Potency control of foot-and-mouth disease vaccine in cattle. Comparison of the 50% protective dose and the protection against generalization.

Potency tests of a total of 658 foot-and-mouth disease (FMD) vaccine batches by bovine protective dose (PD50) showed that 22% of the tests did not follow the expected theoretical model and the results could not be interpreted because of the lack of a dose-response relationship. The protection against generalization (PG) method, using undiluted vaccine, proved to be highly reliable from the analysis of the results of 65 replicate potency tests of three hydroxide-saponin (HS) vaccines and two oil-adjuvanted (OL) vaccines. The PG results were consistent in 64 out of the total of 65 tests. The data obtained indicated that, with regard to direct tests in cattle, the PG test is the preferred method for FMD vaccine potency control. This study also showed that the incorporation of a reference vaccine in routine potency tests is essential to ensure normality of the test system and that good quality HS and OL FMD vaccines may maintain immunogenic stability for at least 27 and 36 months, respectively, when stored at 2-8 degrees C.

Actualizacion de cepas del virus de la fiebre aftosa de importancia epidemiologica en America del Sur / Updating of foot-and-mouth disease virus strains of epidemiological importance in South America

La alta varialbilidad de la fiebre aftosa, debida entre otros factores a la recombinacion genetica y a la presion selectiva de los anticuerpos en areas con vacunacion sistematica, hace que una cepa de virus ocasione una unica onda epidemica. Por lo tanto, la lista de subtipos debe ser actualizadaperiodicamente para eliminar los que no actuan mas en el campo. Los laboratorios de diagnostico han de apoyar a las campanas de control de la enfermedad relacionando antigenica e inmunogenicamente las cepas de campo con las usadas en la produccion de la vacuna. La cobertura de las cepas vacunales, ademas, es de suma utilidad e interes para los bancos de vacunas. Una prueba recomendable para este tipo de estudio es la seroproteccion realizada con sueros de bovinos vacunados y revacunados. Una EPP inferior al 75% en sueros de bovinos revacunados es indicacion de baja proteccion en el campo.

Caracterizacion epidemiologica, antigenica, inmunogenica y bioquimica del virus de la fiebre aftosa A-81 Argentina/87 / Epidemiologic, antigenic, immunogenic and biochemical characterization of aphthovirus A-81 Argentina/87

Estudios soroepidemiologico llevados a cabo en muestras de campo, realizados a fines de 1986 por el Laboratorio de Diagnostico y Referencia para las Americas en el Centro Panamericano de Fiebre Aftos, mostraron un variacion antigenica de virus de la fiebre aftosa tipo A en relacion con el usual A24 y aislamiento de campo A-79 en Argentina. La estrecha relacion entre la industria ganadera agentina y su contraparte en la frontera con Uruguay y la fronteraentre el Uruguay y el estado de Rio Grande do Sul, en Brasil, facilito la diseminacion del virus de la fiebre aftosa entre los paises. Las muestras de campo fueron caracterizadas como virus A-81 Argentina/87

Actualizacion de cepas del virus de la fiebre aftosa de importancia epidemiologica en America del Sur / Updating on food-and-mouth disease virus strains of epidemiological importance in South America

The high variability of foot-and-mouth disease, due to genetic recombination and the selective pressure of antibodies in areas of systematic vaccination, is the reason that one strain of virus causes only one epidemic wave in the field. The list of subtypes should therefore be revised periodically to eliminate those which are not longer found in the field. The diagnostic laboratories have to support the control campaigns of the disease by relating antigenically and immunologically the field strains with those used in the production of vaccines. The coverage of the vaccine strains, furthermore, is of great usefulness and interest for vaccines banks. One test which can be recommended for this type of study is the expected percentage of protection (EPP) determined through the serum protection test with sera from vaccinated and revaccinated cattle. An EPP of less than 75 percent with sera from revaccinated cattle is an indication of a low protection level in the field

Caracterización epidemiológica, antigénica, inmunogénica y bioquímica del virus de la fiebre aftosa A-81 Argentina/87

Estudios seroepidemiológicos llevados a cabo en muestras de campo, realizados a fines de 1986 por el Laboratorio de Diagnóstico y Referencia para las Américas en el Centro Panamericano de Fiebre Aftosa (CPFA), mostraron una variación antigénica de virus de la fiebre aftosa tipo A en relación con el usual A24 y aislamientos de campo A-79 en la Argentina.

Seroepidemiologic studies constantly carried out on field samples by the Diagnostic Reference Laboratory for te Americas at the Pan American Foot-and-Mouth Disease Center (PAFMDC) revealed, late in 1986, an antigenic variation of FMDV type A in relation to the usual A24 and A-79 field isolates in Argentina.