Fecal shedding of, antimicrobial resistance in, and serologic response to SalmonellaTyphimurium in dairy calves
To determine the duration of fecal shedding of and serologic response to Salmonella spp after natural infection in dairy calves and characterize Salmonella organisms recovered from these herds. Longitudinal study. Calves from 2 dairy herds (A and B) in the northeast United States that were identified at the beginning of a Salmonella outbreak. Fecal samples were collected twice per week (herd A) or once per week (herd B); blood samples were collected for serologic testing once per week in both herds. Bacteriologic culture of fecal samples was performed, and Salmonella isolates were characterized by serotype, pulsed-field gel electrophoresis (PFGE) pattern, and antimicrobial resistance profile. All Salmonella isolates from herd A were serovar Typhimurium var Copenhagen, had the same PFGE pattern, and were resistant to at least 9 antimicrobials. All isolates from herd B were Salmonella Typhimurium, represented 2 PFGE patterns, and were susceptible to all antimicrobials evaluated. The estimated duration of fecal shedding was 14 days in herd A and 9 days in herd B. Few calves were seropositive for antibody against Salmonella lipopolysaccharide within the first week after birth (0 of 20 in herd A and 13 of 79 in herd B) or seroconverted (6 in herd A and 4 in herd B). Fecal shedding was more common in calves that seroconverted, but overall, there was not a strong association between seropositivity and fecal shedding of Salmonella organisms. Although the herds differed in serologic response and Salmonella subtype, the duration of fecal shedding among calves was similar between herds.
- [Show abstract] [Hide abstract] ABSTRACT: Host-to-host transmission in most Salmonella serovars occurs primarily via the fecal-oral route. Salmonella enterica serovar Typhi is a human host-adapted pathogen and some S. Typhi patients become asymptomatic carriers. These individuals excrete large numbers of the bacteria in their feces and transmit the pathogen by contaminating water or food sources. The carrier state has also been described in livestock animals and is responsible for food-borne epidemics. Identification and treatment of carriers are crucial for the control of disease outbreaks. In this review, we describe recent advances in molecular profiling of human carriers and the use of animal models to identify potential host and bacterial genes involved in the establishment of the carrier state.0Comments 30Citations
Immunization of man against epidemic typhus by infection with avirulent Rickettsia prowazeki (strain E); observations as to post-vaccination reactions, the relation of serologic response to size and route of infecting dose, and the resistance to challenge with virulent typhus strains. Am J Hyg 59:74