Livestock Disease Eradication Evaluation of the Cooperative State-Federal Bovine Tuberculosis Eradication Program (1994) / Chapter Skim
Currently Skimming:
2 ETIOLOGY, DIAGNOSIS, AND DETECTION OF TUBERCULOSIS
2 ETIOLOGY, DIAGNOSIS, AND DETECTION OF TUBERCULOSIS
Pages 13-34
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 13... ...
Bacteria in tissue are engulfed by neutrophils and macrophages. Some of the infected macrophages migrate carrying Me infection to the regional lymph nodes.
|
From page 14... ...
, and samples collected from infected animals for microscopic examination or culture may not always include the infected tissue. Disease Processes Small numbers of M
|
From page 15... ...
Often a simple wire fence is sufficient to prevent pasture-topasture spread; this principle was used in early campaigns where a clean herd was started on the same premises as an infected herd (the Bang Method; Pritchard, 1988~. On infected premises, other infected animals can include dogs and cats, which serve as reservoirs for infecting other cattle, and the general recommendation is that they be destroyed if they have had contact with infected cattle and Me herd is to be depopulated.
|
From page 16... ...
album and can sensitize an infected host to tuberculin Money et al., 1988~. It is likely that a number of the cattle, cervids, and zoo ungulates that have been cubed because of positive tuberculin skin tests, but were free of visible lesions at necropsy, were sensitized by infection win M
|
From page 17... ...
Interpretation of Diagnostic Tests The availability of an efficient screening test is ~ essential feature for a successful disease control and eradication program such as the Bovine Tuberculosis Eradication Program (U.
|
From page 18... ...
result. PVPr is He probability Hat a positive test result has identified an infected animal and PVNT is He probability that a negative test result has identified a noninfected animal.
|
From page 19... ...
Hence, it is crucial Hat the animals used to evaluate the test be representative of He relative proportion of infected and noninfected animals ~ the population. Diagnosis by Direct Detection By definition, He presence of M
|
From page 20... ...
Tissue samples must be handled in a manner that preserves the viability of mycobacterial organisms and prevents contamination of He 100 80 40 Probability of detecting indicators of infection _ Cultivatable bacteria ..... Visible lesions and clinical signs ~ ~ ~ ~ ~ Cell-n~diated immune responses _ _ .
|
From page 21... ...
New approaches to identify specific bacteria include immunoassay or immunohistochem~cal detection of mycobacterial antigens, Me use of nucleic acid probes for recognition of specific DNA or RNA base sequences, and chemical analysis for the detection of specific metabolic by-products or structural components of M bouts.
|
From page 22... ...
Diagnosis Using Immunological Signals of Infection Because immunological responses depend on antigen presentation followed by lymphocyte differentiation, there will be a variable length of time following infection when immunological response cannot be detected (E: inure 2-~. The first immunological response or signal detected in diagnostic tests is weak.
|
From page 23... ...
Serological Tests Mycobacter~um bows infection of cattle induces a humoral immune response although a prolonged latent period of infection may be present during which antibodies cannot be detected. Studies have indicated Hat this latent period may range up to 20 weeks in experimentally infected cattle (Harboe et al., 1990~.
|
From page 24... ...
Therefore, the specificity of the caudal fold test can be estimated to be greater than 98 percent. Data are not readily available for calculation of the sensitivity and specificity of the single cervical test.
|
From page 25... ...
and submitted for laboratory examination is not adequate to detect bovine tuberculosis when present at very low prevalence. Therefore, Mere is a need for more detailed Inspection and collection of more nonspecific granulomatous lesions as prevalence of tuberculosis decreases ~ order to daect the few remaining infected animals Masker, 19871.
|
From page 26... ...
Preliminary evidence suggests that infected animals would be stimulated to increase antibody production and be more likely to test positive on the subsequent serological test (Harboe et al., 1990; Dowling and SchIeehauf, ~ As noted earlier, deer are considered to be more susceptible to M
|
From page 27... ...
The drawback to the reliance on testing a large number of animals to improve He sensitivity of the herd test is that as the number tested increases, the chance of a fals~positive test result also ~ncreases~thus the herd-level specificity decreases. In this example He herd specificity is only 54 percent, whereas the individual level specificity is 96 percent (Table 2-2~.
|
From page 28... ...
indicates that for any rate of transmission (chiefly by respiratory route in bovine tuberculosis and modeled as Inadequate contact raters, the infection spread greatly depends on population size; larger herds have a greater probability of allowing the infection to persist and cause an Epidemic. Furler, the rate of spread and extent of Infection in a large herd can be much greater than in a small herd, given Me same adequate contact rate.
|
From page 29... ...
Size (Percent removed, i.e., sensitivity from 0.0 to 0.85) N = 50 N = 100 0.65 0.85 0.0 0.65 0.85 Time Period 0.0 N = 300 0.0 1 2 2 2 3 3 3 9 9 9 2 3 1 0 8 3 1 70 27 12 3 4 0 0 19 3 0 195 66 15 4 5 0 0 31 3 0 26 100 17 5 5 0 0 24 3 0 0 64 18 6 4 0 0 8 3 0 0 17 18 7 3 0 0 2 3 0 0 3 17 8 2 0 0 0 2 0 0 0 14 9 1 0 0 0 2 0 0 0 11 10 1 0 0 0 2 0 0 0 8 11 1 0 0 0 2 0 0 0 6 12 1 0 0 0 1 0 0 0 4 13 1 0 0 0 1 0 0 0 3 14 1 0 0 0 1 0 0 0 2 15 0 0 0 0 1 0 0 0 1 16 0 0 0 0 1 0 0 0 1 17 0 0 0 0 1 0 0 0 1 18 0 0 0 0 1 0 0 0 1 19 0 0 0 0 1 0 0 0 1 20 0 0 0 0 1 0 0 0 1 21 0 0 0 0 1 0 0 0 1 22 0 0 0 0 1 0 0 0 1 23 0 0 0 0 1 0 0 0 1 24 0 0 0 0 1 0 0 0 1 Total 34 3 2 95 42 4 300 286 164 Cases NOTE: Number of cases predicted using the Reed-Frost model, with one initial case and an adequate contact rate of 3 percent.
|
From page 30... ...
Present limitations to the Implementation of probe diagnostic tests on a routine basis include He cost of equipment and reagents, extensive laboratory personnel services and expertise, use of radioisotope labels on the probes, and problems with cross-contamination between samples or within the laboratory that will produce false-positive results. Nucleic acid probes have recently been developed with detection systems that do not include a radioactive label, so they can be incorporated into laboratory procedures more readily (Goto et al., 1991; L~im et al., 1991; Evans et al., 1992; Lebrun et al., 1992~.
|
From page 31... ...
Suitable data are not available to determine whether the various assays of CMI responses, including intradermal tuberculin tests, LT tests, and ~y-IFN tests, are capable of detecting different subpopulations of infected animals or different stages of the disease.
|
From page 32... ...
Diagnostic tests based on antigens deleted from the vaccine would allow differentiation between immune responses generated by vaccination and infection; thus vaccination and eradication programs could proceed simultaneously.
|
From page 33... ...
tuberculosis strains resistant to one or more antimicrobial drugs has been report. Poor patient compliance witch Snug treatment regimens, especially among homeless people, drug addicts, and others living in poverty, are considered largely responsible for Me emergence of the drug resistant strains (Culliton, 1992)
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.