Diagnostic performance of a commercial ELISA used as a complementary test for bovine tuberculosis in two bovine herds with different disease status / Desempenho diagnóstico de um ELISA comercial usado como teste complementar para tuberculose bovina em dois rebanhos bovinos com diferentes estágios de controle da doença

Bovine tuberculosis is a worldwide spread zoonotic disease. Intradermal tuberculinizations are the most used diagnostic tests in the world. Serological tests can be an ancillary diagnosis for bovine tuberculosis. The objective of this study was to evaluate the diagnostic performance of the ELISA Mycobacterium Bovis Antibody Test Kit IDEXX ™ in infected herds, which were in different disease control stages. One hundred and twenty animals from two dairy herds of Minas Gerais state, Brazil, were subjected to the ELISA serological test and the comparative cervical tuberculin test (CCT). Diagnostic test parameters were estimated using Bayesian latent class models and concordance between tests estimated by the frequentist approach. The ELISA test presented lower sensitivity than CCT in both herds. Its sensitivity was higher in the herd in sanitation process. Specificity estimates were above 95% in both herds. Kappa index indicated low concordance or even disagreement between tests. According to the results, the ELISA IDEXX should not be used as substitution for CCT. The tests must not be associated in series. Parallel association increased diagnostic sensitivity in the herd which was in the process of sanitation.(AU)

A tuberculose bovina é uma zoonose de distribuição mundial cujos testes mais utilizados para o diagnóstico são as tuberculinizações intradérmicas, simples e compartivas. Contudo, testes sorológicos podem constituir diagnósticos auxiliares. O objetivo deste estudo foi avaliar o desempenho diagnóstico do teste ELISA Mycobacterium Bovis Antibody Test Kit IDEXX ® em rebanhos bovinos infectados, que se encontravam em diferentes estágios de controle da doença. Cento e vinte animais de dois rebanhos leiteiros provenientes do estado de Minas Geais-Brasil foram submetidos ao ELISA e à tuberculinização cervical compartiva (TCC). Avaliou-se o desempenho dos testes por meio de modelos Bayesianos de classe latente e a concordância entre os eles, por meio de estatística frequentista. Uma maior sensibilidade do teste foi observada no rebanho previamente tuberculinizado. Em ambos os rebanhos o TCC foi mais sensível que o ELISA. Especificidade acima de 95% foi encontrada em ambos os rebanhos. Foram observadas baixa concordância ou mesmo discordância entre os testes. De acordo com os resultados obtidos, o teste ELISA-IDEXX não deve ser utilizado em substituição à TCC, tampouco devem ser associados em série. Houve aumento da sensibilidade quando os testes foram associados em paralelo no rebanho que já se encontrava em processo de saneamento.(AU)

Characterization of foot-and-mouth disease virus by monoclonal antibodies.

Monoclonal antibodies (MAbs) were produced against foot-and-mouth disease (FMD) virus types O1 Campos Br1/58, A24 Cruzeiro Br1/55, and C3 Indaial Br1/71, which are the strains used for production of FMD vaccines in the majority of South American countries. Within the library of MAbs produced, a group was selected on the basis of their neutralizing titer in cell culture, protective titer in suckling mice, sensitivity to trypsin, and specificity for virus structural proteins. The MAbs were utilized in an ELISA test format to compare European and South American representative field isolates with vaccine production strains in their r1 relationship as obtained by 50% complement fixation (CF50) with polyclonal antibodies (PAb) and their virus neutralization (VN) relationship obtained with sera from one-time-vaccinated and from revaccinated cattle, respectively. The MAbs selected varied in their reactivity against the different strains and, therefore, enabled us to compare field FMDV strains to those against which the MAbs were produced, with definite advantages over the r1 and VN ratios. Thus, panels of MAb produced with the vaccine strains and appropriately selected are significantly useful for the FMD-control programs because they serve to provide guidance on the immunological coverage provided by the vaccines against FMDV strains circulating in the field. The MAbs are also useful for the differentiation of FMD virus strains.

Cattle response to foot-and-mouth disease virus nonstructural proteins as antigens within vaccines produced using different concentrations.

Four groups of ten nine-month-old Nelore heifers were used for this study. Each group received one of four foot-and-mouth disease (FMD) trivalent vaccines for the duration of the experiment. The four vaccine formulations (Normal, 2X, 4X and 8X) differed in 140S content to determine the serological reactivities to FMD virus (FMDV) nonstructural proteins 2C, 3ABC and 3D. Vaccination was by the intramuscular administration of vaccine on day 0, 180 and 360. Bleedings were done at 30 days post vaccination (dpv), 90 dpv, 30 days post revaccination (dpr), 90 dpr, and 30 days post third administration (dprr). There was a general tendency to have higher mean 3D responses with increased vaccine application but not with increased concentration of antigen. With 2C and 3ABC this tendency was not seen, neither with repeated application of vaccine nor with increased antigen concentration. All individual animal observations to 2C and 3ABC remained within three standard deviations of the average observed for naive bovids. Percent of positive (PP) reactions was determined using an ELISA for nonstructural proteins 2C, 3ABC and 3D expressed in baculovirus as previously described. A value of > 25 PP to 2C or 3ABC could be considered as an indication of previous infection or of the presence of viral activity. PP results between 18 and 25 PP suggest viral activity and animals should be retested. Those responses below 15 PP are suggestive of vaccination or naive status. As diagnosis in the laboratory is not divorced from the field epidemiological scene, the intermediate zone between 10 and 20 PP should be considered and acted upon according to the overall zoosanitary situation of that country or region and the purposes of the ongoing FMD control efforts.

Infectivity assays of foot-and-mouth disease virus: contact transmission between cattle and buffalo (Bubalus bubalis) in the early stages of infection.

No differences were observed between cattle and Indian buffalo (Bubalus bubalis) in terms of temperature, viraemia or virus replication in the pharyngeal area, during the acute phase of foot-and-mouth disease. Like cattle, the Indian buffalo became infected and excreted virus before any clinical signs of foot-and-mouth disease developed. The disease was transmitted from cattle to buffalo and vice versa, during the acute stage of infection, as if the animals had been of the same species, presumably because of their close phylogenetic relationship. There were more tongue lesions in the cattle than in the buffalo. Foot lesions in the buffalo at first had a scaley appearance, but later became vesicular. Anti-virus infection associated antigen and neutralising antibodies were synthesised at the same time in both species and reached similar titres in the same period. Persistent infection in the buffalo during the first 35 days after infection was similar to that in the cattle.