Prevalence of Salmonella enterica in Flies on a Diversified Cattle and Fresh Produce Farm across Two Growing Seasons

Abstract

Flies are a vector for spreading foodborne pathogens pertinent to fresh produce, such as Shiga-toxigenic Escherichia coli and Salmonella; however, most studies focus on concentrated animal feeding operations, which do not reflect low-density animal farming practices that often adjoin fruit and vegetable acreage. In this study, we determined the prevalence of Salmonella in flies collected biweekly on an integrated animal and produce operation over two growing seasons. Eleven pooled samples, out of 889, tested positive for Salmonella. Flies from the Calliphoridae, Muscidae, Sarcophagidae, and Tachinidae families were associated with Salmonella carriage, but fly family was not a significant factor for isolation of Salmonella (p=0.303). Fly species were a significant factor (p=0.026), with five Pentacricia aldrichii pools testing positive for Salmonella. With the exception of single specimen isolation, prevalence ranged from 2.2 to 15.2%. With the exception of the Tachinidae family, these results reflect a strong association of flies that are commonly associated with feces or are pests of animals. Trap location was not significantly associated with isolation of Salmonella-positive flies (p=0.236). Overall, the population of flies was not as abundant as studies conducted with produce grown in close proximity to concentrated animal feeding operations, indicating a reduced risk of transmission; however, similar to these studies, fly families that are commonly isolated from fecal and decaying matter were most frequently associated with Salmonella isolation. Further work is warranted to elucidate the foodborne pathogen transmission rates to produce and subsequent survival over time.

Understanding potential cattle contribution to leafy green outbreaks: A scoping review of the literature and public health reports

“…Hamilton et al. (2021) reported the prevalence of Salmonella in different fly families, around a produce plot nearby two low‐density beef cattle operations, as 2.2%–15.2%. Trap location was not a significant predictor for Salmonella prevalence and the prevalence estimations from this study were different from that of Berry et al.…”

“…Although a few vaccines were shown to be effective against E. coli O157:H7 colonization of cattle, vaccines have not been used extensively in cattle production and vaccine efficacy has not been demonstrated clearly up to date. Other preharvest strategies include controlling wildlife access to produce fields by lethal and nonlethal methods such as hunting, trapping, and fencing (Jay‐Russell et al., 2012; Karp et al., 2015; Mishra et al., 2017), pest control (Berry et al., 2019; Hamilton et al., 2021), dust control (Yanamala et al., 2011), implementation of vegetative buffer zones (Glaize et al., 2021; Karp et al., 2015), and remediation and treatment of soil surrounding production areas (Glaize et al., 2021; Karp et al., 2015). Among these interventions, only the vegetative buffer zones were tested experimentally and reported as effective (Glaize et al., 2021).…”

“…Although a definitive and quantitative explanation was not possible at the time, it was reported that flies were capable of transmitting the acquired pathogens to the plant surface at distances greater than the LGMA recommendations at the time the study was conducted (366 m [1200 ft]). Hamilton et al (2021) reported the prevalence of Salmonella in different fly families, around a produce plot nearby two low-density beef cattle operations, as 2.2%-15.2%. Trap location was not a significant predictor for Salmonella prevalence and the prevalence estimations from this study were different from that of Berry et al (2019).…”

House Flies Are Underappreciated Yet Important Reservoirs and Vectors of Microbial Threats to Animal and Human Health

“…Global surveys demonstrated that adult house flies from urban and agricultural settings possess >200 pathogenic bacterial taxa including key species important to human and animal health such as Salmonella spp. [ 14 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ], pathogenic strains of E. coli [ 22 , 47 , 48 , 49 , 50 , 51 , 52 ], Campylobacter spp. [ 49 , 50 , 53 , 54 , 55 , 56 ], Aeromonas cavie [ 57 ], and bacterial pathogens causing bovine respiratory disease Mannheimia haemolytica , Pasteurella multocida , Histophilus somni [ 58 ].…”