SALMONELLA AND ANTIMICROBIAL RESISTANCE IN HUMANS, LIVESTOCK AND WILD BIRDS

Abstract

Salmonella are Gram negative bacteria that are classified into over 2600 serovars. The serovars that cause typhoid fever are restricted to humans, whereas non-typhoidal Salmonella serovars (NTS) infect multiple hosts worldwide. However, fundamental differences exist between developed countries and sub-Saharan Africa with regards to sources, transmission, host and environmental risk factors, and disease outcome. In United States, although NTS are mainly foodborne, control measures implemented within slaughter and processing facilities have failed to reduce disease incidence implying transmission is not fully understood. In Africa, limited research has been done; hence NTS transmission is poorly understood. This study was conducted to better understand sources and transmission of NTS and associated antimicrobial resistance (AMR). We analyzed long-term human and cattle AMR data from Pacific Northwest using diversity measures and bootstrapping techniques. We show that some AMR profiles in the predominant serovars were common between host populations, but more profiles were unique to source populations than were shared. Also, the expected and observed number of AMR profiles in humans and cattle were different. These results suggest Salmonella and AMR from humans and cattle may not be wholly derived from a common population. We also determined phenotypic antimicrobial structure and genotypic structure of common serovars from various sources (storm-water, human wastewater, abattoir flush-water and floor swab, poultry and swine feces) in Kampala, Uganda. We found similar strains among different sources suggesting NTS disseminates amongst humans, livestock and the environment. Also, more resistance was detected in poultry suggesting poultry are potential reservoirs.Next, we assessed the risk of Salmonella shedding in water-birds utilizing impacted and conserved areas, but found no difference in prevalence by location. Some strains were distinct to birds, while other strains in birds reflected strains in the urban environment. Of concern, an important bird area close to the city attracts high bird diversity, and could favor reemergence of fecal zoonotic pathogens.Finally, we used a mathematical modeling approach to gain insights into NTS transmission. We find the proportion of humans infected via animal contact depends on assumptions of NTS prevalence in animals, and proportion of humans that contact animals.