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

Abstract

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

Genetic and Phenotypic Variation of Foot-and-Mouth Disease Virus during Serial Passages in a Natural Host

“…Virus isolation from pig tonsils at day 26 postcontact confirmed that these animals had been infected without clinical symptoms of disease and that virus had persisted in them for 4 weeks. This case resembles what has been described as a carrier state of FMDV for cattle, sheep, and goats (2,39,46) but not yet demonstrated for pigs. Bottleneck transmission may confer on the virus the ability to ratchet down fitness and virulence to ensure the immunization of at least a fraction of the population rather than kill or debilitate the entire susceptible host population.…”

“…The etiological agent FMD virus (FMDV) of Picornaviridae occurs as seven distinct serotypes and multiple subtypes, reflecting significant genetic and antigenic heterogeneity. In the field, this heterogeneity is reflected by the lack of cross-protection even between intraserotype variants (2,3,46). VP1 (1D), the highly variable FMDV capsid protein with roles in virus entry, immunity, and serotype specificity, has been the subject of extensive comparative sequence analysis (reviewed in reference 22).…”

“…No studies have been conducted to examine FMDV evolution during replication in the natural host, and very few evolutionary analyses have examined genomic regions other than those corresponding to VP1 or its precursor, P1 (4,27). Paradoxically, the few experimental studies conducted with natural isolates suggest extreme constrains for 1D variation (5,6) and loss of fitness during passages in natural hosts (1,22,46). In fact, enhanced mutagenesis experiments have shown infectivity loss for a number of RNA viruses, including FMDV, lymphocytic choriomeningitis virus, and Hantavirus (18,31,32,33,38,42), suggesting that critical variability thresholds that may explain the restrictions for change observed in vivo exist.…”

“…The data indicate rapid accumulation of nucleotide substitutions and fitness loss, suggesting bottleneck transmission effects. Fixation of amino acid changes in nonstructural proteins (NSPs) likely resulted in deleterious effects for virus biology, leading to the establishment of a subclinical infection that resembles the carrier state described for cattle (2,39,46). Furthermore, we found significant differences in evolution parameters between in vivo-and in vitro-passaged virus, reflecting differences in selective pressures operating on virus populations, expressed as differences between numbers of synonymous and nonsynonymous substitutions, frequencies of transitions and transversions, and levels of tolerance for changes in specific viral proteins.…”

Inhibition of Foot-and-Mouth Disease Virus Infections in Cell Cultures with Antisense Morpholino Oligomers

“…FMDV is the first disease for which the Office International des Epizooties (now World Organisation for Animal Health, OIE) established an official list of pathogen-free zones and countries. In the last decade, costly FMD outbreaks have occurred in Europe (United Kingdom and The Netherlands, 2001), Asia (India and Philippines, 1996; Taiwan, 1997; Korea, 2000 and 2002), South Africa (1999 and2000), and South America (Brazil and Argentina, 2001), resulting in the slaughter of a large number of animals as well as implementation of quarantine and decontamination procedures (38), with associated socioeconomic ramifications.…”