Giardia duodenalis cyst survival in cattle slurry.

Giardia duodenalis is a protozoan parasite known to infect animals and humans. Zoonotic transmission of G. duodenalis can occur by the consumption of drinking water produced from surface water that is contaminated by runoff from manure-laden fields or pastures. Although it was previously reported that storing solid cattle manure decreases G. duodenalis cyst viability, no data are available on cyst survival in slurry waste from cattle. In this study the number and the viability of G. duodenalis cysts was determined in cattle slurry for up to 90 days. G. duodenalis cysts were counted in 30 slurry samples with a quantitative direct immunofluorescence assay. The geometric mean number of cysts was reduced by 77% after 90 days (P<0.0014), although there was substantial variability between samples. A fluorogenic dye staining using 4',6'-di-amino-2-phenylindole and propidium iodide showed a decreased viability from 45 days onwards, and after 90 days incubation, only 3% of the cysts were viable. Gerbils and lambs were artificially infected with 50 day-old and 90 day-old cysts and faecal excretion of G. duodenalis was monitored between 5 and 7 days after infection. Seven days after infection the gerbils were euthanized for Giardia trophozoite counts. Although one cyst was found in the faeces of one of the gerbils after infection with 50 day-old cysts, no trophozoites were recovered from the intestines of any gerbil (n=8). Experimental infection of lambs with 10(5)50 day-old and 90 day-old slurry cysts caused low cyst excretion in one out of two and one out of three lambs, respectively. Together, these data show that storage of cattle slurry for 90 days greatly reduces the number and viability of G. duodenalis cysts.