Salmonellosis in Feed Yards

Epidemiology, Clinical Management, and Public Health Risk

Abstract

Since the advent of the germ theory in the late 1800's and George Soper's¹⁰ discovery of the link the between Mary Mallon's employment history and 7 cases of typhoid fever in early 1907, salmonellosis has presented a diagnostic and clinical challenge to medical practitioners. Salmonellosis is caused by gram-negative, rod-shaped, facultative anaerobic, intracellular bacteria of the family Enterobacteriaceae, genus Salmonella.¹² There are at least 2300 serotypes (serovars) of Salmonella based on their somatic or O antigens (lipopolysaccharides or endotoxins), flagellar or H antigens, and in some cases virulence or Vi antigens. There is debate as to whether these serovars are distinct species or are a subspecies of one species, S. enterica, but most often serovars are considered species.

Most of the serovars of Salmonella are potential pathogens, but approximately 15 are commonly identified in diseased animals. Some Salmonellae are host specific, such as S. choleraesuis in swine, S. typhi in people⁸ and S. abortus-ovis in sheep. In contrast others, such as S. typhimurium, infect cattle, sheep, goats, swine, horses, poultry, rodents, people, and occasionally dogs and cats.²² Salmonellosis is a serious zoonotic disease¹ (CDC reported 41,901 cases in people in 1997)¹¹ and is estimated to cost $0.6 to 3.5 billion²³ in medical expenditures and lost production in the U.S. annually. Consequently, educating clients and their employees about the zoonotic hazards of working with animals during a Salmonella outbreak is as important as treating the animals. Salmonellosis is extremely important to all of the food animal industries because their products are common sources of Salmonella for people.¹