Lesions Associated with Postweaning Multisystemic Wasting Syndrome in Pigs from Prince Edward Island, Canada

Postweaning multisystemic wasting syndrome (PMWS) is a recently recognized swine disease originally reported in western Canada.2,9 Retrospective postmortem studies revealed that this condition first appeared in 1991, but it was not recognized as a specific disease until 1996.9 A similar syndrome has been described recently in pigs from the United States4,11 and Europe.1 The etiology of this syndrome is still under investigation, but porcine circovirus (PCV), a member of the family Circoviridae that includes chicken anemia virus, psittacine beak and feather disease virus, and a newly described pigeon circovirus,15 is thought to play an important role in the pathogenesis of this condition. The purpose of this paper is to describe and illustrate the most common microscopic findings associated with PMWS in pigs and to report the presence of PMWS in swine herds from Atlantic Canada. Six pigs, 5–12 weeks of age, from four swine herds located in Prince Edward Island were submitted to the Atlantic Veterinary College for postmortem examination. Five pigs were alive and one (pig no. 3) had been found dead in its pen. Pig nos. 2 and 3 and pig nos. 5 and 6 were herdmates. All pigs had a history of weight loss, dyspnea, and/or scouring, first noticed 1 or 2 weeks after weaning. Blood samples were obtained from live pigs prior to euthanasia. Complete postmortem examination was performed, and tissues were selected for histopathology, bacteriologic culture, and virologic analysis. Tissues for histopathology were fixed in 10% neutral buffered formalin, embedded in paraffin, cut at 5 mm, and stained with hematoxylin and eosin. In two cases, formalin-fixed tissue was fixed in 2% glutaraldehyde and postfixed in 1% osmium tetroxide, dehydrated in a graded series of ethanol, and infiltrated and embedded in epon/araldite for sectioning and examination by transmission electron microscopy. Thin sections were stained with a saturated solution of uranyl acetate and Sato lead stain. Tissues from five pigs (nos. 1, 2, 3, 5, and 6) were sent to the Veterinary Services Branch of Manitoba Agriculture for the detection of pathogenic PCV by polymerase chain reaction (PCR).8 Porcine reproductive and respiratory syndrome (PRRS) serology was done on serum of two pigs by an indirect fluorescent antibody test (IFAT) that was developed in house. Gradual dilutions of the test serum were made and reacted with PRRS virus (PRRSV)-infected MARC cells, washed, mounted, and evaluated by fluorescent microscopy. Lungs from three pigs and lymph nodes from two others were tested for the pres-