PMWS confused With PRRS
When the first cases of severe PMWS suddenly appeared in Quebec in 2004, many practitioners thought these cases were an emergence of atypical PRRS, recalls Francois Cardinal, DVM, a private swine consultant from Drummondville, Quebec.
Most herds in the province are infected with the PRRS virus, according to Cardinal, but the clinical presentation of this new outbreak didn’t exactly fi t with the case description of PRRS – death loss rate was more severe, for one thing.Serum samples and live pigs or carcasses were submitted to the provincial diagnostic laborato-ries. Lesions and immunofl uorescence showed that PRRS was implicated in most of the cases, but there was a new player: PCV2 and its typical lesions in lymphoid tissues.
Cardinal says the fi rst reaction of many practitioners was to deny that PCV2 could be implicated in such an acute clinical presentation. “At this time, we didn’t have much experience interpreting laboratory fi ndings with regards to PMWS. Th e hypothesis of emerging new virulent strains of PRRS was a more comfortable posi-tion,” he says.
Once veterinarians started to share their experiences with other practitioners, it became apparent that the problem they were facing was not PRRS, but PMWS and that it was spreading throughout the province.
Cardinal is one of six Canadian veterinarians involved in a special committee to study the syndrome. University of Montreal veterinary re-searcher Dr. Laura Batista is also a member of the group. She and her colleagues follow fi ve principles to declare a PMWS-positive diagnosis:1 1. Identify aff ected farm, site, or system through good, quality diagnostic submissions of lymph nodes (inguinal, mesenteric, tra-cheobronchial or mediastinic); terminal part of ileum, lungs, liver, spleen and kidneys. 2. Identify the presence of characteristic clinical signs – wasting, anemia, diarrhea and respiratory distress. 3. Presence of characteristic macroscopic lesions at necropsy. 4. Presence of characteristic microscopic lesions by histopathology. 5. Determination of PCV2 by IFA, immuno-peroxidase or PCR.