[Comparative evaluation of the indirect enzyme-linked immunosorbant assay in milk for the detection of cattle infected with Brucella abortus, in herds located in the province of Cundinamarca, Colombia]. / Evaluación comparativa del método inmunoenzimático indirecto en leche para la detección de bovinos infectados con Brucella abortus, en hatos del departamento de Cundinamarca, Colombia.

To perform a comparative evaluation of the indirect enzyme-linked immunosorbent assay (iELISA) in milk, for the detection of Brucella abortus in cattle, 1,523 milk samples were taken from individual animals and bulk milk belonging to 200 herds in the province of Cundinamarca, Colombia. All these herds were part of the official programme of monitoring free herds and determining herd prevalence in the province. The samples were submitted simultaneously to the milk ring test and the iELISA. A total of 584 individual and 497 bulk milk samples taken from free herds were considered negative, and served to determine the initial ELISA cut-off point. An optimised determination of the cut-off point involved an operational analysis, using a statistical programme. In the analysis, the total population was considered: 756 individual positive and negative samples, as defined by herd history and previously established serologies. The cut-off point was set at > 0.20 optical density units, which, expressed in percentage positivity, corresponded to 20.5% against the controls, with a sensitivity of 95.3%, a specificity of 95.1%, and a confidence interval of 95%. Indirect confirmation of the state of infection was made with competitive ELISA in the serum of the individual animals considered positive, and an attempt was made to determine bacterial presence by isolation in culture and by reverse transcription-polymerase chain reaction. The results confirm that the indirect ELISA is highly sensitive and specific, provides confirmed results in strict quality-control conditions, and may be used to test a large number of herd or individual samples, thus enhancing the efficiency of surveillance programmes and control campaigns.

Cellular and humoral response of in ovo-bursectomized chickens to experimental challenge with velogenic Newcastle disease virus.

Humorally deficient, in ovo-bursectomized (Bx) and sham-Bx chickens were vaccinated twice, 1 month apart, with Newcastle disease virus (NDV) Roakin strain and challenged with a velogenic viscerotropic NDV strain via the oronasal route. Hemagglutination-inhibition and seroneutralization tests showed that Bx chickens had reduced antibody-mediated immunity to virus infection. In contrast, they had significantly higher cell-mediated immunity (CMI) before challenge, as estimated simultaneously by determination of blastogenic capacity of peripheral blood lymphocytes induced by phytohemagglutinin and by specific antigen stimulation. After virus challenge, there was transitory inhibition of CMI based on marked reductions in levels of stimulation indices, and this impairment in CMI was supported by persistence of virus in Bx chickens for longer periods. Bx chickens resisted challenge, even though antibody titers were well below those considered predictive of resistance to challenge, suggesting that CMI provides a degree of resistance to velogenic NDV.