The risks posed by the importation of animals vaccinated against foot and mouth disease and products derived from vaccinated animals: a review.

The Terrestrial Animal Health Code of the OIE (World organisation for animal health) (the Terrestrial Code) makes recommendations for international movements of live animals and animal products because of a possible generic risk of foot and mouth disease (FMD) for these different commodities. For instance, international movement of vaccinated live animals or products of such animals is restricted due to the possible masking of clinical disease as a result of vaccination and to the perceived risk of persistently infected animals among vaccinated livestock. In addition, bilateral agreements between exporting and importing countries on the importation of animal products can be based on the 'equivalence' of the animal health conditions in both countries, or on formal or informal risk assessments in accordance with the norms and recommendations of the Terrestrial Code. In this regard, an exporting country may be required to prepare a complete and transparent document describing the animal health situation, including the factors required to assess the risk involved. Furthermore, expert committees of importing countries regularly evaluate and verify these conditions in exporting countries. The level of confidence in the information obtained by the expert committee can then be entered into the risk analysis equation. An important FMD risk reduction factor for the importation of animals and animal products is early recognition of the disease at the source of the commodity by alert stakeholders, such as official and private veterinarians and the chain of the livestock industry. This is true for all countries irrespective of their vaccination status. The risk posed by the importation of vaccinated animals becomes negligible when an adequate protocol--in compliance with the norms and recommendations of the Terrestrial Code--is applied. However, recently, export of live animals from countries that do not practise vaccination has also proven to pose a significant risk and the rules governing such transport may have to be reviewed. Disease surveillance, biosecurity at the farm level, traceability and control of the source cattle and slaughterhouse inspections are the main risk reduction measures for meat and meat products from vaccinated cattle. If these animals are slaughtered and processed under good management practice--in accordance with the norms and recommendations of the Terrestrial Code--these products present a negligible risk for the introduction of FMD. Risk reduction by maturation and deboning is an important procedure, but is probably overemphasised. Mechanical contamination of cattle carcasses with 'carrier virus' from the pharyngeal area during slaughter and processing is very unlikely. Risk assessments showed that the importation of milk products from countries or zones that practise vaccination of dairy herds poses a negligible risk. Risk assessments also demonstrated that the importation of bovine embryos from vaccinated cows--in accordance with the norms and recommendations of the Terrestrial Code--poses a negligible risk. Likewise, the risk from the importation of semen from vaccinated bulls is also negligible when an adequate test protocol is applied in accordance with the Terrestrial Code.

Unapparent foot and mouth disease infection (sub-clinical infections and carriers): implications for control.

Unlike animals which are carriers of foot and mouth disease (FMD), sub-clinically infected animals may be highly contagious. The implications of sub-clinical infections for the control of FMD are serious because such animals are likely to disseminate the disease when in contact with susceptible livestock. Recent dissemination of FMD virus (FMDV) in Europe shows that sub-clinically infected animals render trade in animals or animal products a potential risk for importing countries. This clearly demonstrates that the paradigm 'free of FMD without vaccination' is not synonymous with 'risk-free'. The risk of introduction of subclinical FMD into FMD-free countries may increase significantly, with the occurrence of large susceptible animal populations, changed agricultural practices, expansion of trade in live animals and animal movements, increased trade in animal products and greater mobility of people. Such changes in circumstances require that national and international authorities remain continuously vigilant to determine any altered risk for importation of FMD. A few historical reports and some recent observations in southern Africa indicate the possibility of dissemination of FMD by bovine carriers into herds of susceptible cattle. These reports have greatly influenced FMD trade policies and thus, FMD control and eradication strategies. However, other field evidence does not support this claim and several controlled experiments were unable to show that carriers are able to initiate disease. When millions of cattle were systematically vaccinated with good quality vaccines, FMD disappeared in spite of a large sentinel population in the form of calves and unvaccinated sheep and pigs. A low number of carriers most likely persisted, but they did not hamper the eradication of the disease. Vaccination policies and trade regulation must be based on risk assessments taking these factors into consideration.

Importation of beef from countries infected with foot and mouth disease: a review of risk mitigation measures.

Risk mitigation measures to reduce the risks associated with importing beef from countries affected by foot and mouth disease (FMD) consist of controls at the farm of origin, inspection of slaughterhouses and maturation and deboning of carcasses. This assessment evaluates the effect of these measures on the mitigation of the risks presented by meat from cattle with FMD, for each of the different stages of the disease. The four disease stages considered are the incubation period, the period of clinical signs, convalescence and the carrier stage. Efficient animal health systems, disease surveillance, and ante-mortem and post-mortem inspection of all cattle effectively reduce the risk of FMD transmission from cattle slaughtered during the period of clinical signs or convalescence. These measures fail if the cattle are slaughtered during the incubation period, because of the absence of clinical signs. Cattle in this stage of the infection are likely to be viraemic, with FMD virus present in the skeletal muscles. Maturation of the carcasses of viraemic cattle reduces the risk of virus presence in the beef. In addition, deboning and removal of the principal lymph nodes and large blood vessels eliminate a source of FMD contamination of the beef. However, the slaughter of viraemic cattle creates an additional hazard of gross environmental viral contamination of the slaughterhouse facilities. Therefore, the maturation process may create a false sense of security, and the emphasis should instead be placed on disease surveillance within the infected zone and on the farms of origin, to prevent the slaughter of herds that are incubating FMD. Cattle slaughtered during the carrier stage do not pose a risk for the international beef trade.

The foot-and-mouth disease risk posed by African buffalo within wildlife conservancies to the cattle industry of Zimbabwe.

Quantification of the risk that African buffalo (Syncerus caffer) (isolated within wildlife conservancies in Zimbabwe by a double fencing system) would infect cattle outside the conservancies with foot-and-mouth disease (FMD) virus was assessed by scenario-pathway analysis. Of the five scenarios considered, the greatest annual risk (1:5000) for cattle would be from antelope jumping over the outer perimeter fence of the conservancy and infecting cattle on the outside. The other transmission scenarios (including air-borne transmission) had a FMD risk that was low to very low. Risk management would include means to prevent the escape of antelope from the conservancies and restriction of cattle density in the proximity of the perimeter fence.

Risk of disease transmission by llama embryos.

An assessment was made of the risk of transmission of foot and mouth disease (FMD), vesicular stomatitis, bluetongue, tuberculosis and brucellosis by llama embryos. The study suggests that embryo transfer is a safe method for the international movement of llama embryos despite the special characteristics of these embryos, such as the absence of a zona pellucida, and despite the lack of data on pathogen-embryo interactions. For acute viral diseases such as FMD, vesicular stomatitis or bluetongue, embryo transfer reduces the risk of international embryo movement by a factor of 10(4). Therefore, if favourable epidemiological or ecological conditions exist in the region of origin of the embryos, the risk of contamination of a batch of llama embryos with the above agents is close to zero. The risk of contamination with Mycobacterium or Brucella depends on the incidence of these diseases, but under the most unfavourable prevalence levels, the risk does not exceed 10(-3.3), given that the results of diagnostic tests of the herd and of donor animals are negative before and after collection of the embryos. This study demonstrates that risk assessment can be a valuable tool to facilitate international movement of embryos, particularly for those species for which little or no data are available regarding embryo-pathogen interactions.

A quantitative assessment of the risk of transmission of foot-and-mouth disease, bluetongue and vesicular stomatitis by embryo transfer in cattle.

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.

Risks of introducing foot and mouth disease through the importation of beef from South America.

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.

Contamination of animal products: the minimum pathogen dose required to initiate infection.

When an animal product contains a low level of contamination (perhaps less than the minimum infective dose of a pathogen as determined experimentally), the theoretical probability remains that if a large number of animals are exposed to that product, at least one animal in the group will become infected. Such an infected animal could start an outbreak of the disease. These aspects, therefore, should be considered when risk assessments are performed. Foot and mouth disease virus in milk is used as an example.

The risks of disease transmission by embryo transfer in cattle.

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.

Risk assessment and risk regionalization, based on the surveillance system for foot and mouth disease in South America.

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.

Regionalización en el análisis de riesgo de fiebre aftosa para América del Sur

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.

Quantitative assessment of the risk of disease transmission by bovine embryo transfer

[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.

Almacenamiento de vacuna antiaftosa con adyuvante oleoso a baja temperatura

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.

Estimación de potencia de vacunas contra la fiebre aftosa de acuerdo con los resultados de pruebas de anticuerpos

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.

Los virus de fiebre aftosa usados en la producción y control de vacunas en América del Sur

[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.