PMWS was first seen in Sweden in 2003 but has spread slowly because Swedish pig units are in isolated locations, have a low stocking density, high animal welfare standards and a low pathogen load.

Following the first Swedish PMWS case in December 2003, there have been only sporadic outbreaks, mainly in southern Sweden.

Lately, however, the number of outbreaks has increased. According to the Swedish Veterinary Institute, cases of PMWS have recently been reported at 26 Swedish farms. In addition, 20 suspected outbreaks are under investigation.

However mortality remains low in affected herds (up from 1 percent to 8-12 percent) because there is no parallel virus infection from PRRS. But it is now feared the rise in outbreaks of PMWS, which compromises the immune system, will lead to the spread of PRRS in Sweden.

PRRS is endemic in Denmark and for several years now, Sweden has tried to halt Danish plans to transport its pigs destined for the Baltics and Russia through Sweden, on the grounds that it would lead to the introduction of PRRS in Swedish herds.

To the dismay of the Swedish pig industry, the Swedish court approved the transit of Danish pigs through Sweden, citing European Union regulations on free movement within the union. Transshipments of Danish pigs through Sweden have begun.

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