PRRS (porcine reproductive and respiratory syndrome) is a viral disease caused by the PRRS virus (PRRSV).
Porcine reproductive and respiratory syndrome is characterised by abortion, premature birth and high piglet mortality in sows, as well as pneumonia and mortality in weaned piglets and meat pigs. A typical, but less frequent, symptom is the occurrence of blue ears. For this reason, the disease is also known as blue ear disease.
Origin and transmission of PRRS
The disease originated suddenly at the end of the 1980s, virtually simultaneously in the United States and Europe, spreading around the world since then. It was associated with huge economic damage to the pig sector. In 2006 and 2007, South East Asia showed occurrences of infections with a variant of PRRSV, leading to extremely serious problems in pigs, resulting in with very high mortality rates. This variant contains a new genetic mutation that had arisen shortly before.
Since the inception of this disease, researchers at Wageningen Bioveterinary Research (WBVR) have played a significant role in discovering the virus, describing the disease and the development of vaccines.
PRRS vaccines came onto the market shortly after the virus was discovered. However, none of the current vaccines is able to ensure that animals do not become infected, that unborn piglets do not become infected in the womb and that virus excretion by infected animals is halted completely.
The reasons for this are varied and complex. One reason is that the genetic composition of the virus is extremely variable, with the result that the virus circulating in the field is able to evade the immunity generated by the vaccine. In this way, several types of PRRSV have arisen, such as the European and the American virus type, with several variants in between. New variant strains are increasingly being described. The new strains increase the risk that they can no longer be combated with the current vaccines.
Another important reason for the inadequate effectiveness of the PRRS vaccines - and this is what the WBVR research focusses on in particular - is the capacity of the virus to evade the immune system. The virus slows the capacity of the immune system to recognise it, to process it and to create a proper response. Our researchers are focussing on investigating these virus strategies with a view to developing a new generation of more effective vaccines.
The clinical symptoms are often not immediately indicative of PRRS. Laboratory diagnosis is needed in addition to the clinical symptoms, with the presence of the virus being shown by a PCR test or antibodies to the virus by an ELISA test. These tests are available at Wageningen Bioveterinary Research.
Comparative analysis of the pathogenesis of Porcine Reproductive and Respiratory Syndrome virus strains
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