Salmonella species in piglets and weaners from Uganda: prevalence, antimicrobial resistance and herd-level risk factors.

Non-typhoidal salmonellosis is of concern in humans in sub-Saharan Africa, and this is partly due to the high number of immunocompromised persons. Pork and pork products could be among the sources of these non-typhi Salmonella spp. The aim of this study was to identify Salmonella spp. in piglets and weaners in northern and eastern Uganda, characterize their antimicrobial resistance patterns and determine herd-level risk factors. Fecal samples were collected from 465 piglets and weaners from 93 herds (49 and 44 from northern and eastern Uganda, respectively). In addition, information about the herd management and potential risk factors were collected. The fecal samples were cultured for the identification of Salmonella spp. The Salmonella spp. confirmed by serotyping were further characterized by determination of minimum inhibitory concentration (MIC) to 12 antimicrobials by broth microdilution. At individual level, the total prevalence of Salmonella spp. was 12% (12.2% in northern and 11.9% in eastern Uganda). At herd level, the total prevalence was 39% (43% in northern and 34% in eastern Uganda). From 56 samples with Salmonella spp., 20 serovars were identified including two serovars identified only by their antigenic formulae. The predominant serovars were S. Zanzibar, S. Heidelberg, S. Infantis, S. Typhimurium, S. Stanleyville, S. Aberdeen and S. Kampala. In total, 57% of the 53 Salmonella spp. analyzed, originating from 27% of the herds, were resistant to at least one antimicrobial agent. The majority of drug-resistant isolates (60%) were from northern Uganda. Eight multidrug-resistant (MDR) isolates were from northern Uganda and three MDR isolates were from eastern Uganda. Increased prevalence of Salmonella spp. was associated with feeding the young and adults separately as compared to feeding the young and adults together (p=0.043, OR=4.3; 95% CI 1.1, 17.38). Protective factors were "intensive" method of keeping the pigs versus "tethering and roaming" (p=0.016, OR=0.11; 95% CI 0.02, 0.64), "intensive" method versus "semi-intensive" method (p=0.048, OR=0.12; 95% CI 0.01, 0.96) and cleaning feeders after every two days versus daily (p=0.017, OR=0.18; 95% CI 0.05, 0.72). This study has revealed a high prevalence of infection of piglets and weaners with diverse non-typhi Salmonella serovars and highlights the potential role of pork and pork products as sources of these organisms for humans. In addition, this study has identified protective factors that could be promoted to control Salmonella spp. and in antimicrobial resistance reduction programs in rural pigs from Uganda.