Porcine epidemic diarrhea (PED) in Europe and strategies to control outbreaks

Porcine epidemic diarrhea (PED) has been recognized for the first time in 1971 in the United Kingdom during outbreaks of diarrhea in feeder and fattening pigs. Subsequently, the disease spread to other European countries and clinically also appeared in suckling pigs. During the 1970 and 1980 widespread PED epidemics were prevalent throughout Europe. Thereafter, PED epidemics became rare and the virus responsible for PED, PED virus (PEDV) was more often associated with single outbreaks due to widespread natural stabilization of breeding herd immunity. However, a PEDV epidemic was observed in Italy in 2005-2006 emphasizing that PEDV was still present and active in Europe. The emergence of PEDV in the USA in 2013 has raised concerns from European swine producers over introduction of emerging PEDV strains into the European Union (EU). In 2014, PEDV associated with high mortality was recognized in the Ukraine. Subsequently, PEDV outbreaks associated with watery diarrhea in piglets were also seen in Germany, Portugal, France, the Netherlands, Italy and Belgium. Genomic analysis revealed that the Ukraine PEDV resembled a PEDV genogroup 2 prototype strain. In contrast, in essentially all EU PEDV outbreaks a PEDV genogroup 2 S-INDEL strain different from the PEDV prototype genogroup 2 strains was identified. PEDV S-INDEL strains are associated with lower pathogenicity compared to prototype strains in infected pig populations. Tools to control PED in the EU are limited. During the initial European outbreaks of PEDV in the 1970ies, pregnant sows were deliberately exposed to the intestinal content of pigs that had died of PED. However this practice is currently not recommended and control is largely based on improving biosecurity and stop farm-to-farm transmissions. In December 2015 PED became a notifiable disease in England. Efforts to implement a commercial inactivated sow vaccine in several European countries are ongoing. Overall, PEDV has been re-emerging in Europe but appears to have an altered virulence different from what has been observed in North America and Asia in recent years. Control measures such as improving biosecurity are in many cases sufficient to control the disease.