Use of touch-down polymerase chain reaction to enhance the sensitivity of Mycobacterium bovis detection.

The confirmatory diagnosis of Mycobacterium bovis (M. bovis) in animal samples is carried out by culture in Stonebrink media. However, culture is very slow because of the extremely long duplication time of the bacillus and difficult because of the scarcity of bacilli in diagnostic samples. This study describes the development of a single-tube touch-down polymerase chain reaction (PCR) protocol for the detection of M. bovis using primers that target the IS6110 element. Spiked water and milk as well as routine diagnostic samples (milk and nasal swabs) from M. bovis-positive cattle were tested. This protocol allows the rapid and sensitive detection of M. bovis in bovine samples by enhancing the sensitivity of standard PCR amplification.     

Evaluation of a new antibody-based enzyme-linked immunosorbent assay for the detection of bovine leukemia virus infection in dairy cattle.

The objective of this study was to validate a new blocking enzyme-linked immunosorbent assay (ELISA) (designated M108 for milk and S108 for serum samples) for detecting bovine leukemia virus (BLV) infection in dairy cattle. Milk, serum, and ethylenediaminetetraacetic acid-blood samples were collected from 524 adult Holstein cows originating from 6 dairy herds in Central Argentina. The M108 and S108 were compared with agar gel immunodiffusion (AGID), polymerase chain reaction and a commercial ELISA. Because there is currently no reference test capable of serving as a gold standard, the test sensitivity (SE) and specificity (SP) were evaluated by the use of a latent class model. Statistical inference was performed by classical maximum likelihood and by Bayesian techniques. The maximum-likelihood analysis was performed assuming conditional independence of tests, whereas the Bayesian approach allowed for conditional dependence. No clear conclusion could be drawn about conditional dependence of tests. Results with maximum likelihood (under conditional independence) and posterior Bayes (under conditional dependence) were practically the same. Conservative estimates of SE and SP (with 95% confidence intervals) for M108 were 98.6 (96.7; 99.6) and 96.7 (92.9; 98.8) and for S108 99.5 (98.2; 99.9) and 95.4 (90.9; 98.1), respectively. The ELISA 108 using either milk or serum to detect BLV-infected animals had comparable SE and SP with the official AGID and a commercial ELISA test, which are currently the most widely accepted tests for the serological diagnosis of BLV infection. Therefore, ELISA 108 can be used as an alternative test in monitoring and control programs.     

Microbiological screening test validation for detection of tylosin excretion in milk of cows with low and high somatic cell counts

Antibiotic residues in milk above tolerance levels interfere with dairy product processing and pose potential health risks to consumers. Residue avoidance programmes include, among other components, the observance of withdrawal times indicated in label instructions. Persistence of antibiotics in milk following treatment is influenced by drug, dosage, route of administration, body weight and mammary gland health status. Compositional changes that take place during intramammary infection (IMI) can affect antibiotic excretion in milk, thus modifying milk withdrawal time. The objectives of this study were to validate sensitivity and specificity of a qualitative microbiological method (Charm AIM-96) to detect tylosin in bovine composite milk and to determine the influence of subclinical IMI in tylosin excretion following intramuscular administration. For test validation, two groups of approximately 120 cows were used; one received a single intramuscular injection of tylosin tartrate at a dose of 20 mg/kg, while the other group remained as untreated control. Test sensitivity and specificity were 100% and 94.1% respectively. To determine the influence of subclinical IMI in tylosin excretion, two groups of seven cows, one with somatic cell counts (SCC) < or =250 000 cells/ml and the other with SCC > or =900 000, were administered a single intramuscular injection of tylosin tartrate at a dose of 20 mg/kg. Milk samples were obtained every 12 h for 10 days following treatment. Milk tylosin excretion averaged between 5 and 9 days for cows with low and high SCC respectively (P < 0.0001). Compositional changes in cows with high SCC most likely affect the pharmacokinetic characteristics of tylosin, extending the presence of the antibiotic in milk, thus influencing milk withdrawal times.     

Immunisation against ovine caseous lymphadenitis: efficacy of monocomponent Corynebacterium pseudotuberculosis toxoid vaccine and combined clostridial-corynebacterial vaccines

Sheep were immunised with Corynebacterium pseudotuberculosis toxoid formulated as a monocomponent vaccine with aluminium adjuvant or in combination with 5 clostridial antigens, and also in the combined form with sodium selenate. Immunised and control sheep were experimentally infected 16 days after vaccination and slaughtered and inspected after a further 3 months to determine their resistance to infection. All 3 vaccines afforded an equal and high level of protection; 91% of vaccinated sheep exhibiting no lesions of caseous lymphadenitis compared with 51.5% affected sheep in the control group. Average lesion counts were 1.2 per affected vaccinated sheep and 4.5 per affected control sheep. Antitoxin responses to the clostridial toxoids incorporated in the combined vaccines were not affected by inclusion of the C pseudotuberculosis toxoid or the sodium selenate.     

Immunisation against ovine caseous lymphadenitis: comparison of Corynebacterium pseudotuberculosis vaccines with and without bacterial cells

Sheep were immunised with Corynebacterium pseudotuberculosis vaccines prepared from cell-free toxoid or from toxoid with formalin-killed cells of C pseudotuberculosis added. Resistance of sheep to infection was tested 6 months after immunisation by inoculation with caseous lymphadenitis pus. The outcome was assessed 3 months later by slaughter and inspection of the sheep for lesions of caseous lymphadenitis. immunised sheep were adequately protected against infection as shown by a significant reduction in the number of sheep exhibiting lesions compared with control sheep, and by fewer abscesses in affected vaccinated sheep than in affected control sheep. The protective potency of the vaccines was not improved by the inclusion of cells of C pseudotuberculosis.     

Associations between leptospiral infection and seropositivity in rodents and environmental characteristics in Argentina

Our objective was to look for associations between leptospiral infection in rodents and selected environmental and rodent characteristics in Santa Fe, Argentina. Rodents (n = 214) were trapped alive from January 1998 to December 1999 in three environmental settings. Kidneys from 118 rodents were cultured and serum samples from 201 were processed by enzyme-linked immunosorbent assay (ELISA). Logistic regression was performed with ELISA seropositivity as the dependent variable and rodent characteristics were offered as independent variables. Overall prevalence of positive ELISA reactions was 42% (84/201). In urban areas, leptospiral isolations belonged to the Ballum serogroup; in natural corridors, they belonged to the Icterohaemorragiae serogroup. M. musculus (house mouse) was the most-frequently captured species and the predominant one in urban areas. Most isolates and seropositivity results were obtained on this species. Adults and subadults had higher seroprevalences than juvenile rodents. Oligoryzomys flavescens had higher seroprevalence than Akodon azarae, Mus musculus, Rattus rattus and Rattus norvegicus.     

Associations between farmers' personal characteristics, management practices and farm performance

A survey was carried out in a random sample of 123 dairy farms from the east of Ireland. The monthly mean production per cow was 315 l of milk and 11.5 kg of fat. The mean log herd somatic cell count was 5.45 (arithmetic mean = 372,573 cells/ml), with almost 50% of the monthly counts over 300,000 cells/ml in a 12-month period. Bivariate and multivariate analysis was performed to assess the relative impact of the personal characteristics of the farmer and the management policies he applied on the amount and quality of the milk produced. In five out of six models the group of variables related to farmers' attitudes, values, and sociodemographic profile explained a similar or greater amount (between 14.44 and 34.35%) of the variation of farm performance than the group of management variables (between 14.33 and 25.99%) as measured by the R2. These results stress the importance of the human factors in explaining variation in farm performance.