Classical swine fever is a highly infectious disease of pigs that has important consequences for animal welfare, trade and the pig industry. The disease is caused by a pestivirus, the classical swine fever virus (CSFV). Most of Europe is free from CSFV, although there are still some areas where the disease persists in wild boar and it is still a problem in some eastern European countries. Further afield the virus is endemic in many areas where it is controlled by vaccination. As an island any future outbreak of classical swine fever in the UK is likely to be linked to some form of human activity, such as importation of an infected pig product. The feeding of swill containing meat products to pigs was banned after the FMD outbreak in 2001, which will reduce the likelihood of an animal being exposed to the virus. However, illegal feeding does occur and this may increase in times when the economic situation is poor. The impact of climate change on the location of global food production systems, as well as need to ensure future food security, mean that assessments of the risk that products of porcine origin pose for the introduction of classical swine fever will be increasingly needed.
Assessment of the risks that porcine products pose requires information on how likely a product is to be infected, what level of virus will be present if it is infected, how long will the virus remain viable under the conditions that the product is likely to encounter, how likely a product is to encounter a susceptible animal and how much virus needs to be ingested by that animal to cause infection.
This proposal aims to provide information on two of these areas, namely how much virus is required to be eaten by a pig to result in infection and how long the virus survives.
The first objective is to determine the dose of virus that is required to infect 50% of animals that are feed with a highly virulent strain of classical swine fever virus. We have recently determined the oral dose required for a moderately virulent strain, which is representative of many of the strains that are currently circulating. However, the virulence of a strain affects the dose that is required to cause infection, so to provide data on the worst-case scenario the oral infectious dose of a highly virulent strain is required.
The second objective of this proposal is to examine how long classical swine fever survives within unprocessed pig tissues at different temperatures. In particular we will examine temperatures that are encountered during the processing of by-products, such as the composting of catering waste, ambient temperatures to provide information on the risks of environmental spread during an outbreak, as well as temperatures used for cold storage of uncooked meat. We will focus on the survival of virus in muscle tissue as this forms the majority of pork products. In addition we will examine virus survival in lymphoid tissue, as the virus is present in these at higher levels. Determining the rate of inactivation of virus in these tissues at different temperatures will allow extrapolation of the data to provide estimates of the survival of virus at other temperatures.
The final objective is to examine the survival of virus in meat products that have undergone processing. Many different processes are applied to produce a wide variety of pork products worldwide. For example dry-cured pork products can be salted, smoked and dried under different conditions for varying lengths of time. These types of product are often traditional foods that are produced by diverse cultures and are the sort of highly valued product likely to be transported, from areas where CSFV may be endemic, in passenger baggage. It is not feasible to replicate all the different processes that are applied to pork products to assess their risk for introduction of CSFV. Therefore we propose to examine a selected set of defined curing conditions and determine the rate of CSFV inactivation. This will allow better estimates to be made of CSFV survival in differently processed products.