title: Assessing Transmission of Salmonella to Bovine Peripheral Lymph Nodes upon Horn Fly Feeding.
abstract: Biting arthropods are implicated in the transdermal transmission of Salmonella to bovine peripheral lymph nodes, and such contamination can contribute to increased Salmonella prevalence in processed beef. Since horn flies can acquire Salmonella and then excrete the bacteria in their feces, on-animal fly infestations were conducted in this study to assess whether horn flies have a role in this bacterial transmission. Three Salmonella serotypes were used to assess fly acquisition from and excretion onto cattle. The results indicated that flies can acquire Salmonella from the hide, as assessed by recovery from homogenates of surfacesterilized flies, and that Salmonella persists for at least 5 days in the fly. Fly fecal excreta serves as a bacterial contaminant on the hide, and the overall mean probable estimate of the quantity shed was ≈10(5) most probable number per fly cage area. In 5 days, no transmission of the bacteria to bovine peripheral lymph nodes was evident, prompting an assessment of the effects of prolonged horn fly feeding on transmission. Three groups of animals were infested with flies that had consumed a blood meal containing Salmonella Senftenberg. After 5 days, the study was either terminated or the flies were removed and the cages replenished with unfed flies either once or twice over the course of an 11- or 19-day fly exposure period, respectively. A microlancet-inoculated positive-control animal was included in each group for comparison. The impact of prolonged horn fly feeding was evident, as 8% of lymph nodes cultured were positive from the 5-day exposure, whereas 50 and 42% were positive from 11- and 19-day exposures, respectively. Higher concentrations of Salmonella were recovered from fly-infested animals than from the microlancet-inoculated control, likely a result of repeated inoculations over time by flies versus a single introduction. The data described provide new insights into the transmission dynamics of Salmonella in cattle populations, highlighting a role for biting flies as an important reservoir.
authors.affiliation: U.S. Department of Agriculture Agricultural Research Service, Knipling-Bushland U.S. Livestock Insects Research Laboratory, 2700 Fredericksburg Road, Kerrville, Texas 78028, USA. pia.olafson@ars.usda.gov.
authors.forename: Pia Untalan
authors.initials: PU
authors.lastname: Olafson
authors.affiliation: U.S. Department of Agriculture Agricultural Research Service, Southern Plains Agricultural Research Center, Food and Feed Safety Research, 2881 F & B Road, College Station, Texas 77845, USA.
authors.forename: Tyson R
authors.initials: TR
authors.lastname: Brown
authors.affiliation: U.S. Department of Agriculture Agricultural Research Service, Knipling-Bushland U.S. Livestock Insects Research Laboratory, 2700 Fredericksburg Road, Kerrville, Texas 78028, USA.
authors.forename: Kimberly H
authors.initials: KH
authors.lastname: Lohmeyer
authors.affiliation: U.S. Department of Agriculture Agricultural Research Service, Southern Plains Agricultural Research Center, Food and Feed Safety Research, 2881 F & B Road, College Station, Texas 77845, USA.
authors.forename: Roger B
authors.initials: RB
authors.lastname: Harvey
authors.affiliation: U.S. Department of Agriculture Agricultural Research Service, Southern Plains Agricultural Research Center, Food and Feed Safety Research, 2881 F & B Road, College Station, Texas 77845, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Nisbet
authors.affiliation: International Center for Food Industry Excellence, Department of Animal and Food Sciences, College of Agricultural Sciences and Natural Resources, Texas Tech University, Lubbock, Texas 79409, USA.
authors.forename: Guy H
authors.initials: GH
authors.lastname: Loneragan
authors.affiliation: U.S. Department of Agriculture Agricultural Research Service, Southern Plains Agricultural Research Center, Food and Feed Safety Research, 2881 F & B Road, College Station, Texas 77845, USA.
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Edrington
mesh_terms: D000818:Animals; D002417:Cattle; D005243:Feces / Q000382:microbiology; D008198:Lymph Nodes; D009117:Muscidae; D012475:Salmonella