Surveillance strategies for foot and mouth disease to prove absence of disease and absence of viral circulation

Abstract

Free trade of animals and their products is based on the international or bilateral recognition of the health status of the animal populations being traded. This recognition is based on documentation of their health status by the exporting country, based on the results of continuing surveillance. According to the Terrestrial Animal Health Code of the World Organisation for Animal Health (OIE), this may be based on various methods of surveillance, such as: documenting non-specific surveillance (clinical surveillance, passive notification of suspect cases, etc.); documenting activities that increase the sensitivity of non-specific surveillance (training activities, rewards/sanctions for notification/failure to notify, etc.); documenting all specific surveillance and its results (random surveys, targeted and risk-based surveillance, convenience-testing activities, etc.). Usually, the infection is the subject of the declaration of freedom. While clinical and passive surveillance can provide a high level of confidence that foot and mouth disease (FMD) infection is absent, this is not the case in vaccinated populations. In these populations, specific surveillance becomes much more important than non-specific clinical surveillance. Specific surveillance is severely restricted by the performance of the test(s) employed. The imperfect specificity of any serological test is further complicated when techniques to differentiate infected from vaccinated animals (DIVA) are used, because imperfect purification of the antigen used for vaccination may foster the production of undesired antibodies in the vaccinated animals. The authors discuss various approaches to overcome this problem; their merits and flaws in documenting the absence of infection or virus circulation for animal diseases in general, and for FMD in particular. Particular attention is paid to finding methods that can be applied in a variety of epidemiological conditions and organisational structures, since these vary greatly among OIE Members.