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Follow-up report on pig disease investigations in Australia
AUSTRALIA - 'You will recall my letter of 6 Jul 2005, in which I reported on investigations being undertaken by state veterinary authorities into incidents potentially involving the disease "post-weaning multisystemic wasting syndrome" (PMWS) at 2 Australian piggeries, 1 in South Australia (SA) and 1 in New South Wales (NSW).'
I write now
to provide final advice on the conclusions of those investigations.
Ongoing surveillance in the herd in NSW has revealed no evidence of
the characteristic clinical signs of PMWS. It has therefore been
determined that PMWS was not present in the herd.
The herd from SA, however, required an in-depth investigation.
Initially, histopathological changes suggestive of PMWS were detected
in samples submitted as part of an investigation into low-level
weaner mortality and ill-thrift. Further investigations involved an
assessment of the particulars in this case against a case definition
developed specifically for what would have been the 1st diagnosis of
PMWS in Australia. Veterinary authorities carried out a detailed
retrospective assessment of production and clinical data and
laboratory findings, and a prospective study of pig health on the
affected property and on properties related to the affected property
by common ownership, common sources of pigs, and by trace-forward of
pigs.
Based on the Australian case definition for PMWS, a 1st diagnosis of
this disease would require that the case meet clinical,
histopathological and virological criteria. Specifically, we would
expect to see a herd syndrome of wasting in post-weaning pigs that is
generally unresponsive to intervention, with characteristic
histopathology and abundant PCV2 in lesions.
The current case met the histopathological and virological criteria
but it did not meet the clinical criterion. While there was elevated
morbidity and mortality in post-weaning pigs, there was no evidence
of wasting in growing pigs and no evidence of disease spread between
units or farms. The disease situation was readily explained by
infections with endemic disease agents in association with abnormal
stress on young pigs and responded well to modified management and
appropriate treatment with antibacterial agents. This rapid response
to management changes is not characteristic of PMWS.
The investigation confirms that, although porcine circovirus type 2
is widespread in the Australian pig herd, Australia continues to be
free from PMWS.
Gardner Murray
Australian Chief Veterinary Officer/Special Adviser
Source: ProMed - 10th November 2005
