Experimental evaluation of Salmonella Choleraesuis pathogenicity and porcine reproductive and respiratory syndrome virus synergy in weaned pigs.

Abstract

BACKGROUND: Salmonella enterica serovar Choleraesuis (S. Choleraesuis) causes septicemic salmonellosis in pigs, which requires differential diagnosis from African swine fever (ASF). Porcine reproductive and respiratory syndrome virus (PRRSV) facilitates S. Choleraesuis dissemination. Herein, we determined the pathogenicity of S. Choleraesuis and the synergistic effect of PRRSV in septicemic salmonellosis. Furthermore, we compared the pathological characteristics of septicemic salmonellosis and ASF. RESULTS: Two experimental studies were conducted using weaning pigs (8- and 6-week-old pigs). In the first study, 8-week-old pigs (n = 36) were divided into three groups and inoculated with S. Choleraesuis (SC group), Salmonella Typhimurium (ST group), and phosphate-buffered saline (PBS, control group). Necropsies and Salmonella quantification were performed at 1, 3, 7, and 14 days post-inoculation (dpi). Salmonella was isolated only from mesenteric lymph nodes in the SC (3–14 dpi) and ST (3 dpi) groups. The SC group showed relatively higher body temperatures, more severe clinical signs, and pronounced histopathological lesions in mesenteric lymph nodes and Peyer’s patches than did the ST group. In the second study, 40 pigs were assigned to four groups: 12 pigs coinfected with S. Choleraesuis and PRRSV (PRRSV + SC group), 12 pigs infected with S. Choleraesuis (SC group), 8 pigs infected with PRRSV, and 8 pigs inoculated with PBS (control group). They were monitored until 16 dpi and euthanized on 2, 6, 8, and 16 dpi to determine body weight, clinical signs, hematological changes, histopathological examination, and S. Choleraesuis colonization. PRRSV + SC pigs had the lowest average daily weight gain and higher mean values, including body temperatures and clinical signs than those of the other groups. They also showed more extensive tissue colonization with S. Choleraesuis than that in the SC group. Compared to the principal pathological characteristics of ASF, some pigs in the SC and PRRSV + SC groups showed splenomegaly with dark discoloration and gastrohepatic lymph node enlargement without hemorrhage. However, renal lymph nodes remained unaffected. CONCLUSIONS: Pigs infected with S. Choleraesuis revealed higher pathogenicity than did those infected with S. Typhimurium, and coinfections with PRRSV enhanced systemic infection. Distinct lesions in gastrohepatic and renal lymph nodes aid differential diagnosis between septicemic salmonellosis and ASF.