Assessment of Giardia and Cryptosporidium spp. as a Microbial Source Tracking Tool for Surface Water: Application in a Mixed-Use Watershed
ABSTRACTKnowledge of host specificity, combined with genomic sequencing ofGiardiaandCryptosporidiumspp., has demonstrated a microbial source tracking (MST) utility for these common waterborne microbes. To explore the source attribution potential of these pathogens, water samples were collected in a mixed rural-urban watershed in the Township of Langley, in southwestern British Columbia (BC), Canada, over a 2-year period.Cryptosporidiumwas detected in 63% of surface water samples at concentrations ranging from no positive detection (NPD) to 20,600 oocysts per 100 liters.Giardiawas detected in 86% of surface water samples at concentrations ranging from NPD to 3,800 cysts per 100 liters of water. Sequencing at the 18S rRNA locus revealed that 50% ofCryptosporidiumsamples and 98% ofGiardiasamples contained species/genotypes (Cryptosporidium) or assemblages (Giardia) that are capable of infecting humans, based on current knowledge of host specificity and taxonomy.Cryptosporidiumgenotyping data were more promising for source tracking potential, due to the greater number of host-adapted (i.e., narrow-host-range) species/genotypes compared toGiardia, since 98% ofGiardiaisolates were zoonotic and the potential host could not be predicted. This report highlights the benefits of parasite genomic sequencing to complement Method 1623 (U.S. Environmental Protection Agency) and shows thatCryptosporidiumsubtyping for MST purposes is superior to the use ofGiardiasubtyping, based on better detection limits forCryptosporidium-positive samples than forGiardia-positive samples and on greater host specificity amongCryptosporidiumspecies. These additional tools could be used for risk assessment in public health and watershed management decisions.