200 Rev. sci. tech. Off. int. Epiz., 30 (1)

From " Cattle, sheep and pigs vaccinated against foot and mouth disease: does trade in these animals and their products present a risk of transmitting the disease?" by A.J.M. Garland & K. de Clercq see http://www.warmwell.com/15garland189206.pdf

Discussion

The international trade in livestock and animal products is enormous and increasing. For example, Brazil accounts for some 28% of all international commerce in bovine meat and in 2008 the country exported around 2.2 million tonnes with a value of US$5.3 billion. The exports comprised 1.5 million tonnes of fresh meat, 0.5 million tonnes of processed beef, 0.07 million tonnes of offal, 0.08 million tonnes of casings and 0.006 million tonnes of salted materials. Of the fresh meat, 0.65 million tonnes were imported into Western and Eastern Europe and 0.5 million tonnes into Russia (12). The vaccination status of the source cattle is unknown, but Brazilian regions permitted to export to Europe must meet the OIE criteria for an ‘FMD-free zone where vaccination is practised’. No introductions of FMD have been associated with these imports.

As evident from this review, there have been relatively few studies published on the quantitative survival of FMD virus in the tissues of vaccinated animals exposed to infection; the investigations which have been carried out have been restricted to a few serotypes only, with information on the SAT and Asia serotypes being particularly sparse (60). The studies have been concerned principally with cattle vaccinated repeatedly and they employed methods of virus detection of lower sensitivity than those currently available. Nevertheless, the limited data suggest that effective vaccination significantly reduces the risk that immunised animals or their products could carry FMD infection (25). However, the lack of information leaves us with a number of unanswered questions, namely:

– what would be the result if cattle were vaccinated less frequently or challenged sooner after vaccination?
– what would be the result of vaccination against each of the seven serotypes and for heterologous virus challenge?
– what would be the result of applying more sensitive methods of virus detection?
– what would be the results of vaccination in sheep and pigs?

These areas could be targeted for further research (35, 60).
However, considering (i) the lack of evidence for transboundary transmission, even by unvaccinated animals and their products, when proper safeguards are observed, (ii) the cost of such studies and (iii) the aspect of statistical significance, the question arises of the experiment’s expected return on investment, especially when ranked against competing research priorities.

Faced with the paucity of factual data, an alternative approach could be the application of ‘scenario tree’ methods of combining multiple sources of evidence (44) to determine whether a particular source of live animals and animal products poses a level of FMD risk which meets an importing country’s appropriate level of protection (so-called ALOP). This approach has been applied in a number of situations (2, 58, 61, 68, 82, 89) and could be developed further. Vaccination would be one of the factors

Animals with effective, solid immunity to FMD, having been properly vaccinated with well-controlled vaccines incorporating appropriate strains, pose a very small risk of spreading the disease. The same applies to the products derived from such animals, provided that they comply with the recommendations of the Terrestrial Code.

However, even though the risk may be small, it cannot be assumed to be zero. Quantitative risk assessment is of limited application because of the lack of key factual data. Nevertheless, and with the provisos discussed, empirical evidence over many years strongly indicates the absence of FMD risk from vaccinated animals or products derived from them.

200 Rev. sci. tech. Off. int. Epiz., 30 (1)