Outbreak of salmonellosis in pigs with PMWS

June 29, 2005 — Adam Moeser (ed. MontseTorremorell)
  [ES]

Postweaning multisystemic wasting syndrome (PMWS) is a viral disease occurring primarily in 6-8 week old pigs. The causal agent responsible for PMWS is porcine circovirus 2 (PCV-2) and the clinical signs include progressive weight loss, respiratory disease, diarrhea, and jaundice. Microscopic findings associated with PCV-2 disease include lymphoid depletion, macrophage-associated inflammation, and the presence and level of PCV-2 in affected tissues. The lymphoid depletion and compromised immunity resulting from PCV-2 predisposes pigs to secondary bacterial infections. Salmonella typhimurium and Salmonella cholerasuis have been reported to cause severe diarrheal disease in PMWS-affected pigs. This article describes an outbreak of salmonellosis in PMWS affected swine herds in the Republic of Korea.

Thirty seven cases of severe diarrhea in post-weaned pigs (28-63 days of age) from January 2003 to April 2004 were reported on 24 pig farms. Affected pigs experienced growth retardation with 10-20% morbidity and 70-80% mortality in all herds tested. Diarrhea in the early stages of disease was characterized as yellowish and progressed to black. Antimicrobial therapy was ineffective. Postmortem analysis was performed on 37 pigs and samples of lung, liver, kidney, small and large intestine, tonsil, spleen, an inguinal lymph nodes were harvested for histological and immunohistochemical analyses.

Consistent histological findings in affected pigs were lymphoid depletion in the lymphoid follicle and paracortical zone of the lymph nodes which was replaced by fibrovascular stroma with grape-like clusters of basophillic intracytoplasmic inclusion bodies. There was a strong hybridization signal with PCV-2 in the cytoplasm of macrophages in lymph nodes, spleen, and Peyer's patches in all pigs tested. Necrosis was observed in the colon that extended into the lamina propria, submucosa, muscularis mucosa, and lymphoid follicles. Necrotic areas were separated from normal tissue by a marginal zone of leukocytes. The lamina propria had numerous neutrophils and macrophages.

Salmonellae were detected in the small and large intestine in all pigs by PCR. Other bacterial pathogens detected by PCR in the gut were Lawsonia intracellularis (n = 3 pigs) and B. pilosicoli (n=2 pigs). Salmonella typhimurium isolated from 23 pigs and Salmonella cholerasuis in 2 pigs. PCV-2 was isolated from small and large intestine in 22 pigs and confirmed by in situ hybridization of infected cell cultures.

Depletion of lymphoid tissue and immunosuppression in PMWS affected pigs likely predisposed pigs to infection with Salmonella species. [Editor's note: What if Salmonella predisposed pigs to PMWS?] Co-infection of PMWS and Salmonella can result in more severe clinical disease and increased mortality (up to 80%).

Reference:

Ha Y, Jung K, Choi C, Chae C. Outbreak of salmonellosis in pigs with
postweaning multisystemic wasting syndrome. Veterinary record.156:583-584,2005.