title: Climate and on-farm risk factors associated with Giardia duodenalis cysts in storm runoff from California coastal dairies.
abstract: Climatic factors and on-farm management practices were evaluated for their association with the concentrations (cyst/liter) and instantaneous loads (cysts/second) of Giardia duodenalis in storm-based runoff from dairy lots and other high-cattle-use areas on five coastal California farms over two storm seasons. Direct fluorescent antibody analysis was used to quantitate cysts in 350 storm runoff samples. G. duodenalis was detected on all five dairy farms, with fluxes of 1 to 14,000 cysts/liter observed in 16% of samples. Cysts were detected in 41% of runoff samples collected near cattle less than 2 months old, compared to 10% of runoff samples collected near cattle over 6 months old. Furthermore, the concentrations and instantaneous loads of cysts were > or =65 and > or =79 times greater, respectively, in runoff from sites housing young calves than in sites housing other age classes of animals. Factors associated with environmental loading of G. duodenalis included cattle age, cattle stocking number, and precipitation but not lot area, land slope, or cattle density. Vegetated buffer strips were found to significantly reduce waterborne cysts in storm runoff: each additional meter of vegetated buffer placed below high-cattle-use areas was associated with reductions in the concentration and instantaneous load of cysts by factors of 0.86 and 0.79 (-0.07 and -0.10 log(10)/m), respectively. Straw mulch, seed application, scraping of manure, and cattle exclusion did not significantly affect the concentration or load of G. duodenalis cysts. The study findings suggest that vegetated buffer strips, especially when placed near dairy calf areas, should help reduce the environmental loading of these fecal protozoa discharging from dairy farms.
authors.affiliation: Department of Pathology, Microbiology, and Immunology, School of Veterinary Medicine, University of California, Davis, California 95616, USA.
authors.forename: Woutrina A
authors.initials: WA
authors.lastname: Miller
authors.forename: David J
authors.initials: DJ
authors.lastname: Lewis
authors.forename: Michael
authors.initials: M
authors.lastname: Lennox
authors.forename: Maria G C
authors.initials: MG
authors.lastname: Pereira
authors.forename: Kenneth W
authors.initials: KW
authors.lastname: Tate
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Conrad
authors.forename: Edward R
authors.initials: ER
authors.lastname: Atwill
mesh_terms: D000383:Agriculture / Q000379:methods*; D000818:Animals; D002140:California; D002417:Cattle; D002418:Cattle Diseases / Q000382:microbiology; D002980:Climate; D003612:Dairying / Q000379:methods*; D005243:Feces / Q000382:microbiology; D005872:Giardia / Q000254:growth & development / Q000302:isolation & purification*; D006801:Humans; D011634:Public Health; D011786:Quality Control; D011891:Rain; D012307:Risk Factors; D012621:Seasons; D012988:Soil Microbiology; D014871:Water Microbiology; D014873:Water Pollutants / Q000633:toxicity
chemical_list: D014873:Water Pollutants