The efficacy of mesenteric lymph node biopsy in the eradication of paratuberculosis from an infected dairy farm

Comparison of Bacterial Culture, Histopathology, and Immunohistochemistry for the Diagnosis of Johne's Disease in Culled Dairy Cows

Paired samples of formalin-fixed, paraffin-embedded ileum and lymph node from 204 culled dairy cows were investigated for evidence of infection by Mycobacterium avium subsp. paratuberculosis. Of the samples, 151 were from animals that were tissue-culture positive for M. avium subsp. paratuberculosis, and 53 were from animals that were tissue and fecal culture negative. From the culture-positive animals, M. avium subsp. paratuberculosis was isolated from 78 samples of ileum and from 107 samples of lymph node. Ziehl-Neelsen acid-fast and immunoperoxidase stained slides were examined for 15 minutes each. Acid-fast organisms were identified in 7 of 78 (8.97%) and 6 of 106 (5.61%) culture-positive ileum and lymph node samples, respectively. Immunohistochemical (IHC) analysis of the same tissues identified infection in the ileum of 9 of 78 (11.54%) and in the lymph node of 5 of 106 (4.67%) culture-positive tissues. All tissues from culture-negative animals tested negative when using acid-fast and IHC staining. The sensitivity of these 2 tests in detecting M. avium subsp. paratuberculosis in culled dairy cows was not significantly different, and the tests exhibited substantial to almost perfect agreement. Both tests were much less sensitive than bacterial culture, detecting less than 6% of tissues positive compared with culture.

Consensus recommendations on diagnostic testing for the detection of paratuberculosis in cattle in the United States

The report provided here contains a simplified set of diagnostic testing recommendations. These recommendations were developed on the basis of research funded by the USDA-Animal and Plant Health Inspection Service-Veterinary Services through a cooperative agreement. The report is intended to provide simple, practical, cost-effective consensus testing recommendations for cattle herds that are not enrolled in the US Test-Negative Program. The information has been reviewed by paratuberculosis (Johne's disease) experts at the USDA and academic centers as well as stakeholders in various segments of the cattle industry. The recommendations were accepted by the National Johne's Working Group and Johne's Disease Committee of the US Animal Health Association during their annual meetings in October 2006. The report is intended to aid veterinarians who work with cattle producers in the United States. The recommendations are based on information available up to October 2006. There is a paucity of large-scale, high-quality studies of multiple tests conducted on samples obtained from the same cattle. It is understood that there may be special circumstances that require deviation from these recommendations. Furthermore, as new information becomes available and assays are improved and their accuracy is critically evaluated, changes to these recommendations may be necessary.

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.

Factors influencing the isolation of Mycobacterium avium subsp. paratuberculosis from bovine fecal samples

A modified procedure was used for culture of Mycobacterium paratuberculosis (Mptb) from bovine feces. Bovine fecal samples were decontaminated with NaOH, exposed to a mixture of oxalic acid and malachite green, incubated in a mixture of neomycin and amphotericin B. Decontaminated specimens were inoculated onto modified Löwenstein-Jensen medium. Specimens processed by high-speed centrifugation showed growth earlier than specimens prepared by low-speed centrifugation. However, the overall number of positive cultures at 16 weeks was not different for the 2 methods. When infected dairy herds were sampled 4 times at 6-month intervals and culture-positive cows were culled, the prevalence of infected cattle declined over time. After selective culling, the cattle left in the herds shed low numbers of Mptb, which explains why it took longer for cultures to become positive. No heifers younger than 11 months were culture positive, but heifers 13-14 months of age were more frequently culture positive than were heifers of any other age. The 16-week culture period is needed with this method to detect cattle shedding low numbers of Mptb. High-speed centrifugation of samples does not increase the efficiency of identification of animals shedding Mptb.

Detection of Mycobacterium avium subsp. paratuberculosis in infected tissues by new species-specific immunohistological procedures

We have previously described the cloning and sequencing of a gene portion coding for the terminal part of a 34-kDa protein of Mycobacterium avium subsp. paratuberculosis, the etiological agent of Johne's disease (P. Gilot, M. De Kesel, L. Machtelinckx, M. Coene, and C. Cocito, J. Bacteriol. 175:4930-4935, 1993). The recombinant polypeptide (a362) carries species-specific B-cell epitopes which do not cross-react with other mycobacterial pathogens (M. De Kesel, P. Gilot, M.-C. Misonne, M. Coene, and C. Cocito, J. Clin. Microbiol. 31:947-954, 1993). The present work describes the preparation of polyclonal and monoclonal antibodies directed against a362 and the use of these immunoglobulins for histopathological diagnosis of Johne's disease. The new immunohistological procedures herewith detailed proved to be able to identify M. avium subsp. paratuberculosis antigens in the intestinal tissues and lymph nodes of cattle affected by either the paucibacillary or pluribacillary form of the disease. They yielded negative responses not only with healthy animals but also with those affected by tuberculosis (Mycobacterium bovis). Both immunohistological procedures proved to be as sensitive as or more sensitive than Ziehl-Neelsen staining and, in addition, to be endowed with species specificity.

Diagnosis of paratuberculosis

The currently available and accurate diagnostic tests for paratuberculosis are reviewed. Technical issues concerning test performance are briefly mentioned and the advantages, disadvantages, and comparative accuracy are described. The article concludes with recommendations on which tests to use in eight different situations requiring laboratory diagnostics for paratuberculosis.

Paratuberculosis

Paratuberculosis (Johne's disease) is a chronic, wasting, widespread mycobacteriosis of ruminants. It involves extensive mycobacterial shedding, which accounts for the high contagiousness, and ends with a fatal enteritis. Decreases in weight, milk production, and fertility produce severe economic loss. The DNA of the etiological agent (Mycobacterium paratuberculosis) has a base composition (66 to 67% G+C) within the range of that of mycobacteria (62 to 70% G+C), a size (4.4 x 10(6) to 4.7 x 10(6) bp) larger than that of most pathogenic mycobacteria (2.0 x 10(6) to 4.2 x 10(6) bp), and a high relatedness (> 90%) to Mycobacterium avium DNA. However, the DNAs of the two organisms can be distinguished by restriction fragment length polymorphism analysis. M. paratuberculosis genes coding for a transposase, a cell wall-associated protein (P34), and two heat shock proteins have been cloned and sequenced. Nucleic acid probes (two of which are species specific) are used, after PCR amplification, for M. paratuberculosis identification in stools and milk. As in leprosy, with disease progression, cellular immune reactions decrease and humoral immune reactions increase. Cutaneous testing with sensitins, lymphocyte proliferation assays, and cytokine tests are used to monitor cellular immune reactions in paratuberculosis, but these tests lack specificity. Complement fixation, immunodiffusion, and enzymometric tests based on antibodies to M. paratuberculosis extracts, to mycobacterial antigen complex A36, to glycolipids, and to proteins help identify affected cattle but are not species specific. The carboxyl-terminal portion of the 34-kDa cell wall-associated A36 protein (P34) carries species-specific B-cell epitopes and is the basis for an enzyme-linked immunosorbent assay. Diagnostic tests for paratuberculosis are also used in Crohn's disease, a chronic human ileitis mimicking Johne's disease, in which isolates identified as M. paratuberculosis have been found.

Ancillary tests for assessment of the ruminant digestive system

This article reviews the ancillary tests that are available to evaluate disease and function of the gastrointestinal system. Procedures and tests such as abdominocentesis and peritoneal fluid cytology; rumen fluid analysis; abomasal pH and pepsinogen; upper digestive tract endoscopy; ultrasonography and radiology; hematologic and biochemical assessments; cytology, culture, and histopathology of aspirates; serology, liver function tests and biopsy; exploratory laparotomy; fecal examination; and microbiology are described.