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 >65 and >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.

Longitudinal Poisson Regression To Evaluate the Epidemiology of Cryptosporidium, Giardia, and Fecal Indicator Bacteria in Coastal California Wetlands

“…Previous studies have examined the role of dairies and other intensive livestock operations in pathogen transmission and identified potential risk factors for nearby surface water contamination, including application of manure on agricultural fields (30) and surface runoff from areas with high animal densities, such as dairies and beef cattle operations (23). Consistent with these results, the data from this study demonstrate that the wetland in closest proximity to a livestock operation exhibited the greatest protozoal and bacterial loading.…”

“…Rainfall occurring within the previous 12 h was associated with increased Cryptosporidium and Giardia counts in the dairy wetland water, a result which is likely due to enhanced runoff from fecally contaminated soils. In livestock operations that utilized vegetative buffer strips to reduce watershed contamination from storm runoff, previous studies have documented reduced pathogen loading of adjacent waterways (6,23,24). Reductions in water quality, characterized by increased water temperature, total dissolved solids, and decreased dissolved oxygen, were also associated with higher Cryptosporidium and Giardia concentrations.…”

“…Second, reducing or more carefully controlling field applications of manure and slurry can greatly decrease the number of pathogens released into the environment (16). Finally, incorporation of vegetative filter strips, or "buffer strips," can reduce the number of oocysts and cysts transported out of intensive livestock operations (3,16,23,24). Implementation of these BMPs at dairies and other livestock operations may considerably reduce their contribution to pathogen loading of adjacent wetlands.…”

“…First, reduction of cattle density may reduce the spread of infection within the herd and reduce the amount of contaminated manure released into the environment (23,24). Second, reducing or more carefully controlling field applications of manure and slurry can greatly decrease the number of pathogens released into the environment (16).…”

Hydrologic and Vegetative Removal of Cryptosporidium parvum, Giardia lamblia, and Toxoplasma gondii Surrogate Microspheres in Coastal Wetlands

“…The utility of vegetation for microbial removal was demonstrated in previous studies, which showed that vegetated buffer strips can effectively remove microbial pathogens from contaminated runoff (18,(33)(34)(35). However, different aquatic plants may vary in their ability to remove parasites due to distinct surface properties, unique biofilms, and differential effects on water flow and drag (36,37).…”