Comparison of the specificity of human and bovine tuberculin PPD for testing cattle. 2. South-eastern England.

A tuberculin testing trial was carried out in eight counties of south-eastern England to compare the specificity for bovine tuberculosis of Weybridge human PPD with that of Rotterdam bovine PPD. The matching of these two tuberculins for potency in naturally infected cattle had already been established, the bovine PPD being approximately one-and-a-half times more potent than the human PPD per unit of weight. In 1110 cattle in 25 herds with histories of long-standing freedom from tuberculosis and in which non-specific tuberculin sensitivity was present, cross reactions were less to the bovine PPD than to the human PPD, showing that in the environment of this trial the bovine PPD was more specific than the human PPD. Induration diameter was a satisfactory alternative to skin thickening as a measure of tuberculin reactions in cattle under field conditions. Due to the steep slope of the dose-response curves of the avian PPD in the different groups of non-tuberculous cattle, the discriminating power of the comparative test, using avian and mammalian tuberculins, was less at lower doses of tuberculin. Concentrations of 1-0 mg per ml of bovine PPD and 0-5 mg per ml of avian PPD are recommended for use in a comparative tuberculin test.     

Comparison of sampling techniques for measuring the antimicrobial susceptibility of enteric Escherichia coli recovered from feedlot cattle

OBJECTIVE: To evaluate the effectiveness of various sampling techniques for determining antimicrobial resistance patterns in Escherichia coli isolated from feces of feedlot cattle. SAMPLE POPULATION: Fecal samples obtained from 328 beef steers and 6 feedlot pens in which the cattle resided. PROCEDURE: Single fecal samples were collected from the rectum of each steer and from floors of pens in which the cattle resided. Fecal material from each single sample was combined into pools containing 5 and 10 samples. Five isolates of Escherichia coli from each single sample and each pooled sample were tested for susceptibility to 17 antimicrobials. RESULTS: Patterns of antimicrobial resistance for fecal samples obtained from the rectum of cattle did not differ from fecal samples obtained from pen floors. Resistance patterns from pooled samples differed from patterns observed for single fecal samples. Little pen-to-pen variation in resistance prevalence was observed. Clustering of resistance phenotypes within samples was detected. CONCLUSIONS AND CLINICAL RELEVANCE: Studies of antimicrobial resistance in feedlot cattle can rely on fecal samples obtained from pen floors, thus avoiding the cost and effort of obtaining fecal samples from the rectum of cattle. Pooled fecal samples yielded resistance patterns that were consistent with those of single fecal samples when the prevalence of resistance to an antimicrobial was > 2%. Pooling may be a practical altemative when investigating patterns of resistance that are not rare. Apparent clustering of resistance phenotypes within samples argues for examining fewer isolates per fecal sample and more fecal samples per pen.     

Comparison of the specificty of human and bovine tuberculin PPD for testing cattle. 1--Republic of Ireland.

A tuberculin testing trial in cattle was carried out in the Republic of Ireland to compare the specificity for bovine tuberculosis of a human purified protein derivative (PPD) tuberculin (Weybridge) with that of a bovine PPD (Rotterdam), and to determine whether discrimination between specific and non-specific reactions to mammalian tuberculin is better with doses of tuberculins smaller than those traditonally used for testing cattle. Tests were carried out in 510 cattle, 395 of which were shown by post mortem examination to be tuberculous and 115 non-tuberculous. Three dilutions at five-fold intervals of both mammalian tuberculins were used together with two dose levels of avian tuberculin PPD (Weybridge), and all reactions were measured both by increase in skin fold thickness and by diameter of induration. In the environment of this trial, the bovine PPD was shown to be more specific for bovine tuberculosis than the human PPD, and particularly in differentiating from "skin tuberculosis". There was no indication of greater specificity at lower doses of tuberculin. Measurement of induration diameter proved a satisfactory alternative method of reading tuberculin reactions in cattle under field conditions.     

Comparison of the specificity of human and bovine tuberculin PPF for testing cattle. 3. National trial in Great Britain.

A field trial on a country-wide basis was undertaken to compare the specificity for bovine tuberculosis of single and comparative tuberculin tests in cattle using either Weybridge human or Weybridge bovine PPD. The tests were made on 10,305 cattle in 179 herds distributed throughout all regions of England, Scotland and Wales. Results showed that a comparative tuberculin test using avian PPD with either human or bovine PPD had a much higher efficiency than a single injection of mammalian tuberculin in the neck of cattle, and confirmed that a comparative test is still essential in the British environment. Weybridge bovine PPD gave significantly better discrimination between tuberculous and non-tuberculous cattle than Weybridge human PPD when used together with avian PPD in a comparative tuberculin test. The diameter of induration gave an absolute measure of the extent of oedema, if present, and induration diameter used in conjunction with skin thickening increased the sensitivity and specificity of the test. Rules of interpretation were developed and are presented for an intradermal comparative tuberculin test in cattle using Weybridge avian and bovine PPDs.     

IgG isotype antibody responses to epitopes of the Mycobacterium bovis protein MPB70 in immunised and in tuberculin skin test-reactor cattle

Serological assays may have merit in identifying animals in advanced stages of bovine tuberculosis, but most tests have had sub-optimal sensitivities and specificities. The Mycobacterium bovis protein MPB70 has been identified as a B-cell target with diagnostic potential in measurement of pre- and post-skin-test antibody responses. One observation, which has potential practical application, has been that skin testing with tuberculin boosts IgG(1) anti-MPB70 antibody responses in cattle with tuberculous lesions. However, serological cross-reactivities with bacteria, such as Nocardia asteroides, have been described for this protein. With the aim of identifying candidate reagents for improved diagnostic tests, this study investigated IgG isotype antibody responses to MPB70 at the epitope level and, because of the previous findings, focused on IgG(1) responses following skin testing. Screening of a panel of overlapping synthetic peptides using sera from cattle immunised with MPB70 and cattle infected with M. bovis showed that two regions of the protein (residues 21-70 and 101-120) contain dominant B-cell epitopes. No individual epitope appeared to be selectively recognised by one isotype of IgG antibody. Investigation of IgG(1) responses showed that recognition of the epitope within residues 51-70 was boosted strongly by tuberculin injections in skin-test positive cattle and that this memory response was generally a feature of cattle which were found to have macroscopic, tuberculous lesions.     

Effects of limb tourniquet ischemia on local and systemic acid-base and blood gases of cattle.

Effects of forelimb tourniquet ischemia of 90 minute duration were investigated in six bulls aged two to three years. Studies were also conducted up to 150 minutes after release of the tourniquet. Parameters investigated were pH, PCO2, PO2, oxygen saturation and HCO3. In systemic circulation no variations in different parameters were observed during 90 minutes of ischemia. However, significant increase in arterial and venous pH were observed after 30 and 45 minutes of the release of tourniquet, respectively. These increases were accompanied by an increase in HCO3. In the affected limb, ischemia resulted in severe acidosis with a significant increase in PCO2 and a nonsignificant decrease of HCO3. There was a significant fall in PO2 and oxygen saturation. After release of the tourniquet, limb venous pH increased significantly due to a significant fall in PCO2 and a nonsignificant increase in HCO3. A significant increase in the limb venous PO2 and oxygen saturation post tourniquet was observed up to the end of the experiments. There was evidence of very poor oxygen exchange and utilization up to 150 minutes after release of the tourniquet. These results demonstrated that tourniquet ischemia of 90 minutes duration of the limb of cattle may not be safe.     

Method for evaluation of Mycobacterium bovis purified protein derivative tuberculin in experimentally infected cattle.

A method for the evaluation of Mycobacterium bovis purified protein derivative (PPD) tuberculin in experimentally infected cattle is presented. The development of skin test responses in M bovis-infected cattle was determined for International Standard PPD-S, M bovis PPD-2, and M bovis PPD-5 at 24, 48, and 72 hours. Significantly larger reactions (dermal thickness) were observed at 48 and 72 hours than at 24 hours (P = 0.001). Statistically significant differences were not detected in the responses obtained with M bovis PPD-2, M bovis PPD-5, and International Standard PPD-S if comparisons were made at approximately the same concentrations in M bovis-infected cattle (P greater than 0.25). In Mycobacterium avium-infected cattle, M bovis PPD-2 produced skin test responses that were significantly smaller than responses obtained using M avium PPD-2 (P = 0.001). Significant variation was not observed in the PPD-S responses in 2 groups of M bovis-infected cattle (P greater than 0.1).     

Mycobacteria isolated from nasal secretions of tuberculin test reactor cattle.

Nasal secretions of 103 Holstein cows from a tuberculosis-infected herd in Argentina were bacteriologically cultured for mycobacteria. Mycobacterium bovis was isolated in 8.7% of the cultures. This method was useful for the detection of active tuberculosis with open lesions. Other mycobacteria, most of which grew rapidly on culture media, were isolated in 32% of the cultures and were of little importance as sensitizing agents to mammalian tuberculin in experimental studies in guinea pigs.