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This paper addresses the risks involved when bovine embryos are moved internationally and, specifically, the possibilities of transmitting foot-and-mouth disease, bluetongue and vesicular stomatitis by embryos originating from an area in South America. The risk scenario pathway was divided into three phases for analysis. The first phase dealt with the potential for embryo contamination which depends on the disease situation in the exporting country and/or region, the health status of the herds and the donor cows from which the embryos are collected, and the pathogenetic characteristics of the specified disease agent. The second phase covers risk mitigation by use of internationally accepted standards for processing of embryos, and the third phase encompassed the risk reductions resulting from post-collection surveillance of the donors and donor herds, and also from testing of embryo-collection (flushing) fluids for the disease agent. Quantitative risk analysis showed that under the circumstances specified in the paper, the risk of transmission of foot-and-mouth disease and vesicular stomatitis by embryos would be likely to be less than 1 in 100 billion (10(-11.0)) and 1 in 100 million (10(-8.0)), respectively. The values for bluetongue were 1 in 30,000 (10(-4.2)) when embryos were collected in the vector season and 1 in 1 million (10(-6.0)) in the season with low vector activity. These risk values were influenced by the incidence of each disease in the area of origin and the ease with which clinical signs can be recognised. Competent embryo processing according to procedures recommended by the International Embryo Transfer Society were also of great importance. The analysis showed that the reasons for the low levels of risk of transmission differed for each of the three diseases. In the case of bluetongue, vector ecology was of major importance.

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The safety of beef with respect to foot and mouth disease (FMD) is determined by the level of risk which the exporting region poses through disease prevalence, the reliability of the surveillance system of the region, the efficacy of the prevention and control measures, the efficiency of the Veterinary Services and the support of the private sector. The South American continent has been regionalised in accordance with these criteria. Today there are approximately 90 million cattle in a territory of over 5 million km2 comprising regions classified as having a very low to low level risk for FMD with regard to the export of animals and animal products. Another 50 million cattle live in regions classified as posing a moderate risk. These risk categories reflect varying levels of risk. The harvest of beef in the meat-exporting regions of South America includes a series of risk mitigation measures, from the origin of the source herd to the final packing of the beef. These measures reduce the unrestricted risk estimate by almost six orders of magnitude. Therefore, the final risk of FMD for the global trade of beef originating from the low risk regions in South America is extremely small.

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Guidelines for the safe international movement of livestock embryos are provided in the International Animal Health Code of the Office International des Epizooties, and recommendations for embryo processing, based on numerous research papers on embryo-pathogen interaction studies, are given in the Manual of the International Embryo Transfer Society. Risk assessment is the logical extension of these approaches, since it provides veterinary authorities with a complete package of information on which to base their import/export decisions. Risk assessment includes evaluation of disease prevalence, effectiveness of Veterinary Services and competence of the embryo collection team. It also takes account of the epidemiology and pathogenesis of the disease concerned. The application of risk assessment for embryo movement is illustrated in this paper by comparisons of the probabilities of transmitting foot and mouth disease, bluetongue and vesicular stomatitis by bovine embryos. The risk scenario pathway was divided into three phases for analysis. The first phase deals with the potential for embryo contamination, which depends on the disease situation in the exporting region, the health status of donor herds and donor cows, and on the pathogenetic properties of the disease agent. The second phase covers risk mitigation by use of the internationally accepted standards for embryo processing, and the third phase considers the risk reductions resulting from post-collection surveillance of donors and donor herds, and also from testing of embryo-collection (flushing) fluids for the disease agent. It was evident from this assessment that low risks of transmitting disease by international movement of bovine embryos depend initially on a low disease incidence in the exporting region and on easily recognisable disease signs. Competent embryo processing was also of great importance, and in the case of bluetongue, vector ecology had a major influence. In addition to providing a logical basis for import/export decisions, risk assessment is useful for evaluating the potential outcome of new research and for assessing the safety of the movement of embryos of other species for which little or no research information is available on embryo-pathogen interactions.

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Within the framework of the International Animal Health Code of the Office International des Epizooties (OIE), important contributions have been made by the Animal and Plant Health Inspection Service/United States Department of Agriculture (APHIS/USDA), the Ministry of Agriculture of Canada, the Ministry of Agriculture and Fisheries of New Zealand and other organisations, by the development of risk assessment methods and regionalization criteria for risk assessment. The authors attempt to contribute to these efforts by proposing a regional risk evaluation of foot and mouth disease (FMD) in South America. Two examples of risk assessments for international trade, i.e., in bovine embryos and in meat, are used to demonstrate the importance of an effective disease surveillance system as the basis for risk regionalization for international trade in animals and animal products. As a result of progress in the control and eradication of FMD in South America, it is expected that major livestock production regions will soon be in low- to very low-risk categories.

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En este trabajo se propone una evaluación de riesgo específica y regional de la fiebre aftosa en América del Sur para la exportación de productos animales basada en la situación de los programas de control, erradicación y prevención de la fiebre aftosa de cada país o región.

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[Introduction] The objective of Part I of this publication is the development of a QRA model for disease transmission by ET. Bovine ET was chosen for the discussions because bovine embryos are the most commonly used in international trade. In Part I, Section 1 some of the general aspects of bovine ET procedures are briefly reviewed, while Section 2 contains a general discussion of the risk factors involved. In Section 3 the scenario pathway is show and the general principles of risk quantification are outlined. Practical application of the QRA model is presented in Part II of the paper. This deals with the construction os a specific QRA model for the risk of transmission of FMD by bovine ET from a FMD infected country. Because of the important potential for export of embryos of Zebu cattle breeds from Brazil, particurlarly from the area comprising the model. Part II Section 1 gives some specific details of the epidemiology and conrol od FMD in the area concerned. The status of the ET industry of Brazil and in the selected area is also reviewed. In section 2 a quantification of the risks is proposed. Also, documentation is provided on the evidence and information used for the proposed risk values, followed by the statistical elaboration of the risk estimates, discussion and conclusions.

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En abril de 1980, el Centro Panamericano de Fiebre Aftosa (CPFA) almacenó cerca de 3000 dosis de vacuna antiaftosa inactivada con adyuvante oleoso a-70§C. Esta vacuna fue preparada 8 meses antes y mantenida a +4§C hasta el momento de su congelación. La vacuna fue formulada de acuerdo con los métodos estándar usados en esa época en el CPFA. Resultados demuestran que la vacuna antiaftosa con adyuvante oleoso puede ser almacenada a -70§ por un largo período de tiempo, sin que se compruebe pérdida de potencia.

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En este estudio, un total de 62 series de vacuna sin dilución o diluidas fueron clasificadas de acuerdo con el promedio de las EPP de los bovinos, determinados por ambos métodos a los 21-28 días posvacunación (DPV). Los resultados fueron comparados con la protección observada a la inoculación de virus en la lengua a los 21-28 DPV.

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[Introducción] El presente trabajo describe las características antigénicas e inmunogénicas de las cepas usadas en la producción y control de vacunas en América del Sur. A la vez, describe aquellas que fueron importantes epidemiológicamente en esta región.

[Introduction] This paper descibes the antigenic and immunogenic characteristics o the virus strains utilized in the production and control of vaccines in South America. Strains that have been epidemiologically important in the region are also described.

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La existencia de bovinos portadores de virus de la fiebre aftosa (FA) fue confirmada por investigadores del Centro Panamericano de Fiebre Aftosa (CPFA), al comienzo de la década de 1960. Desde entonces, la denominada prueba de probang para portadores ha sido extensamente utilizada en programas de importación y exportación de bovinos y ocasionalmente, en encuestas como indicador epidemiológico. Durante los últimos años el CPFA viene utilizando el método para determinar la presencia o ausencia del virus de la FA en rebaños bovinos experimentales o en áreas piloto donde se aplican vacunas antiaftosa con adyuvante oleoso.

The existence of foot-and-mouth disease (FMD) virus carriers in the field was confirmed by workers of the Pan American Foot-and-Mouth Disease Center (PAFMDC), Rio de Janeiro, Brazil, in the early 1960's. Since then the so-called probang test for carriers has been extensively used in import and export programs and occasionally for virus surveys. During the last few years the PAFMDC used the method to determine the absence or presence od FMD viral activity in experimental fams and pilot areas or demonstration areas where oil adjuvanted vaccines were used.

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Se examinaron 532 sueros de bovinos vacunados mediante la prueba de microneutralización adoptada como rutina en el Centro Panamericano de Fiebre Aftosa. El suero provenía de bovinos utilizados en pruebas de potencia de vacunas, infectados por vía intradermolingual. Se calculó la expectativa porcentual de protección (EPP) para los títulos de seroneutralización. Se propone que la media de la EPP de un grupo de bovinos es una medida singificativa del estado de inmunidad.

A total of 532 sera from vaccinated cattle were assayed by the microneutralization test as used routinely at the Pan American Foot-and-Mouth Disease Center. The sera were from cattle used in vaccine potency tests and were challenged by the intradermolingual route of infection. An expected percentage of protection (EPP) was established for the serum neutralization titers. It is proposed that the mean EPP of a group of cattle is a meaningful measurement of the immune status.

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En otra publicación (1) se informó sobre la respuesta inmunitaria de 72 bovinos vacunados con vacunas antiaftosa de emulsión primaria y doble. Al fin de ese experimento, 6 meses después de la vacunación, la media aritmética de los títulos neutralizantes de los diversos grupos experimentales variaba entre 2,2 y 2,8. Para este trabajo, esos 72 bovinos fueron divididos aleatoriamente en tres grupos, manteniendo una correlación con los grupos del trabajo anterior. Los bovinos del grupo 1 no se revacunaron, los del grupos 2 se revacunaron con 10 ml de una vacuna antiaftosa de emulsión doble y los del grupo 3 con 5 ml de una vacuna de emulsión primaria.

An accompanying paper (1) reported on the immune response of 72 cattle after vaccination with primary and double emulsion foot-and-mouth disease (FMD) vaccines. An the end of that experiment at 6 months post-vaccination the mean neutralization titers of the various experimental groups ranged from 2.2 to 2.8. For the present experiment these 72 cattle were randomly divided in 3 groups, with equal contribution of each of the original experimental groups to the three new groups. Cttle of group 1 were left without revaccination, cattle of group 2 were revaccinated with 10 ml of a double emulsion FMD vaccine and group was revaccinated with 5 ml primary emulsion FMD vaccine.

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Mediante la prueba de seroneutralización en tubo, en el Centro Panamericano de Fiebre Aftosa (CPFA) se examinaron sueros sanguíneos de 791 bovinos vacunados y expuestos al virus de la fiebre aftosa (FA). Como sistema para detectar virus no neutralizado se aplicó la técnica de virus estándar-suero variable en monocamadas de células BHK21. La infección de los bovinos con el virus de la FA se hizo por vía intradermolingual, en tres laboratorios diferentes. Hubo diferencias significativas en la relación título de anticuerpos y protección frente al desafío entre los tres laboratorios y entre los distintos tipos de virus. Puesto que todos los sueros fueron examinados en el CPFA, estas diferencias señalan la dificultad de la estandarización de pruebas relacionadas con la infección de bovinos. Los títulos de neutralización sobre 1:64 indicaron un alto grado de protección. Es difícil interpretar el rango 1:8 a 1:32, en términos de protección al desafío.

A total of 791 sera from vaccinated cattle exposed to foot-and-mouth disease (FMD) virus were tested at the Pan American Foot-and-Mouth Disease Center (PAFMDC) by the tube serum neutralization test using the variable serum-constant virus technique with BHK21 cell monolayers as the indicator system to detect non-neutralized virus. The cattle were exposed to FMD virus at three different facilities by the intradermalingual route. Important differences in the relationship antibody titer and protection at challenge were observed between te three testing facilities and between the different virus types used. Since all sera were tested at the PAFMDC these differences point to the difficulty in standardizing tests involving the exposure of cattle. Neutralization titers above 1:64 would indicate a high level of protection. Titers in the range between 1:8 to 1:32 are diffcult to interpret in terms of protection at challenge.

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Both primary emulsion (water-in-oil) and double emulsion (water-in-oil-water) foot-and-mouth disease vaccines with different viscosities produced exellent persistent levels of neutralizing antibodies. The degree of dispersion of the aqueous antgenic phase in the oily phase, which determined the viscosity of the vaccine, did not have a demonstrable effect on the long-term immunogenicity of the vaccines.

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Treinta vacas, que habían sido vacunadas 3 veces a intrevalos de 6 meses con vacunas antiaftosa con adyuvante oleoso, fueron expuestas 13 meses después de la última vacunación al virus tipo O1 por vía intradermolingual y al contacto con bovinos y cerdos infectados. De acuerdo con los niveles de anticuerpos previos al desafío de virus se esperaba una elevada protección, la que fue confirmada por la prueba de desafío de virus. Sólo uno de los 30 bovinos desarrolló fiebre aftosa generalizada. De los 29 animales sólo 6 tuvieron una lesión en el punto de inoculación. Estas observaciones confirman, en general, que en las encuestas serológicas realizadas en la población bovina a la que pretenecían esos animales, vacunados con vacuna antiaftosa con adyuvante oleoso, los elevados niveles de anticuerpos indican una sólida inmunidad.

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El presente estudio mostró la especificidad de la respuesta local a los subtipos por virus de la FA.

The present stydy also showed the specificity of the local response to FMD virus infection.

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El presente estudio fue realizado con el propósito de determinar si ocurriría replicación de virus en la faringe y cómo sería la viremia después de la inoculación intradermolingual en bovinos en bovinos utilizados en una prueba de potencua de una vacuna.

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During the period 1953-1956 Government meat inspectors in the Netherlands Antilles observed Cryptococcus neoformans infections in goats. Of the 6,578 animals slaughtered in the period under review, 51 were infected, while the corresponding figures for Curacao were 19,854 and 20 respectively. The diseased animals came from the Leeward Islands of the Netherlands Antilles (Aruba, Bonaire and Curacao), Colombia and Venezuela. Pathological-anatomical changes were mainly restricted to foci in the lungs. (AU)

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