Assessing Risk of Introduction via Import
A quantitative approach to estimate the likelihood of introduction of an infectious disease agent into a disease-free country through the movement of animals is essential to assess the risk of introduction of such disease agent. This approach was used to establish the likelihood of introduction of vesicular stomatitis virus (VSV) in Europe based on probability theory and a set of assumptions in relation to the shipment size of importation (values ranging from 1 up to 4,000 animals), prevalence scenarios from the exporting country for each of the susceptible species and the characteristics of the testing system in place to detect VSV. Several scenarios were modelled. Considering animals imported to Europe with a testing system sensitivity of 0.98 and a prevalence of 1 out of 4,000 in the population of concern (i.e. belonging to a susceptible species and destined to export) the number of single shipments that are needed in order to have VSV introduced in Europe are 199,951. Taking into account that each year approximately 4,000 animals are imported to Europe, at least 50 years are needed for the introduction of an infected animal. When the prevalence is around 9 out of 10,000 and keeping the sensitivity at 0.98, it takes 54,193 single shipments (at least 14 years) to introduce an infected animal. Similarly, it can also be stated that if the prevalence is 1 out of 4,000 and the sensitivity is 0.99, then around 400,000 animals are to be imported (100 years) to introduce an infected animal in Europe. When the prevalence is around 9/10,000 and the sensitivity is 0.99, then the number of imported animals needed to introduce an infected animal in Europe is 108,385 taking at least 27 years.