There was a significant fall in diagnoses of PMWS (as a percentage of relevant diagnostic submissions) during the quarter compared with the same quarter last year (24% to 12%). This was in line with indications of a trend for fewer PMWS diagnoses since 2002, and may well reflect a reduction in the disease but also a reduced demand to confirm a diagnosis of PMWS based on a full pathological investigation. In contrast, the quarterly percentage diagnoses of PDNS, from relevant submissions, rose sharply to an all time high of 14%. This was a significant rise on the same quarter last year (3%), and also on the previous quarter (5%). See figure of January–March data.

This supports anecdotal evidence from practitioners early in the quarter who reported an upsurge in PDNS-like disease contributing to increased mortality in growers and finishers. Interestingly their perception was that this rise in mortality due to PDNS was occurring on farms experiencing less PMWS than formerly. PDNS is typically described as affecting pigs 12 to 14-weeks-old and the increased mortality occurring in these older pigs results in greater financial loss than PMWS, which commonly presents in pigs from 6-weeks of age.

The rising morbidity and mortality commencing in the grower and finisher stage has prompted a systematic investigation of incidents in pigs from 10-weeks of age to establish whether they have common features in terms of pathology, pathogens and pig husbandry. Early indications are that multiple viral infections, including porcine circovirus type 2 (PCV-2), are involved and incidents often present as respiratory disease.

As a result some PCV2-related cases are included in the respiratory disease section below. Incidents investigated included the typical onset of PMWS two weeks postweaning diagnosed histologically in wasting pigs at seven to ten-week of age. Actinobacillus pleuropneumoniae was isolated from the lungs and enterotoxigenic Escherichia coli (ETEC) from small intestinal contents. PRRS virus was also isolated from lung and lymph nodes. However, there were also instances of PMWS commencing later than usual.

In one such incident PMWS was diagnosed in 14-week-old pigs; sixty pigs of a group of 1200 had respiratory distress and loss of condition with three deaths. Gross findings were of enlarged lymph nodes and pneumonia. Elsewhere, PDNS caused mortality of 10% a week in batches of 220 pigs on a large finishing unit that had recently changed supplier. Deaths were occurring at 18 weeks of age. This quarter is the first time, since the earliest cases of PMWS, that PDNS was diagnosed more frequently than PMWS. The figure below illustrates the seasonal trend for PMWS and PDNS from 2001 (though PMWS was first confirmed in Britain in July 1999). The diagnoses are as a percentage of relevant submissions.