Descriptive summary of an outbreak of porcine post-weaning multisystemic wasting syndrome (PMWS) in New Zealand

Abstract

CASE HISTORY: Investigations were conducted to determine the cause of an acute, multi-farm outbreak of porcine respiratory disease that included diarrhoea and subsequent loss of body condition in affected pigs. A definition for post-weaning multisystemic wasting syndrome (PMWS) including both clinical and pathological features, previously developed for the pig industry in New Zealand, was applied to the current outbreak. In addition to self-reporting by owners of affected farms, local veterinarians, disease and epidemiology consultants, and animal health officials from the Ministry of Agriculture and Forestry (MAF) were involved in conducting farm visits and submission of diagnostic specimens.

CLINICAL FINDINGS AND DIAGNOSIS: Pathogens known to be endemic in the pig industry in New Zealand as well as likely exotic diseases were excluded as causative agents of the outbreak. Clinical signs including dyspnoea, diarrhoea, and rapid loss of body condition were consistent with the New Zealand case definition for PMWS. Interstitial pneumonia, pulmonary oedema, generalised lymph-node enlargement, and presence of porcine circovirus type 2 (PCV2) inclusion bodies were consistently identified in affected pigs. Classical swine fever virus (CSFv), Porcine reproductive and respiratory syndrome virus (PRRSv), and Influenza virus were ruled out, using molecular and traditional virological techniques. Spread of the disease between farms was hypothesised to be facilitated by locally migrating flocks of black-backed seagulls. The original source of the disease incursion was not identified.

DIAGNOSIS: Based on the consistent presence of circovirusassociated lesions in lymphoid tissues in combination with generalised enlargement of lymph nodes, histiocytic interstitial pneumonia, clinical wasting, and poor response to antibiotic therapy, a diagnosis of PMWS was made.

CLINICAL RELEVANCE: PMWS should be considered in the differential diagnoses of sudden onset of respiratory dyspnoea, diarrhoea, and rapid loss of body condition in young pigs in New Zealand pig herds.

KEY WORDS:

• Pigs
• post-weaning multisystemic wasting syndrome
• porcine circovirus
• respiratory disease
• disease investigation
• disease transmission

Acknowledgements

The authors gratefully acknowledge interpretation of histopathology by Alastair Johnstone at Massey University, assistance with farm investigations by David Lawton, collection of field necropsy samples by Lachlan McIntyre and Donald Arthur, coordination of the MAF response by Thomas Rawdon, PCV2 sequencing by Patricia Jaros, and exotic disease diagnostic testing by staff at the MAF Investigation and Diagnostic Centre. The financial support of the NZPIB and MAF, and the owners of the affected farms helped to make this work possible. The map for Figure 1 was kindly supplied by AsureQuality Ltd and AgriBase.