Classical swine fever (CSF) is a highly contagious and deadly disease in pigs which, despite intensive efforts, has not been eradicated from Europe. Outbreaks continue to occur and it is enzootic in some countries. An EU funded FAIR project has contributed enormously to rapid diagnosis of the disease and to tracing the origins of each outbreak.
Swine fever - a porcine plague
Classical swine fever is a notifiable viral disease caused by a member of the Pestivirus genus of the Flaviviridae family of ribonucleic acid (RNA) viruses. It is a particularly dangerous disease as it is highly contagious and can cause high mortality rates with no effective treatment. A global battle is underway to eliminate the disease; Europe has many disease-free countries but it still experiences outbreaks such as have recently occurred in Spain, Germany and Luxembourg and were seen in the UK in 2000 and the Netherlands in 1997.
It is devastating to pig producers with multiple infection routes, including: pig to pig (wild or domestic); infected food; or contact with infected vehicles, premises or clothing, animal waste and semen. The virus is also very stable under favourable conditions, such as in frozen meat where it may survive for years. Vaccines are available but are recommended for use only in emergencies as vaccination hampers detection of infected animals.
As part of Europe's increasingly cohesive approach to eradication and outbreak control, scientists from across Europe worked together in the project, "Control of swine fever by molecular diagnosis and epidemiology" to provide the genetic tools and knowledge to help rid Europe of the disease.
The project was run by a consortium that included the Veterinary and Agrochemical Research Centre (Belgium), Hannover Veterinary School (Germany), National Veterinary Institute (Sweden), Institute of Virology and Immunoprophylaxis (Switzerland), National Veterinary Institute (Poland) and the Instituto Zooprofilattico Sperimentale Dell'Umbria (Italy) and was headed by the Central Veterinary Laboratory (UK).
Each partner is their country's central scientific laboratory dealing with swine fever and the Hannover Veterinary School is recognised by the European Commission as the official Community Reference Laboratory for swine fever. The consortium worked together for over three years between 1996 and 2000 to achieve the following aims:
- Development of novel techniques for faster and more accurate diagnosis of swine fever.
- Establishing molecular epidemiology as a forensic tool to trace the origin of outbreaks. This is critical for tracing the geographical route of the disease and for tracking how it is transmitted.
- Accelerating the introduction of molecular techniques into routine use for swine fever research and tracking. This will allow more effective research into the disease, speeding up the scientific learning vital for the elimination of the disease in Europe.
Building a genetic foundation
The project collated a bank of over 600 CSF viruses, which are now held at the Hannover Veterinary School. All samples had been collected from outbreaks across the globe and are stored along with background information on their origins. The bank also contains sequence data from each of the viral genomes and will provide an invaluable source of genetic information on the virus to aid molecular epidemiology and more fundamental research.
Different virus subtypes exist and knowledge of their RNA sequence enables scientists to pinpoint disease sources more accurately, measure its transmission between wild and domestic pigs and differentiate between vaccine and field virus. A library of viral sequences is available on the internet and will be added to as new sequences are revealed.
One of the key tools in the fight against swine fever is the plethora of new molecular analysis technologies becoming available. The project looked carefully at how the diagnosis of CSF and research into the virus could be improved using molecular technologies:
- A highly effective molecular method for accurate detection of swine fever virus in blood samples was established. This minimises the risk of false negative or positive results and will ensure that the spread of swine fever is tracked very rapidly, allowing better control and reducing the duration and severity of outbreaks.
- The consortium carried out extensive testing of commercially available kits for extracting viral RNA. The most effective kit was identified and is now used widely throughout Europe.
- The method of virus detection increasingly used in swine fever research was improved during the project, with higher accuracy, sensitivity and suitability for automation. An important part of detection and identification is the amplification of the viral RNA to levels where it can be easily detected and sequenced. Traditional methods are slow, but new fluorogenic probes, developed during the project, allow scientists to monitor the development of the test reactions in situ and confirm the identity of the virus in the samples being examined.
Putting research into action
Developments in the diagnosis and analysis of classical swine fever from the project have already been put to good use. When the UK suffered the 2000 outbreak, scientists were able to identify the type of virus responsible and its likely source. Viral subgroup 2.1 was determined to be responsible: this particular sub group is found predominantly in Asia and the outbreak is likely to have originated from there.
Improved analytical sensitivity also allowed the pooling of blood samples for analysis; where 10,000 blood samples would originally have been individually analysed using slow and labour intensive cell culture methods, just 1,000 analysis runs were required to obtain all 10,000 results. Largely as a result of the efforts of the consortium, the detection of CSF viral genome is now established as a confirmatory test within the EU.
The project has focused European scientists in their fight against swine fever,
allowing rapid and accurate Europe-wide disease monitoring