mesenteric lymph nodes. We have successfully isolated two Map strains, which both were Map-C. The current genome-wide analysis showed that the genome size of our isolates are respectively 4,750,273 and 4,727,050 bp with a same G + C content of 69.3 %, and the numbers of single nucleotide polymorphisms (SNPs) against Map K-10 are respectively 292 and 296.

CONCLUSION

Map is a prevalent pathogen among dairy cattle in China. This study successfully isolated two Map strains from one Chinese dairy herd with signs of diarrhoea, and identified that the two isolates were both Map-C. Furthermore, these isolates were most closely related to Map K-10.

Dairy farms testing positive for Mycobacterium avium ssp. paratuberculosis have poorer hygiene practices and are less cautious when purchasing cattle than test-negative herds

Mycobacterium avium ssp. paratuberculosis (MAP), the causative agent of Johne's disease, is present on most dairy farms in Alberta, causing economic losses and presenting a potential public health concern. The objective of this cross-sectional study was to identify risk factors for Alberta dairy herds being MAP-positive based on environmental samples (ES). Risk assessments were conducted and ES were collected on 354 Alberta dairy farms (62% of eligible producers) voluntarily participating in the Alberta Johne's Disease Initiative. In univariate logistic regression, risk factors addressing animal and pen hygiene, as well as the use of feeding equipment to remove manure and manure application on pastures, were all associated with the number of positive ES. Furthermore, based on factor analysis, risk factors were clustered and could be summarized as 4 independent factors: (1) animal, pen, and feeder contamination; (2) shared equipment and pasture contamination; (3) calf diet; and (4) cattle purchase. Using these factor scores as independent variables in multivariate logistic regression models, a 1-unit increase in animal, pen, and feeder contamination resulted in 1.31 times higher odds of having at least 1 positive ES. Furthermore, a 1-unit increase in cattle purchase also resulted in 1.31 times the odds of having at least 1 positive ES. Finally, a 100-cow increase in herd size resulted in an odds ratio of 2.1 for having at least 1 positive ES. In conclusion, cleanliness of animals, pens, and feeders, as well as cattle purchase practices, affected risk of herd infection with MAP. Therefore, improvements in those management practices should be the focus of effective tools to control MAP on dairy farms.

Short communication: Evaluation of sampling socks for detection of Mycobacterium avium ssp. paratuberculosis on dairy farms

Mycobacterium avium ssp. paratuberculosis (MAP) causes Johne's disease, a production-limiting disease in cattle. Detection of infected herds is often done using environmental samples (ES) of manure, which are collected in cattle pens and manure storage areas. Disadvantages of the method are that sample accuracy is affected by cattle housing and type of manure storage area. Furthermore, some sampling locations (e.g., manure lagoons) are frequently not readily accessible. However, sampling socks (SO), as used for Salmonella spp. testing in chicken flocks, might be an easy to use and accurate alternative to ES. The objective of the study was to assess accuracy of SO for detection of MAP in dairy herds. At each of 102 participating herds, 6 ES and 2 SO were collected. In total, 45 herds had only negative samples in both methods and 29 herds had ≥1 positive ES and ≥1 positive SO. Furthermore, 27 herds with ≥1 positive ES had no positive SO, and 1 herd with no positive ES had 1 positive SO. Bayesian simulation with informative priors on sensitivity of ES and MAP herd prevalence provided a posterior sensitivity for SO of 43.5% (95% probability interval=33-58), and 78.5% (95% probability interval=62-93) for ES. Although SO were easy to use, accuracy was lower than for ES. Therefore, with improvements in the sampling protocol (e.g., more SO per farm and more frequent herd visits), as well as improvements in the laboratory protocol, perhaps SO would be a useful alternative for ES.

Invited review: Changes in the dairy industry affecting dairy cattle health and welfare

The dairy industry in the developed world has undergone profound changes over recent decades. In this paper, we present an overview of some of the most important recent changes in the dairy industry that affect health and welfare of dairy cows, as well as the science associated with these changes. Additionally, knowledge gaps are identified where research is needed to guide the dairy industry through changes that are occurring now or that we expect will occur in the future. The number of farms has decreased considerably, whereas herd size has increased. As a result, an increasing number of dairy farms depend on hired (nonfamily) labor. Regular professional communication and establishment of farm-specific protocols are essential to minimize human errors and ensure consistency of practices. Average milk production per cow has increased, partly because of improvements in nutrition and management but also because of genetic selection for milk production. Adoption of new technologies (e.g., automated calf feeders, cow activity monitors, and automated milking systems) is accelerating. However, utilization of the data and action lists that these systems generate for health and welfare of livestock is still largely unrealized, and more training of dairy farmers, their employees, and their advisors is necessary. Concurrently, to remain competitive and to preserve their social license to operate, farmers are increasingly required to adopt increased standards for food safety and biosecurity, become less reliant on the use of antimicrobials and hormones, and provide assurances regarding animal welfare. Partly because of increasing herd size but also in response to animal welfare regulations in some countries, the proportion of dairy herds housed in tiestalls has decreased considerably. Although in some countries access to pasture is regulated, in countries that traditionally practiced seasonal grazing, fewer farmers let their dairy cows graze in the summer. The proportion of organic dairy farms has increased globally and, given the pressure to decrease the use of antimicrobials and hormones, conventional farms may be able to learn from well-managed organic farms. The possibilities of using milk for disease diagnostics and monitoring are considerable, and dairy herd improvement associations will continue to expand the number of tests offered to diagnose diseases and pregnancy. Genetic and genomic selection for increased resistance to disease offers substantial potential but requires collection of additional phenotypic data. There is every expectation that changes in the dairy industry will be further accentuated and additional novel technologies and different management practices will be adopted in the future.

Susceptibility to and diagnosis of Mycobacterium avium subspecies paratuberculosis infection in dairy calves: A review

The primary objectives of paratuberculosis control programs are reducing exposure of calves to Mycobacterium avium subspecies paratuberculosis (MAP), reducing herd infection pressure and regular testing of cattle >36 months of age. Although control programs based on these principles have reduced prevalence of MAP infection in dairy herds, they have generally not eliminated the infection. Recent infection trial(s) have yielded new knowledge regarding diagnostic testing and age- and dose-dependent susceptibility to MAP infection. Calves up to 1 year of age are still susceptible to MAP infection; therefore, control programs should refrain from referring to specific ages with respect to susceptibility and prevention of new infections. Notwithstanding, lesions were more severe when calves were inoculated at 2 weeks versus 1 year of age. Furthermore, a high inoculation dose resulted in more pronounced lesions than a low inoculation dose, especially in young calves. Consequently, keeping infection pressure low should decrease the incidence of new MAP infections and severity of JD in cattle that do acquire the infection. It was also evident that early diagnosis of MAP infection was possible and could improve efficacy of control programs. Although its use will still need to be validated in the field, a combination of antibody ELISA and fecal culture in young stock, in addition to testing cattle >36 months of age when screening a herd for paratuberculosis, was expected to improve detection of dairy cattle infected with MAP. Although calves were inoculated using a standardized method in a controlled environment, there were substantial differences among calves with regards to immune response, shedding and pathology. Therefore, we inferred there were genetic differences in susceptibility. Important insights were derived from experimental infection trials. Therefore, it was expected that these could improve paratuberculosis control programs by reducing severity and incidence of JD by lowering infection pressure on-farm, and reducing exposure of young calves and older cattle. Furthermore, an earlier diagnosis could be achieved by combining ELISA and fecal shedding in young stock, in addition to testing cattle >36 months of age.