Johne's Disease Control Research Articles

Characterization of Minnesota dairy herds participating in a Johne's disease control program and evaluation of the program risk assessment tool

The objectives of this study were to: (1) characterize Minnesota dairy herds participating in a Johne's disease control program (JDCP) based on herd size, milk production, and clinical Johne's disease (JD) history, (2) evaluate if change in farm management practices, expressed in risk assessment (RA) total score, is associated with the change between the first and most recent ELISA test herd seroprevalence or change in clinical JD culling rate, and (3) identify farm factors associated with ELISA seroprevalence. A total of 1234 RA, performed between January 2000 and February 2004, were available for analysis from 714 dairy herds. ELISA test results from herd sampling between 2000 and 2004 were obtained from the Minnesota board of animal health (MBAH) database, and were available for 474 herds. Both the first and the most recent ELISA test results for herds with more than one RA were available for 262 herds. Mean herd size and mean annual milk production per cow was higher in JDCP dairy herds (161 milking cows) than either all Minnesota dairy herds or Minnesota dairy herd improvement association (DHIA) herds. For herds with more than one RA available, the most recent RA total score was significantly lower (mean 11% less) than the first. The change in RA total score (and any RA subtotal scores) between the first and most recent RA was not associated with the change between the first and the most recent ELISA within-herd seroprevalence or the change in JD culling rate between the first and most recent RA. The most recent ELISA test results were positively associated with postweaned heifer score and JD culling rate. The RA score was not found to be an effective tool for the prediction of ELISA seroprevalence.

Evaluation of Environmental Sampling to Determine Distribution and Dairy Herd Infection Status for Mycobacterium avium subspecies paratuberculosis

An important component of the Voluntary Bovine Johne's Disease Control Program is to determine herd infection status for Mycobacterium avium subspecies paratuberculosis (MAP). To help prevent the transmission of MAP, dairy and beef herds providing replacement cattle should know their infection status. Herds acquiring cattle should be fairly confident that the source herd is at low risk for MAP infection. The current requirements for a herd to be considered Level 1 of the test-negative component requires ELISA testing 30 animals followed by fecal culture confirmation of ELISA-positive cattle. Since the ELISA is approximately 25-50% sensitive, many infected herds are classified as low risk and enter Level 1 based on this testing scheme.

Comparison of Two Enzyme-Linked Immunosorbent Assays for Diagnosis of Mycobacterium Avium Subsp. Paratuberculosis

Enzyme-linked immunosorbent assays (ELISAs) are used in Johne's disease (JD) control programs as a first screening for presence of the disease in a herd. A high sensitivity of the ELISA is therefore important, yet the commonly used ELISAs have relatively low sensitivity. The inclusion of an absorption phase, although improving specificity, potentially decreases sensitivity. Sera and feces of 383 adult dairy cows in 8 herds were used to compare the test characteristics of an absorbed and a nonabsorbed indirect ELISA for the detection of JD. The absorbed ELISA is based on a protoplasmic antigen, whereas the nonabsorbed uses a lipoarabinomannan-based antigen. The potential advantage of the nonabsorbed ELISA is that it may be less specific and more sensitive. Two herds certified free of JD were used to compare the specificity of the ELISAs. The other herds used to compare sensitivity were either infected with Mycobacterium avium subsp. paratuberculosis or had unknown status. Using fecal culture as a gold standard, the diagnostic specificity for the absorbed and nonabsorbed ELISAs were 98.4% and 87.9%, respectively. The diagnostic sensitivity was 72.4% and 65.5% for the absorbed and the nonabsorbed ELISA, respectively. Furthermore, a comparison using a fecal DNA probe as the comparison standard resulted in both ELISAs having a sensitivity of 61.9%. Agreement between the 2 ELISAs was moderate, with a kappa statistic of 0.58. The nonabsorbed ELISA did not have a higher sensitivity and had a lower specificity than the absorbed ELISA. Therefore, in this population, there was no advantage gained with using the nonabsorbed ELISA.

Effects of Seasonal Climatic Conditions on the Diagnosis of Mycobacterium avium Subspecies paratuberculosis in Dairy Cattle

Validity of Johne's disease programs and control protocols that rely on established cut points [e.g., specified sample-to-positive (S/P) ratios] for ELISA serological tests depends on interpreted results that are not susceptible to variable test accuracy. It was hypothesized that seasonal variability exists in serological response to Mycobacterium avium subsp. paratuberculosis (MAP) infection. Further, a reciprocal response may occur, resulting in greater risk of fecal shedding in subclinically infected animals. A testing regimen was invoked that included multiple testing of individual adult cows during the 4 seasons. Serum was collected on a cyclic, monthly basis from 3 randomly selected cohorts of dairy cows, and fecal samples were collected from the 20% of cows with the greatest ELISA test S/P ratios. Staggered, quarterly sampling was continued for 1 yr, and at the conclusion, serum was analyzed en masse. The ELISA outcome values (i.e., S/P ratio) were treated both as categorical and continuous variables. The potential lagged effects of temperature-related seasonality on S/P ratio, as well as the potential for a change in test result caused by temperature were assessed. Results for fecal culture were analyzed on a categorical scale and compared with the ELISA results to explore the possibility of reciprocal fecal shedding. No significant seasonal effects on either S/P ratios or the proportion of cows seropositive to MAP were observed. Furthermore, no evidence was found linking temperature-related seasonality to a reciprocal increase in the risk of fecal culture positivity for MAP.

Effect of compliance with recommended calf‐rearing practices on control of bovine Johne's disease

To assess the degree of compliance with recommended management procedures for the control of bovine Johne's disease and study the relationship between aspects of calf management and testing/disease outcomes in the herds. Fifty-four south Gippsland dairy herds participating in the Victorian bovine Johne's disease test and control program were visited between July and November 2002 and an audit of calf rearing practices was conducted. The results of testing completed under the program were analysed for each of the herds. Twenty seven management factors were examined for a relationship with the presence of clinical cases of Johne's disease or cattle with positive ELISA test results that were born after the completion of the second whole herd test. Logistic regression was used to examine the strength of relationships between the management practices and the frequency with which new cases of Johne's disease arose. RESULTS AND CONCULSIONS: Calves were removed from their dams within 12 hours of birth in only 17 (31.5%) of the herds. However, in all but one herd the calves were removed within 24 hours of birth. In 42 herds (77.8%) calf rearing facilities were adequately separated from adult cattle and the faeces from adult cattle. In 41 herds (75.9%) calves up to the age of 12 months were grazed on paddocks that were free of manure or effluent from adult cattle. However, in only 10 (18.5%) of the herds were all three of these calf management practices applied. Feeding whole milk containing antibiotic residues, or providing water for calves from birth, were found to have statistically significant associations with an increased occurrence of cases of bovine Johne's disease in the study herds. The practice of allowing cows to calve in a paddock was found to be associated with reduced occurrence of bovine Johne's disease. These associations were still found after analysis that included herd size, the number of clinical cases that had occurred in the herds before the start of testing, the number of animals with positive ELISA tests that were detected at the first test and the number of years of participation in the test and cull program. Early separation of newborn calves from cows and grazing calves under 12 months of age in areas free of adult cattle were not found to be protective against Johne's disease.

Effect of Management Related Disease Control Methods on the Development of Johne's Disease in Dairy Cattle in Texas

With the primary objective of evaluating long-term effectiveness and feasibility of management-related disease control methods in large dairies and on beef operations on the development of Johne's disease (JD) in cattle in Texas, USDA-APHIS and Texas A&M University have initiated the Johne's Disease Control Demonstration Project for the Texas dairy and beef industries. The epidemiological and production analysis of one of the dairy demonstration herds (n=3534) is presented, and the effect of JD on the herd's production parameters is evaluated.

Use of Environmental Sampling as a Herd Screening Diagnostic Tool for the Detection of Mycobacterium avium Subsp paratuberculosis on Minnesota Dairy Farms

Johne's disease (JD) is a chronic and progressive intestinal disease in ruminants caused by Mycobacterium avium subspecies paratuberculosis (Map). The usual route of infection is fecal-oral. The disease manifests in adult cows and results in economic losses. Although Map does not propagate in the environment, it survives for long periods in different environmental conditions expected on many dairy farms. Johne's disease control programs have been developed in different countries and in several US states with a goal to test and classify herds of cattle as infected or presumptively noninfected with maximum accuracy and least cost. Generally, these programs utilize recognized laboratory tests such as ELISA or direct microbiological individual fecal culture. However, these tests have several disadvantages, especially when applied in herds with subclinical disease or low prevalence. Since Map is shed into the environment by dairy cattle through fecal contamination and appears to survive well, a better understanding of Map distribution in the environment could lead to improved herd-screening alternatives.
 Objectives of the study were: 1) to describe Map distribution and prevalence in the environment on Minnesota dairy farms, and 2) to assess the relationship between culture status of Map in the farm environment and fecal-pooled culture status on dairy farms.

Distribution of Mycobacterium avium paratuberculosis in Minnesota Dairy Farms Using Bacterial Culture of Fecal Pools

Paratuberculosis, or Johne's disease, is a chronic and progressive intestinal disease in ruminants caused by Mycobacterium avium subspecies paratuberculosis (MAP). The usual route of infection is fecal-oral, with young cattle becoming infected by exposure to infected adults or their contaminated environment. The disease becomes manifest in adulthood and results in economic losses due to premature culling, reduced milk production and loss of body weight in cattle sold for slaughter. Johne's disease control programs have been developed in different countries and in several US states, with a goal to test and classify herds of cattle as infected or presumptively non-infected with maximum accuracy and least cost. Generally, these programs utilize recognized laboratory tests such as ELISA or direct microbiological individual fecal culture. However, these tests have several disadvantages, especially when applied in herds with subclinical disease or low prevalence. A pooled fecal culture method, which aggregates several cows' fecal samples to one culture unit, has been recently suggested as a good alternative strategy for lowering the procedure cost for herd screening programs for dairy cattle. The objectives of the current study were to: 1) describe the apparent fecal pool prevalence of MAP in known to be infected and non infected Minnesota dairy herds based on pooled fecal culture, 2) estimate the animal-level prevalence based on fecal pool results, 3) characterize the association between cow age and pool status and shedding level results, and 4) characterize the association between pooled culture results and serum ELISA results at the herd level.

The Distribution of Mycobacterium avium ssp. paratuberculosis in the Environment Surrounding Minnesota Dairy Farms

The objective of this study was to characterize the distribution of Mycobacterium paratuberculosis (Map) in the environment of infected and uninfected Minnesota dairy farms. Eighty herds known to be infected from Minnesota's Johne's Disease Control Program (JDCP) and 28 herds known to be uninfected from Minnesota Voluntary Johne's Disease Herd Status Program (VJDHSP) were sampled. Fecal samples from up to 100 cows in each herd were cultured in pools of 5 cows. Two environmental samples were obtained from each farm from various locations. All samples were tested using bacterial culture for Map. Eighty percent of the JDCP herds had at least one positive pool. Environmental samples were cultured positive in 78% of the JDCP herds. Two (7%) of the VJDHSP herds had one positive pool, and one herd had one positive environmental sample. Environmental samples were cultured positive in cow alleyways (77% of the herds), manure storage (68%), calving area (21%), sick cow pen (18%), water runoff (6%), and postweaned calves areas (3%). There was an association between maximum level of colonies per tube from cow alleyways and manure storage and fecal pool prevalence. Herds with both areas cultured negative were estimated to have 0.3 to 4% fecal pool prevalence. Herds with both areas having a heavy load of bacteria were estimated to have 53 to 73% fecal pool prevalence. The study results indicate that targeted sampling of cow alleyways and manure storage areas appears to be an alternative strategy for herd screening and Johne's infection status assessment and for estimating herd fecal prevalence.

Effect of a test and control program for bovine Johne's disease in Victorian dairy herds 1992 - 2002.

To report on progress in Johne's disease (JD) control in infected dairy herds participating in the Victorian Johne's disease Test and Control Program (TCP). Clinical histories and JD testing data recorded by the Department of Natural Resources and Environment (now called Department of Primary Industries) were analysed for 542 dairy herds participating in the TCP. The herds were required to conduct annual herd tests of cattle 2 years old and older with an enzyme linked immunosorbent assay (ELISA), cull the reactors and manage the younger cattle to minimise infection. Testing of over 680,000 animals identified over 10,000 reactors giving an average prevalence of reactors at the first whole-herd test (T1) of 1.78%. There was a relatively rapid increase in the incidence of clinical disease before the TCP started and then it markedly declined. There was a slow and interrupted decline in reactor prevalence, with a marked peak occurring at the fourth herd test (T4). The average age of reactors and clinical cases was 5.7 and 5.9 years, respectively. Of the reactors and clinical cases detected during the TCP, 87% and 95% respectively, were born before the TCP started. Thirty herds completed the program by achieving three successive negative whole herd tests and 91 herds dropped out because of inability to comply with the agreed requirements of the program. There were no home-bred reactors born after the start of the program in 253 (47%) herds and of the 522 herds that were tested more than once, there were 319 (61%) herds in which no home-bred reactors were detected after the first year of testing. The number of ELISA positive animals detected at T1 appeared to be only about 26% of the animals from that round that subsequently became positive or developed clinical disease at later test rounds. The TCP caused a marked decline in the number of clinical cases, probably because animals in which clinical disease was imminent were detected by testing and removed. A reduction in prevalence of reactors occurred only when most herd members were born after the TCP started. The sensitivity of the ELISA appears to be low based on the large number of reactors that were negative at T1 but were positive at later tests. Low sensitivity of diagnostic tests and the long incubation period of the disease limits meaningful analysis of the program until it has continued for some years. Measures adopted in the TCP have not broken the cycle of infection in many participating herds. It is unsure if this was because of poor compliance with control recommendations or a poor understanding of methods of transmission by scientists. Eradication is not feasible in the short-term.

Effect of a test and control program for Johne's disease in Victorian beef herds 1992-2002.

To report on progress in Johne's disease (JD) control in infected beef herds participating in the Victorian Johne's disease test and control program (TCP). Clinical histories and JD testing data recorded by the Department of Primary Industries were analysed for 18 beef herds participating in the TCP. The herds were required to conduct annual whole herd tests with an absorbed ELISA, cull reactors and control the grazing of young cattle to minimise infection. Testing of over 11,000 animals identified 68 reactors giving an average prevalence of reactors at the first whole-herd test round (T1) of 0.77%. There had been 20 clinical cases detected in the 7 years before the TCP started and two cases detected in the 10 years after TCP started. Most reactors and all clinical cases were born before the TCP started. Of 34 reactors necropsied, 25 (74%) were confirmed to have JD by histology or culture of tissues. The modal age of reactors and clinical cases was 5 and 6 years respectively. Six herds completed the program by achieving three successive negative whole herd tests, four herds dropped out and eight continued to test. There were 18 reactors detected at T1 and 33 reactors that were negative at T1 but detected at subsequent tests. The TCP was associated with a marked decline in clinical cases. The similar age distributions of clinical cases and reactors probably meant that testing detected animals for which clinical disease was imminent. Whether the measures used in the TCP were adequate to control the disease in beef herds could not be determined because of the long incubation period of the disease. The relatively high proportion of the reactors investigated that were confirmed as infected provided confidence that the test was continuing to operate at a high specificity. If all unconfirmed reactors were presumed to be uninfected, the minimum specificity of the ELISA was 99.83%. The sensitivity of the ELISA appeared to be very low because of the large number of reactors that were negative at T1 but positive at later tests.

Comparison of Management Practices Between Ohio Dairy Herds Involved in Johne's Disease Testing Programs Versus Herds Not Involved in a Testing Program

The purpose of this survey was to compare the adoption of management practices recommended for Johne's disease control between herds involved in whole-herd testing programs versus those that do not routinely test for Johne's disease. Eight hundred-ten Ohio dairy herds were selected to participate in a mail survey, and a total of 266 questionnaires were returned (32.8% response rate).

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

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

Progress in national control and assurance programs for bovine Johne's disease in Australia.

Cattle strains of Mycobacterium paratuberculosis are known to infect cattle, goats and alpaca in southeastern Australia, where there are also significant numbers of farmed deer. Although sheep strains have recently been identified in some cattle in Australia, epidemiological evidence to date supports the distinction (between bovine Johne's disease (JD), caused by cattle strains in cattle, goats and alpaca, and ovine JD, caused by sheep strains in sheep and goats) for the purposes of control and assurance programs. The National Johne's Disease Control Program is coordinated by the Australian Animal Health Council, working with the livestock industries and with the Commonwealth, state and territory governments. The council also brokers industry and government funding for the program. The National Johne's Disease Market Assurance Program for Cattle was launched in 1996 as the first of a suite of voluntary national market assurance programs (MAPs) to assess and certify herds as negative for JD. By December 1998, over 550 herds had achieved an assessed negative status. A MAP was also launched for alpaca in 1998 and a program for goats should be finalized in early 1999. National standards for state control of JD through zoning, movement controls and procedures in infected and suspect herds have also been developed. The paper covers factors affecting development and implementation, uptake of and improvements to national control and assurance programs for bovine JD in Australia.

Herd testing to control bovine Johne's disease.

In 1996, the cattle industries and government in the Australian state of Victoria established a Johne's disease (JD) test and control program under which participating farmers are provided with an annual ELISA test of their adult herd and advice on disease control that is tailored to their farm. The program is delivered through private veterinarians under contract with the government. There are over 600 herds enrolled in the program and about one third of these have had three or more whole herd tests. This paper provides a review of the program to date. It describes changes in ELISA reactor rates and numbers of clinical cases, and provides evidence for progress in the program.

Compliance of Victorian dairy farmers with current calf rearing recommendations for control of Johne's disease.

Questionnaires were posted to 800 randomly selected registered Victorian dairy farmers in 1996. Five hundred and thirty-four responses were received and analysed. Johne's disease (JD) had been diagnosed on the farm of 13.2% of respondents in the last 5 years. JD was rated second only to neonatal diarrhoea in importance as a disease of calves, even though other diseases occurred more frequently. However, there was a low level of compliance with JD control recommendations by the respondents. There was no significant difference in the number of JD control recommendations adopted by farmers between the three major Victorian regions. There was a significant difference in compliance between farms having had a diagnosed case of JD and those that had not. Although there is awareness among dairy farmers of the importance of JD, there appears to be a poor implementation of measures by farmers to prevent the spread of the disease. Current JD control recommendations and the method of information transfer to Victorian dairy farms should be reassessed to ensure that dairy heifers are reared with minimal risk of transmission of JD.

Herd-level risk factors for infection with Mycobacterium paratuberculosis in US dairies and association between familiarity of the herd manager with the disease or prior diagnosis of the disease in that herd and use of preventive measures.

To evaluate associations among herd infection status, herd management practices, and familiarity of the herd manager with Mycobacterium paratuberculosis (Johne's disease) or prior disease diagnosis in that herd to support development of Johne's disease-control programs. Population-based cross-sectional study. 1,004 US dairies, each with > or = 30 cows, representing 79.4% of US dairy cows. Questionnaires were administered to dairy managers, and blood samples were collected from cows during herd visits. Sera were tested for antibodies to M paratuberculosis, using a commercially available ELISA. Multivariable logistic regression analyses were used to evaluate associations between use of management practices, herd disease status, and familiarity of the manager with Johne's disease or prior diagnosis of Johne's disease in that herd. Results from serologic testing revealed that 3.4% of cows and 21.6% of dairy herds were infected with M paratuberculosis. Factors associated with infection included number of cows in herd, region of country, percentage of cows born at other dairies, group housing for periparturient cows, and group housing for preweaned calves. Few preventive practices were positively associated with prior diagnosis of Johne's disease (time of separation of newborn calf from dam) or familiarity of the manager with the disease (teats and udder washed before colostrum collected). Risk factors associated with Johne's disease in this study confirmed those management practices generally recommended for disease control. An educational problem, however, is the finding that herd managers familiar with Johne's disease generally use management practices similar to those used by managers unfamiliar with the disease.

Approach for designing appropriate Johne's disease control programs on the farm

Testing is a critical tool in controlling Johne's disease. However, the limitations and options associated with commonly used tests can create confusion about herd testing as a part of a control program. Rational test choices can be made by veterinarians and producers with a basic understanding of the tests available, what they do, what results mean, and how results can be appropriately used. Understanding the tests underlies their usefulness. The issues that influence choice of commonly used tests and test strategies include basic performance characteristics (sensitivity, specificity, predictive value), cost, interpretation of results, herd test strategies (frequency, portion of herd tested, one or combination of tests), and action to be taken based on test results. These issues preclude a generic proscription for the most appropriate test scheme. Instead, each should be weighed in the context of the farm situation to determine the most appropriate strategy for their control program.

JOhne's Disease Eradication and Control: Regulatory Implications

The time has come for the livestock industry and the veterinary profession to take Johne's disease seriously in the United States. The continued spread of the disease with accompanying economic hardship to infected herds and the possibility that M. paratuberculosis may be a food-borne pathogen makes inaction a costly proposition. Efforts have started at the national level with NJWG to have guidelines written for a national control program for Johne's disease. A national control program is desirable because it would provide uniformity to control efforts. Veterinarians and livestock owners should be aware of the effort and let their views be known. In addition, national program guidelines already have been written (see the appendix) to certify test-negative herds for paratuberculosis. States that do not offer the certification program should consider it. A list of test-negative herds for Johne's disease that livestock owners could use to buy low risk animals would be a significant step forward in our efforts to control Johne's disease. Federal regulations concerning Johne's disease are outdated and should be changed to facilitate participation by the livestock industry in a Johne's disease control and eradication program.