Flies As Carriers of Pathogens Associated with Manure.

Filth flies are known mechanical vectors of several foodborne pathogens, but is there specificity of transmission between fly species and human pathogens? Pathogen transmission by flies can occur by at least two distinct mechanisms; defecation/regurgitation and release of pathogen by casual contact.   To test vector specificity, competency of two flies, a blow fly, Phormia regina, and the house fly, Musca domestica, was compared for two foodborne pathogens, Salmonella enterica and Escherichia coli O157:H7 when acquired from contaminated manure and inoculated to food plants by casual contact. We found that both fly species deposit bacteria on lettuce during short exposure periods of 10 or 30 seconds.  However, blow flies pick up and deposit more bacterial cells than do house flies. Also, E. coli O1457:H7 cells are transmitted much more efficiently than are Salmonella cells by both fly species.  Thus, transmission specificity exists, but the underlying mechanisms are unknown.